Re: [time-nuts] Regulating a pendulum clock
In my post below I didn't understand how a constant electromagnet on the side of the pendulum could adjust the pendulum rate. Well I've worked it out. Despite common misconceptions pendulum swing rate is not independent of amplitude. It is to the first order but not when calculated properly. The magnet when applied either reduces or increases the amplitude and hence makes minor adjustments in timing. Pretty neat for 40s technology. Jim Palfreyman On Sunday, August 8, 2010, Jim Palfreyman jim77...@gmail.com wrote: Hi all, I have a Seimens master clock with a Reiffler pendulum. A lovely piece of work that used to provide time services in the 40s. Being a master clock it has contacts that open and close on each pendulum swing and so I can monitor it's accuracy quite easily using gps and my 5370B. I've adjusted it as best I can and the best I can get is about 50 ms over 24 hours. However that was a one off. Temp and air pressure cause variations of up to 300 ms and it changes direction too. Basically it's hard to keep accurate. It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labelled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) It's about 25v in the coil and goes up to 60mA max. Even at levels of 2mA has an effect. Using this control it's quite easy to manually bring the clock back to the right time if it's say half a second fast. What I want to do is control the current in the coil with a micro controller which I have attached to a rubidium oscillator. Getting the pps from the pendulum clock in and comparing to actual time is easy, but I need a way to control the current through the coil so it can dynamically adjust the clock. I need the current to go from say -10 to +10 mA (at 25v) and this needs to be controlled via a micro controller output (which goes from 0 to 5 with 2.5 being the 0mA point). I can either use the D/A in the controller (or PWM an output I suppose). I'd appreciate some thoughts on circuits to do this. Software side is not a problem. Jim Palfreyman ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Food for thought. I find it interesting that no one has suggested alternatives to improving the performance of a pendulum clock other than controlling it with a higher performance clock. If the goal is a better clock why not attempt to understand the source of the errors and work on methods to control or compensate for them? Teddy Hall has been taken to task for using a quartz controlled oscillator to measure the amplitude of a pendulum in the control loop of his Littlemore clock. Tom Van Baak has developed techniques for analyzing the performance and hence potential error sources of pendulum clocks - perhaps he will share some of his work here. Horological history is full of many attempts at solutions to the problem, but it would seem that the creativity of this group might generate some new ideas that are more in the spirit of better timekeeping than attaching the pendulum to a better oscillator. How about a wireless controlled device attached to the pendulum that changes its position based on error sensor readings, not time errors, but instead, temperature, barometric pressure, gravity, etc. that would maintain a more constant pendulum period? Bob Holmström Editor Horological Science Newsletter www.hsn161.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Hi For that matter, how hard is it to put it in a vacuum with temperature control? Gets two big issues out of the way pretty fast. We certainly buy crystal oscillators that are heated and enclosed in pressure tight containers (not quite the same as vacuum, but close). Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Holmstrom Sent: Monday, August 09, 2010 12:47 PM To: time-nuts@febo.com Subject: Re: [time-nuts] Regulating a pendulum clock Food for thought. I find it interesting that no one has suggested alternatives to improving the performance of a pendulum clock other than controlling it with a higher performance clock. If the goal is a better clock why not attempt to understand the source of the errors and work on methods to control or compensate for them? Teddy Hall has been taken to task for using a quartz controlled oscillator to measure the amplitude of a pendulum in the control loop of his Littlemore clock. Tom Van Baak has developed techniques for analyzing the performance and hence potential error sources of pendulum clocks - perhaps he will share some of his work here. Horological history is full of many attempts at solutions to the problem, but it would seem that the creativity of this group might generate some new ideas that are more in the spirit of better timekeeping than attaching the pendulum to a better oscillator. How about a wireless controlled device attached to the pendulum that changes its position based on error sensor readings, not time errors, but instead, temperature, barometric pressure, gravity, etc. that would maintain a more constant pendulum period? Bob Holmström Editor Horological Science Newsletter www.hsn161.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Le 09/08/2010 18:46, Bob Holmstrom a écrit : Food for thought. I find it interesting that no one has suggested alternatives to improving the performance of a pendulum clock other than controlling it with a higher performance clock. If the goal is a better clock why not attempt to understand the source of the errors and work on methods to control or compensate for them? Teddy Hall has been taken to task for using a quartz controlled oscillator to measure the amplitude of a pendulum in the control loop of his Littlemore clock. Tom Van Baak has developed techniques for analyzing the performance and hence potential error sources of pendulum clocks - perhaps he will share some of his work here. Horological history is full of many attempts at solutions to the problem, but it would seem that the creativity of this group might generate some new ideas that are more in the spirit of better timekeeping than attaching the pendulum to a better oscillator. How about a wireless controlled device attached to the pendulum that changes its position based on error sensor readings, not time errors, but instead, temperature, barometric pressure, gravity, etc. that would maintain a more constant pendulum period? Yup. We have temperature and pressure ICs available , I think that gravity is pretty constant if the clock isn't being moved about. Humididty might also need logging aswell. So it should be easy enough to predict the pendulums response to changes given a reasonable time of observation. That said, clocks have always been adjusted against better references.. IIRC Harrison (and probably others) was using star transits to regulate his long case clocks. Bob Holmström Editor Horological Science Newsletter www.hsn161.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Unfortunately Gravity is not constant. Pendulum clocks show cyclic errors due to the influences of the Moon's and Sun's Gravitational fields. I forget the amounts but it is in the region of parts in 10 to the 7, which is easily measurable. This limits the compensations one can put into a pendulum clock. -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of mike cook Sent: 09 August 2010 18:21 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Regulating a pendulum clock Le 09/08/2010 18:46, Bob Holmstrom a écrit : Food for thought. I find it interesting that no one has suggested alternatives to improving the performance of a pendulum clock other than controlling it with a higher performance clock. If the goal is a better clock why not attempt to understand the source of the errors and work on methods to control or compensate for them? Teddy Hall has been taken to task for using a quartz controlled oscillator to measure the amplitude of a pendulum in the control loop of his Littlemore clock. Tom Van Baak has developed techniques for analyzing the performance and hence potential error sources of pendulum clocks - perhaps he will share some of his work here. Horological history is full of many attempts at solutions to the problem, but it would seem that the creativity of this group might generate some new ideas that are more in the spirit of better timekeeping than attaching the pendulum to a better oscillator. How about a wireless controlled device attached to the pendulum that changes its position based on error sensor readings, not time errors, but instead, temperature, barometric pressure, gravity, etc. that would maintain a more constant pendulum period? Yup. We have temperature and pressure ICs available , I think that gravity is pretty constant if the clock isn't being moved about. Humididty might also need logging aswell. So it should be easy enough to predict the pendulums response to changes given a reasonable time of observation. That said, clocks have always been adjusted against better references.. IIRC Harrison (and probably others) was using star transits to regulate his long case clocks. Bob Holmström Editor Horological Science Newsletter www.hsn161.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
You could put a large mass of concrete or somehing above the clock and crank it up and down, to balance out the computed gravity changes. :) -John == Unfortunately Gravity is not constant. Pendulum clocks show cyclic errors due to the influences of the Moon's and Sun's Gravitational fields. I forget the amounts but it is in the region of parts in 10 to the 7, which is easily measurable. This limits the compensations one can put into a pendulum clock. -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of mike cook Sent: 09 August 2010 18:21 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Regulating a pendulum clock Le 09/08/2010 18:46, Bob Holmstrom a écrit : Food for thought. I find it interesting that no one has suggested alternatives to improving the performance of a pendulum clock other than controlling it with a higher performance clock. If the goal is a better clock why not attempt to understand the source of the errors and work on methods to control or compensate for them? Teddy Hall has been taken to task for using a quartz controlled oscillator to measure the amplitude of a pendulum in the control loop of his Littlemore clock. Tom Van Baak has developed techniques for analyzing the performance and hence potential error sources of pendulum clocks - perhaps he will share some of his work here. Horological history is full of many attempts at solutions to the problem, but it would seem that the creativity of this group might generate some new ideas that are more in the spirit of better timekeeping than attaching the pendulum to a better oscillator. How about a wireless controlled device attached to the pendulum that changes its position based on error sensor readings, not time errors, but instead, temperature, barometric pressure, gravity, etc. that would maintain a more constant pendulum period? Yup. We have temperature and pressure ICs available , I think that gravity is pretty constant if the clock isn't being moved about. Humididty might also need logging aswell. So it should be easy enough to predict the pendulums response to changes given a reasonable time of observation. That said, clocks have always been adjusted against better references.. IIRC Harrison (and probably others) was using star transits to regulate his long case clocks. Bob Holmström Editor Horological Science Newsletter www.hsn161.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
What happens when the rope breaks? -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of J. Forster Sent: 09 August 2010 19:10 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Regulating a pendulum clock You could put a large mass of concrete or somehing above the clock and crank it up and down, to balance out the computed gravity changes. :) -John == Unfortunately Gravity is not constant. Pendulum clocks show cyclic errors due to the influences of the Moon's and Sun's Gravitational fields. I forget the amounts but it is in the region of parts in 10 to the 7, which is easily measurable. This limits the compensations one can put into a pendulum clock. -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of mike cook Sent: 09 August 2010 18:21 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Regulating a pendulum clock Le 09/08/2010 18:46, Bob Holmstrom a écrit : Food for thought. I find it interesting that no one has suggested alternatives to improving the performance of a pendulum clock other than controlling it with a higher performance clock. If the goal is a better clock why not attempt to understand the source of the errors and work on methods to control or compensate for them? Teddy Hall has been taken to task for using a quartz controlled oscillator to measure the amplitude of a pendulum in the control loop of his Littlemore clock. Tom Van Baak has developed techniques for analyzing the performance and hence potential error sources of pendulum clocks - perhaps he will share some of his work here. Horological history is full of many attempts at solutions to the problem, but it would seem that the creativity of this group might generate some new ideas that are more in the spirit of better timekeeping than attaching the pendulum to a better oscillator. How about a wireless controlled device attached to the pendulum that changes its position based on error sensor readings, not time errors, but instead, temperature, barometric pressure, gravity, etc. that would maintain a more constant pendulum period? Yup. We have temperature and pressure ICs available , I think that gravity is pretty constant if the clock isn't being moved about. Humididty might also need logging aswell. So it should be easy enough to predict the pendulums response to changes given a reasonable time of observation. That said, clocks have always been adjusted against better references.. IIRC Harrison (and probably others) was using star transits to regulate his long case clocks. Bob Holmström Editor Horological Science Newsletter www.hsn161.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Not so simple... you should move it around in order to balance the gravity force vector :) Regards, Javier El 09/08/2010 20:09, J. Forster escribió: You could put a large mass of concrete or somehing above the clock and crank it up and down, to balance out the computed gravity changes. :) -John == Unfortunately Gravity is not constant. Pendulum clocks show cyclic errors due to the influences of the Moon's and Sun's Gravitational fields. I forget the amounts but it is in the region of parts in 10 to the 7, which is easily measurable. This limits the compensations one can put into a pendulum clock. -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of mike cook Sent: 09 August 2010 18:21 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Regulating a pendulum clock Le 09/08/2010 18:46, Bob Holmstrom a écrit : Food for thought. I find it interesting that no one has suggested alternatives to improving the performance of a pendulum clock other than controlling it with a higher performance clock. If the goal is a better clock why not attempt to understand the source of the errors and work on methods to control or compensate for them? Teddy Hall has been taken to task for using a quartz controlled oscillator to measure the amplitude of a pendulum in the control loop of his Littlemore clock. Tom Van Baak has developed techniques for analyzing the performance and hence potential error sources of pendulum clocks - perhaps he will share some of his work here. Horological history is full of many attempts at solutions to the problem, but it would seem that the creativity of this group might generate some new ideas that are more in the spirit of better timekeeping than attaching the pendulum to a better oscillator. How about a wireless controlled device attached to the pendulum that changes its position based on error sensor readings, not time errors, but instead, temperature, barometric pressure, gravity, etc. that would maintain a more constant pendulum period? Yup. We have temperature and pressure ICs available , I think that gravity is pretty constant if the clock isn't being moved about. Humididty might also need logging aswell. So it should be easy enough to predict the pendulums response to changes given a reasonable time of observation. That said, clocks have always been adjusted against better references.. IIRC Harrison (and probably others) was using star transits to regulate his long case clocks. Bob Holmström Editor Horological Science Newsletter www.hsn161.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Javier HerreroEMAIL: jherr...@hvsistemas.com HV Sistemas S.L. PHONE: +34 949 336 806 Los Charcones, 17 FAX: +34 949 336 792 19170 El Casar - Guadalajara - Spain WEB: http://www.hvsistemas.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Time stands still. I later thought you could equally use a tank of mercury and pump it up and down. :) -John = What happens when the rope breaks? -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of J. Forster Sent: 09 August 2010 19:10 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Regulating a pendulum clock You could put a large mass of concrete or somehing above the clock and crank it up and down, to balance out the computed gravity changes. :) -John == Unfortunately Gravity is not constant. Pendulum clocks show cyclic errors due to the influences of the Moon's and Sun's Gravitational fields. I forget the amounts but it is in the region of parts in 10 to the 7, which is easily measurable. This limits the compensations one can put into a pendulum clock. -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of mike cook Sent: 09 August 2010 18:21 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Regulating a pendulum clock Le 09/08/2010 18:46, Bob Holmstrom a écrit : Food for thought. I find it interesting that no one has suggested alternatives to improving the performance of a pendulum clock other than controlling it with a higher performance clock. If the goal is a better clock why not attempt to understand the source of the errors and work on methods to control or compensate for them? Teddy Hall has been taken to task for using a quartz controlled oscillator to measure the amplitude of a pendulum in the control loop of his Littlemore clock. Tom Van Baak has developed techniques for analyzing the performance and hence potential error sources of pendulum clocks - perhaps he will share some of his work here. Horological history is full of many attempts at solutions to the problem, but it would seem that the creativity of this group might generate some new ideas that are more in the spirit of better timekeeping than attaching the pendulum to a better oscillator. How about a wireless controlled device attached to the pendulum that changes its position based on error sensor readings, not time errors, but instead, temperature, barometric pressure, gravity, etc. that would maintain a more constant pendulum period? Yup. We have temperature and pressure ICs available , I think that gravity is pretty constant if the clock isn't being moved about. Humididty might also need logging aswell. So it should be easy enough to predict the pendulums response to changes given a reasonable time of observation. That said, clocks have always been adjusted against better references.. IIRC Harrison (and probably others) was using star transits to regulate his long case clocks. Bob Holmström Editor Horological Science Newsletter www.hsn161.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Personally, I would get out of the way. : ) Joe -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on Behalf Of Ian Sheffield Sent: Monday, August 09, 2010 1:17 PM To: j...@quik.com; 'Discussion of precise time and frequency measurement' Subject: Re: [time-nuts] Regulating a pendulum clock What happens when the rope breaks? -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of J. Forster Sent: 09 August 2010 19:10 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Regulating a pendulum clock You could put a large mass of concrete or somehing above the clock and crank it up and down, to balance out the computed gravity changes. :) -John == Unfortunately Gravity is not constant. Pendulum clocks show cyclic errors due to the influences of the Moon's and Sun's Gravitational fields. I forget the amounts but it is in the region of parts in 10 to the 7, which is easily measurable. This limits the compensations one can put into a pendulum clock. -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of mike cook Sent: 09 August 2010 18:21 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Regulating a pendulum clock Le 09/08/2010 18:46, Bob Holmstrom a écrit : Food for thought. I find it interesting that no one has suggested alternatives to improving the performance of a pendulum clock other than controlling it with a higher performance clock. If the goal is a better clock why not attempt to understand the source of the errors and work on methods to control or compensate for them? Teddy Hall has been taken to task for using a quartz controlled oscillator to measure the amplitude of a pendulum in the control loop of his Littlemore clock. Tom Van Baak has developed techniques for analyzing the performance and hence potential error sources of pendulum clocks - perhaps he will share some of his work here. Horological history is full of many attempts at solutions to the problem, but it would seem that the creativity of this group might generate some new ideas that are more in the spirit of better timekeeping than attaching the pendulum to a better oscillator. How about a wireless controlled device attached to the pendulum that changes its position based on error sensor readings, not time errors, but instead, temperature, barometric pressure, gravity, etc. that would maintain a more constant pendulum period? Yup. We have temperature and pressure ICs available , I think that gravity is pretty constant if the clock isn't being moved about. Humididty might also need logging aswell. So it should be easy enough to predict the pendulums response to changes given a reasonable time of observation. That said, clocks have always been adjusted against better references.. IIRC Harrison (and probably others) was using star transits to regulate his long case clocks. Bob Holmström Editor Horological Science Newsletter www.hsn161.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Advisable given the required mass will probably be in the 10-100 ton range. Bruce J. L. Trantham, M. D. wrote: Personally, I would get out of the way. : ) Joe -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on Behalf Of Ian Sheffield Sent: Monday, August 09, 2010 1:17 PM To: j...@quik.com; 'Discussion of precise time and frequency measurement' Subject: Re: [time-nuts] Regulating a pendulum clock What happens when the rope breaks? -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of J. Forster Sent: 09 August 2010 19:10 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Regulating a pendulum clock You could put a large mass of concrete or somehing above the clock and crank it up and down, to balance out the computed gravity changes. :) -John == Unfortunately Gravity is not constant. Pendulum clocks show cyclic errors due to the influences of the Moon's and Sun's Gravitational fields. I forget the amounts but it is in the region of parts in 10 to the 7, which is easily measurable. This limits the compensations one can put into a pendulum clock. -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of mike cook Sent: 09 August 2010 18:21 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Regulating a pendulum clock Le 09/08/2010 18:46, Bob Holmstrom a écrit : Food for thought. I find it interesting that no one has suggested alternatives to improving the performance of a pendulum clock other than controlling it with a higher performance clock. If the goal is a better clock why not attempt to understand the source of the errors and work on methods to control or compensate for them? Teddy Hall has been taken to task for using a quartz controlled oscillator to measure the amplitude of a pendulum in the control loop of his Littlemore clock. Tom Van Baak has developed techniques for analyzing the performance and hence potential error sources of pendulum clocks - perhaps he will share some of his work here. Horological history is full of many attempts at solutions to the problem, but it would seem that the creativity of this group might generate some new ideas that are more in the spirit of better timekeeping than attaching the pendulum to a better oscillator. How about a wireless controlled device attached to the pendulum that changes its position based on error sensor readings, not time errors, but instead, temperature, barometric pressure, gravity, etc. that would maintain a more constant pendulum period? Yup. We have temperature and pressure ICs available , I think that gravity is pretty constant if the clock isn't being moved about. Humididty might also need logging aswell. So it should be easy enough to predict the pendulums response to changes given a reasonable time of observation. That said, clocks have always been adjusted against better references.. IIRC Harrison (and probably others) was using star transits to regulate his long case clocks. Bob Holmström Editor Horological Science Newsletter www.hsn161.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
This limits the compensations one can put into a pendulum clock unless you actually build compensation for those effects too :) I would think the timing of gravitational effects of the moon and the sun can be easily predicted. I am not sure the amplitude of these effects can be precisely modeled, but that would be an interesting part of the project. If you know the timing of a perturbation, you can measure the effect from the instrument itself (by checking it against a reference that is insensitive to that perturbation and applying the proper filtering algorithms) and determine the coefficients experimentally. That is what the Thunderbolt does while it is locked to GPS, so that when it loses the signal, it can keep its OCXO in check. Didier Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: Ian Sheffield ian.sheffie...@tesco.net Sender: time-nuts-boun...@febo.com Date: Mon, 9 Aug 2010 18:34:40 To: 'Discussion of precise time and frequency measurement'time-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Regulating a pendulum clock Unfortunately Gravity is not constant. Pendulum clocks show cyclic errors due to the influences of the Moon's and Sun's Gravitational fields. I forget the amounts but it is in the region of parts in 10 to the 7, which is easily measurable. This limits the compensations one can put into a pendulum clock. -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of mike cook Sent: 09 August 2010 18:21 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Regulating a pendulum clock Le 09/08/2010 18:46, Bob Holmstrom a écrit : Food for thought. I find it interesting that no one has suggested alternatives to improving the performance of a pendulum clock other than controlling it with a higher performance clock. If the goal is a better clock why not attempt to understand the source of the errors and work on methods to control or compensate for them? Teddy Hall has been taken to task for using a quartz controlled oscillator to measure the amplitude of a pendulum in the control loop of his Littlemore clock. Tom Van Baak has developed techniques for analyzing the performance and hence potential error sources of pendulum clocks - perhaps he will share some of his work here. Horological history is full of many attempts at solutions to the problem, but it would seem that the creativity of this group might generate some new ideas that are more in the spirit of better timekeeping than attaching the pendulum to a better oscillator. How about a wireless controlled device attached to the pendulum that changes its position based on error sensor readings, not time errors, but instead, temperature, barometric pressure, gravity, etc. that would maintain a more constant pendulum period? Yup. We have temperature and pressure ICs available , I think that gravity is pretty constant if the clock isn't being moved about. Humididty might also need logging aswell. So it should be easy enough to predict the pendulums response to changes given a reasonable time of observation. That said, clocks have always been adjusted against better references.. IIRC Harrison (and probably others) was using star transits to regulate his long case clocks. Bob Holmström Editor Horological Science Newsletter www.hsn161.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Ahhh, this is more like it! Large gears and thick ropes moving heavy weights up and down. :) Of course, you wouldn't want anything digital doing this. Just a large pendulum clock driving a maze of gears that calculate solar and lunar positions. Bill Hawkins -Original Message- From: J. L. Trantham, M. D. Sent: Monday, August 09, 2010 3:10 PM Personally, I would get out of the way. : ) Joe -Original Message- From: Ian Sheffield Sent: Monday, August 09, 2010 1:17 PM What happens when the rope breaks? -Original Message- From: J. Forster Sent: 09 August 2010 19:10 You could put a large mass of concrete or somehing above the clock and crank it up and down, to balance out the computed gravity changes. :) -John Unfortunately Gravity is not constant. Pendulum clocks show cyclic errors due to the influences of the Moon's and Sun's Gravitational fields. I forget the amounts but it is in the region of parts in 10 to the 7, which is easily measurable. This limits the compensations one can put into a pendulum clock. -Original Message- From: mike cook Sent: 09 August 2010 18:21 On 09/08/2010 18:46, Bob Holmstrom has written: Food for thought. I find it interesting that no one has suggested alternatives to improving the performance of a pendulum clock other than controlling it with a higher performance clock. If the goal is a better clock why not attempt to understand the source of the errors and work on methods to control or compensate for them? Teddy Hall has been taken to task for using a quartz controlled oscillator to measure the amplitude of a pendulum in the control loop of his Littlemore clock. Tom Van Baak has developed techniques for analyzing the performance and hence potential error sources of pendulum clocks - perhaps he will share some of his work here. Horological history is full of many attempts at solutions to the problem, but it would seem that the creativity of this group might generate some new ideas that are more in the spirit of better timekeeping than attaching the pendulum to a better oscillator. How about a wireless controlled device attached to the pendulum that changes its position based on error sensor readings, not time errors, but instead, temperature, barometric pressure, gravity, etc. that would maintain a more constant pendulum period? Yup. We have temperature and pressure ICs available , I think that gravity is pretty constant if the clock isn't being moved about. Humididty might also need logging aswell. So it should be easy enough to predict the pendulums response to changes given a reasonable time of observation. That said, clocks have always been adjusted against better references.. IIRC Harrison (and probably others) was using star transits to regulate his long case clocks. Bob Holmström Editor Horological Science Newsletter www.hsn161.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Oh Dear! What have I started? ;-) -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Bill Hawkins Sent: 09 August 2010 21:36 To: 'Discussion of precise time and frequency measurement' Subject: Re: [time-nuts] Regulating a pendulum clock Ahhh, this is more like it! Large gears and thick ropes moving heavy weights up and down. :) Of course, you wouldn't want anything digital doing this. Just a large pendulum clock driving a maze of gears that calculate solar and lunar positions. Bill Hawkins -Original Message- From: J. L. Trantham, M. D. Sent: Monday, August 09, 2010 3:10 PM Personally, I would get out of the way. : ) Joe -Original Message- From: Ian Sheffield Sent: Monday, August 09, 2010 1:17 PM What happens when the rope breaks? -Original Message- From: J. Forster Sent: 09 August 2010 19:10 You could put a large mass of concrete or somehing above the clock and crank it up and down, to balance out the computed gravity changes. :) -John Unfortunately Gravity is not constant. Pendulum clocks show cyclic errors due to the influences of the Moon's and Sun's Gravitational fields. I forget the amounts but it is in the region of parts in 10 to the 7, which is easily measurable. This limits the compensations one can put into a pendulum clock. -Original Message- From: mike cook Sent: 09 August 2010 18:21 On 09/08/2010 18:46, Bob Holmstrom has written: Food for thought. I find it interesting that no one has suggested alternatives to improving the performance of a pendulum clock other than controlling it with a higher performance clock. If the goal is a better clock why not attempt to understand the source of the errors and work on methods to control or compensate for them? Teddy Hall has been taken to task for using a quartz controlled oscillator to measure the amplitude of a pendulum in the control loop of his Littlemore clock. Tom Van Baak has developed techniques for analyzing the performance and hence potential error sources of pendulum clocks - perhaps he will share some of his work here. Horological history is full of many attempts at solutions to the problem, but it would seem that the creativity of this group might generate some new ideas that are more in the spirit of better timekeeping than attaching the pendulum to a better oscillator. How about a wireless controlled device attached to the pendulum that changes its position based on error sensor readings, not time errors, but instead, temperature, barometric pressure, gravity, etc. that would maintain a more constant pendulum period? Yup. We have temperature and pressure ICs available , I think that gravity is pretty constant if the clock isn't being moved about. Humididty might also need logging aswell. So it should be easy enough to predict the pendulums response to changes given a reasonable time of observation. That said, clocks have always been adjusted against better references.. IIRC Harrison (and probably others) was using star transits to regulate his long case clocks. Bob Holmström Editor Horological Science Newsletter www.hsn161.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Nah! No ropes or gears. Just a SS tank on steel stilts and a big mercury reservoir and a pump. And it might not have to hold tons. Think of a hollow SS donut with the pendulum in the clear space. KISS, -John === Ahhh, this is more like it! Large gears and thick ropes moving heavy weights up and down. :) Of course, you wouldn't want anything digital doing this. Just a large pendulum clock driving a maze of gears that calculate solar and lunar positions. Bill Hawkins -Original Message- From: J. L. Trantham, M. D. Sent: Monday, August 09, 2010 3:10 PM Personally, I would get out of the way. : ) Joe -Original Message- From: Ian Sheffield Sent: Monday, August 09, 2010 1:17 PM What happens when the rope breaks? -Original Message- From: J. Forster Sent: 09 August 2010 19:10 You could put a large mass of concrete or somehing above the clock and crank it up and down, to balance out the computed gravity changes. :) -John Unfortunately Gravity is not constant. Pendulum clocks show cyclic errors due to the influences of the Moon's and Sun's Gravitational fields. I forget the amounts but it is in the region of parts in 10 to the 7, which is easily measurable. This limits the compensations one can put into a pendulum clock. -Original Message- From: mike cook Sent: 09 August 2010 18:21 On 09/08/2010 18:46, Bob Holmstrom has written: Food for thought. I find it interesting that no one has suggested alternatives to improving the performance of a pendulum clock other than controlling it with a higher performance clock. If the goal is a better clock why not attempt to understand the source of the errors and work on methods to control or compensate for them? Teddy Hall has been taken to task for using a quartz controlled oscillator to measure the amplitude of a pendulum in the control loop of his Littlemore clock. Tom Van Baak has developed techniques for analyzing the performance and hence potential error sources of pendulum clocks - perhaps he will share some of his work here. Horological history is full of many attempts at solutions to the problem, but it would seem that the creativity of this group might generate some new ideas that are more in the spirit of better timekeeping than attaching the pendulum to a better oscillator. How about a wireless controlled device attached to the pendulum that changes its position based on error sensor readings, not time errors, but instead, temperature, barometric pressure, gravity, etc. that would maintain a more constant pendulum period? Yup. We have temperature and pressure ICs available , I think that gravity is pretty constant if the clock isn't being moved about. Humididty might also need logging aswell. So it should be easy enough to predict the pendulums response to changes given a reasonable time of observation. That said, clocks have always been adjusted against better references.. IIRC Harrison (and probably others) was using star transits to regulate his long case clocks. Bob Holmström Editor Horological Science Newsletter www.hsn161.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
There are many pieces of technology developed in the 20th century that have not been applied to pendulum clocks. My take on much of the technology is that it is too volatile to be of use in making a better clock. The task is not to keep better time, that has already been done with non-mechanical clocks by atomic clocks. But atomic clocks only work a few years before they fail. Electronics and computing are outdated in a few years and any use of these technologies in a clock fails due to lack of spare parts and closure of the plant that made the components. What we need is a clock that can continue for 400 years with the skills and technology that will be available over that time span. Even in mechanical clocks, technology may fail through lack of understanding. I was once a fan of an escapement devised by Reid, later LeRoy, that used no crutch on the pendulum. Then I read of clocks with this escapement being convert back to a Graham escapement by clock repairers who did not understand the superior escapement. So progress in mechanical clocks should be for a clock that is simple to maintain and more precise than alternate clocks. To do this the known defects of traditional clocks need to be overcome. In the 20th century the big step was a free pendulum, this usually required a secondary pendulum to clock (using electronic terms) the system so that the free pendulum would be impulsed at the correct time. These clocks removed much of what was known as escapement error. Circular error is another defect, the frequency of a pendulum is slightly dependent on amplitude. Either really accurate control of amplitude is required (in some ways equivalent of an oven on a crystal) or a method is required to null the circular error. Barometric error is another defect. Buoyancy error can be eliminated in a compound pendulum of suitable design, but the error due to inertial effects of displaced air by the pendulum require a vaccuum (which is very inconvenient) or perhaps an idea I am working on of a container around the pendulum oscillating in the same phase and amplitude to move the air with the pendulum. This container could be the second pendulum which is phase-locked to the free pendulum and whose minor timing problems would not be significant. There is a geometric solution to circular error, a bit similar to the tempco turn-over in crystals, where locally the defect has zero amplitude. The remaining problem is to incorporate these ideas into a design that is entertaining to behold, simple to fix and durable enough to last long enough to make it worth maintaining. As for technology, electromagnets are robust, we have some great new materials, rare earth magnets and some great methods of construction. I look forward to a clock that, compared to an atomic clock, is really just an accurate gravity meter. cheers, Neville Michie On 10/08/2010, at 2:46 AM, Bob Holmstrom wrote: Food for thought. I find it interesting that no one has suggested alternatives to improving the performance of a pendulum clock other than controlling it with a higher performance clock. If the goal is a better clock why not attempt to understand the source of the errors and work on methods to control or compensate for them? Teddy Hall has been taken to task for using a quartz controlled oscillator to measure the amplitude of a pendulum in the control loop of his Littlemore clock. Tom Van Baak has developed techniques for analyzing the performance and hence potential error sources of pendulum clocks - perhaps he will share some of his work here. Horological history is full of many attempts at solutions to the problem, but it would seem that the creativity of this group might generate some new ideas that are more in the spirit of better timekeeping than attaching the pendulum to a better oscillator. How about a wireless controlled device attached to the pendulum that changes its position based on error sensor readings, not time errors, but instead, temperature, barometric pressure, gravity, etc. that would maintain a more constant pendulum period? Bob Holmström Editor Horological Science Newsletter www.hsn161.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/ time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Hi Ian, Unfortunately Gravity is not constant. Pendulum clocks show cyclic errors due to the influences of the Moon's and Sun's Gravitational fields. I forget the amounts but it is in the region of parts in 10 to the 7, which is easily measurable. This limits the compensations one can put into a pendulum clock. http://en.wikipedia.org/wiki/Tidal_force gives 1.1e-7g and 0.52e-7g for Moon and Sun acceleration at Earth. Hmmm that is ca 0.1 microg (ug). Leaving the pendulum clock line of thought... by instead measuring this change of apparent gravity and the models for Moon-Earth relative positions we have a source of time! Hmmm... spec sheet of my best accelerometer Temp stability 30 ug/degC 1 year bias stability 250 ug Threshold/resolution 1ug The accelerometer clearly needs to be ovenized, and hopefully the spec is is conservative and I need to have luck with a really good accel. You also need to mount it on a structure separate from where you walk. No nearby heavy vehicles and so on. Well we will need a stable sampling clock, so maybe the pendulum is back in the picture. As the sensing element in the acc is made of quartz, and adding an oven - there are quite a few similarities with an OCXO! Lesser models of these accelerometers are operated as temperature compensated or without any temperature compensations - compare with TCXOs and XOs... http://www.inertialsensor.com/ Sorry if this went off topic! -- Björn ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Hi Putting a computing device on a pendulum to compensate for known effects is really no different than what you do with a analog or digital TCXO. I suspect that the gravitational impact of the sun and moon can be calculated with pretty good precision. The same would be true of secondary pressure effects. Bob -- From: b...@lysator.liu.se Sent: Monday, August 09, 2010 7:07 PM To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Regulating a pendulum clock Hi Ian, Unfortunately Gravity is not constant. Pendulum clocks show cyclic errors due to the influences of the Moon's and Sun's Gravitational fields. I forget the amounts but it is in the region of parts in 10 to the 7, which is easily measurable. This limits the compensations one can put into a pendulum clock. http://en.wikipedia.org/wiki/Tidal_force gives 1.1e-7g and 0.52e-7g for Moon and Sun acceleration at Earth. Hmmm that is ca 0.1 microg (ug). Leaving the pendulum clock line of thought... by instead measuring this change of apparent gravity and the models for Moon-Earth relative positions we have a source of time! Hmmm... spec sheet of my best accelerometer Temp stability 30 ug/degC 1 year bias stability 250 ug Threshold/resolution 1ug The accelerometer clearly needs to be ovenized, and hopefully the spec is is conservative and I need to have luck with a really good accel. You also need to mount it on a structure separate from where you walk. No nearby heavy vehicles and so on. Well we will need a stable sampling clock, so maybe the pendulum is back in the picture. As the sensing element in the acc is made of quartz, and adding an oven - there are quite a few similarities with an OCXO! Lesser models of these accelerometers are operated as temperature compensated or without any temperature compensations - compare with TCXOs and XOs... http://www.inertialsensor.com/ Sorry if this went off topic! -- Björn ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
In principle, there is no real reason a Rb, Cs, ot atomic fountain could not be made to last a very, very long time in a lab. It would certainly be possible to design a source that is either continuously fed from the outside or a pair of sources that can be changed to maintain continuous operation. Ditto for the vacuum system, and detector assembly. It'd be a christmas tree of SS and Conflat. Not small but do-able. Electronics can be designed to be hot-swapped at the functional block level. -John There are many pieces of technology developed in the 20th century that have not been applied to pendulum clocks. My take on much of the technology is that it is too volatile to be of use in making a better clock. The task is not to keep better time, that has already been done with non-mechanical clocks by atomic clocks. But atomic clocks only work a few years before they fail. Electronics and computing are outdated in a few years and any use of these technologies in a clock fails due to lack of spare parts and closure of the plant that made the components. What we need is a clock that can continue for 400 years with the skills and technology that will be available over that time span. Even in mechanical clocks, technology may fail through lack of understanding. I was once a fan of an escapement devised by Reid, later LeRoy, that used no crutch on the pendulum. Then I read of clocks with this escapement being convert back to a Graham escapement by clock repairers who did not understand the superior escapement. So progress in mechanical clocks should be for a clock that is simple to maintain and more precise than alternate clocks. To do this the known defects of traditional clocks need to be overcome. In the 20th century the big step was a free pendulum, this usually required a secondary pendulum to clock (using electronic terms) the system so that the free pendulum would be impulsed at the correct time. These clocks removed much of what was known as escapement error. Circular error is another defect, the frequency of a pendulum is slightly dependent on amplitude. Either really accurate control of amplitude is required (in some ways equivalent of an oven on a crystal) or a method is required to null the circular error. Barometric error is another defect. Buoyancy error can be eliminated in a compound pendulum of suitable design, but the error due to inertial effects of displaced air by the pendulum require a vaccuum (which is very inconvenient) or perhaps an idea I am working on of a container around the pendulum oscillating in the same phase and amplitude to move the air with the pendulum. This container could be the second pendulum which is phase-locked to the free pendulum and whose minor timing problems would not be significant. There is a geometric solution to circular error, a bit similar to the tempco turn-over in crystals, where locally the defect has zero amplitude. The remaining problem is to incorporate these ideas into a design that is entertaining to behold, simple to fix and durable enough to last long enough to make it worth maintaining. As for technology, electromagnets are robust, we have some great new materials, rare earth magnets and some great methods of construction. I look forward to a clock that, compared to an atomic clock, is really just an accurate gravity meter. cheers, Neville Michie On 10/08/2010, at 2:46 AM, Bob Holmstrom wrote: Food for thought. I find it interesting that no one has suggested alternatives to improving the performance of a pendulum clock other than controlling it with a higher performance clock. If the goal is a better clock why not attempt to understand the source of the errors and work on methods to control or compensate for them? Teddy Hall has been taken to task for using a quartz controlled oscillator to measure the amplitude of a pendulum in the control loop of his Littlemore clock. Tom Van Baak has developed techniques for analyzing the performance and hence potential error sources of pendulum clocks - perhaps he will share some of his work here. Horological history is full of many attempts at solutions to the problem, but it would seem that the creativity of this group might generate some new ideas that are more in the spirit of better timekeeping than attaching the pendulum to a better oscillator. How about a wireless controlled device attached to the pendulum that changes its position based on error sensor readings, not time errors, but instead, temperature, barometric pressure, gravity, etc. that would maintain a more constant pendulum period? Bob Holmström Editor Horological Science Newsletter www.hsn161.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/ time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Bob Holmstrom wrote: Food for thought. I find it interesting that no one has suggested alternatives to improving the performance of a pendulum clock other than controlling it with a higher performance clock. If the goal is a better clock why not attempt to understand the source of the errors and work on methods to control or compensate for them? Teddy Hall has been taken to task for using a quartz controlled oscillator to measure the amplitude of a pendulum in the control loop of his Littlemore clock. Tom Van Baak has developed techniques for analyzing the performance and hence potential error sources of pendulum clocks - perhaps he will share some of his work here. Horological history is full of many attempts at solutions to the problem, but it would seem that the creativity of this group might generate some new ideas that are more in the spirit of better timekeeping than attaching the pendulum to a better oscillator. Perhaps you really mean better pendulum (or mechanical) timekeeping, because by pretty much any measure except aesthetics, vibrating rocks or atoms does a better job. Mind you, I think that this is a worthy goal, because complex mechanisms that work well are a thing of beauty. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Bob Camp wrote: Hi For that matter, how hard is it to put it in a vacuum with temperature control? Gets two big issues out of the way pretty fast. We certainly buy crystal oscillators that are heated and enclosed in pressure tight containers (not quite the same as vacuum, but close). Bob temperature compensation to ppm accuracy is pretty easy, and has been done for 100 years or more. Compensating for air drag changes with temperature might be trickier. however, the period doesn't change very much with drag. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Ian Sheffield wrote: What happens when the rope breaks? -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of J. Forster Sent: 09 August 2010 19:10 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Regulating a pendulum clock You could put a large mass of concrete or somehing above the clock and crank it up and down, to balance out the computed gravity changes. :) who said anything about rope?? Titanium cable, of course.. Or what we do in the space biz... multiple redundancy ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Javier Herrero wrote: Not so simple... you should move it around in order to balance the gravity force vector :) Regards, Javier two large masses rotating around the pendulum, one synchronized with the sun, one sync'd with the moon. Having just looked up the orrery stuff, a suitable gear train on a massive scale is called for. But hey, they made gears for the 70m antennas in the Deep Space Network, so it's clearly possible. One might want some smaller masses, driven by still more gears to counteract the forces from, say, Jupiter. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Bruce Griffiths wrote: Advisable given the required mass will probably be in the 10-100 ton range. Bruce J. L. Trantham, M. D. wrote: Personally, I would get out of the way. : ) Joe Wait a minute.. is it that big? or is it much, much bigger.. Inverse square is involved. The moon's mass is 7.3E22 kg, and it's 400 km away (eccentric 0.055) Let's say our mass is 4 meters from the pendulum... that's a factor of 1e5, so the inverse square is 1e10.. 7.3E22 /1e10 = 7.3E12 kg required... A bit more than 100 tons..grin Call it 7E9 tonnes. If it were water, a sphere about 1200 meters in radius... I'm assuming you'll be using something really really dense (depleted Uranium, perhaps.. very, very inexpensive in 80,000 pound lots) that will get you about 20 times denser.. get you down to a 400 meter radius sphere. Not sounding too practical yet... ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
I screwed up by a factor of a million.. jimlux wrote: Bruce Griffiths wrote: Advisable given the required mass will probably be in the 10-100 ton range. Bruce J. L. Trantham, M. D. wrote: Personally, I would get out of the way. : ) Joe Wait a minute.. is it that big? or is it much, much bigger.. Inverse square is involved. The moon's mass is 7.3E22 kg, and it's 400 km away (eccentric 0.055) 400 E3 km away... Let's say our mass is 4 meters from the pendulum... that's a factor of 1e5, so the inverse square is 1e10.. 7.3E22 /1e10 = 7.3E12 kg required... A bit more than 100 tons..grin 7.3E6 kg.. Call it 7E9 tonnes. If it were water, a sphere about 1200 meters in radius... 7E3 tonnes.. not too bad 12 meters in diameter I'm assuming you'll be using something really really dense (depleted Uranium, perhaps.. very, very inexpensive in 80,000 pound lots) that will get you about 20 times denser.. get you down to a 400 meter radius sphere. 4 meters in diameter... starting to be feasible, eh? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
All this talk about regulating a pendulum clock... are you people buying them, building them, or what? I'm interested! I keep thinking about it and something keeps bringing me back to the bob being a neodymium magnet itself. I'm sure you can guess where I'm headed with that... 73 Brice KA8MAV ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Oh, yeah. A combined gravity and earth's magnetic field detector. A 1 second pendulum will be driven using a Nd magnet about the size of 1/2 a pencil eraser :-) Don - Original Message - From: Heathkid heath...@heathkid.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Monday, August 09, 2010 9:53 PM Subject: Re: [time-nuts] Regulating a pendulum clock All this talk about regulating a pendulum clock... are you people buying them, building them, or what? I'm interested! I keep thinking about it and something keeps bringing me back to the bob being a neodymium magnet itself. I'm sure you can guess where I'm headed with that... 73 Brice KA8MAV ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock (Jim Palfreyman)
This is very interesting and I wonder if the capabilities of this system being applied to any clock pendulum. If this sort of control any pendulum, then I wonder if it's possible to sync it to some standard. Steve On 08/08/2010, Don Mimlitch donm...@yahoo.com wrote: Jim Said: It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labeled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) I have a Warren Telechron Master Clock used in Power Stations in the 20's to regulate the 60 Cycle so that household clocks using synchronous motors would be accurate to seconds a day. This clock has a similar permanent magnet at the end of the Pendulum and a battery connected to a potentiometer to adjust the current flow positive or negative in an electro-magnet below the pendulum.. If the bottom of the magnet in the pendulum is north and the current in the electromagnet is flowing such that its top face is North, then this will repel the pendulum causing its swing to be wider and contrary to common knowledge the swing of a fixed length pendulum is not constant regardless of the swing. (Huygens discovered this in 1670 an found by forcing the arc of the swing to be cycloid instead of circular he could produce uniform oscillation) Thus if the arc is longer the swing takes more time and the clock runs slower. If the current flows in the opposite direction and the two magnets attract then the arc is shortened and the clock runs faster. Of course my master clock isn't as accurate as a Riefler pendulum clock. Also the magnet in my clock has lost it's magnetism over time and I can't use this regulation. So the goal of your adaptation is to have precision control of the current flow in the positive or negative direction. Others on the list are better then me at describing how you might achieve this. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Steve Rooke - ZL3TUV G8KVD The only reason for time is so that everything doesn't happen at once. - Einstein ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock (Jim Palfreyman)
This is very interesting and I wonder if the capabilities of this system being applied to any clock pendulum. If this sort of control any pendulum, then I wonder if it's possible to sync it to some standard. Steve On 08/08/2010, Don Mimlitch donm...@yahoo.com wrote: Jim Said: It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labeled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) I have a Warren Telechron Master Clock used in Power Stations in the 20's to regulate the 60 Cycle so that household clocks using synchronous motors would be accurate to seconds a day. This clock has a similar permanent magnet at the end of the Pendulum and a battery connected to a potentiometer to adjust the current flow positive or negative in an electro-magnet below the pendulum.. If the bottom of the magnet in the pendulum is north and the current in the electromagnet is flowing such that its top face is North, then this will repel the pendulum causing its swing to be wider and contrary to common knowledge the swing of a fixed length pendulum is not constant regardless of the swing. (Huygens discovered this in 1670 an found by forcing the arc of the swing to be cycloid instead of circular he could produce uniform oscillation) Thus if the arc is longer the swing takes more time and the clock runs slower. If the current flows in the opposite direction and the two magnets attract then the arc is shortened and the clock runs faster. Of course my master clock isn't as accurate as a Riefler pendulum clock. Also the magnet in my clock has lost it's magnetism over time and I can't use this regulation. So the goal of your adaptation is to have precision control of the current flow in the positive or negative direction. Others on the list are better then me at describing how you might achieve this. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Steve Rooke - ZL3TUV G8KVD The only reason for time is so that everything doesn't happen at once. - Einstein ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock (Jim Palfreyman)
Sorry for double post, modem dropped during sending and a refresh on the browser when it was up resent the message. Steve On 08/08/2010, Steve Rooke sar10...@gmail.com wrote: This is very interesting and I wonder if the capabilities of this system being applied to any clock pendulum. If this sort of control any pendulum, then I wonder if it's possible to sync it to some standard. Steve On 08/08/2010, Don Mimlitch donm...@yahoo.com wrote: Jim Said: It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labeled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) I have a Warren Telechron Master Clock used in Power Stations in the 20's to regulate the 60 Cycle so that household clocks using synchronous motors would be accurate to seconds a day. This clock has a similar permanent magnet at the end of the Pendulum and a battery connected to a potentiometer to adjust the current flow positive or negative in an electro-magnet below the pendulum.. If the bottom of the magnet in the pendulum is north and the current in the electromagnet is flowing such that its top face is North, then this will repel the pendulum causing its swing to be wider and contrary to common knowledge the swing of a fixed length pendulum is not constant regardless of the swing. (Huygens discovered this in 1670 an found by forcing the arc of the swing to be cycloid instead of circular he could produce uniform oscillation) Thus if the arc is longer the swing takes more time and the clock runs slower. If the current flows in the opposite direction and the two magnets attract then the arc is shortened and the clock runs faster. Of course my master clock isn't as accurate as a Riefler pendulum clock. Also the magnet in my clock has lost it's magnetism over time and I can't use this regulation. So the goal of your adaptation is to have precision control of the current flow in the positive or negative direction. Others on the list are better then me at describing how you might achieve this. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Steve Rooke - ZL3TUV G8KVD The only reason for time is so that everything doesn't happen at once. - Einstein -- Steve Rooke - ZL3TUV G8KVD The only reason for time is so that everything doesn't happen at once. - Einstein ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock (Jim Palfreyman)
Not many clocks are set up with the gear to modulate the rate, but they are all still sensitive to injection locking. A tiny rare earth magnet on the pendulum (say 1/2 way down the pendulum rod) and a coil fed with a stretched (say 250ms long) PPS or for a seconds pendulum PP2S pulse will pull the pendulum into phaselock with a surprisingly small amount of power. In fact if you turn off the drive it would keep the pendulum swinging. Cheers, Neville Michie On 08/08/2010, at 6:00 PM, Steve Rooke wrote: This is very interesting and I wonder if the capabilities of this system being applied to any clock pendulum. If this sort of control any pendulum, then I wonder if it's possible to sync it to some standard. Steve On 08/08/2010, Don Mimlitch donm...@yahoo.com wrote: Jim Said: It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labeled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) I have a Warren Telechron Master Clock used in Power Stations in the 20's to regulate the 60 Cycle so that household clocks using synchronous motors would be accurate to seconds a day. This clock has a similar permanent magnet at the end of the Pendulum and a battery connected to a potentiometer to adjust the current flow positive or negative in an electro-magnet below the pendulum.. If the bottom of the magnet in the pendulum is north and the current in the electromagnet is flowing such that its top face is North, then this will repel the pendulum causing its swing to be wider and contrary to common knowledge the swing of a fixed length pendulum is not constant regardless of the swing. (Huygens discovered this in 1670 an found by forcing the arc of the swing to be cycloid instead of circular he could produce uniform oscillation) Thus if the arc is longer the swing takes more time and the clock runs slower. If the current flows in the opposite direction and the two magnets attract then the arc is shortened and the clock runs faster. Of course my master clock isn't as accurate as a Riefler pendulum clock. Also the magnet in my clock has lost it's magnetism over time and I can't use this regulation. So the goal of your adaptation is to have precision control of the current flow in the positive or negative direction. Others on the list are better then me at describing how you might achieve this. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Steve Rooke - ZL3TUV G8KVD The only reason for time is so that everything doesn't happen at once. - Einstein ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/ time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock (Jim Palfreyman)
I was rather more thinking of the setup that Don was suggesting as not many domestic clocks have a seconds pendulum and it would otherwise take dividing down a referenced oscillator to the correct frequency. Cheers, Steve On 08/08/2010, Neville Michie namic...@gmail.com wrote: Not many clocks are set up with the gear to modulate the rate, but they are all still sensitive to injection locking. A tiny rare earth magnet on the pendulum (say 1/2 way down the pendulum rod) and a coil fed with a stretched (say 250ms long) PPS or for a seconds pendulum PP2S pulse will pull the pendulum into phaselock with a surprisingly small amount of power. In fact if you turn off the drive it would keep the pendulum swinging. Cheers, Neville Michie On 08/08/2010, at 6:00 PM, Steve Rooke wrote: This is very interesting and I wonder if the capabilities of this system being applied to any clock pendulum. If this sort of control any pendulum, then I wonder if it's possible to sync it to some standard. Steve On 08/08/2010, Don Mimlitch donm...@yahoo.com wrote: Jim Said: It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labeled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) I have a Warren Telechron Master Clock used in Power Stations in the 20's to regulate the 60 Cycle so that household clocks using synchronous motors would be accurate to seconds a day. This clock has a similar permanent magnet at the end of the Pendulum and a battery connected to a potentiometer to adjust the current flow positive or negative in an electro-magnet below the pendulum.. If the bottom of the magnet in the pendulum is north and the current in the electromagnet is flowing such that its top face is North, then this will repel the pendulum causing its swing to be wider and contrary to common knowledge the swing of a fixed length pendulum is not constant regardless of the swing. (Huygens discovered this in 1670 an found by forcing the arc of the swing to be cycloid instead of circular he could produce uniform oscillation) Thus if the arc is longer the swing takes more time and the clock runs slower. If the current flows in the opposite direction and the two magnets attract then the arc is shortened and the clock runs faster. Of course my master clock isn't as accurate as a Riefler pendulum clock. Also the magnet in my clock has lost it's magnetism over time and I can't use this regulation. So the goal of your adaptation is to have precision control of the current flow in the positive or negative direction. Others on the list are better then me at describing how you might achieve this. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Steve Rooke - ZL3TUV G8KVD The only reason for time is so that everything doesn't happen at once. - Einstein ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/ time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Steve Rooke - ZL3TUV G8KVD The only reason for time is so that everything doesn't happen at once. - Einstein ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock (Jim Palfreyman)
Check out Bryan Mumfords page. http://www.bmumford.com/clocks/em2/index.html Le 08/08/2010 11:14, Steve Rooke a écrit : I was rather more thinking of the setup that Don was suggesting as not many domestic clocks have a seconds pendulum and it would otherwise take dividing down a referenced oscillator to the correct frequency. Cheers, Steve On 08/08/2010, Neville Michienamic...@gmail.com wrote: Not many clocks are set up with the gear to modulate the rate, but they are all still sensitive to injection locking. A tiny rare earth magnet on the pendulum (say 1/2 way down the pendulum rod) and a coil fed with a stretched (say 250ms long) PPS or for a seconds pendulum PP2S pulse will pull the pendulum into phaselock with a surprisingly small amount of power. In fact if you turn off the drive it would keep the pendulum swinging. Cheers, Neville Michie On 08/08/2010, at 6:00 PM, Steve Rooke wrote: This is very interesting and I wonder if the capabilities of this system being applied to any clock pendulum. If this sort of control any pendulum, then I wonder if it's possible to sync it to some standard. Steve On 08/08/2010, Don Mimlitchdonm...@yahoo.com wrote: Jim Said: It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labeled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) I have a Warren Telechron Master Clock used in Power Stations in the 20's to regulate the 60 Cycle so that household clocks using synchronous motors would be accurate to seconds a day. This clock has a similar permanent magnet at the end of the Pendulum and a battery connected to a potentiometer to adjust the current flow positive or negative in an electro-magnet below the pendulum.. If the bottom of the magnet in the pendulum is north and the current in the electromagnet is flowing such that its top face is North, then this will repel the pendulum causing its swing to be wider and contrary to common knowledge the swing of a fixed length pendulum is not constant regardless of the swing. (Huygens discovered this in 1670 an found by forcing the arc of the swing to be cycloid instead of circular he could produce uniform oscillation) Thus if the arc is longer the swing takes more time and the clock runs slower. If the current flows in the opposite direction and the two magnets attract then the arc is shortened and the clock runs faster. Of course my master clock isn't as accurate as a Riefler pendulum clock. Also the magnet in my clock has lost it's magnetism over time and I can't use this regulation. So the goal of your adaptation is to have precision control of the current flow in the positive or negative direction. Others on the list are better then me at describing how you might achieve this. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Steve Rooke - ZL3TUV G8KVD The only reason for time is so that everything doesn't happen at once. - Einstein ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/ time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
The attached single ended inverting driver is perhaps a better choice as it allows a dc coupled noniverting amplifier with gain and significant offset and drift to be substituted for the LT1010 buffer depicted if the frequency compensation is adjusted to suit. The series RC across the coil damps the coil resonance and the 1nF caps approximate wiring and coil capacitance to ground. A 10nF coil shunt capacitance and a series R of 400 ohms is included in the model. In practice the compensation should be adjusted to suit the actual coil used. A dc coupled discrete (or IC) audio power amplifier is one option for the noninverting amplifier. The noninverting amplifier may also have higher supply rails should this be useful/necessary. Bruce Bruce Griffiths wrote: A high voltage opamp (or a low voltage opamp with a discrete output stage with a voltage gain of at least 2) with -3V and + 30V supplies is perhaps the simplest method. The opamp merely senses the current flowing in a current sensing resistor and regulates this voltage drop to equal the output of a DAC. Alternatively it should be feasible to use a pair of opamps (plus output buffers) configured in a bridge arrangement to drive the coil from a single 30V supply. If one end of the coil has to remain near ground then a unity gain difference amplifier (with a discrete buffer with voltage gain) could be employed to implement a current source. A difference amplifier could also be employed together with an opamp (plus unity voltage gain discrete ouput stage) inverter to drive the coil from a single 30V supply. Bruce J. Forster wrote: Since it's inside a closed loop, the design is uncritical. One option is a high voltage Op-Amp with +/- 25 to 30 VDC supplies. You would set the OA gain to about 10, so 2.5 V in would yield 25 V out. and sum in a negative offset voltage so that +2.5 from the DAC yields 0.0 V out. I'd use something like a 100 K FB resistor and a 10K from the DAC, assuming it's a voltage output DAC. A 1 M to the -25 V supply would provide the 2.5 V offset. Another option would be to use two series opamps with the first set up as above, and the second as a unity gain inverter with input connected to the output of the first. The coil would connect between the two OA outputs. As one output swings high, the other mirrors that and goes low (just as in an H bridge). Stability might be an issue, but this has the advantage of only needing a +/- 15 supplies. FWIW, -John = Hi all, I have a Seimens master clock with a Reiffler pendulum. A lovely piece of work that used to provide time services in the 40s. Being a master clock it has contacts that open and close on each pendulum swing and so I can monitor it's accuracy quite easily using gps and my 5370B. I've adjusted it as best I can and the best I can get is about 50 ms over 24 hours. However that was a one off. Temp and air pressure cause variations of up to 300 ms and it changes direction too. Basically it's hard to keep accurate. It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labelled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) It's about 25v in the coil and goes up to 60mA max. Even at levels of 2mA has an effect. Using this control it's quite easy to manually bring the clock back to the right time if it's say half a second fast. What I want to do is control the current in the coil with a micro controller which I have attached to a rubidium oscillator. Getting the pps from the pendulum clock in and comparing to actual time is easy, but I need a way to control the current through the coil so it can dynamically adjust the clock. I need the current to go from say -10 to +10 mA (at 25v) and this needs to be controlled via a micro controller output (which goes from 0 to 5 with 2.5 being the 0mA point). I can either use the D/A in the controller (or PWM an output I suppose). I'd appreciate some thoughts on circuits to do this. Software side is not a problem. Jim Palfreyman ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock (Jim Palfreyman)
On 08/08/2010, mike cook mike.c...@orange.fr wrote: Check out Bryan Mumfords page. http://www.bmumford.com/clocks/em2/index.html I did not want to kick the pendulum with a pulse each swing as the drive would be part and parcel of the existing clock mechanism. What I was interested in was Don Mimlitch's description of how the Riefler Pendulum and Warren Telechron Master Clocks work. The control of constant current to the electromagnet under the pendulum seems quite similar to an EFC and could perhaps be used in a PLL to sync with a reference source, as Jim was originally proposing. Of course, retrofitting a conventional clock like this would require the attachment of a magnet to the pendulum, necessitating reducing the weight of the pendulum to account for it, installing an electromagnet under the pendulum and arranging for each swing of the pendulum to produce some form of pulse signal. Of course, the timing in pulses per second of the original clock would have to be determined and the frequency standard divided down to match this rate before both signals are fed to a comparator and LPF to provide the 'EFC' voltage to control the electromagnetic current. Steve Le 08/08/2010 11:14, Steve Rooke a écrit : I was rather more thinking of the setup that Don was suggesting as not many domestic clocks have a seconds pendulum and it would otherwise take dividing down a referenced oscillator to the correct frequency. Cheers, Steve On 08/08/2010, Neville Michienamic...@gmail.com wrote: Not many clocks are set up with the gear to modulate the rate, but they are all still sensitive to injection locking. A tiny rare earth magnet on the pendulum (say 1/2 way down the pendulum rod) and a coil fed with a stretched (say 250ms long) PPS or for a seconds pendulum PP2S pulse will pull the pendulum into phaselock with a surprisingly small amount of power. In fact if you turn off the drive it would keep the pendulum swinging. Cheers, Neville Michie On 08/08/2010, at 6:00 PM, Steve Rooke wrote: This is very interesting and I wonder if the capabilities of this system being applied to any clock pendulum. If this sort of control any pendulum, then I wonder if it's possible to sync it to some standard. Steve On 08/08/2010, Don Mimlitchdonm...@yahoo.com wrote: Jim Said: It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labeled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) I have a Warren Telechron Master Clock used in Power Stations in the 20's to regulate the 60 Cycle so that household clocks using synchronous motors would be accurate to seconds a day. This clock has a similar permanent magnet at the end of the Pendulum and a battery connected to a potentiometer to adjust the current flow positive or negative in an electro-magnet below the pendulum.. If the bottom of the magnet in the pendulum is north and the current in the electromagnet is flowing such that its top face is North, then this will repel the pendulum causing its swing to be wider and contrary to common knowledge the swing of a fixed length pendulum is not constant regardless of the swing. (Huygens discovered this in 1670 an found by forcing the arc of the swing to be cycloid instead of circular he could produce uniform oscillation) Thus if the arc is longer the swing takes more time and the clock runs slower. If the current flows in the opposite direction and the two magnets attract then the arc is shortened and the clock runs faster. Of course my master clock isn't as accurate as a Riefler pendulum clock. Also the magnet in my clock has lost it's magnetism over time and I can't use this regulation. So the goal of your adaptation is to have precision control of the current flow in the positive or negative direction. Others on the list are better then me at describing how you might achieve this. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Steve Rooke - ZL3TUV G8KVD The only reason for time is so that everything doesn't happen at once. - Einstein ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/ time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions
Re: [time-nuts] Regulating a pendulum clock (Jim Palfreyman)
Hi all, I think at this point I need to explain the electromagnet positioning. The permanent magnet is on the rod about 25cm down (out of 100cm). The electromagnet is on the left side and so gets close to the permanent magnet every two seconds. Injection locking would be a simple solution and worth a try. I could use a solid state relay triggered by the micro controller that passes a fixed current every second to the coil (it would of course only interact every other second). The location of the coil and magnet I think are perfect for that. My original proposal is more true because it acts like a gpsdo and let's the original pendulum do most of the work. But the injection locking is quick and dirty and exactly how the slave to this clock would have worked anyway. So I think I will do that. In the meantime tvb has convinced me to run it free in the meantime to see if it can detect tidal forces. Jim Palfreyman On Sunday, August 8, 2010, Steve Rooke sar10...@gmail.com wrote: On 08/08/2010, mike cook mike.c...@orange.fr wrote: Check out Bryan Mumfords page. http://www.bmumford.com/clocks/em2/index.html I did not want to kick the pendulum with a pulse each swing as the drive would be part and parcel of the existing clock mechanism. What I was interested in was Don Mimlitch's description of how the Riefler Pendulum and Warren Telechron Master Clocks work. The control of constant current to the electromagnet under the pendulum seems quite similar to an EFC and could perhaps be used in a PLL to sync with a reference source, as Jim was originally proposing. Of course, retrofitting a conventional clock like this would require the attachment of a magnet to the pendulum, necessitating reducing the weight of the pendulum to account for it, installing an electromagnet under the pendulum and arranging for each swing of the pendulum to produce some form of pulse signal. Of course, the timing in pulses per second of the original clock would have to be determined and the frequency standard divided down to match this rate before both signals are fed to a comparator and LPF to provide the 'EFC' voltage to control the electromagnetic current. Steve Le 08/08/2010 11:14, Steve Rooke a écrit : I was rather more thinking of the setup that Don was suggesting as not many domestic clocks have a seconds pendulum and it would otherwise take dividing down a referenced oscillator to the correct frequency. Cheers, Steve On 08/08/2010, Neville Michienamic...@gmail.com wrote: Not many clocks are set up with the gear to modulate the rate, but they are all still sensitive to injection locking. A tiny rare earth magnet on the pendulum (say 1/2 way down the pendulum rod) and a coil fed with a stretched (say 250ms long) PPS or for a seconds pendulum PP2S pulse will pull the pendulum into phaselock with a surprisingly small amount of power. In fact if you turn off the drive it would keep the pendulum swinging. Cheers, Neville Michie On 08/08/2010, at 6:00 PM, Steve Rooke wrote: This is very interesting and I wonder if the capabilities of this system being applied to any clock pendulum. If this sort of control any pendulum, then I wonder if it's possible to sync it to some standard. Steve On 08/08/2010, Don Mimlitchdonm...@yahoo.com wrote: Jim Said: It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labeled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) I have a Warren Telechron Master Clock used in Power Stations in the 20's to regulate the 60 Cycle so that household clocks using synchronous motors would be accurate to seconds a day. This clock has a similar permanent magnet at the end of the Pendulum and a battery connected to a potentiometer to adjust the current flow positive or negative in an electro-magnet below the pendulum.. If the bottom of the magnet in the pendulum is north and the current in the electromagnet is flowing such that its top face is North, then this will repel the pendulum causing its swing to be wider and contrary to common knowledge the swing of a fixed length pendulum is not constant regardless of the swing. (Huygens discovered this in 1670 an found by forcing the arc of the swing to be cycloid instead of circular he could produce uniform oscillation) Thus if the arc is longer the swing takes more time and the clock runs slower. If the current flows in the opposite direction and the two magnets attract then the arc is shortened and the clock runs faster. Of course my master clock isn't as accurate as a Riefler pendulum clock. Also the magnet in my clock has lost it's
Re: [time-nuts] Regulating a pendulum clock (Jim Palfreyman)
I real purist would adjust the pendulum moment-of-inertia, rather than drive it. If I ever get around to it, I will attach a long tube of mercury (or cesium) to my pendulum and use heat to adjust the column height. A slightly less elegant solution would use a stepping motor to adjust the location of a weight along the pendulum. -RL --- -- From: Steve Rooke sar10...@gmail.com Sent: Sunday, August 08, 2010 7:30 AM To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Regulating a pendulum clock (Jim Palfreyman) On 08/08/2010, mike cook mike.c...@orange.fr wrote: Check out Bryan Mumfords page. http://www.bmumford.com/clocks/em2/index.html I did not want to kick the pendulum with a pulse each swing as the drive would be part and parcel of the existing clock mechanism. What I was interested in was Don Mimlitch's description of how the Riefler Pendulum and Warren Telechron Master Clocks work. The control of constant current to the electromagnet under the pendulum seems quite similar to an EFC and could perhaps be used in a PLL to sync with a reference source, as Jim was originally proposing. Of course, retrofitting a conventional clock like this would require the attachment of a magnet to the pendulum, necessitating reducing the weight of the pendulum to account for it, installing an electromagnet under the pendulum and arranging for each swing of the pendulum to produce some form of pulse signal. Of course, the timing in pulses per second of the original clock would have to be determined and the frequency standard divided down to match this rate before both signals are fed to a comparator and LPF to provide the 'EFC' voltage to control the electromagnetic current. Steve Le 08/08/2010 11:14, Steve Rooke a écrit : I was rather more thinking of the setup that Don was suggesting as not many domestic clocks have a seconds pendulum and it would otherwise take dividing down a referenced oscillator to the correct frequency. Cheers, Steve On 08/08/2010, Neville Michienamic...@gmail.com wrote: Not many clocks are set up with the gear to modulate the rate, but they are all still sensitive to injection locking. A tiny rare earth magnet on the pendulum (say 1/2 way down the pendulum rod) and a coil fed with a stretched (say 250ms long) PPS or for a seconds pendulum PP2S pulse will pull the pendulum into phaselock with a surprisingly small amount of power. In fact if you turn off the drive it would keep the pendulum swinging. Cheers, Neville Michie On 08/08/2010, at 6:00 PM, Steve Rooke wrote: This is very interesting and I wonder if the capabilities of this system being applied to any clock pendulum. If this sort of control any pendulum, then I wonder if it's possible to sync it to some standard. Steve On 08/08/2010, Don Mimlitchdonm...@yahoo.com wrote: Jim Said: It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labeled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) I have a Warren Telechron Master Clock used in Power Stations in the 20's to regulate the 60 Cycle so that household clocks using synchronous motors would be accurate to seconds a day. This clock has a similar permanent magnet at the end of the Pendulum and a battery connected to a potentiometer to adjust the current flow positive or negative in an electro-magnet below the pendulum.. If the bottom of the magnet in the pendulum is north and the current in the electromagnet is flowing such that its top face is North, then this will repel the pendulum causing its swing to be wider and contrary to common knowledge the swing of a fixed length pendulum is not constant regardless of the swing. (Huygens discovered this in 1670 an found by forcing the arc of the swing to be cycloid instead of circular he could produce uniform oscillation) Thus if the arc is longer the swing takes more time and the clock runs slower. If the current flows in the opposite direction and the two magnets attract then the arc is shortened and the clock runs faster. Of course my master clock isn't as accurate as a Riefler pendulum clock. Also the magnet in my clock has lost it's magnetism over time and I can't use this regulation. So the goal of your adaptation is to have precision control of the current flow in the positive or negative direction. Others on the list are better then me at describing how you might achieve this. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow
Re: [time-nuts] Regulating a pendulum clock
The LH0032, LH0033 and LH0063 come to mind again. - Regards - Mike Mike B. Feher, N4FS 89 Arnold Blvd. Howell, NJ 07731 732-886-5960 -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Bruce Griffiths Sent: Saturday, August 07, 2010 10:29 PM To: j...@quik.com; Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Regulating a pendulum clock The 60mA load current would be problematic for most common opamps without an output buffer stage. High voltage opamps are relatively rare. Bruce J. Forster wrote: Since it's inside a closed loop, the design is uncritical. One option is a high voltage Op-Amp with +/- 25 to 30 VDC supplies. You would set the OA gain to about 10, so 2.5 V in would yield 25 V out. and sum in a negative offset voltage so that +2.5 from the DAC yields 0.0 V out. I'd use something like a 100 K FB resistor and a 10K from the DAC, assuming it's a voltage output DAC. A 1 M to the -25 V supply would provide the 2.5 V offset. Another option would be to use two series opamps with the first set up as above, and the second as a unity gain inverter with input connected to the output of the first. The coil would connect between the two OA outputs. As one output swings high, the other mirrors that and goes low (just as in an H bridge). Stability might be an issue, but this has the advantage of only needing a +/- 15 supplies. FWIW, -John = Hi all, I have a Seimens master clock with a Reiffler pendulum. A lovely piece of work that used to provide time services in the 40s. Being a master clock it has contacts that open and close on each pendulum swing and so I can monitor it's accuracy quite easily using gps and my 5370B. I've adjusted it as best I can and the best I can get is about 50 ms over 24 hours. However that was a one off. Temp and air pressure cause variations of up to 300 ms and it changes direction too. Basically it's hard to keep accurate. It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labelled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) It's about 25v in the coil and goes up to 60mA max. Even at levels of 2mA has an effect. Using this control it's quite easy to manually bring the clock back to the right time if it's say half a second fast. What I want to do is control the current in the coil with a micro controller which I have attached to a rubidium oscillator. Getting the pps from the pendulum clock in and comparing to actual time is easy, but I need a way to control the current through the coil so it can dynamically adjust the clock. I need the current to go from say -10 to +10 mA (at 25v) and this needs to be controlled via a micro controller output (which goes from 0 to 5 with 2.5 being the 0mA point). I can either use the D/A in the controller (or PWM an output I suppose). I'd appreciate some thoughts on circuits to do this. Software side is not a problem. Jim Palfreyman ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
You are picking very unimportant nits. If there were a small noise spike from the opamp, it'd goose the pendulum a tiny amount. That would be corrected on the next swing. You are turning a trip to the corner store into an Apollo Moon Mission. BTW, since the =drive does not to be bipolar, one of the NPN and PNP transistors can be deleted. They never turn on. So you are left with two opamsa, =each with a simple emitter follower. -John == J. Forster wrote: OK. You know better. BTW, op-amp noise is essentially irrelevant in this application, and the C's across the FB resistors limit slew rates so there is no significant dI/dt to cause voltage spikes. Noise is never irrelevant. You havent shown that its insignificant either. In the real world such dv/dt assumptions with inductive loads lead to fried parts. For example if the circuit oscillates at high frequency because the compensation isnt correct/effective or the feedback wire becomes detached or the power supply goes down suddently due to a crowbar event then high dv/dt at the opamp/buffer output is possible. -John Bruce Your naive stabilisation scheme wont work, try simulating it. 741's are somewhat noisier than necessary. Omitting the diodes with an inductive load almost inevitably leads to transistor or opamp destruction. Bruce J. Forster wrote: IMO, far too complicated. I'd use a series pair of u741s each with a complementary emitter follower. 2 u741s, 2x 2N2102, 2x 2N4036, 5 resistors. Maybe 2x .01 caos to stabilize the thing - |\| |---|c DAC --o--| \ | |\ 2N2102 | | / --o-o |--C R |/| | |/ 2N4036 || | |---|c || || |o-to input of mirror image Best, -J = The attached circuit schematic illustrates the Howland current source plus inverting amplifier drive technique. It also illustrates a method of frequency compensation (series RC connected across the coil). Of course one can either use discrete buffers or high current opamps. However for improved accuracy using a difference amplifier with built in pretrimmed resistors for the Howland current source may be preferable, in which case a discrete buffer stage or equivalent may be required. Bruce J. Forster wrote: There are cheap, split supply audio amp ICs that'd work, or you could use a u741 with a complementary-symmetry output buffer of discrete transistors. Crossover distortion would be essentially irrelevant, keeping the parts count very low. -John The 60mA load current would be problematic for most common opamps without an output buffer stage. High voltage opamps are relatively rare. Bruce J. Forster wrote: Since it's inside a closed loop, the design is uncritical. One option is a high voltage Op-Amp with +/- 25 to 30 VDC supplies. You would set the OA gain to about 10, so 2.5 V in would yield 25 V out. and sum in a negative offset voltage so that +2.5 from the DAC yields 0.0 V out. I'd use something like a 100 K FB resistor and a 10K from the DAC, assuming it's a voltage output DAC. A 1 M to the -25 V supply would provide the 2.5 V offset. Another option would be to use two series opamps with the first set up as above, and the second as a unity gain inverter with input connected to the output of the first. The coil would connect between the two OA outputs. As one output swings high, the other mirrors that and goes low (just as in an H bridge). Stability might be an issue, but this has the advantage of only needing a +/- 15 supplies. FWIW, -John = Hi all, I have a Seimens master clock with a Reiffler pendulum. A lovely piece of work that used to provide time services in the 40s. Being a master clock it has contacts that open and close on each pendulum swing and so I can monitor it's accuracy quite easily using gps and my 5370B. I've adjusted it as best I can and the best I can get is about 50 ms over 24 hours. However that was a one off. Temp and air pressure cause variations of up to 300 ms and it changes direction too. Basically it's hard to keep accurate. It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labelled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) It's about 25v in the coil and goes up to 60mA max. Even at levels of 2mA
Re: [time-nuts] Regulating a pendulum clock (Jim Palfreyman)
That's why I suggested killing the BW of the opamps in the partial H bridge configuration previously suggested. Transient response is almost unneeded. -John == On 08/08/2010, mike cook mike.c...@orange.fr wrote: Check out Bryan Mumfords page. http://www.bmumford.com/clocks/em2/index.html I did not want to kick the pendulum with a pulse each swing as the drive would be part and parcel of the existing clock mechanism. What I was interested in was Don Mimlitch's description of how the Riefler Pendulum and Warren Telechron Master Clocks work. The control of constant current to the electromagnet under the pendulum seems quite similar to an EFC and could perhaps be used in a PLL to sync with a reference source, as Jim was originally proposing. Of course, retrofitting a conventional clock like this would require the attachment of a magnet to the pendulum, necessitating reducing the weight of the pendulum to account for it, installing an electromagnet under the pendulum and arranging for each swing of the pendulum to produce some form of pulse signal. Of course, the timing in pulses per second of the original clock would have to be determined and the frequency standard divided down to match this rate before both signals are fed to a comparator and LPF to provide the 'EFC' voltage to control the electromagnetic current. Steve Le 08/08/2010 11:14, Steve Rooke a écrit : I was rather more thinking of the setup that Don was suggesting as not many domestic clocks have a seconds pendulum and it would otherwise take dividing down a referenced oscillator to the correct frequency. Cheers, Steve On 08/08/2010, Neville Michienamic...@gmail.com wrote: Not many clocks are set up with the gear to modulate the rate, but they are all still sensitive to injection locking. A tiny rare earth magnet on the pendulum (say 1/2 way down the pendulum rod) and a coil fed with a stretched (say 250ms long) PPS or for a seconds pendulum PP2S pulse will pull the pendulum into phaselock with a surprisingly small amount of power. In fact if you turn off the drive it would keep the pendulum swinging. Cheers, Neville Michie On 08/08/2010, at 6:00 PM, Steve Rooke wrote: This is very interesting and I wonder if the capabilities of this system being applied to any clock pendulum. If this sort of control any pendulum, then I wonder if it's possible to sync it to some standard. Steve On 08/08/2010, Don Mimlitchdonm...@yahoo.com wrote: Jim Said: It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labeled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) I have a Warren Telechron Master Clock used in Power Stations in the 20's to regulate the 60 Cycle so that household clocks using synchronous motors would be accurate to seconds a day. This clock has a similar permanent magnet at the end of the Pendulum and a battery connected to a potentiometer to adjust the current flow positive or negative in an electro-magnet below the pendulum.. If the bottom of the magnet in the pendulum is north and the current in the electromagnet is flowing such that its top face is North, then this will repel the pendulum causing its swing to be wider and contrary to common knowledge the swing of a fixed length pendulum is not constant regardless of the swing. (Huygens discovered this in 1670 an found by forcing the arc of the swing to be cycloid instead of circular he could produce uniform oscillation) Thus if the arc is longer the swing takes more time and the clock runs slower. If the current flows in the opposite direction and the two magnets attract then the arc is shortened and the clock runs faster. Of course my master clock isn't as accurate as a Riefler pendulum clock. Also the magnet in my clock has lost it's magnetism over time and I can't use this regulation. So the goal of your adaptation is to have precision control of the current flow in the positive or negative direction. Others on the list are better then me at describing how you might achieve this. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Steve Rooke - ZL3TUV G8KVD The only reason for time is so that everything doesn't happen at once. - Einstein ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/ time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
J. Forster wrote: You are picking very unimportant nits. If there were a small noise spike from the opamp, it'd goose the pendulum a tiny amount. That would be corrected on the next swing. Heuristic analysis of this type is counter productive. You are turning a trip to the corner store into an Apollo Moon Mission. Reliability is paramount in a circuit that may be required to work for decades. BTW, since the =drive does not to be bipolar, one of the NPN and PNP transistors can be deleted. They never turn on. So you are left with two opamsa, =each with a simple emitter follower. The original request was for a bipolar drive. The lack of short circuit protection is poor design practice when driving an external load. -John == Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Hmmm lemme see. I think I'd use a 12 volt supply and two transistors driven by two outputs on my Arduino,basic stamp,picaxe or other whizzie. I'd then implement a PID controller essentially using the 1 sec pulse from the pendulum and the 1 sec pulse from my Rb, satellite receiver, crystal clock, or whatever. The appropriate output pin will be brought to ground, and the other driven as a pdf with the rate given by the pid loop. Temperature and even pressure corrections can be applied within the gizzie software. External parts, minimum. Opportunity to play with tuning, maximum. Don Bruce Griffiths J. Forster wrote: You are picking very unimportant nits. If there were a small noise spike from the opamp, it'd goose the pendulum a tiny amount. That would be corrected on the next swing. Heuristic analysis of this type is counter productive. You are turning a trip to the corner store into an Apollo Moon Mission. Reliability is paramount in a circuit that may be required to work for decades. BTW, since the =drive does not to be bipolar, one of the NPN and PNP transistors can be deleted. They never turn on. So you are left with two opamsa, =each with a simple emitter follower. The original request was for a bipolar drive. The lack of short circuit protection is poor design practice when driving an external load. -John == Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Neither the voice of authority nor the weight of reason and argument are as significant as experiment, for thence comes quiet to the mind. R. Bacon Dr. Don Latham AJ7LL Six Mile Systems LLP 17850 Six Mile Road POB 134 Huson, MT, 59846 VOX 406-626-4304 www.lightningforensics.com www.sixmilesystems.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
No protection against external shorts or other undesired events. Extensive analog filtering to avoid creating an effective radiator of noise may also be necessary. Simple analog techniques are probably simpler/cheaper once the necessary filtering and protection are included. Bruce Don Latham wrote: Hmmm lemme see. I think I'd use a 12 volt supply and two transistors driven by two outputs on my Arduino,basic stamp,picaxe or other whizzie. I'd then implement a PID controller essentially using the 1 sec pulse from the pendulum and the 1 sec pulse from my Rb, satellite receiver, crystal clock, or whatever. The appropriate output pin will be brought to ground, and the other driven as a pdf with the rate given by the pid loop. Temperature and even pressure corrections can be applied within the gizzie software. External parts, minimum. Opportunity to play with tuning, maximum. Don Bruce Griffiths J. Forster wrote: You are picking very unimportant nits. If there were a small noise spike from the opamp, it'd goose the pendulum a tiny amount. That would be corrected on the next swing. Heuristic analysis of this type is counter productive. You are turning a trip to the corner store into an Apollo Moon Mission. Reliability is paramount in a circuit that may be required to work for decades. BTW, since the =drive does not to be bipolar, one of the NPN and PNP transistors can be deleted. They never turn on. So you are left with two opamsa, =each with a simple emitter follower. The original request was for a bipolar drive. The lack of short circuit protection is poor design practice when driving an external load. -John == Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
fast blow fuse, resonate the coil to the pwm frequency. Parts count small, tinkering in software instead of breathing lead fumes or whatever noxious stuff the Europeans have forced us to use... Don Bruce Griffiths No protection against external shorts or other undesired events. Extensive analog filtering to avoid creating an effective radiator of noise may also be necessary. Simple analog techniques are probably simpler/cheaper once the necessary filtering and protection are included. Bruce Don Latham wrote: Hmmm lemme see. I think I'd use a 12 volt supply and two transistors driven by two outputs on my Arduino,basic stamp,picaxe or other whizzie. I'd then implement a PID controller essentially using the 1 sec pulse from the pendulum and the 1 sec pulse from my Rb, satellite receiver, crystal clock, or whatever. The appropriate output pin will be brought to ground, and the other driven as a pdf with the rate given by the pid loop. Temperature and even pressure corrections can be applied within the gizzie software. External parts, minimum. Opportunity to play with tuning, maximum. Don Bruce Griffiths J. Forster wrote: You are picking very unimportant nits. If there were a small noise spike from the opamp, it'd goose the pendulum a tiny amount. That would be corrected on the next swing. Heuristic analysis of this type is counter productive. You are turning a trip to the corner store into an Apollo Moon Mission. Reliability is paramount in a circuit that may be required to work for decades. BTW, since the =drive does not to be bipolar, one of the NPN and PNP transistors can be deleted. They never turn on. So you are left with two opamsa, =each with a simple emitter follower. The original request was for a bipolar drive. The lack of short circuit protection is poor design practice when driving an external load. -John == Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Neither the voice of authority nor the weight of reason and argument are as significant as experiment, for thence comes quiet to the mind. R. Bacon Dr. Don Latham AJ7LL Six Mile Systems LLP 17850 Six Mile Road POB 134 Huson, MT, 59846 VOX 406-626-4304 www.lightningforensics.com www.sixmilesystems.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Mere fast blow fuses aren't usually precise enough to protect transistors against over current unless one uses rather large transistors. Overcurrent protected drivers are available and readily designed/built. Protection against di/dt transients due to external events is also advisable. Minimising the parts count isn't necessarily conducive to improved reliability when external hazards aren't taken into account. Merely resonating the coil without other filtering doesnt necessarily lead to low EMI when driving it with a voltage waveform having high edge slew rates. Some edge filtering to control the current flowing in the load capacitance is also advisable. Bruce Don Latham wrote: fast blow fuse, resonate the coil to the pwm frequency. Parts count small, tinkering in software instead of breathing lead fumes or whatever noxious stuff the Europeans have forced us to use... Don Bruce Griffiths No protection against external shorts or other undesired events. Extensive analog filtering to avoid creating an effective radiator of noise may also be necessary. Simple analog techniques are probably simpler/cheaper once the necessary filtering and protection are included. Bruce Don Latham wrote: Hmmm lemme see. I think I'd use a 12 volt supply and two transistors driven by two outputs on my Arduino,basic stamp,picaxe or other whizzie. I'd then implement a PID controller essentially using the 1 sec pulse from the pendulum and the 1 sec pulse from my Rb, satellite receiver, crystal clock, or whatever. The appropriate output pin will be brought to ground, and the other driven as a pdf with the rate given by the pid loop. Temperature and even pressure corrections can be applied within the gizzie software. External parts, minimum. Opportunity to play with tuning, maximum. Don Bruce Griffiths J. Forster wrote: You are picking very unimportant nits. If there were a small noise spike from the opamp, it'd goose the pendulum a tiny amount. That would be corrected on the next swing. Heuristic analysis of this type is counter productive. You are turning a trip to the corner store into an Apollo Moon Mission. Reliability is paramount in a circuit that may be required to work for decades. BTW, since the =drive does not to be bipolar, one of the NPN and PNP transistors can be deleted. They never turn on. So you are left with two opamsa, =each with a simple emitter follower. The original request was for a bipolar drive. The lack of short circuit protection is poor design practice when driving an external load. -John == Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock (Jim Palfreyman)
Well last night I did a quick and dirty. I got my (GPS locked) 3325B to generate square waves (0-5V) at 1 Hz. 500ms on. 500ms off. I ran this through a relay that delivered 10mA at 25V to the coil. By adjusting the phase of the 3325B I got the ON to occur as the magnets approached. But I had no idea whether the magnets were attracting or repelling at that point. Watching the timing of the pendulum it started to radically deviate. I concluded it was repelling and so reverse the polarity. It started heading back the other way. Cool. As it was late - I went to bed. Next morning the pendulum had locked in nicely. It was only deviating a few ms either side of a fixed point. I will let this run for today and make sure it has settled in and doesn't vary. The pendulum clock is fast by 200ms and so I'll adjust the phase to correct it tonight. Next step will be to drive it properly from my rubidium driven microcontroller. While I organise that I'll turn off the electromagnet and see if I can pick up the tides. Regards, Jim Palfreyman ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Now I will get myself in a lot of trouble. Why wouldn't a constant pulse at a 2 sec interval essentially lock the pendulum after a bit. If the pulse is always there and occurs just after the mid swing. I suspect you do need to adjust current with a pot to get things settled. But essentially open loop. I have often thought about tinkering exactly like this if I ever ran across a nice clock like the one at television network TVA in Montreal that used to run network time. Unfortunately they would not part with it. Good luck On Sun, Aug 8, 2010 at 7:22 PM, Bruce Griffiths bruce.griffi...@xtra.co.nzwrote: Mere fast blow fuses aren't usually precise enough to protect transistors against over current unless one uses rather large transistors. Overcurrent protected drivers are available and readily designed/built. Protection against di/dt transients due to external events is also advisable. Minimising the parts count isn't necessarily conducive to improved reliability when external hazards aren't taken into account. Merely resonating the coil without other filtering doesnt necessarily lead to low EMI when driving it with a voltage waveform having high edge slew rates. Some edge filtering to control the current flowing in the load capacitance is also advisable. Bruce Don Latham wrote: fast blow fuse, resonate the coil to the pwm frequency. Parts count small, tinkering in software instead of breathing lead fumes or whatever noxious stuff the Europeans have forced us to use... Don Bruce Griffiths No protection against external shorts or other undesired events. Extensive analog filtering to avoid creating an effective radiator of noise may also be necessary. Simple analog techniques are probably simpler/cheaper once the necessary filtering and protection are included. Bruce Don Latham wrote: Hmmm lemme see. I think I'd use a 12 volt supply and two transistors driven by two outputs on my Arduino,basic stamp,picaxe or other whizzie. I'd then implement a PID controller essentially using the 1 sec pulse from the pendulum and the 1 sec pulse from my Rb, satellite receiver, crystal clock, or whatever. The appropriate output pin will be brought to ground, and the other driven as a pdf with the rate given by the pid loop. Temperature and even pressure corrections can be applied within the gizzie software. External parts, minimum. Opportunity to play with tuning, maximum. Don Bruce Griffiths J. Forster wrote: You are picking very unimportant nits. If there were a small noise spike from the opamp, it'd goose the pendulum a tiny amount. That would be corrected on the next swing. Heuristic analysis of this type is counter productive. You are turning a trip to the corner store into an Apollo Moon Mission. Reliability is paramount in a circuit that may be required to work for decades. BTW, since the =drive does not to be bipolar, one of the NPN and PNP transistors can be deleted. They never turn on. So you are left with two opamsa, =each with a simple emitter follower. The original request was for a bipolar drive. The lack of short circuit protection is poor design practice when driving an external load. -John == Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Oh, well, I have some 15 v baxck-to-back zeners extremely fast to help the fuse out. In any case, the max current is limited by the power supply Something can be worked out... 12 v actually limits the current through the coil(s) and heating even at full on will not destroy anything. I'd probably use igbt transistors, I've become quite fond of them :-) Note that the design will not deliver any current through the coil if both gizzie outputs are either positive or negative. I'll bet there's a small half-bridge or full h-bridge that will work extremely well, say sparkfun or the like. On fact, that's probably the best way to go; as the h-bridges are designed to drive inductive loads. Neat, I'm glad you kept my mind on task. A simple small motor driver will do the trick nicely. Doe to age, my current philosophy is buy the biggest piece you can Don - Original Message - From: Bruce Griffiths bruce.griffi...@xtra.co.nz To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Sunday, August 08, 2010 5:22 PM Subject: Re: [time-nuts] Regulating a pendulum clock Mere fast blow fuses aren't usually precise enough to protect transistors against over current unless one uses rather large transistors. Overcurrent protected drivers are available and readily designed/built. Protection against di/dt transients due to external events is also advisable. Minimising the parts count isn't necessarily conducive to improved reliability when external hazards aren't taken into account. Merely resonating the coil without other filtering doesnt necessarily lead to low EMI when driving it with a voltage waveform having high edge slew rates. Some edge filtering to control the current flowing in the load capacitance is also advisable. Bruce Don Latham wrote: fast blow fuse, resonate the coil to the pwm frequency. Parts count small, tinkering in software instead of breathing lead fumes or whatever noxious stuff the Europeans have forced us to use... Don Bruce Griffiths No protection against external shorts or other undesired events. Extensive analog filtering to avoid creating an effective radiator of noise may also be necessary. Simple analog techniques are probably simpler/cheaper once the necessary filtering and protection are included. Bruce Don Latham wrote: Hmmm lemme see. I think I'd use a 12 volt supply and two transistors driven by two outputs on my Arduino,basic stamp,picaxe or other whizzie. I'd then implement a PID controller essentially using the 1 sec pulse from the pendulum and the 1 sec pulse from my Rb, satellite receiver, crystal clock, or whatever. The appropriate output pin will be brought to ground, and the other driven as a pdf with the rate given by the pid loop. Temperature and even pressure corrections can be applied within the gizzie software. External parts, minimum. Opportunity to play with tuning, maximum. Don Bruce Griffiths J. Forster wrote: You are picking very unimportant nits. If there were a small noise spike from the opamp, it'd goose the pendulum a tiny amount. That would be corrected on the next swing. Heuristic analysis of this type is counter productive. You are turning a trip to the corner store into an Apollo Moon Mission. Reliability is paramount in a circuit that may be required to work for decades. BTW, since the =drive does not to be bipolar, one of the NPN and PNP transistors can be deleted. They never turn on. So you are left with two opamsa, =each with a simple emitter follower. The original request was for a bipolar drive. The lack of short circuit protection is poor design practice when driving an external load. -John == Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock (Jim Palfreyman)
Nice! Don - Original Message - From: Jim Palfreyman jim77...@gmail.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Sunday, August 08, 2010 6:12 PM Subject: Re: [time-nuts] Regulating a pendulum clock (Jim Palfreyman) Well last night I did a quick and dirty. I got my (GPS locked) 3325B to generate square waves (0-5V) at 1 Hz. 500ms on. 500ms off. I ran this through a relay that delivered 10mA at 25V to the coil. By adjusting the phase of the 3325B I got the ON to occur as the magnets approached. But I had no idea whether the magnets were attracting or repelling at that point. Watching the timing of the pendulum it started to radically deviate. I concluded it was repelling and so reverse the polarity. It started heading back the other way. Cool. As it was late - I went to bed. Next morning the pendulum had locked in nicely. It was only deviating a few ms either side of a fixed point. I will let this run for today and make sure it has settled in and doesn't vary. The pendulum clock is fast by 200ms and so I'll adjust the phase to correct it tonight. Next step will be to drive it properly from my rubidium driven microcontroller. While I organise that I'll turn off the electromagnet and see if I can pick up the tides. Regards, Jim Palfreyman ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Yep, injection locling works just fine Don - Original Message - From: paul swed paulsw...@gmail.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Sunday, August 08, 2010 7:37 PM Subject: Re: [time-nuts] Regulating a pendulum clock Now I will get myself in a lot of trouble. Why wouldn't a constant pulse at a 2 sec interval essentially lock the pendulum after a bit. If the pulse is always there and occurs just after the mid swing. I suspect you do need to adjust current with a pot to get things settled. But essentially open loop. I have often thought about tinkering exactly like this if I ever ran across a nice clock like the one at television network TVA in Montreal that used to run network time. Unfortunately they would not part with it. Good luck On Sun, Aug 8, 2010 at 7:22 PM, Bruce Griffiths bruce.griffi...@xtra.co.nzwrote: Mere fast blow fuses aren't usually precise enough to protect transistors against over current unless one uses rather large transistors. Overcurrent protected drivers are available and readily designed/built. Protection against di/dt transients due to external events is also advisable. Minimising the parts count isn't necessarily conducive to improved reliability when external hazards aren't taken into account. Merely resonating the coil without other filtering doesnt necessarily lead to low EMI when driving it with a voltage waveform having high edge slew rates. Some edge filtering to control the current flowing in the load capacitance is also advisable. Bruce Don Latham wrote: fast blow fuse, resonate the coil to the pwm frequency. Parts count small, tinkering in software instead of breathing lead fumes or whatever noxious stuff the Europeans have forced us to use... Don Bruce Griffiths No protection against external shorts or other undesired events. Extensive analog filtering to avoid creating an effective radiator of noise may also be necessary. Simple analog techniques are probably simpler/cheaper once the necessary filtering and protection are included. Bruce Don Latham wrote: Hmmm lemme see. I think I'd use a 12 volt supply and two transistors driven by two outputs on my Arduino,basic stamp,picaxe or other whizzie. I'd then implement a PID controller essentially using the 1 sec pulse from the pendulum and the 1 sec pulse from my Rb, satellite receiver, crystal clock, or whatever. The appropriate output pin will be brought to ground, and the other driven as a pdf with the rate given by the pid loop. Temperature and even pressure corrections can be applied within the gizzie software. External parts, minimum. Opportunity to play with tuning, maximum. Don Bruce Griffiths J. Forster wrote: You are picking very unimportant nits. If there were a small noise spike from the opamp, it'd goose the pendulum a tiny amount. That would be corrected on the next swing. Heuristic analysis of this type is counter productive. You are turning a trip to the corner store into an Apollo Moon Mission. Reliability is paramount in a circuit that may be required to work for decades. BTW, since the =drive does not to be bipolar, one of the NPN and PNP transistors can be deleted. They never turn on. So you are left with two opamsa, =each with a simple emitter follower. The original request was for a bipolar drive. The lack of short circuit protection is poor design practice when driving an external load. -John == Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Regulating a pendulum clock
Hi all, I have a Seimens master clock with a Reiffler pendulum. A lovely piece of work that used to provide time services in the 40s. Being a master clock it has contacts that open and close on each pendulum swing and so I can monitor it's accuracy quite easily using gps and my 5370B. I've adjusted it as best I can and the best I can get is about 50 ms over 24 hours. However that was a one off. Temp and air pressure cause variations of up to 300 ms and it changes direction too. Basically it's hard to keep accurate. It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labelled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) It's about 25v in the coil and goes up to 60mA max. Even at levels of 2mA has an effect. Using this control it's quite easy to manually bring the clock back to the right time if it's say half a second fast. What I want to do is control the current in the coil with a micro controller which I have attached to a rubidium oscillator. Getting the pps from the pendulum clock in and comparing to actual time is easy, but I need a way to control the current through the coil so it can dynamically adjust the clock. I need the current to go from say -10 to +10 mA (at 25v) and this needs to be controlled via a micro controller output (which goes from 0 to 5 with 2.5 being the 0mA point). I can either use the D/A in the controller (or PWM an output I suppose). I'd appreciate some thoughts on circuits to do this. Software side is not a problem. Jim Palfreyman ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
A high voltage opamp (or a low voltage opamp with a discrete output stage with a voltage gain of at least 2) with -3V and + 30V supplies is perhaps the simplest method. The opamp merely senses the current flowing in a current sensing resistor and regulates this voltage drop to equal the output of a DAC. Alternatively it should be feasible to use a pair of opamps (plus output buffers) configured in a bridge arrangement to drive the coil from a single 30V supply. If one end of the coil has to remain near ground then a unity gain difference amplifier (with a discrete buffer with voltage gain) could be employed to implement a current source. A difference amplifier could also be employed together with an opamp (plus unity voltage gain discrete ouput stage) inverter to drive the coil from a single 30V supply. Bruce Jim Palfreyman wrote: Hi all, I have a Seimens master clock with a Reiffler pendulum. A lovely piece of work that used to provide time services in the 40s. Being a master clock it has contacts that open and close on each pendulum swing and so I can monitor it's accuracy quite easily using gps and my 5370B. I've adjusted it as best I can and the best I can get is about 50 ms over 24 hours. However that was a one off. Temp and air pressure cause variations of up to 300 ms and it changes direction too. Basically it's hard to keep accurate. It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labelled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) It's about 25v in the coil and goes up to 60mA max. Even at levels of 2mA has an effect. Using this control it's quite easy to manually bring the clock back to the right time if it's say half a second fast. What I want to do is control the current in the coil with a micro controller which I have attached to a rubidium oscillator. Getting the pps from the pendulum clock in and comparing to actual time is easy, but I need a way to control the current through the coil so it can dynamically adjust the clock. I need the current to go from say -10 to +10 mA (at 25v) and this needs to be controlled via a micro controller output (which goes from 0 to 5 with 2.5 being the 0mA point). I can either use the D/A in the controller (or PWM an output I suppose). I'd appreciate some thoughts on circuits to do this. Software side is not a problem. Jim Palfreyman ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Since it's inside a closed loop, the design is uncritical. One option is a high voltage Op-Amp with +/- 25 to 30 VDC supplies. You would set the OA gain to about 10, so 2.5 V in would yield 25 V out. and sum in a negative offset voltage so that +2.5 from the DAC yields 0.0 V out. I'd use something like a 100 K FB resistor and a 10K from the DAC, assuming it's a voltage output DAC. A 1 M to the -25 V supply would provide the 2.5 V offset. Another option would be to use two series opamps with the first set up as above, and the second as a unity gain inverter with input connected to the output of the first. The coil would connect between the two OA outputs. As one output swings high, the other mirrors that and goes low (just as in an H bridge). Stability might be an issue, but this has the advantage of only needing a +/- 15 supplies. FWIW, -John = Hi all, I have a Seimens master clock with a Reiffler pendulum. A lovely piece of work that used to provide time services in the 40s. Being a master clock it has contacts that open and close on each pendulum swing and so I can monitor it's accuracy quite easily using gps and my 5370B. I've adjusted it as best I can and the best I can get is about 50 ms over 24 hours. However that was a one off. Temp and air pressure cause variations of up to 300 ms and it changes direction too. Basically it's hard to keep accurate. It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labelled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) It's about 25v in the coil and goes up to 60mA max. Even at levels of 2mA has an effect. Using this control it's quite easy to manually bring the clock back to the right time if it's say half a second fast. What I want to do is control the current in the coil with a micro controller which I have attached to a rubidium oscillator. Getting the pps from the pendulum clock in and comparing to actual time is easy, but I need a way to control the current through the coil so it can dynamically adjust the clock. I need the current to go from say -10 to +10 mA (at 25v) and this needs to be controlled via a micro controller output (which goes from 0 to 5 with 2.5 being the 0mA point). I can either use the D/A in the controller (or PWM an output I suppose). I'd appreciate some thoughts on circuits to do this. Software side is not a problem. Jim Palfreyman ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
Hi, the range of the adjustment is probably far wider than you would ever need as you will be applying it continuously instead of over a few hours to correct the clock to the latest observations. So all you need is an amplifier run off + and - 15 Volts with enough gain for the DAC output. That should give you + or - 10Volts. You may also need a reference diode, say 2.5 volts, to provide an offset voltage to the input of the amplifier if you want to set the zero of the control range and possibly offset a single ended DAC output to span either side of zero. cheers, Neville Michie On 08/08/2010, at 12:10 PM, J. Forster wrote: Since it's inside a closed loop, the design is uncritical. One option is a high voltage Op-Amp with +/- 25 to 30 VDC supplies. You would set the OA gain to about 10, so 2.5 V in would yield 25 V out. and sum in a negative offset voltage so that +2.5 from the DAC yields 0.0 V out. I'd use something like a 100 K FB resistor and a 10K from the DAC, assuming it's a voltage output DAC. A 1 M to the -25 V supply would provide the 2.5 V offset. Another option would be to use two series opamps with the first set up as above, and the second as a unity gain inverter with input connected to the output of the first. The coil would connect between the two OA outputs. As one output swings high, the other mirrors that and goes low (just as in an H bridge). Stability might be an issue, but this has the advantage of only needing a +/- 15 supplies. FWIW, -John = Hi all, I have a Seimens master clock with a Reiffler pendulum. A lovely piece of work that used to provide time services in the 40s. Being a master clock it has contacts that open and close on each pendulum swing and so I can monitor it's accuracy quite easily using gps and my 5370B. I've adjusted it as best I can and the best I can get is about 50 ms over 24 hours. However that was a one off. Temp and air pressure cause variations of up to 300 ms and it changes direction too. Basically it's hard to keep accurate. It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labelled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) It's about 25v in the coil and goes up to 60mA max. Even at levels of 2mA has an effect. Using this control it's quite easy to manually bring the clock back to the right time if it's say half a second fast. What I want to do is control the current in the coil with a micro controller which I have attached to a rubidium oscillator. Getting the pps from the pendulum clock in and comparing to actual time is easy, but I need a way to control the current through the coil so it can dynamically adjust the clock. I need the current to go from say -10 to +10 mA (at 25v) and this needs to be controlled via a micro controller output (which goes from 0 to 5 with 2.5 being the 0mA point). I can either use the D/A in the controller (or PWM an output I suppose). I'd appreciate some thoughts on circuits to do this. Software side is not a problem. Jim Palfreyman ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/ time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
The 60mA load current would be problematic for most common opamps without an output buffer stage. High voltage opamps are relatively rare. Bruce J. Forster wrote: Since it's inside a closed loop, the design is uncritical. One option is a high voltage Op-Amp with +/- 25 to 30 VDC supplies. You would set the OA gain to about 10, so 2.5 V in would yield 25 V out. and sum in a negative offset voltage so that +2.5 from the DAC yields 0.0 V out. I'd use something like a 100 K FB resistor and a 10K from the DAC, assuming it's a voltage output DAC. A 1 M to the -25 V supply would provide the 2.5 V offset. Another option would be to use two series opamps with the first set up as above, and the second as a unity gain inverter with input connected to the output of the first. The coil would connect between the two OA outputs. As one output swings high, the other mirrors that and goes low (just as in an H bridge). Stability might be an issue, but this has the advantage of only needing a +/- 15 supplies. FWIW, -John = Hi all, I have a Seimens master clock with a Reiffler pendulum. A lovely piece of work that used to provide time services in the 40s. Being a master clock it has contacts that open and close on each pendulum swing and so I can monitor it's accuracy quite easily using gps and my 5370B. I've adjusted it as best I can and the best I can get is about 50 ms over 24 hours. However that was a one off. Temp and air pressure cause variations of up to 300 ms and it changes direction too. Basically it's hard to keep accurate. It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labelled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) It's about 25v in the coil and goes up to 60mA max. Even at levels of 2mA has an effect. Using this control it's quite easy to manually bring the clock back to the right time if it's say half a second fast. What I want to do is control the current in the coil with a micro controller which I have attached to a rubidium oscillator. Getting the pps from the pendulum clock in and comparing to actual time is easy, but I need a way to control the current through the coil so it can dynamically adjust the clock. I need the current to go from say -10 to +10 mA (at 25v) and this needs to be controlled via a micro controller output (which goes from 0 to 5 with 2.5 being the 0mA point). I can either use the D/A in the controller (or PWM an output I suppose). I'd appreciate some thoughts on circuits to do this. Software side is not a problem. Jim Palfreyman ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
A high voltage opamp (or a low voltage opamp with a discrete output stage with a voltage gain of at least 2) with -3V and + 30V supplies is perhaps the simplest method. The opamp merely senses the current flowing in a current sensing resistor and regulates this voltage drop to equal the output of a DAC. Alternatively it should be feasible to use a pair of opamps (plus output buffers) configured in a bridge arrangement to drive the coil from a single 30V supply. If one end of the coil has to remain near ground then a unity gain difference amplifier (with a discrete buffer with voltage gain) could be employed to implement a current source. A difference amplifier could also be employed together with an opamp (plus unity voltage gain discrete ouput stage) inverter to drive the coil from a single 30V supply. Bruce J. Forster wrote: Since it's inside a closed loop, the design is uncritical. One option is a high voltage Op-Amp with +/- 25 to 30 VDC supplies. You would set the OA gain to about 10, so 2.5 V in would yield 25 V out. and sum in a negative offset voltage so that +2.5 from the DAC yields 0.0 V out. I'd use something like a 100 K FB resistor and a 10K from the DAC, assuming it's a voltage output DAC. A 1 M to the -25 V supply would provide the 2.5 V offset. Another option would be to use two series opamps with the first set up as above, and the second as a unity gain inverter with input connected to the output of the first. The coil would connect between the two OA outputs. As one output swings high, the other mirrors that and goes low (just as in an H bridge). Stability might be an issue, but this has the advantage of only needing a +/- 15 supplies. FWIW, -John = Hi all, I have a Seimens master clock with a Reiffler pendulum. A lovely piece of work that used to provide time services in the 40s. Being a master clock it has contacts that open and close on each pendulum swing and so I can monitor it's accuracy quite easily using gps and my 5370B. I've adjusted it as best I can and the best I can get is about 50 ms over 24 hours. However that was a one off. Temp and air pressure cause variations of up to 300 ms and it changes direction too. Basically it's hard to keep accurate. It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labelled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) It's about 25v in the coil and goes up to 60mA max. Even at levels of 2mA has an effect. Using this control it's quite easy to manually bring the clock back to the right time if it's say half a second fast. What I want to do is control the current in the coil with a micro controller which I have attached to a rubidium oscillator. Getting the pps from the pendulum clock in and comparing to actual time is easy, but I need a way to control the current through the coil so it can dynamically adjust the clock. I need the current to go from say -10 to +10 mA (at 25v) and this needs to be controlled via a micro controller output (which goes from 0 to 5 with 2.5 being the 0mA point). I can either use the D/A in the controller (or PWM an output I suppose). I'd appreciate some thoughts on circuits to do this. Software side is not a problem. Jim Palfreyman ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. attachment: Coil_Driver.gif___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
OK. You know better. BTW, op-amp noise is essentially irrelevant in this application, and the C's across the FB resistors limit slew rates so there is no significant dI/dt to cause voltage spikes. -John Your naive stabilisation scheme wont work, try simulating it. 741's are somewhat noisier than necessary. Omitting the diodes with an inductive load almost inevitably leads to transistor or opamp destruction. Bruce J. Forster wrote: IMO, far too complicated. I'd use a series pair of u741s each with a complementary emitter follower. 2 u741s, 2x 2N2102, 2x 2N4036, 5 resistors. Maybe 2x .01 caos to stabilize the thing - |\| |---|c DAC --o--| \ | |\ 2N2102 | | / --o-o |--C R |/| | |/ 2N4036 || | |---|c || || |o-to input of mirror image Best, -J = The attached circuit schematic illustrates the Howland current source plus inverting amplifier drive technique. It also illustrates a method of frequency compensation (series RC connected across the coil). Of course one can either use discrete buffers or high current opamps. However for improved accuracy using a difference amplifier with built in pretrimmed resistors for the Howland current source may be preferable, in which case a discrete buffer stage or equivalent may be required. Bruce J. Forster wrote: There are cheap, split supply audio amp ICs that'd work, or you could use a u741 with a complementary-symmetry output buffer of discrete transistors. Crossover distortion would be essentially irrelevant, keeping the parts count very low. -John The 60mA load current would be problematic for most common opamps without an output buffer stage. High voltage opamps are relatively rare. Bruce J. Forster wrote: Since it's inside a closed loop, the design is uncritical. One option is a high voltage Op-Amp with +/- 25 to 30 VDC supplies. You would set the OA gain to about 10, so 2.5 V in would yield 25 V out. and sum in a negative offset voltage so that +2.5 from the DAC yields 0.0 V out. I'd use something like a 100 K FB resistor and a 10K from the DAC, assuming it's a voltage output DAC. A 1 M to the -25 V supply would provide the 2.5 V offset. Another option would be to use two series opamps with the first set up as above, and the second as a unity gain inverter with input connected to the output of the first. The coil would connect between the two OA outputs. As one output swings high, the other mirrors that and goes low (just as in an H bridge). Stability might be an issue, but this has the advantage of only needing a +/- 15 supplies. FWIW, -John = Hi all, I have a Seimens master clock with a Reiffler pendulum. A lovely piece of work that used to provide time services in the 40s. Being a master clock it has contacts that open and close on each pendulum swing and so I can monitor it's accuracy quite easily using gps and my 5370B. I've adjusted it as best I can and the best I can get is about 50 ms over 24 hours. However that was a one off. Temp and air pressure cause variations of up to 300 ms and it changes direction too. Basically it's hard to keep accurate. It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labelled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) It's about 25v in the coil and goes up to 60mA max. Even at levels of 2mA has an effect. Using this control it's quite easy to manually bring the clock back to the right time if it's say half a second fast. What I want to do is control the current in the coil with a micro controller which I have attached to a rubidium oscillator. Getting the pps from the pendulum clock in and comparing to actual time is easy, but I need a way to control the current through the coil so it can dynamically adjust the clock. I need the current to go from say -10 to +10 mA (at 25v) and this needs to be controlled via a micro controller output (which goes from 0 to 5 with 2.5 being the 0mA point). I can either use the D/A in the controller (or PWM an output I suppose). I'd appreciate some thoughts on circuits to do this. Software side is not a problem. Jim Palfreyman ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Regulating a pendulum clock
J. Forster wrote: OK. You know better. BTW, op-amp noise is essentially irrelevant in this application, and the C's across the FB resistors limit slew rates so there is no significant dI/dt to cause voltage spikes. Noise is never irrelevant. You havent shown that its insignificant either. In the real world such dv/dt assumptions with inductive loads lead to fried parts. For example if the circuit oscillates at high frequency because the compensation isnt correct/effective or the feedback wire becomes detached or the power supply goes down suddently due to a crowbar event then high dv/dt at the opamp/buffer output is possible. -John Bruce Your naive stabilisation scheme wont work, try simulating it. 741's are somewhat noisier than necessary. Omitting the diodes with an inductive load almost inevitably leads to transistor or opamp destruction. Bruce J. Forster wrote: IMO, far too complicated. I'd use a series pair of u741s each with a complementary emitter follower. 2 u741s, 2x 2N2102, 2x 2N4036, 5 resistors. Maybe 2x .01 caos to stabilize the thing - |\| |---|c DAC --o--| \ | |\ 2N2102 | | / --o-o |--C R |/| | |/ 2N4036 || | |---|c || || |o-to input of mirror image Best, -J = The attached circuit schematic illustrates the Howland current source plus inverting amplifier drive technique. It also illustrates a method of frequency compensation (series RC connected across the coil). Of course one can either use discrete buffers or high current opamps. However for improved accuracy using a difference amplifier with built in pretrimmed resistors for the Howland current source may be preferable, in which case a discrete buffer stage or equivalent may be required. Bruce J. Forster wrote: There are cheap, split supply audio amp ICs that'd work, or you could use a u741 with a complementary-symmetry output buffer of discrete transistors. Crossover distortion would be essentially irrelevant, keeping the parts count very low. -John The 60mA load current would be problematic for most common opamps without an output buffer stage. High voltage opamps are relatively rare. Bruce J. Forster wrote: Since it's inside a closed loop, the design is uncritical. One option is a high voltage Op-Amp with +/- 25 to 30 VDC supplies. You would set the OA gain to about 10, so 2.5 V in would yield 25 V out. and sum in a negative offset voltage so that +2.5 from the DAC yields 0.0 V out. I'd use something like a 100 K FB resistor and a 10K from the DAC, assuming it's a voltage output DAC. A 1 M to the -25 V supply would provide the 2.5 V offset. Another option would be to use two series opamps with the first set up as above, and the second as a unity gain inverter with input connected to the output of the first. The coil would connect between the two OA outputs. As one output swings high, the other mirrors that and goes low (just as in an H bridge). Stability might be an issue, but this has the advantage of only needing a +/- 15 supplies. FWIW, -John = Hi all, I have a Seimens master clock with a Reiffler pendulum. A lovely piece of work that used to provide time services in the 40s. Being a master clock it has contacts that open and close on each pendulum swing and so I can monitor it's accuracy quite easily using gps and my 5370B. I've adjusted it as best I can and the best I can get is about 50 ms over 24 hours. However that was a one off. Temp and air pressure cause variations of up to 300 ms and it changes direction too. Basically it's hard to keep accurate. It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labelled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) It's about 25v in the coil and goes up to 60mA max. Even at levels of 2mA has an effect. Using this control it's quite easy to manually bring the clock back to
[time-nuts] Regulating a pendulum clock (Jim Palfreyman)
Jim Said: It also has a coil mounted near the pendulum and a fixed magnet on the pendulum bar and this coil connects to a box down below with a meter and a knob. They are labeled in sec/day. The electronics in the box are not clear (being quite old) but by measuring the current in the coil it quite simply increases the current one way to slow the clock and the other way to speed it up. (I'll admit the physics of this doesn't make sense to me - but it works!) I have a Warren Telechron Master Clock used in Power Stations in the 20's to regulate the 60 Cycle so that household clocks using synchronous motors would be accurate to seconds a day. This clock has a similar permanent magnet at the end of the Pendulum and a battery connected to a potentiometer to adjust the current flow positive or negative in an electro-magnet below the pendulum.. If the bottom of the magnet in the pendulum is north and the current in the electromagnet is flowing such that its top face is North, then this will repel the pendulum causing its swing to be wider and contrary to common knowledge the swing of a fixed length pendulum is not constant regardless of the swing. (Huygens discovered this in 1670 an found by forcing the arc of the swing to be cycloid instead of circular he could produce uniform oscillation) Thus if the arc is longer the swing takes more time and the clock runs slower. If the current flows in the opposite direction and the two magnets attract then the arc is shortened and the clock runs faster. Of course my master clock isn't as accurate as a Riefler pendulum clock. Also the magnet in my clock has lost it's magnetism over time and I can't use this regulation. So the goal of your adaptation is to have precision control of the current flow in the positive or negative direction. Others on the list are better then me at describing how you might achieve this. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
