[time-nuts] Stable Watch Clocks
Typical 32KHz clock crystals are very stable in frequency if you can keep them close to the turnover temp. If you can hold 1 degC it is .04 ppm. That is 40ppb - very good. If you can hold .1 deg C it is .0004 ppm. That is .4 ppb. Very expensive. (it goes as the square of the difference in temperature from the turn over temp - which varies from crystal to crystal. ). The turn over temp is around 25 degC. I saw some 40mm on a side thermoelectric heaters/coolers units for $15 at Spark Fun. I thought I might have some fun. Two units and a power supply. Plus a honking current amp. Although with milliwatts for the oscillator it might not take a lot of heat pumping to keep the osc at a constant temp. And +/- 10C to 20C is probably enough range for experiments. Be interesting to see if this could be engineered to compete with OCXOs. A VariCap would be included in later experiments for tuning. If the initial experiments show promise. 6 wires out to start: 2 pwr, 2 thermistor, and 2 Freq out. with the oscillator in the center of the coolers the material arrangement: Osc potted in high thermal conductivity. Void. Outer Insulation. With another thermistor or temp sensor in the outer insulation. Another in the vicinity on the outside. I'm open to suggestion. And also possible proof I'm barking up the wrong tree. The idea is to keep the whole package as thin as possible to minimize heat flow to or from the outside - except through the coolers/heaters. Some uP to run a PID loop for temp. An update rate of 100 times a second for the PID should make it fine grained enough. DACs and ADCs good to 16 bits. Initial exploration eqpt need not be so good. Unless it is cheap. And then once you have the contraption running, disciplining it with 1 PPS might be of further interest. I currently have no method for testing such a rig for stability. Simon Engineering is the art of making what you want from what you can get at a profit. ___ 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] Stable Watch Clocks
Typical 32KHz clock crystals are very stable in frequency if you can keep them close to the turnover temp. If you can hold 1 degC it is .04 ppm. That's far better than I thought. Do you have a reference for this spec? I agree you might be able to make one accurate to 0.04 ppm, however briefly, but I've never seen one stable to 0.04 ppm. I mean, that's like 1 second a year. I currently have no method for testing such a rig for stability. Oh, the slipperly slope you are on. I have just the solution for you ... /tvb ___ 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] Stable Watch Clocks
http://www.abracon.com/Resonators/AB26T.pdf This quotes .038 ppm/C^2 delta T from the turn over point: http://www.iqdfrequencyproducts.com/app-notes/timekeeping/ The fly in the ointment is the aging rate of 5 ppm the first year (13ppb/day) and 3 ppm (8ppb/day) after. I'm sure holding 1 degC is easy. .1 C with some care and .01 C - my measuring eqpt ain't that good. So temperature ceases to be a problem. Is the other stuff workable? I would go with a 32KHz crystal for a production version to make it easy to multiply up to 10MHz. Simon Engineering is the art of making what you want from what you can get at a profit. From: Tom Van Baak t...@leapsecond.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wednesday, December 12, 2012 3:55 AM Subject: Re: [time-nuts] Stable Watch Clocks Typical 32KHz clock crystals are very stable in frequency if you can keep them close to the turnover temp. If you can hold 1 degC it is .04 ppm. That's far better than I thought. Do you have a reference for this spec? I agree you might be able to make one accurate to 0.04 ppm, however briefly, but I've never seen one stable to 0.04 ppm. I mean, that's like 1 second a year. I currently have no method for testing such a rig for stability. Oh, the slipperly slope you are on. I have just the solution for you ... /tvb ___ 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] Stable Watch Clocks
Hi Simon, Thanks for the URL. That's one of those tiny 6x2 mm crystals, 20 ppm crystals (ouch). The tempco (-0.034 ± 0.006 ppm/ T²) is excellent, though. Now, you can adjust rate; and temperature you can control. Notice they don't specify the stability, which is the key to timekeeping. So I see a very interesting experiment/opportunity for you. Get one of these xtals and have it generate 1PPS. Then: 1) measure the accuracy (vs. spec) 2) confirm the tempco (vs. spec) 3) measure the stability (note: no spec given) 4) measure the daily or monthly or annual drift (vs. spec) If you get one of these 32 kHz xtals, I'm happy to send you the other gear you need, if you have the time to do the experiment(s). You'll end up with some very nice plots and a wonderful article or series of articles for your electronics blog. /tvb - Original Message - From: M. Simon To: Tom Van Baak ; Discussion of precise time and frequency measurement Sent: Tuesday, December 11, 2012 9:01 PM Subject: Re: [time-nuts] Stable Watch Clocks http://www.abracon.com/Resonators/AB26T.pdf This quotes .038 ppm/C^2 delta T from the turn over point: http://www.iqdfrequencyproducts.com/app-notes/timekeeping/ The fly in the ointment is the aging rate of 5 ppm the first year (13ppb/day) and 3 ppm (8ppb/day) after. I'm sure holding 1 degC is easy. .1 C with some care and .01 C - my measuring eqpt ain't that good. So temperature ceases to be a problem. Is the other stuff workable? I would go with a 32KHz crystal for a production version to make it easy to multiply up to 10MHz. Simon Engineering is the art of making what you want from what you can get at a profit. From: Tom Van Baak t...@leapsecond.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wednesday, December 12, 2012 3:55 AM Subject: Re: [time-nuts] Stable Watch Clocks Typical 32KHz clock crystals are very stable in frequency if you can keep them close to the turnover temp. If you can hold 1 degC it is .04 ppm. That's far better than I thought. Do you have a reference for this spec? I agree you might be able to make one accurate to 0.04 ppm, however briefly, but I've never seen one stable to 0.04 ppm. I mean, that's like 1 second a year. I currently have no method for testing such a rig for stability. Oh, the slipperly slope you are on. I have just the solution for you ... /tvb ___ 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] Stable Watch Clocks
Yes. I have already decided to do it. I want some feedback from the list before I get past the thinking stage though. Initial rough calibration will be easy once the temp control is functional. Let every thing get nice and stable. Read Freq. Step 1 deg C. Wait 10 minutes. Read frequency. Step temp. 1 degC. etc. Plot the results. Compute the aprox peak of the parabola. Home in with .1 deg steps. OTOH consider the same design with a 40MHz or ???MHz TCVCXO. What would .1C (.01C?) room temperature control give you? Lots of different oscs might be suitable. The power cost will probably be higher than an OCXO - at least to start. But the range of things that might be done is wide. Or consider running an AT Cut crystal at its lower inflection point. It will probably age slower. But a thousand hour bake at the higher inflection point might be good. As I like to tell beginners - when you get close enough to fundamentals it is all made of rubber or silly putty. Simon Engineering is the art of making what you want from what you can get at a profit. From: Tom Van Baak t...@leapsecond.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wednesday, December 12, 2012 5:20 AM Subject: Re: [time-nuts] Stable Watch Clocks Hi Simon, Thanks for the URL. That's one of those tiny 6x2 mm crystals, 20 ppm crystals (ouch). The tempco (-0.034 ± 0.006 ppm/ T²) is excellent, though. Now, you can adjust rate; and temperature you can control. Notice they don't specify the stability, which is the key to timekeeping. So I see a very interesting experiment/opportunity for you. Get one of these xtals and have it generate 1PPS. Then: 1) measure the accuracy (vs. spec) 2) confirm the tempco (vs. spec) 3) measure the stability (note: no spec given) 4) measure the daily or monthly or annual drift (vs. spec) If you get one of these 32 kHz xtals, I'm happy to send you the other gear you need, if you have the time to do the experiment(s). You'll end up with some very nice plots and a wonderful article or series of articles for your electronics blog. /tvb - Original Message - From: M. Simon To: Tom Van Baak ; Discussion of precise time and frequency measurement Sent: Tuesday, December 11, 2012 9:01 PM Subject: Re: [time-nuts] Stable Watch Clocks http://www.abracon.com/Resonators/AB26T.pdf This quotes .038 ppm/C^2 delta T from the turn over point: http://www.iqdfrequencyproducts.com/app-notes/timekeeping/ The fly in the ointment is the aging rate of 5 ppm the first year (13ppb/day) and 3 ppm (8ppb/day) after. I'm sure holding 1 degC is easy. .1 C with some care and .01 C - my measuring eqpt ain't that good. So temperature ceases to be a problem. Is the other stuff workable? I would go with a 32KHz crystal for a production version to make it easy to multiply up to 10MHz. Simon Engineering is the art of making what you want from what you can get at a profit. From: Tom Van Baak t...@leapsecond.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wednesday, December 12, 2012 3:55 AM Subject: Re: [time-nuts] Stable Watch Clocks Typical 32KHz clock crystals are very stable in frequency if you can keep them close to the turnover temp. If you can hold 1 degC it is .04 ppm. That's far better than I thought. Do you have a reference for this spec? I agree you might be able to make one accurate to 0.04 ppm, however briefly, but I've never seen one stable to 0.04 ppm. I mean, that's like 1 second a year. I currently have no method for testing such a rig for stability. Oh, the slipperly slope you are on. I have just the solution for you ... /tvb ___ 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.
