Re: [time-nuts] Considerations When Using The SR620
I'm curious, which way you went and which accuracy you achieved... :-) Can you tell us? Volker Am 06.12.2012 19:10, schrieb Paul DeStefano: On Tuesday, 4 December 2012, Tom Van Baak wrote: We are using the SR620 to measure the interval between 1PPS signals from two clocks. One is the Septentrio PolaRx4 GPS receiver and the other is a Rubidium clock. Many Thanks, Paul 1) If you are making frequency measurements, the warm-up of the internal oscillator is the major factor limiting accuracy. ... Plotting digits of precision as a function of warm-up time would make a very educational graph you could tape to the top of your SR620. 2) If you are making time interval measurements and using an external standard, the warm-up time will also affect the accuracy of your TI measurements, but to a far lesser degree. Here are informal results for TI (time interval) mode after a 5 minute power-down (see also attached plots): - if you need 1 ns accuracy, you can use the SR620 immediately after power-up - if you need 100 ps accuracy, wait 2+ minutes - if you need 10 ps accuracy, wait 15+ minutes - if you need 1 ps accuracy, you need a seriously stable lab environment or a different counter. Given that you plan to use the SR620 with high-end GPS gear I would suggest you try this quick experiment for yourself to see what *your* SR620 does, with *your* inputs, in *your* environment. Your numbers will come out different than mine; but the methodology is the same. Your procedures can then be based on measurement and confidence instead of guesswork and folklore. Tom Co., Thank you! These plots are excellent and will be very helpful. You are quite right; we should do the test ourselves. We will definitely do that. Obviously, there is not need to worry, as we can characterize the instrument behavior ourselves, which is probably necessary anyway if we're going to publish these measurements with error values. Many Thanks, Paul ___ 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] Considerations When Using The SR620
On Tuesday, 4 December 2012, Tom Van Baak wrote: We are using the SR620 to measure the interval between 1PPS signals from two clocks. One is the Septentrio PolaRx4 GPS receiver and the other is a Rubidium clock. Many Thanks, Paul 1) If you are making frequency measurements, the warm-up of the internal oscillator is the major factor limiting accuracy. ... Plotting digits of precision as a function of warm-up time would make a very educational graph you could tape to the top of your SR620. 2) If you are making time interval measurements and using an external standard, the warm-up time will also affect the accuracy of your TI measurements, but to a far lesser degree. Here are informal results for TI (time interval) mode after a 5 minute power-down (see also attached plots): - if you need 1 ns accuracy, you can use the SR620 immediately after power-up - if you need 100 ps accuracy, wait 2+ minutes - if you need 10 ps accuracy, wait 15+ minutes - if you need 1 ps accuracy, you need a seriously stable lab environment or a different counter. Given that you plan to use the SR620 with high-end GPS gear I would suggest you try this quick experiment for yourself to see what *your* SR620 does, with *your* inputs, in *your* environment. Your numbers will come out different than mine; but the methodology is the same. Your procedures can then be based on measurement and confidence instead of guesswork and folklore. Tom Co., Thank you! These plots are excellent and will be very helpful. You are quite right; we should do the test ourselves. We will definitely do that. Obviously, there is not need to worry, as we can characterize the instrument behavior ourselves, which is probably necessary anyway if we're going to publish these measurements with error values. Many Thanks, Paul -- Paul DeStefano ___ 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] Considerations When Using The SR620
Volker, That's a great question and I'm afraid I don't have a good answer for you. If pressed, I would estimate less than 100ps. The error of this measurement contributes to the error in our final measurement which has many components. I haven't worked out an error budget for each contributor. Our goal is a final error of less than 10ns. But a few contributors are already expected to be around 1ns, so this error really needs to be less than 1ns, preferably less than 100ps. Cheers, Paul On Tuesday, 4 December 2012, Volker Esper wrote: I agree. Since Paul want's to use an SR620 I presume he needs precision. Otherwise almost any TIC with a fairly stable osc would do, for example one with a battery backup. So I further presume that he needs nearly the full accuracy / stability. But that's just speculation, surely Paul can answere this question? -- Paul DeStefano ___ 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] Considerations When Using The SR620
We are using the SR620 to measure the interval between 1PPS signals from two clocks. One is the Septentrio PolaRx4 GPS receiver and the other is a Rubidium clock. Many Thanks, Paul Hi Paul, 1) If you are making frequency measurements, the warm-up of the internal oscillator is the major factor limiting accuracy. This doesn't mean you have wait 12 hours. For example, if all you need is 6 digits of precision, a one-minute warm-up may be sufficient. For each further digit of precision you wait longer. You can probably get 9 digits with 1/2 hour of warm-up. It depends on the oscillator. Plotting digits of precision as a function of warm-up time would make a very educational graph you could tape to the top of your SR620. 2) If you are making time interval measurements and using an external standard, the warm-up time will also affect the accuracy of your TI measurements, but to a far lesser degree. Here are informal results for TI (time interval) mode after a 5 minute power-down (see also attached plots): - if you need 1 ns accuracy, you can use the SR620 immediately after power-up - if you need 100 ps accuracy, wait 2+ minutes - if you need 10 ps accuracy, wait 15+ minutes - if you need 1 ps accuracy, you need a seriously stable lab environment or a different counter. Given that you plan to use the SR620 with high-end GPS gear I would suggest you try this quick experiment for yourself to see what *your* SR620 does, with *your* inputs, in *your* environment. Your numbers will come out different than mine; but the methodology is the same. Your procedures can then be based on measurement and confidence instead of guesswork and folklore. Note also if your data collection is automated, there's really no reason to wait after power-up at all. Just collect data as soon as you can and skip the predetermined number of samples. I can send you the SR620 GPIB scripts I used for my test. This way you have a record of the warm-up settling time itself, which further gives you confidence in the data that follows. /tvbattachment: sr620-warmup-tic-500ps.pngattachment: sr620-warmup-tic-50ps.png___ 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] Considerations When Using The SR620
Tom, I agree. Since Paul want's to use an SR620 I presume he needs precision. Otherwise almost any TIC with a fairly stable osc would do, for example one with a battery backup. So I further presume that he needs nearly the full accuracy / stability. But that's just speculation, surely Paul can answere this question? Volker Am 04.12.2012 14:11, schrieb Tom Van Baak: We are using the SR620 to measure the interval between 1PPS signals from two clocks. One is the Septentrio PolaRx4 GPS receiver and the other is a Rubidium clock. Many Thanks, Paul Hi Paul, 1) If you are making frequency measurements, the warm-up of the internal oscillator is the major factor limiting accuracy. This doesn't mean you have wait 12 hours. For example, if all you need is 6 digits of precision, a one-minute warm-up may be sufficient. For each further digit of precision you wait longer. You can probably get 9 digits with 1/2 hour of warm-up. It depends on the oscillator. Plotting digits of precision as a function of warm-up time would make a very educational graph you could tape to the top of your SR620. 2) If you are making time interval measurements and using an external standard, the warm-up time will also affect the accuracy of your TI measurements, but to a far lesser degree. Here are informal results for TI (time interval) mode after a 5 minute power-down (see also attached plots): - if you need 1 ns accuracy, you can use the SR620 immediately after power-up - if you need 100 ps accuracy, wait 2+ minutes - if you need 10 ps accuracy, wait 15+ minutes - if you need 1 ps accuracy, you need a seriously stable lab environment or a different counter. Given that you plan to use the SR620 with high-end GPS gear I would suggest you try this quick experiment for yourself to see what *your* SR620 does, with *your* inputs, in *your* environment. Your numbers will come out different than mine; but the methodology is the same. Your procedures can then be based on measurement and confidence instead of guesswork and folklore. Note also if your data collection is automated, there's really no reason to wait after power-up at all. Just collect data as soon as you can and skip the predetermined number of samples. I can send you the SR620 GPIB scripts I used for my test. This way you have a record of the warm-up settling time itself, which further gives you confidence in the data that follows. /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] Considerations When Using The SR620
I would be interested in those scripts as well. as soon as the replacement TCXO for my sr620 arrives I can put it back together and this would be fun to try. -eric On Tue, Dec 4, 2012 at 5:11 AM, Tom Van Baak t...@leapsecond.com wrote: We are using the SR620 to measure the interval between 1PPS signals from two clocks. One is the Septentrio PolaRx4 GPS receiver and the other is a Rubidium clock. Many Thanks, Paul Hi Paul, 1) If you are making frequency measurements, the warm-up of the internal oscillator is the major factor limiting accuracy. This doesn't mean you have wait 12 hours. For example, if all you need is 6 digits of precision, a one-minute warm-up may be sufficient. For each further digit of precision you wait longer. You can probably get 9 digits with 1/2 hour of warm-up. It depends on the oscillator. Plotting digits of precision as a function of warm-up time would make a very educational graph you could tape to the top of your SR620. 2) If you are making time interval measurements and using an external standard, the warm-up time will also affect the accuracy of your TI measurements, but to a far lesser degree. Here are informal results for TI (time interval) mode after a 5 minute power-down (see also attached plots): - if you need 1 ns accuracy, you can use the SR620 immediately after power-up - if you need 100 ps accuracy, wait 2+ minutes - if you need 10 ps accuracy, wait 15+ minutes - if you need 1 ps accuracy, you need a seriously stable lab environment or a different counter. Given that you plan to use the SR620 with high-end GPS gear I would suggest you try this quick experiment for yourself to see what *your* SR620 does, with *your* inputs, in *your* environment. Your numbers will come out different than mine; but the methodology is the same. Your procedures can then be based on measurement and confidence instead of guesswork and folklore. Note also if your data collection is automated, there's really no reason to wait after power-up at all. Just collect data as soon as you can and skip the predetermined number of samples. I can send you the SR620 GPIB scripts I used for my test. This way you have a record of the warm-up settling time itself, which further gives you confidence in the data that follows. /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. -- --Eric _ Eric Garner ___ 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] Considerations When Using The SR620
All, The following comment appeared on this list recently and it scared me a little: Though the SR620 TIC is a great instrument when hunting the pico seconds we have to realize, that it's a thermal design desaster (I have to apologize to all sr620 friends). I have to run it for at least 12 hoursif not 24 to be shure, that every single part is at a more or less stationary thermal state. Some (NERC) say ...never switch it off. I assume this instability is due to the instability of the internal frequency standard. There are two options for the SR620: the standard oscillator and an ovenized oscillator. In fact, in our measurements, we plan to use a Cesium frequency standard as the timebase to our SR620. Does this anecdotal warning apply generally to the instrument or mainly to the use of the internal standard oscillator? We are using the SR620 to measure the interval between 1PPS signals from two clocks. One is the Septentrio PolaRx4 GPS receiver and the other is a Rubidium clock. Many Thanks, Paul -- Paul DeStefano ___ 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] Considerations When Using The SR620
Hi Some of the problem comes from the OCXO. Some of it also comes from the stability of the internal circuitry. They do some interesting things with delay lines and the like in the SR620. Best bet is to let it warm up for a while before you need it to perform at it's top level of performance. Bob On Dec 2, 2012, at 2:45 PM, Paul DeStefano paul.destef...@willamettealumni.com wrote: All, The following comment appeared on this list recently and it scared me a little: Though the SR620 TIC is a great instrument when hunting the pico seconds we have to realize, that it's a thermal design desaster (I have to apologize to all sr620 friends). I have to run it for at least 12 hoursif not 24 to be shure, that every single part is at a more or less stationary thermal state. Some (NERC) say ...never switch it off. I assume this instability is due to the instability of the internal frequency standard. There are two options for the SR620: the standard oscillator and an ovenized oscillator. In fact, in our measurements, we plan to use a Cesium frequency standard as the timebase to our SR620. Does this anecdotal warning apply generally to the instrument or mainly to the use of the internal standard oscillator? We are using the SR620 to measure the interval between 1PPS signals from two clocks. One is the Septentrio PolaRx4 GPS receiver and the other is a Rubidium clock. Many Thanks, Paul -- Paul DeStefano ___ 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] Considerations When Using The SR620
Paul wrote: The following comment appeared on this list recently and it scared me a little: Though the SR620 TIC is a great instrument when hunting the pico seconds we have to realize, that it's a thermal design desaster (I have to apologize to all sr620 friends). I have to run it for at least 12 hoursif not 24 to be shure, that every single part is at a more or less stationary thermal state. Some (NERC) say ...never switch it off. I assume this instability is due to the instability of the internal frequency standard. * * * In fact, in our measurements, we plan to use a Cesium frequency standard as the timebase to our SR620. Does this anecdotal warning apply generally to the instrument or mainly to the use of the internal standard oscillator? I concur with the comment above that the thermal design of the 620 could have been better -- the sensing thermistor is in an exhaust stack between the fan (which is blowing out) and the rear enclosure wall. This means that, instead of trying to maintain the internal instrument temerature at a constant level, it tries to maintain the exhaust stack temperature constant with a viciously fast response time that leads to instability at startup. I have more than once considered moving the thermistor to a location near the TCXO, but since the fans always run up to full speed rather quickly at room temperature anyway, I have never bothered to try to improve the fan circuit. Additionally. the TCXO remains powered during standby, but not exactly on frequency because the DAC that adjusts it during operation is not powered. So, there is some settling from that adding to the temperature drift. Note also that the DAC steps are not very fine, so you cannot expect to get the internal oscillator trimmed to better than e-9 or so. SR apparently thought that most users would connect 620s to external standards, so there was no reason to make them pay for a high-precision internal standard they would not use. IME -- operating with an external reference that is better than the specified accuracy of the 620 -- they meet SR's specifications within a few minutes at most after switching on from room temperature storage. (The trigger circuitry may drift a bit as it warms up, so you may want to check the trigger drift if your application involves slowish sine waves. I have not investigated this.) Ideally, you would let the instrument warm up for at least an hour and then perform an internal calibration before starting your measurements. All that said, the only way you will know for sure how your particular instrument and standard will perform is to characterize them before you start your mobile measurements. In doing so, you should observe a protocol that resembles the actual travel between measurements, at least with respect to time and temperature. I strongly urge you to do this so you can have confidence in your measurements. Best regards, Charles ___ 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] Considerations When Using The SR620
On 12/02/2012 10:25 PM, Charles P. Steinmetz wrote: Paul wrote: The following comment appeared on this list recently and it scared me a little: Though the SR620 TIC is a great instrument when hunting the pico seconds we have to realize, that it's a thermal design desaster (I have to apologize to all sr620 friends). I have to run it for at least 12 hoursif not 24 to be shure, that every single part is at a more or less stationary thermal state. Some (NERC) say ...never switch it off. I assume this instability is due to the instability of the internal frequency standard. * * * In fact, in our measurements, we plan to use a Cesium frequency standard as the timebase to our SR620. Does this anecdotal warning apply generally to the instrument or mainly to the use of the internal standard oscillator? I concur with the comment above that the thermal design of the 620 could have been better -- the sensing thermistor is in an exhaust stack between the fan (which is blowing out) and the rear enclosure wall. This means that, instead of trying to maintain the internal instrument temerature at a constant level, it tries to maintain the exhaust stack temperature constant with a viciously fast response time that leads to instability at startup. I have more than once considered moving the thermistor to a location near the TCXO, but since the fans always run up to full speed rather quickly at room temperature anyway, I have never bothered to try to improve the fan circuit. Never thought about that part, other than the fact that the fan is annoying like hell. Additionally. the TCXO remains powered during standby, but not exactly on frequency because the DAC that adjusts it during operation is not powered. So, there is some settling from that adding to the temperature drift. Note also that the DAC steps are not very fine, so you cannot expect to get the internal oscillator trimmed to better than e-9 or so. SR apparently thought that most users would connect 620s to external standards, so there was no reason to make them pay for a high-precision internal standard they would not use. Which is why a high stability reference is an option, like most. In contrast it is interesting to note that the HP5370 had a lower stability oscillator as option, so removing the 10811 was thus using a negative option. IME -- operating with an external reference that is better than the specified accuracy of the 620 -- they meet SR's specifications within a few minutes at most after switching on from room temperature storage. (The trigger circuitry may drift a bit as it warms up, so you may want to check the trigger drift if your application involves slowish sine waves. I have not investigated this.) Ideally, you would let the instrument warm up for at least an hour and then perform an internal calibration before starting your measurements. Another source of temperature dependence is the analogue interpolator. All that said, the only way you will know for sure how your particular instrument and standard will perform is to characterize them before you start your mobile measurements. In doing so, you should observe a protocol that resembles the actual travel between measurements, at least with respect to time and temperature. I strongly urge you to do this so you can have confidence in your measurements. This is good advice. Consider what you need to do. You might want to consider having a rubidium doing your hold-over. for instance. A PRS-10 would be an interesting option for instance. Cheers, Magnus ___ 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] Considerations When Using The SR620
Volker, On 12/02/2012 11:36 PM, Volker Esper wrote: Hi, I was the one who wrote those nasty things about a fantastic instrument. I bought such a counter a few weeks ago. When I first peeked into it (because the fan was running at top speed after a few minutes) I noticed, that the arrangement of the components was anything but optimal. Examples: The osc is only one or two inches away from the linear voltage regulators. These are cooled by a 1mm iron sheet. The iron sheet has some cooling slots where the air can flow through, but these slots are miles away from the regulators. The sheet gets so hot that you won't touch it voluntarily. If at least the air could flow directly along the regulators - but they sit in a corner and the air flows diagonally through the case, avoiding contact with the regulators. I am also not very impressed with the location of the linear regulators. This forms a nice interesting relationship between line voltage and room temperature. As line voltage shifts, the rectified voltage varies, and then the voltage that the linear regulator needs to burn off varies, and thus their heat contribution varies with the line voltage. Now, the ambient temperature then controls how easy we get rid of this excess heat. The way the airflow goes, this cooling makes sure it couples very well with the electronics, so fan speed amongst other things depend on ambient temperature... and line voltage. All this assist to give us an interesting temperature dependence. In contrast, I was impressed by how the HP10811A was located in a turbolence free corner of the HP5070A/B assembly. While itself also not particularly well designed in heat context, at least the heat of the linear regulators was supposed to mostly affect an external self-convection stream. Forces convection (fan) to stabilize the temperature of the heat sink would be a good thing there. Cheers, Magnus ___ 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.
