Re: [time-nuts] Digital temperature compensation
On 11/1/2014 6:03 PM, Hal Murray wrote: dan-timen...@drown.org said: I'm experimenting with using a temperature sensor to estimate local oscillator frequency changes. My goal is to have a decent holdover clock for a NTP server with not so great GPS antenna placement. This is for ntpd rather than chrony, but it's a good read: NTP temperature compensation http://www.ijs.si/time/temp-compensation/ Thank you, I hadn't seen this one. I chose chrony because it has built-in support for temperature compensation. I couldn't find anyone else talking about using it, so I posted my trial run information: http://blog.dan.drown.org/beaglebone-black-ntpgps-server-temperature-compensation/ Chrony's support looks very similar in implementation to that page, so I assume that's what it was inspired by. My trial run was exciting because it suggested around 25ppb-60ppb was possible. With the colder temperatures, there's a sudden drop off in frequency that I'm having a hard time finding a equation that fits as nicely. That section of the graph doesn't make sense to me. I suspect a glitch in your setup. I suspect what I'm running into is some interaction of other components (perhaps the resistors and capacitors) with the crystal oscillator. When does your GPS unit run out of satellites? I've only included data when the GPS is locked and the PPS offset is within +/- 15us. Where is your temperature probe? Is it in contact with the crystal inside the PC? Is the PC doing anything? In particular at the times when the data doesn't make sense? The probe is nearby, on a breadboard. The system in question is a beaglebone black and dedicated to just NTP. I'm also collecting the (less precise) CPU temperature sensor data, and there's no relationship between it and the frequency spikes. I've gone ahead and attached that graph. PCs can do a lot of self heating. Try running a big workload when the temperature is in the middle of the good range. Yup, you can see an example of this on the blog page. I've posted a part 2 to my blog to go over my estimation of what should be possible using this hardware, and came to the conclusion of around 700ppb: http://blog.dan.drown.org/beaglebone-black-ntpgps-server-temperature-compensation-part-2/ ___ 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] Digital temperature compensation
I'm experimenting with using a temperature sensor to estimate local oscillator frequency changes. My goal is to have a decent holdover clock for a NTP server with not so great GPS antenna placement. I've been sampling temperature every minute, measured by a DS18B20. I've been measuring local clock frequency differences, using chronyd's logs from the GPS's PPS. At 28C through 21C, I get a pretty good result that fits a quadratic polynomial decently (0.117 ppm stddev). I've attached the graph of that as temp-clock-warmer.png. With the colder temperatures, there's a sudden drop off in frequency that I'm having a hard time finding a equation that fits as nicely. All the examples I can find on the web look like third degree polynomials, while my data doesn't seem to fit that exactly. The best result I've had so far (0.198 ppm stddev) is attached as temp-clock.png and uses the function: f(x) = -abs(a * (x - 20.88)) + b * ((x - 20.88)**2) + c * ((x - 20.88)**3) a = 0.888582 b = 0.113806 c = -0.00445763 Does anyone have any advice on how to better model this? Has anyone seen this behavior? I can provide the raw data if that would help any. ___ 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] Digital temperature compensation
Hi This sort of thing is normally done with a precisely controlled temperature chamber and multi day temperature ramp runs. Even then there is a bit of “wonder what that was, let’s try it again”. If you are looking at a crystal oscillator, what you have is a perturbation in the frequency / temperature curve. The response you get will be temperature rate of change dependent. Bob On Nov 1, 2014, at 4:40 PM, Dan Drown dan-timen...@drown.org wrote: I'm experimenting with using a temperature sensor to estimate local oscillator frequency changes. My goal is to have a decent holdover clock for a NTP server with not so great GPS antenna placement. I've been sampling temperature every minute, measured by a DS18B20. I've been measuring local clock frequency differences, using chronyd's logs from the GPS's PPS. At 28C through 21C, I get a pretty good result that fits a quadratic polynomial decently (0.117 ppm stddev). I've attached the graph of that as temp-clock-warmer.png. With the colder temperatures, there's a sudden drop off in frequency that I'm having a hard time finding a equation that fits as nicely. All the examples I can find on the web look like third degree polynomials, while my data doesn't seem to fit that exactly. The best result I've had so far (0.198 ppm stddev) is attached as temp-clock.png and uses the function: f(x) = -abs(a * (x - 20.88)) + b * ((x - 20.88)**2) + c * ((x - 20.88)**3) a = 0.888582 b = 0.113806 c = -0.00445763 Does anyone have any advice on how to better model this? Has anyone seen this behavior? I can provide the raw data if that would help any. temp-clock-warmer.pngtemp-clock.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. ___ 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] Digital temperature compensation
You could try submitting your data to zunzun.com It will fit it to around 40,000 different curves and find the best ones. Beware that with all curve fitting formulas, once your live data starts to wander out of the range of your original curve fit data, things can go rather badly... ___ 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] Digital temperature compensation
Ok, I hadn't considered rate of change. This data is currently 3 day's worth and seems to repeat itself on both days at the same temperature point. Attached is a time based graph to show that. The ppm axis (on the right) is inverted to make it easier to see the relationship between the two. Quoting Bob Camp kb...@n1k.org: Hi This sort of thing is normally done with a precisely controlled temperature chamber and multi day temperature ramp runs. Even then there is a bit of “wonder what that was, let’s try it again”. If you are looking at a crystal oscillator, what you have is a perturbation in the frequency / temperature curve. The response you get will be temperature rate of change dependent. Bob On Nov 1, 2014, at 4:40 PM, Dan Drown dan-timen...@drown.org wrote: I'm experimenting with using a temperature sensor to estimate local oscillator frequency changes. My goal is to have a decent holdover clock for a NTP server with not so great GPS antenna placement. I've been sampling temperature every minute, measured by a DS18B20. I've been measuring local clock frequency differences, using chronyd's logs from the GPS's PPS. At 28C through 21C, I get a pretty good result that fits a quadratic polynomial decently (0.117 ppm stddev). I've attached the graph of that as temp-clock-warmer.png. With the colder temperatures, there's a sudden drop off in frequency that I'm having a hard time finding a equation that fits as nicely. All the examples I can find on the web look like third degree polynomials, while my data doesn't seem to fit that exactly. The best result I've had so far (0.198 ppm stddev) is attached as temp-clock.png and uses the function: f(x) = -abs(a * (x - 20.88)) + b * ((x - 20.88)**2) + c * ((x - 20.88)**3) a = 0.888582 b = 0.113806 c = -0.00445763 Does anyone have any advice on how to better model this? Has anyone seen this behavior? I can provide the raw data if that would help any. temp-clock-warmer.pngtemp-clock.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. ___ 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] Digital temperature compensation
I gave zunzun a try and the one with the lowest root mean squared error was: f(x) = a( x**0.5) + b( x ) + c( sin(x) ) + d( cos(x) ) It got 0.202 RMSE, so I guess I'll stick with my original function as it seems to be closer to what I expect will happen at colder/hotter temps. You have a good point about temperatures outside my data samples. Once it gets hot again in the summertime, I'm sure I'll have to re-evaluate this. Quoting Mark Sims hol...@hotmail.com: You could try submitting your data to zunzun.com It will fit it to around 40,000 different curves and find the best ones. Beware that with all curve fitting formulas, once your live data starts to wander out of the range of your original curve fit data, things can go rather badly... ___ 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] Digital temperature compensation
Hi On Nov 1, 2014, at 5:09 PM, Dan Drown dan-timen...@drown.org wrote: Ok, I hadn't considered rate of change. It’s one of the limits on this sort of thing in general. It’s even more of an issue with a coupled mode like the one you show. Since there are an enormous number of possible variables, it’s always tough to know exactly how much of an issue you will have. One common answer - run your profile runs at the temperature change rate you are most likely to see in practice. Another very common answer - don’t use that crystal, get one that does not have the problem. You can get parts with slopes 0.1 ppm / C over 10 to 50 C. You might have to spend some quality time sorting them out …. Bob This data is currently 3 day's worth and seems to repeat itself on both days at the same temperature point. Attached is a time based graph to show that. The ppm axis (on the right) is inverted to make it easier to see the relationship between the two. Quoting Bob Camp kb...@n1k.org: Hi This sort of thing is normally done with a precisely controlled temperature chamber and multi day temperature ramp runs. Even then there is a bit of “wonder what that was, let’s try it again”. If you are looking at a crystal oscillator, what you have is a perturbation in the frequency / temperature curve. The response you get will be temperature rate of change dependent. Bob On Nov 1, 2014, at 4:40 PM, Dan Drown dan-timen...@drown.org wrote: I'm experimenting with using a temperature sensor to estimate local oscillator frequency changes. My goal is to have a decent holdover clock for a NTP server with not so great GPS antenna placement. I've been sampling temperature every minute, measured by a DS18B20. I've been measuring local clock frequency differences, using chronyd's logs from the GPS's PPS. At 28C through 21C, I get a pretty good result that fits a quadratic polynomial decently (0.117 ppm stddev). I've attached the graph of that as temp-clock-warmer.png. With the colder temperatures, there's a sudden drop off in frequency that I'm having a hard time finding a equation that fits as nicely. All the examples I can find on the web look like third degree polynomials, while my data doesn't seem to fit that exactly. The best result I've had so far (0.198 ppm stddev) is attached as temp-clock.png and uses the function: f(x) = -abs(a * (x - 20.88)) + b * ((x - 20.88)**2) + c * ((x - 20.88)**3) a = 0.888582 b = 0.113806 c = -0.00445763 Does anyone have any advice on how to better model this? Has anyone seen this behavior? I can provide the raw data if that would help any. temp-clock-warmer.pngtemp-clock.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. ___ 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. temp-vs-clock.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. ___ 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] Digital temperature compensation
dan-timen...@drown.org said: I'm experimenting with using a temperature sensor to estimate local oscillator frequency changes. My goal is to have a decent holdover clock for a NTP server with not so great GPS antenna placement. This is for ntpd rather than chrony, but it's a good read: NTP temperature compensation http://www.ijs.si/time/temp-compensation/ With the colder temperatures, there's a sudden drop off in frequency that I'm having a hard time finding a equation that fits as nicely. That section of the graph doesn't make sense to me. I suspect a glitch in your setup. When does your GPS unit run out of satellites? Where is your temperature probe? Is it in contact with the crystal inside the PC? Is the PC doing anything? In particular at the times when the data doesn't make sense? PCs can do a lot of self heating. Try running a big workload when the temperature is in the middle of the good range. -- These are my opinions. I hate spam. ___ 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] Digital temperature compensation
If this is just for holdover then I don't think you even want a general solution. Have the controller always keep the last few days of data for temperature vs. EFC value. Then if GPS fails use the most recent data for the current temperature. This makes for a self adapting system accounting for aging too. Not just crystal aging but the aging of the resisters, the temperature sensor itself and other components. I don't think holdover should fall back onto a model that was created from data that might be months or years old. Use hours or days old data. This will give the desired response which is this: If the temperature is constant when the GPS fails the EFC value as determined by your holdover temperature modeling should give you the EXACT same EFC value as just before the GPS failure. I don't think you can do that with a model. You'd nee to use logged data. On Sat, Nov 1, 2014 at 4:01 PM, Bob Camp kb...@n1k.org wrote: Hi On Nov 1, 2014, at 5:09 PM, Dan Drown dan-timen...@drown.org wrote: Ok, I hadn't considered rate of change. It’s one of the limits on this sort of thing in general. It’s even more of an issue with a coupled mode like the one you show. Since there are an enormous number of possible variables, it’s always tough to know exactly how much of an issue you will have. One common answer - run your profile runs at the temperature change rate you are most likely to see in practice. Another very common answer - don’t use that crystal, get one that does not have the problem. You can get parts with slopes 0.1 ppm / C over 10 to 50 C. You might have to spend some quality time sorting them out …. Bob This data is currently 3 day's worth and seems to repeat itself on both days at the same temperature point. Attached is a time based graph to show that. The ppm axis (on the right) is inverted to make it easier to see the relationship between the two. Quoting Bob Camp kb...@n1k.org: Hi This sort of thing is normally done with a precisely controlled temperature chamber and multi day temperature ramp runs. Even then there is a bit of “wonder what that was, let’s try it again”. If you are looking at a crystal oscillator, what you have is a perturbation in the frequency / temperature curve. The response you get will be temperature rate of change dependent. Bob On Nov 1, 2014, at 4:40 PM, Dan Drown dan-timen...@drown.org wrote: I'm experimenting with using a temperature sensor to estimate local oscillator frequency changes. My goal is to have a decent holdover clock for a NTP server with not so great GPS antenna placement. I've been sampling temperature every minute, measured by a DS18B20. I've been measuring local clock frequency differences, using chronyd's logs from the GPS's PPS. At 28C through 21C, I get a pretty good result that fits a quadratic polynomial decently (0.117 ppm stddev). I've attached the graph of that as temp-clock-warmer.png. With the colder temperatures, there's a sudden drop off in frequency that I'm having a hard time finding a equation that fits as nicely. All the examples I can find on the web look like third degree polynomials, while my data doesn't seem to fit that exactly. The best result I've had so far (0.198 ppm stddev) is attached as temp-clock.png and uses the function: f(x) = -abs(a * (x - 20.88)) + b * ((x - 20.88)**2) + c * ((x - 20.88)**3) a = 0.888582 b = 0.113806 c = -0.00445763 Does anyone have any advice on how to better model this? Has anyone seen this behavior? I can provide the raw data if that would help any. temp-clock-warmer.pngtemp-clock.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. ___ 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. temp-vs-clock.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. ___ 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. -- Chris Albertson Redondo Beach, California ___ 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] Digital temperature compensation
Mmmm yes you can see the equation evaluation starting to rise in your Warmer plot, as Mark says, which will make a nonsense of the formula if your summer temps get above 28. Why not a table and then interpolate between the table data points?. You might have more points where the changes are greater. The colder plot looks cubic maybe for a crystal made for 20 deg C ?? But depending on the oscillator electronics you may have component tempcos affecting the frequency as well? I suspect the turnover at 21deg C should be a smooth curve not as your formula predicts. Which suggests that you have too too high an order of polynomial I think, but you may not get a good fit with a cubic if other effects are present. Alan G3NYK - Original Message - From: Dan Drown dan-timen...@drown.org To: time-nuts@febo.com Sent: Saturday, November 01, 2014 10:07 PM Subject: Re: [time-nuts] Digital temperature compensation I gave zunzun a try and the one with the lowest root mean squared error was: f(x) = a( x**0.5) + b( x ) + c( sin(x) ) + d( cos(x) ) It got 0.202 RMSE, so I guess I'll stick with my original function as it seems to be closer to what I expect will happen at colder/hotter temps. You have a good point about temperatures outside my data samples. Once it gets hot again in the summertime, I'm sure I'll have to re-evaluate this. Quoting Mark Sims hol...@hotmail.com: You could try submitting your data to zunzun.com It will fit it to around 40,000 different curves and find the best ones. Beware that with all curve fitting formulas, once your live data starts to wander out of the range of your original curve fit data, things can go rather badly... ___ 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] Digital temperature compensation
I think you have a good point - any model is going to have a larger error than the data itself. I'll be looking into this. Quoting Chris Albertson albertson.ch...@gmail.com: If this is just for holdover then I don't think you even want a general solution. Have the controller always keep the last few days of data for temperature vs. EFC value. Then if GPS fails use the most recent data for the current temperature. This makes for a self adapting system accounting for aging too. Not just crystal aging but the aging of the resisters, the temperature sensor itself and other components. I don't think holdover should fall back onto a model that was created from data that might be months or years old. Use hours or days old data. This will give the desired response which is this: If the temperature is constant when the GPS fails the EFC value as determined by your holdover temperature modeling should give you the EXACT same EFC value as just before the GPS failure. I don't think you can do that with a model. You'd nee to use logged data. On Sat, Nov 1, 2014 at 4:01 PM, Bob Camp kb...@n1k.org wrote: Hi On Nov 1, 2014, at 5:09 PM, Dan Drown dan-timen...@drown.org wrote: Ok, I hadn't considered rate of change. It’s one of the limits on this sort of thing in general. It’s even more of an issue with a coupled mode like the one you show. Since there are an enormous number of possible variables, it’s always tough to know exactly how much of an issue you will have. One common answer - run your profile runs at the temperature change rate you are most likely to see in practice. Another very common answer - don’t use that crystal, get one that does not have the problem. You can get parts with slopes 0.1 ppm / C over 10 to 50 C. You might have to spend some quality time sorting them out …. Bob This data is currently 3 day's worth and seems to repeat itself on both days at the same temperature point. Attached is a time based graph to show that. The ppm axis (on the right) is inverted to make it easier to see the relationship between the two. Quoting Bob Camp kb...@n1k.org: Hi This sort of thing is normally done with a precisely controlled temperature chamber and multi day temperature ramp runs. Even then there is a bit of “wonder what that was, let’s try it again”. If you are looking at a crystal oscillator, what you have is a perturbation in the frequency / temperature curve. The response you get will be temperature rate of change dependent. Bob On Nov 1, 2014, at 4:40 PM, Dan Drown dan-timen...@drown.org wrote: I'm experimenting with using a temperature sensor to estimate local oscillator frequency changes. My goal is to have a decent holdover clock for a NTP server with not so great GPS antenna placement. I've been sampling temperature every minute, measured by a DS18B20. I've been measuring local clock frequency differences, using chronyd's logs from the GPS's PPS. At 28C through 21C, I get a pretty good result that fits a quadratic polynomial decently (0.117 ppm stddev). I've attached the graph of that as temp-clock-warmer.png. With the colder temperatures, there's a sudden drop off in frequency that I'm having a hard time finding a equation that fits as nicely. All the examples I can find on the web look like third degree polynomials, while my data doesn't seem to fit that exactly. The best result I've had so far (0.198 ppm stddev) is attached as temp-clock.png and uses the function: f(x) = -abs(a * (x - 20.88)) + b * ((x - 20.88)**2) + c * ((x - 20.88)**3) a = 0.888582 b = 0.113806 c = -0.00445763 Does anyone have any advice on how to better model this? Has anyone seen this behavior? I can provide the raw data if that would help any. temp-clock-warmer.pngtemp-clock.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. ___ 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. temp-vs-clock.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. ___ 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. -- Chris Albertson Redondo Beach, California ___ 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
