Hi A great starting point is Rick’s paper on the Hockey Puck.
Bob > On Jun 11, 2017, at 9:09 AM, Magnus Danielson <[email protected]> > wrote: > > Hi, > > What papers would you recommend reading? > > One of the things that we experimented on and improved was the passive wall > to prohibit quick cooling of oven. A puff of air or the forced convection > (fans) needed for other electronics would tie the metal shield very well to > surrounding environment. Using a simple plastic wall/box as a windshield has > a quite drastic effect at the rate of change in temperature, and allowed the > oven to react better to it. > It has proven a very good strategy to reduce the systematic effect that eats > up stability. As systematic effect, it should not be part of ADEV, but if you > ADEV it is there loud and clear. > > Cheers, > Magnus > > On 06/11/2017 04:45 AM, Bob kb8tq wrote: >> Hi >> >> One of the bigger unknowns in all this is how tight your control point >> needs to be held >> in order that your crystal only sees 0.1C. So far we have sort of assumed >> that the >> control point and the crystal see the same thing. That’s never the case. >> >> If the outside temperature goes from -30 to +70 (100C range), a 0.1 C change >> would >> be a thermal gain of 1,000. A +/- 0.1 C change would be a thermal gain of >> 500. Both >> are pretty respectable numbers for a basic single oven. >> >> It is not at all uncommon to see references to “0.0001C temperature control” >> (or some >> looney number) on ovens that obviously do not have a thermal gain of much >> over 100. >> Yes, those references were a lot more common 40 years ago than they are >> today. The >> take away is that often set point control is much tighter at the sensor than >> at the crystal. >> >> It is not uncommon for people to ask “what is the control at a constant >> ambient (room >> conditions maybe). The answer is inevitably a very small change. If your >> room varies >> by 1 C and you have a thermal gain of 1,000, the oven changes by 0.001C. If >> your room >> changes by 0.1 C then the oven would change by 0.0001 C. Inevitably the >> phrase “plus >> circuit noise” needs to be added in there somewhere as the numbers get ever >> smaller. >> ADEV is a more common way to look at controller noise than TC. >> >> As I keep pointing out, there are some good papers on all of this. I claim >> absolutely >> no original insight in any of the above. >> >> Bob >> >>> On Jun 10, 2017, at 9:11 PM, Hal Murray <[email protected]> wrote: >>> >>> >>> [email protected] said: >>>> I say "effective" because we can dither the low order bits to gain maybe 6 >>>> effective bits form 4 real bits (we can filter the switching noise from a >>>> low frequency dither) >>> >>> It's hard to filter low frequencies and the more bits you gain by dithering >>> the lower the filter you need and the closer in the spurs move. >>> >>> >>>> Lets say my goal is regulation within 0.1C. After filtering I have 10 >>>> "good" bits in my ADC. That is 1024 counts. My set point is S. >>> >>>> I scale the ADC so that 0 == (S - 0.5) and 1023 == (S + 0.5) This means >>>> that each ADC count is 0.001 degree C and within the 0.1C range there are >>>> 100 ADC counts. >>> >>> That's not enough to describe the system so you can decide if it will meet >>> your 0.1C goal. >>> >>> You also need to know the sampling rate, the delay time from heater to >>> temperature sensor, the PID parameters, and maybe the rate of change of the >>> environmental temperature and the delay from the environment to your system. >>> ("delay" should probably be transfer function or impulse response but a >>> simple exponential is probably good enough.) >>> >>> >>> >>> -- >>> These are my opinions. I hate spam. >>> >>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
