[time-nuts] Curve fitting
Mark Sims
holrum at hotmail.com
Wed Dec 23 22:46:38 UTC 2009
Here are a couple of images of what can be done with a cardboard box, a small fan, and a DC solid state relay (or transistor)...
The first is of the DAC voltage over 8 hours with the temperature stabilized (note with an RMS error of under .001C over 8 hours... much of which is due to those false temperature sensor spikes).
The temp controller PID parameters were not tuned for the box/fan configuration. With optimized values and no furnace to contend with, I have seen rms errors in the low tens of microdegrees over 8 hours...
It also shows the FFT of the temperature data over that time... some temp control wobbles around 1200-1400 seconds due to furnace cycling).
The second image shows the calculated oscillator drift at -2.239E-9 parts/day. The osc tempco number is rather bogus since it needs to be calculated when the temp is moving a lot more.
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