[time-nuts] Thunderbolt oven / non-stable operating temperature

Charles P. Steinmetz charles_steinmetz at lavabit.com
Wed Dec 12 00:11:55 UTC 2012

Warren wrote:

>During normal operation my Tbolt uses the temperature and ADC data 
>to in its Kalman filter that then can predict a simple linear 
>temperature constant, and simple linear ageing rate.
>    *   *   *
>But the **Only** time the Kalman filter is used is during 
>Holdover.  It does this by adjusting the EFC voltage in small steps 
>making a simple linear ramp as a function of time, Plus a simple 
>linear output as function of delta temperature.
>I've also found that if the Temperature chip is the new one that 
>gives only about 1 deg of resolution, All still works the same, But 
>during hold over instead of seeing small continuous DAC changes as 
>temperature changes, you see Big EFC steps.

That all sounds like the way it should work, if the temp sensor data 
is used internally by the Tbolt.

My notes indicate that I tried cooling and warming the isolated 
sensor during holdover and observed no effect.  However, the Kalman 
filter may not have been operating because I tested the unit 
immediately after it reached basic stability, before it had time to 
learn anything.

>So what does this mean for the average Nut's Tbolt?   Mostly nothing.

I agree.  I presume that most time nuts would not ordinarily rely on 
a GPSDO during holdover -- particularly, a long holdover.


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