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

Charles P. Steinmetz charles_steinmetz at lavabit.com
Tue Dec 11 12:39:59 UTC 2012


Bill wrote:

>Well, perhaps you are not looking close enough.  That is you need to 
>be observing
>at a finer level of comparison.  The changes, observed here and at another
>location, are in parts in 10-10 to 10-11 range, sometimes 
>larger.  At one of the
>locations there was a direct correlation to the air conditioning cycle.

It is not clear what part of my message you are referring to.

My main point was that the information from the DS1620 temperature 
sensor does not appear to be used internally by the Tbolt.  In my 
observation, subjecting the sensor alone (thermally isolated from the 
rest of the Tbolt) to wide temperature swings (-10 to +120 C) did not 
produce any observabe effect on the operation of the Tbolt.  If the 
temp sensor data were used internally by the Tbolt, one would expect 
a significant effect from such a wide swing -- one that couldn't be 
missed.  If that large and fast a reported temperature swing produced 
effects only at the e-10 or 11 level, I would attribute it to 
imperfect thermal isolation of the Tbolt from the temperature 
stimulus (i.e., stimulus affecting the oven temperature or EFC 
circuitry of the Tbolt), not as the Tbolt's response to the 
temperature change reported by the DS1620 sensor.

If you were referring to my side point -- that allowing slow changes 
to the Tbolt housing temperature does not appear to be materially 
different from regulating the housing temperature -- my observations 
were that this was true down to at least 5e-13.  Of course, there are 
two variables -- total swing and rate of change.  By "slow," I mean a 
rate of change of 0.25C per hour or less [DS1620 reported 
temperature].  My diurnal swings are no more than 2C per day and 
usually less [DS1620 reported temperature] (they can be as much as 5 
or 6C seasonally, but those changes happen over weeks).  A/C cycling 
likely subjects the Tbolt to a significantly greater rate of change 
than what I mean by "slow," even if basic precautions are taken 
(e.g., putting it in a cardboard box).

Best regards,

Charles











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