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

Bob Camp lists at rtty.us
Tue Dec 11 17:11:21 UTC 2012


The only place the sensor *might* be used is during holdover. There is no
practical reason to use it while the TBolt is locked to GPS. 

*If* it's used in holdover, it gets "trained" by watching the control
voltage and the temperature while the beast is locked to GPS. That
information is then used when it goes into holdover to improve time drift
while in holdover. 

The first test would be to put one in holdover and see if the DAC voltage
changes at all while it's there. If it changes, the next step would be to
see if the change is simply a function of time (= aging correction).


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Bill Dailey
Sent: Tuesday, December 11, 2012 10:45 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Thunderbolt oven / non-stable operating temperature

If it is used for tempco it should affect the temp by stabilizing offset
with temp changes correct?  Maybe a more correct approach would be to
disconnect it and test.  Has been awhile since I read that testing stuff.


Sent from mobile

On Dec 11, 2012, at 6:39 AM, "Charles P. Steinmetz"
<charles_steinmetz at lavabit.com> wrote:

> Bill wrote:
>> Well, perhaps you are not looking close enough.  That is you need to be
>> at a finer level of comparison.  The changes, observed here and at
>> 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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