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

Bob Camp lists at rtty.us
Tue Dec 11 12:01:52 UTC 2012


Hi

I suspect that to use the temperature chip data, it needs to be running on GPS for several days while ramping temperature. After that, put it in holdover, observe the time drift over the next four hours with a similar ramp. Since they work with the later chip, the ramp would have to be pretty aggressive (many degrees C per hour).

Bob

On Dec 10, 2012, at 11:23 PM, Charles P. Steinmetz <charles_steinmetz at lavabit.com> wrote:

> 
>> That temperature sensor does have an effect on the final outcome as it is part of
>> the internal equation.  So buffering the ambient temperature is important.
> 
> I've heard this before, but the evidence I have seen does not seem to support the proposition.
> 
> While switching the Dallas chip in one, I used the opportunity to bring the chip temporarily outside of the Tbolt housing on a cable to investigate whether the Tbolt makes any internal use of the temperature data.  Neither freeze spray nor bringing a soldering iron near the chip, when it was outside of the Tbolt housing and the Tbolt housing was well insulated from the changes in chip temperature, seemed to have any effect on the operation of the Tbolt, either normal or in holdover.
> 
> I have also run Tbolts with the newer ("wrong") temperature chips for long periods, and have not observed any systematic differences in performance between them and units with the older chips, either in normal operation or in holdover.  In Tbolts with the newer chips, the reported temperature often has little connection with the actual temperature and, at times, jumps abruptly, yet the Thunderbolts operate normally with no corresponding jumps in operating parameters.
> 
> My supposition/conclusion is that the temperature sensor was provided so telcom operators could get a rough idea of the temperature in remote cell-site transmitter shacks, not for internal use by the Tbolt.
> 
> As long as the Tbolt is housed so that its reported temperature does not change too rapidly, the oven control loop will keep the crystal very close to its set temperature over a wide range of ambient temperatures.  I have used this approach and have also actively controlled the housing temperature, and have not observed any material difference in frequency or timing stability between the two approaches.
> 
> Best regards,
> 
> Charles
> 
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