[time-nuts] Re: Temperature accuracy / repeatability / drift of double ovens

[Ed Marciniak]

Linear technology made a thermoelectric full H bridge temperature controller. At the time, I’d like to say it came as a lot of two components. The second was an op-amp that may have been selected or trimmed unless there was a good reason to include it with samples (maybe less commonly available).

It was supposed to be able to achieve 10 millikelvin stability easily, and with more care in design, 1 millikelvin stability was supposed to be not too difficult to achieve.

It was a moderately expensive part…about $20 for the two components. A handful of passives and a a pair of N-channel and a pair of P-channel MOSFETs were required.

If memory serves correctly it was also switched mode rather than linear.

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________________________________
From: Bob Camp via time-nuts <time-nuts at lists.febo.com>
Sent: Thursday, March 30, 2023 6:01:55 PM
To: Discussion of precise time and frequency measurement <time-nuts at lists.febo.com>
Cc: Bob Camp <kb8tq at n1k.org>
Subject: [time-nuts] Re: Temperature accuracy / repeatability / drift of double ovens

Hi

Simple answers (and likely not much help):

Thermal gain on a single oven is likely in the 300 to 600 range.

Double oven boosts that by 10 to 30X

Thermal gain in this case: take the ambient change divide it by the thermal gain
and you get the oven temperature change.

Long term stability:

low enough that it does not impact aging. ( = that’s how you test it). Since that gets back
to the specific thermistor being used, you are into the ‘likely not much help” range.

Best guess info: The crystal + circuit is < 1x10^-9 / C in the vicinity of the turn. The operating
point is offset from turn to minimize the combination of crystal + circuit. Just what the net
is ….

Still, if you can “see” aging at the parts in the (low?) 10^-11 range, it sort of kind of gets
you to a number. Maybe 0.01C / day.

Since you are canceling the circuit with the crystal, if things got to far off, a year later the
temperature performance would not be any good. That likely gets you to something
in the < 1C per year range.

Bob

> On Mar 30, 2023, at 6:16 PM, Gerhard Hoffmann via time-nuts <time-nuts at lists.febo.com> wrote:
>
> Temperature accuracy / repeatability / drift of double ovens:
>
> What can be reached here, with a tolerable effort?
> Is there anything known about that in the public? mK-numbers?
>
> The application is not a crystal oven this time, but diode lasers
> that interrogate Rb atoms and must be kept in lockstep at a certain
> beat frequency. The frequency tuning is mostly by temperature;
> laser diode current plays a minor role, but probably via changing the
> local temperature in the junction and a little bit later in the cavity.
>
> Are there any GoTo thermistors / circuits for stability?
>
> Cheers, Gerhard
> (stumbling into new territory)
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