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

[Javier Herrero]

Hello,

Of course, the data sheet has Jim Williams signature. Take a look to his 
app note 
https://www.analog.com/media/en/technical-documentation/application-notes/an89.pdf 
and don't miss the last page :)

Regards,

Javier, EA1CRB

On 4/1/23 23:11, Gerhard Hoffmann via time-nuts wrote:
> Am 2023-03-31 20:13, schrieb Ed Marciniak via time-nuts:
>> 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.
>
> That really gives me some hope, I'll take the care :-)
> The question is now how to prove it!
>
>
>> 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.
>
> Thanks for the pointer, also to Jim Lux.
>
> As a first try, I used the Analog Devices ADN 8834, also from AD, now 
> that
> they have bought LT. But the Linear Technology LTC1923 data sheet is in
> a different league, they even give absolute numbers and strip charts.
> I'd bet that this went over the desk of Jim Williams, RIP. Simply top 
> notch.
> The ADN8843 has the H-Bridge built-in and it worked for someone I know.
>
> I'm not too excited by the cascaded TECs. They can only provide a
> temperature difference, and absolute temperature only with a regulation
> loop with more time constants between the TEC and the NTC. The low 
> thermal
> impedance path through the TEC is a real drawback, and probably the
> culprit for the low efficiency. No wonder that no one uses them in OCXOs.
> But 87°C like in my Morion OCXOs is no solution, either, even if we could
> dim down the absolute temperature.
>
>
>> From: Bob Camp via time-nuts <time-nuts at lists.febo.com>
>> Sent: Thursday, March 30, 2023 6:01:55 PM
>
>> 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 ….
>
> No crystal today, just VCSELs...
>
>> 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.
>
>
>>> Cheers, Gerhard
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