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From: Jan Panteltje <alien@comet.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Instead scopes
Date: Sun, 01 Sep 2024 07:36:34 GMT
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On a sunny day (Sat, 31 Aug 2024 11:57:03 -0700) it happened john larkin
<jl@650pot.com> wrote in <t5p6djh6vdfl5kmosb54bdpnn7e9np0smg@4ax.com>:

>>> Here's my millikelven temperature controller.
>>> 
>>> https://www.dropbox.com/scl/fi/emxfaurnyj35t0y84tvwl/Oven_Cables_pub.jpg?rlkey=jpcnmnt1pcooz9nj7d0j4rah0&raw=1
>>> 
>>> That's a dual-stage Mach-Zender e/o modulator whose extinction is
>>> much better if the temperature is stable to milllikelvins. The big
>>> hogged-aluminum box is heated by six mosfets on the bottom, and there
>>> are four thermistors for feedback. It runs at 30C.
>>
>>Why four thermistors? The only temperature that matters is that of the 
>>modulator itself. People who need to minimise temperature gradients do 
>>need more than one temperature sensor, but it isn't clear why you would 
>>have. I used a second thermistor to monitor the temperature of the 
>>exhaust side of my Peltier cooler (which does matter) but you seem to 
>>have used mosfets as resistive heaters which is rather easier.
>
>One thermistor is on the heater board, on the bottom of the big block.
>Three are on the platform that mounts the e/o modulator. We really
>don't need three up there, but we wanted to error check and snoop for
>gradients and optionally do some averaging if we had noise.
>
>The EOM platform is spaced off the bottom of the big block, which
>makes us a 2nd order thermal system. The main block has a 75 minute
>time constant, and the platform inside is 17 minutes. Our control
>algorithm uses the difference as, essentially, a derivative term.
>
>Coolers have lots of problems, including condensation. Heating to 30C
>worked fine. This is in maybe the world's  biggest single clean room
>and the local air is always 20C.


Decent temperature stability over several years:
 https://panteltje.nl/panteltje/tri_pic/
 https://panteltje.nl/panteltje/tri_pic/tritium_decay_experiment_black_box_open_on_main_PCB_with_beeper_IMG_3874.GIF
 https://panteltje.nl/panteltje/tri_pic/tritium_decay_experiment_closed_black_box_IMG_3868.GIF


Much better time constant, much cheaper, took an hour to code, maybe 2 to build 
Uses less power, can run on batteries if main fails, 
:-)