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Unread 07-10-2004, 05:31 AM   #23
Groth
Cooling Savant
 
Join Date: Mar 2003
Location: MO
Posts: 781
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Quote:
Originally Posted by unregistered
I have an environmental chamber which has an RTD thermostat which will maintain the temp at 22°C
- with a toggle switch I can select 'manual control', and then by means of a pot set the temp manually
- I substituted a 10 turn pot and relocated it, works fine

the problem:
I would like to be able to manually change the set point to something other than 22°, and then have the thermostat maintain that temp
I don't quite understand the problem. When you use your pot, you ARE changing the set point. Does the thermostat not hold the chamber at that temp? Or is it a matter reproducibly setting various chamber temperatures?

More info on the chamber would be good. What kind of cooling does it have? Pelt? Phase-change? If phase, is the compresser variable speed or does it cycle on/off? What are the connections to the terminals on your schematic?

Anyway, if you really want to control it from LabView, I'd bypass their entire temperature comparator section and feed a logic signal from your virtual PID into optoisolator U4. Maybe even scrap their board entirely.
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