🚀 go-pugleaf

danube@max.physics.sunysb.edu writes:

>   I need to control the temperature of a small infrared window to 
>0.1 degrees C or better.  The actual value need not be so precise, but
>changes in temperature must be kept to a minumum.  At present, the
>window is heated by a ring of brass wrapped with heater wire. Adjusting
>the current changes the temperature, which is typically 100-200 C.
>The temperature is measured with a thermocouple (5 mil Chromel-Alumel wire,
>"type K").  Heater current is about 200 mA.

You can buy from Omega Engineering for about $180 an 1/16th DIN sized
intelligent self-tuning PID controller capable of either analog 
proportional output or duty-cycle on-off control.  It comes complete
with a nice digital display and the ability to enter the setpoint
from a keypad.  Settability in the unit I use (0-2000 deg F) is to
0.1 degree and in my experience with our kilns, is capable of maintaining
control to +- one count.  Numerous options are available including 
voltage input so you could amplify the thermocouple voltage 10X if the
resolution is not enough.  The unit I use is Omega part #CN9111A.
The minor digits specify options so you'd need to look in the 
catalog.  Much more sophisticated controllers are available from them
for less than $500.

Unless part of your experimental goals is to learn how to design
a control circuit, I'd recommend buying one of these so you can 
concentrate on your experiment.

John
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