Wet Bulb Thermometer

[Tom Droege <tdroege2@earthlink.net>]

I have added a wet bulb thermometer to the Mark IV TOM1 and TOM2.

As you all may recall, the way I generate chilled water for cooling TOM1 is 
by a home de-humidifier with it's coils bent into a water bucket.  A pump 
in the bucket circulates chilled water.  One can now use one of the 
auxilliary channels to turn the AC power on and off to the 
de-humidifier.  This works fine, except you have to know where to set the 
temperature or water will condense on the cool surfaces.

I have added another thermometer to channel 4.  This is marked Temp 2 on 
the ADC readout.  The control loop is simple.  I check the temperatures 
periodically and turn the chiller on if the water temperature is above the 
wet bulb temperature.  I turn the chiller off if the water temperature is 
below the wet bulb temperature.

The wet bulb thermometer consists of a standard AD590 temperature probe 
with a wick wrapped around it which dips in a bottle of water.

One cannot do any better than this unless the water tubing and the camera 
heads are well insulated.  Possible, but a pain to do.  I hope this will be 
good enough so that I can run cold enough during the summer so that CCD 
thermal noise is not a factor.

Tom Droege