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Yet Another Cooling Test at RIT
Results of one last set of tests, Wednesday morning, Jan 9, 2002.
I show my results side-by-side with those of Tom and Mike G.
I first set the DACs to -2, and then to -9. Note the increase
in the water temperature during the three hours of the test!
Value TOM Mike RIT (DAC -2) RIT (DAC -9)
TEC Power 11.954 11.35 11.96 11.93
+15 14.798 14.66 14.61 14.60
+5 4.88 4.86 4.87 4.87
Ground -0.02 0.00 -0.00 -0.00
-5 -5.048 -5.10 -5.15 -5.15
-15 -15.338 -15.01 -15.08 -15.08
VCO Ref. 5.020 5.03 5.03 5.03
ADC Ref 2.514 2.49 2.52 2.52
DAC 14 set -2 -2 -2 -9
DAC 15 set -2 -2 -2 -9
DAC 14 read -1.992 -1.98 -1.99 -8.94
DAC 15 read -2.036 -2.03 -1.98 -8.92
Temp CCD0 -19.58 -23.64 -7.07 -9.58
Curr CCD0 0.875 0.78 1.35 1.34
Temp CCD1 -19.37 -23.06 -14.42 -12.21
Curr CCD1 0.813 0.91 0.58 0.74
Water Temp 7.27 4.80 6.94 9.88
Tom wrote of the TEC units:
> One way I have found for sure to break them is
> to drop a camera. Just a couple of inches on to a hard surface will do
> it. I have not seen any damage from vibration, as in moving a long
> distance by automobile. Still, I always pack the camera heads in foam when
> I move them.
When I moved the unit from our lab to the RIT Observatory, I had to
pick it up, place it on a table, roll the table outside, place the unit
onto the back of a pickup truck, drive a mile, lift it off the truck
and set it down on a table, push the table over asphalt path to the
shed, lift off the table and place on the shed floor. I do not recall
any sharp drops or bumps during the journey, but it's possible that
there were enough jiggles to damage the coolers.
My guess is that I did just enough damage to loosen the thermal contact
enough so that the cameras don't get _really_ cold enough. Sigh.
I ran some tests of dark frames back when the cameras could reach
-20 C, and found that the histogram of pixel values was MUCH nicer
at -20 than at -12, and the noise was MUCH lower (stdev of 15 DN
versus 45 DN). I can and will continue to use the Mark IV in its
current state, but if there's some way I can try to repair the
damage eventually, I'd like very much to do so.
The way the Mark IV fits into its shed, there's really no chance
to do any work on the cameras (or the electronics). I will have to
move the unit into the Observatory House to work on it. Hmmmm.
Given the weather here in Rochester, this might be a good time to
take it indoors for a while. My student, Mark Teseny, has built
some flatfield light boxes, and we can test them indoors just as well
as we could outside.
> I can rebuild the cameras if that is
> needed. I will just build more and trade you.
I might take you up on this offer, Tom, but let me do what I can
to diagnose the problem (and perform other tests).
Michael