Temperature Control of Science CCD Cameras
Temperature Cable Pin Designations
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The Marconi Deep Depletion CCD has an
embedded thermistor
connected between pins D1 and F1
Temperature control circuit
within cryostats and cabling within SDSU (PDF)
The internal cryostat temperature sensors are PT100 with a resistance of 100 Ohms at 0 C and a coefficient of 0.41 Ohms per degree C.
The accuracy of the temp circuit is limited to 10K by the Util card circuitry, specifically the poor offset voltage on the LM324 used to interface the sensor. If an application requires more precise control, this chip should be replaced with the pin-compatible OP400.
For dark current =1e/hour, the temperature of the EEV chips should be 153K (Pt100=50.8Ohms) , for the TEK and SITe chips it should be 168K (Pt100=57Ohms). Dark current approximately doubles with every 5 degree rise in temperature.
The following locations in the Utility Board memory space are useful for diagnostic purposes ;
X:&0F9 - Demand Temperature in mK
Y:&0F9 - Actual Temperature in mK
This PT100Hex table lists camera temperatures in HEX as seen by the SDSU to make the above a little easier.
Y:&003 - heater resistor DAC output (&FFF =12V)
The demand temperature is downloaded from the CCD configuration files by uDAS during system star-tup. Operational temperature can be changed by editing this file:
/wht/etc/*.dat for WHT detectors
/int/etc/*.dat for INT detectors
Although the method below is still possible, Dewars Charts is now the preferred method.
If problems are encountered with temperature servoing, it is possible to access temperature information in the uDAS log file on Taurus as follows :
grep 'cryostat temperature' /var/log/talker/talker.debug
Alternatively if you want to be more camera specific (for example if there have been problems with EEV12) :
grep 'cryostat temperature' /var/log/talker/talker.debug | grep 'EEV12'