Chapter 11 Tips and Tricks 141
After temperature lock has been established, wait 30 minutes for the detector temperature
to completely stabilize. Then try taking a few dark charge readings with the detector
operated with the MCP On/Off switch set to OFF.
Note: Do not be concerned about either the baseline level of this background or its
shape, unless it is very high, i.e., > 1000 counts. What you see is not noise. It is a fully
subtractable readout pattern. Each CCD has its own dark charge pattern, unique to that
particular device. Every device has been thoroughly tested to ensure its compliance with
Princeton Instruments' demanding specifications.
Temperature Lock
If the PI-MAX Detector loses temperature lock, the internal temperature of the camera
has gotten too high, such as might occur if the operating environment is particularly
warm or if you are attempting to operate at a too cold temperature. If this happens, an
internal thermo-protection switch will disable the cooler circuits to protect them.
Although the thermo-protection switch will protect the camera, users are advised to
power down and correct the operating conditions that caused the thermal-overload to
occur. Note that the cooling performance of the detector can be enhanced by circulating
water coolant. See "Temperature Control", page 57.
Turn the controller off for fifteen or twenty minutes. Then turn it back on and set a
warmer temperature from the software Detector Temperature dialog box. Temperature
lock should be re-established within a few minutes.
Intensifier Alarm
To reduce the risk of detector damage, PI-MAX detectors are equipped with an audible
alarm in the detector head, activated when the intensity of light falling on the image
intensifier exceeds a preset threshold. While the alarm is sounding, the photocathode is
temporarily disabled. Toggle the MCP On/Off switch on the back of the PI-MAX to the
OFF position. Cover the detector window and only switch the MCP On/Off switch to
ON after the illumination level has been lowered. If the alarm sounds continuously even
when the illumination level is adequately low, shut the system down and contact the
factory for guidance.
Some controllers may also provide an audible alarm, indicating the same over-threshold
condition as the detector alarm. Note that it is normal for the alarm to sound momentarily
when the system is turned on.
Contact the factory at once if sporadic or continuous unwarranted alarms occur. They
may indicate intensifier damage or another situation that requires immediate attention.
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