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Chapter 15 Tips and Tricks 235
15.6 Baseline Signal
With the camera completely blocked, the CCD will collect a dark charge pattern, dependent
on the exposure time, camera temperature, and intensifier gain setting. The longer the
exposure time and the warmer the camera the larger and less uniform this background will
appear.
After temperature lock has been established, wait about 5 minutes for the camera
temperature to completely stabilize. Then try taking a few dark charge readings with the
camera operated with the I.I.T. 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 (or > 3000 counts at Gain = 2 for some cameras.) 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. In addition, a small offset is built in to
prevent noise or pattern from going below zero. Every device
has been thoroughly tested to ensure its compliance with
Princeton Instruments’ demanding specifications.
15.7 Temperature Lock
If the PI-MAX4Detector 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 camera can be enhanced by circulating water coolant. Refer to
Section 5.5, Temperature Control, on page 66.
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. Temperature lock should be
re-established within a few minutes.
15.8 Intensifier Alarm
CAUTION!
!
Contact the factory at once if sporadic or continuous
unwarranted alarms occur. They may indicate intensifier
damage or another situation that requires immediate attention.
To reduce the risk of camera damage, PI-MAX4 cameras are equipped with an audible
alarm in the camera 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
I.I.T. switch on the back of the PI-MAX4 to the OFF
position. Cover the camera window and only switch the
I.I.T. switch to ON after the
illumination level has been lowered. If the alarm sounds repetitively even when the
illumination level is adequately low, select
Safe Mode in the WinX application or shut the
system down and contact the factory for guidance.