82 PI-MAX/PI-MAX2 System Manual Version 5.F
Precautionary Measures
Intensified CCD detectors, such as the PI-MAX, when biased ON, can be irreparably
damaged if continuously exposed to light levels higher than twice the A/D saturation
level. Thus it is critical that you not establish conditions that could result in damage to
the intensifier. Although intensified detectors are less prone to damage from background
light when operated gated, they are at significant risk of damage from high-intensity light
sources such as lasers. High intensity sources can damage the intensifier before the
protection circuits have time to respond, or even cause spot damage without the
protection circuits acting at all. In Shutter Mode operation, it will be necessary to keep
the lab lighting be subdued when working with an intensified detector. If a sustained
alarm indication occurs when the controller is turned on, immediately switch 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 to safe operating conditions.
Intensifier Modes and Safety
The Experiment Setup Main screen allows selection of three modes, Shutter Mode,
Gate Mode and Safe Mode. In Shutter Mode operation, the photocathode is biased
on continuously during the exposure time and the room illumination must be subdued to
prevent an overload alarm from occurring. In Gate Mode, the photocathode is biased on
only during the time each gate pulse
*
is applied. As a result, the tolerance to room light is
higher in gated operation, but the risk of damaging overload from intense light sources
such as lasers remains. Intense light sources in gated experiments can cause spot damage
that would be undetected by the alarm circuit. In Safe Mode, the photocathode is
continuously biased OFF and the intensifier is as safe as it can be.
Alarm
To reduce the risk of detector damage, the PI-MAX detector is 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
disabled. Immediately 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.
Note: It is normal for the alarm to sound briefly when the system is turned on.
Discontinue operation and contact the factory at once if sporadic or continuous
unwarranted alarms occur. They may indicate intensifier damage or another situation that
requires immediate attention.
*
The Gate pulse is produced inside the PI-MAX from the Start and Stop signals supplied by the
Timing Generator.
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