Ccd Temperature; Dark Charge - Teledyne ProEM Series System Manual

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5.3.4

CCD Temperature

As stated before, lowering the temperature of the CCD will generally enhance the
quality of the acquired signal by lowering dark noise. In EMCCD cameras, lower
temperatures will also result in higher EM gain.
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Initially, the default temperature appropriate for your specific model is displayed.
Once the Target Temperature {Temperature Setpoint} has been set, the software
controls the camera's cooling circuits to reach set array temperature. On reaching that
temperature, the control loop locks to that temperature for stable and reproducible
performance. When temperature lock has been reached (temperature within 0.05°C of
set value) the current temperature is Locked. The on-screen indication allows easy
verification of temperature lock.
The time required to achieve lock can vary over a considerable range, depending on
such factors as the camera type, CCD array type, ambient temperature, etc. Once lock
occurs, it is okay to begin focusing. However, you should wait an additional twenty
minutes before taking quantitative data so that the system has time to achieve optimum
thermal stability.
When vibration may affect results, you can turn off the fan operation while making sure
that the coolant is circulating through the camera to maintain the CCD cooling
temperature. If the fan is turned off and there is no coolant circulating through the
camera, the built-in thermo-protection switch may shut the camera down to prevent
thermal damage. In the event that this occurs, wait about ten minutes, correct the
situation that caused the shutdown, and re-power the camera.
The deepest operating temperature for a system depends on the CCD array size and
packaging. Refer to Table 5 (page 108), for default cooling temperatures.
5.3.5

Dark Charge

Dark charge (or dark current) is the thermally induced buildup of charge in the CCD
over time. The statistical noise associated with this charge is known as dark noise. Dark
charge values vary widely from one CCD array to another and are temperature
dependent.
With the light into the camera completely blocked, the CCD pixels accumulate
thermally generated electrons, dependent on the exposure time and camera
temperature. The longer the exposure time and the warmer the camera, the less
uniform this background will appear. Thus, to minimize dark-charge effects, you should
operate at the default CCD temperature.
ProEM System Manual
When WinX/32 is the controlling software, temperature control is done via
►
Setup Detector Temperature.
When LightField is being used, temperature control is done on the Sensor
expander.
NOTE:
If the CCD is cooled to low temperatures (below -50°C),
exposure to ambient light will over-saturate it. This may
increase dark charge significantly. If the camera remains
saturated after all light sources are removed, you may have
to bring the camera back to room temperature to restore
dark charge to its original level.
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