Piranha Color Camera User’s Manual 73
DALSA 03-032-10211-01 5/9/2007
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5
5
CCD Handling Instructions
5.1 Electrostatic Discharge and the CCD
Sensor
Cameras contain charge-coupled device (CCD) image sensors, which are metal oxide
semiconductor (MOS) devices and are susceptible to damage from electrostatic
discharge (ESD).
Electrostatic charge introduced to the sensor window surface can induce charge buildup
on the underside of the window that cannot be readily dissipated by the dry nitrogen gas
in the sensor package cavity. When charge buildup occurs, surface-gated photodiodes
(SGPDs) may exhibit higher image lag. Some SGPD sensors, such as the IL-P4 and the
IT-P4 used in the Piranha Color cameras, may also exhibit a highly non-uniform
response when affected by charge buildup, with some pixels displaying a much higher
response when the sensor is exposed to uniform illumination. The charge normally
dissipates within 24 hours and the sensor returns to normal operation.
WARNING: Charge buildup will affect the camera’s flat-field correction calibration. To
avoid an erroneous calibration, ensure that you perform flat-field correction only after a
charge buildup has dissipated over 24 hours.
5.2 Protecting Against Dust, Oil and
Scratches
The CCD window is part of the optical path and should be handled like other optical
components, with extreme care.
Dust can obscure pixels, producing dark patches on the sensor response. Dust is most
visible when the illumination is collimated. The dark patches shift position as the angle
of illumination changes. Dust is normally not visible when the sensor is positioned at
the exit port of an integrating sphere, where the illumination is diffuse.
Dust can normally be removed by blowing the window surface using a compressed air
blower, unless the dust particles are being held by an electrostatic charge, in which case
either an ionized air blower or wet cleaning is necessary.
Oil is usually introduced during handling. Touching the surface of the window
barehanded will leave oily residues. Using rubber fingercots and rubber gloves can
prevent oil contamination. However, the friction between the rubber and the window
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