Teledyne Princeton Instruments PI-MAX 3, System Manual

Page: 238 / 250

238 PI-MAX
®
3 System Manual Issue 2
Dark Charge or
Dark Current:
The thermally induced buildup of charge in the CCD over time.
Dark charge values vary widely from one CCD array to another
and are exponentially temperature dependent. In the case of
cameras that have MPP type arrays, the average dark charge is
extremely small. However, the dark-charge distribution is such
that a significant number of pixels may exhibit a much higher
dark charge, limiting the maximum practical exposure. To
minimize the collection of dark charge, operate the camera at the
lowest CCD temperature possible.
Since each CCD has its own dark charge pattern, unique to that
particular device, acquiring and saving a dark charge
"background image" under conditions identical to those used to
acquire the "actual" image and then subtracting that image from
the actual image will significantly reduce dark-charge effects.
EBI:
Equivalent Background Illumination. EBI comes from
thermally-generated electrons that cannot be distinguished from
those generated by light photons. EBI can be reduced by cooling
the intensifier (or environment) and is usually negligible in gated
applications.
Exposure Time:
The period during which the camera allows incoming signal to
integrate on the CCD array. For signal to be detected and
integrated on the CCD array, it must both fall in a valid gate width
and in a valid exposure time. In Gate Mode, the exposure time is
determined by an internal pulse ensemble defined by the internal
timing generator gating setup.
External Sync:
Readout synchronization mode where the CCD array is
synchronized to an external source (i.e., the array is scanned
upon arrival of an external trigger pulse.)
External Trigger
Mode:
Trigger mode where gate pulses are delayed from external input
trigger pulses. Also a detector readout synchronization mode
where the detector is scanned continuously but data storage
does not begin until the arrival of an external trigger pulse.
Frame:
The area of the CCD array that is readout after an exposure time
ends.
For a 1024 x 1024 array, a full frame would consist of the entire
1024 x 1024 pixel area. In the WinX/32 software, the number of
frames to be acquired during a data acquisition is determined by
the Number of Images (or Number of Spectra) parameter on the
Experiment Setup
►
Main tab. If the parameter value is greater
than 1, multiple frames of data will be acquired and stored in a
single data file.