A:
In normal (CW) operation, the CCD is automatically triggered
to start a measurement. At the end of the integration time,
the voltage for each pixel is read out of the CCD serially
and converted by the A-to-D into a 12-bit digital value
When the PLD has finished reading all the pixels of the
CCD it signals to the PC that data is ready to be read.
After the PC has finished reading the data, the next available
measurement of the CCD is again stored and the cycle continues.
In Pulsed Mode for Long Pulses ( >5µs ), the CCD is triggered
by the trigger circuit instead of automatically as for CW
mode. As the pulses are long, their intensity can be read
by the CCD after it is triggered, by setting the appropriate
shutter time for the length of pulses.
In Pulsed Mode for Short Pulses ( <5µs ), the same method
as for long pulses cannot be used because once the circuit
is triggered, the pulse has already finished. Therefore,
the CCD is triggered automatically as with the CW mode,
but after each measurement of the CCD, the PLD checks to
see whether the trigger circuit received a pulse while the
CCD was measuring. If so, the data is and the cycle continues
as normal; otherwise a new CCD measurement is made.
In most cases of pulsed light sources, CW operation will
be sufficient (and the intensity can be adjusted by adding
filters or reducing the Shutter Time). In that case, the
Shutter Time should be adjusted to capture a few pulses
of light for each CCD integration, to avoid having 'empty'
measurement cycles where no light is captured by the CCD.
In the case that the pulses are slow, and/or the Shutter
Time would have to be excessively long to guarantee capturing
at least one pulse each time, the Pulse Mode operation can
be used instead.
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