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New iStar ICCD
5.3.5.1 - shutter transfer time
Shutters take a finite time to open or close and this is sometimes called the
S
hutter
T
ransfer
T
ime
(STT
). This is typically
in the order of a few tens of milliseconds, and will vary from one shutter type to the other. The STT should give enough
time for the shutter to open before acquisition starts, and enough time to close after acquisition finishes and before
readout commences.
Note: Mechanical shutters are limited to repetition rates of a few Hz for correct ‘opening’ and ‘closing’
operation. This frequency will vary from one shutter type to the other. If acquisition rate of the CCD
exceeds the maximum recommended shutter rate, then this will cause partial operation of the shutter
blades and potential damage to the device. At that stage, shutter should either be left fully opened (and
image intensifier photocathode becomes the sole signal shuttering interface in the system), or CCD
acquisition rate should be decreased.
By default, the value entered in the exposure time text box on the
Setup Acquisition
dialog box determines the length
of time the shutter will be in the open state. However, to accommodate the transfer time, the rising edge of the shutter
output is sent before the Fire output signal by an amount equal to the preset STT. The system automatically adds the
transfer time to the end of the acquisition sequence, introducing an appropriate delay between the start of the shutter
closed state and the commencement of the data being read out as shown in the following example diagram:
Important note: If no shutter is connected, the time to open or close should be set to 0. Setting the Time
to open or close to any other value will insert extra delays into cycle time calculations.
Pre Acquisition Setup - Shutter
