User`s guide

TRIGGERING
SDK SECTION 5
Page 50
Internal
In Internal Trigger Mode once an acquisition has been started via the
StartAcquisition function the Andor
system determines when data is actually acquired. Before the camera starts the data capture process it
ensures that the CCD is in the appropriate state. This ensures that all acquisitions are identical no matter
how long a time has elapsed since data was last acquired (in fact the camera continually reads out the
CCD to help prevent it from being saturated by light falling on it whilst it is not acquiring data). The camera
also generates all the necessary pulses for shuttering and firing external sources. These pulses are
accessed directly on the camera or via the Auxiliary Connector depending on the model. The Fire Output
defines the position in time during which it is safe to allow a pulsed source to fire. The figure below
illustrates the timing sequence for this mode of operation.
Internal Trigger Mode is ideal for situations where you are using ‘continuous wave’ (CW) light sources (an
ordinary room light for instance) and incoming data, for the purposes of your observation, are steady and
unbroken: thus you can begin acquisitions ‘at will’.
You may use Internal Trigger Mode when you are able to send a trigger signal or ‘Fire Pulse’ to a short-
duration, pulsed source (a laser, for example): in this case, initiating the data acquisition process can also
signal the pulsed source to fire.