| Functionality |
26
Figure 23: I/O Trigger setup
The exposure time in external trigger mode can be defined by the setting of the exposure time register (camera
controlled exposure mode) or by the width of the incoming trigger pulse (trigger controlled exposure mode).
An external trigger pulse starts the exposure of one image. In Burst Trigger Mode however, a trigger pulse starts the
exposure of a user defined number of images. The start of the exposure is shortly after the active edge of the incoming
trigger. An additional trigger delay can be applied that delays the start of the exposure by a user defined time. This
often used to start the exposure after the trigger to a flash lighting source.
Trigger source
The trigger signal can be configured to be active high or active low. One of the following trigger sources can be used:
•
Free running:
The trigger is generated internally by the camera. Exposure starts immediately after the camera
is ready and the maximal possible frame rate is attained, if Constant Frame Rate mode is disabled. In Constant
Frame Rate mode, exposure starts after a user-specified time (Frame Time) has elapsed from the previous
exposure start and therefore the frame rate is set to a user defined value.
•
Interface Trigger:
In the interface trigger mode, the trigger signal is applied to the camera by the CameraLink
®
interface. The trigger is generated by the frame grabber board and sent on the CC1 signal through the
CameraLink
®
interface. Some frame grabbers allow the connection external trigger devices through an I/O card.
•
I/O Trigger:
In the I/O trigger mode, the trigger signal is applied directly to the camera by the power supply
connector (via an optocoupler).
Exposure time control
Depending on the trigger mode, the exposure time can be determined either by the camera or by the trigger signal
itself.
In
camera-controlled exposure time
the exposure time is defined by the camera. For an active high trigger signal,
the camera starts the exposure with a positive trigger edge and stops it when the preprogrammed exposure time has
elapsed. The exposure time is defined by the software.
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