| Functionality |
27
In
trigger-controlled exposure time
the exposure time is defined by the pulse width of the trigger pulse. For an
active high trigger signal, the camera starts the exposure with the positive edge of the trigger signal and stops it with
the negative edge.
External Trigger with Camera controlled Exposure Time
In the external trigger mode with camera controlled exposure time the rising edge of the trigger pulse starts the
camera states machine, which controls the sensor and optional external strobe output. The following figure shows the
detailed timing diagram for the external trigger mode with camera controlled exposure time.
Figure 24: Timing diagram for the camera controlled exposure time
The rising edge of the trigger signal is detected in the camera control electronic which is implemented in an FPGA.
Before the trigger signal reaches the FPGA it is isolated from the camera environment to allow robust integration of
the camera into the vision system. In the signal isolator the trigger signal is delayed by time t
d−iso−input
. This signal
is clocked into the FPGA which leads to a jitter of t
jitter
. The pulse can be delayed by the time t
trigger−delay
which can
be configured by a user defined value via camera software. The trigger offset delay t
trigger−offset
results then from the
synchronous design of the FPGA state machines. The exposure time t
exposure
is controlled with an internal exposure
time controller.
The trigger pulse from the internal camera control starts also the strobe control state machines. The strobe can be
delayed by t
strobe−delay
with an internal counter which can be controlled by the customer via software settings. The
strobe offset delay t
strobe−delay
results then from the synchronous design of the FPGA state machines. A second
counter determines the strobe duration t
strobe−duration
(strobe-duration). For a robust system design the strobe output is
also isolated from the camera electronic which leads to an additional delay of t
d−iso−output
. The following tables give
an overview over the minimum and maximum values of the parameters.
External Trigger with Pulse width controlled Exposure Time
In the external trigger mode with Pulsewidth controlled exposure time the rising edge of the trigger pulse starts the
camera states machine, which controls the sensor. The falling edge of the trigger pulse stops the image acquisition.
Additionally the optional external strobe output is controlled by the rising edge of the trigger pulse. The timing
diagram below shows the detailed timing for the external trigger mode with pulse width controlled exposure time.
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