National Instruments NI 1712 User Manual - page 53
6-4
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Chapter 6
Image Acquisition
The incoming trigger is synchronized to the line rate of the smart camera. This adds an additional
delay that can vary on a frame by frame basis. The maximum variability is shown in Table 6-1.
The amount of time required from the assertion of a trigger to the start of the light strobe and
image exposure varies by application. For example, if a sensor that detects the presence of a part
is positioned before the NI 17xx Smart Camera on a conveyor belt, a trigger delay is required to
ensure that the image is not exposed until the part to be inspected passes in front of the NI 17xx
Smart Camera. In this case, specifying the trigger delay in terms of edge counts allows the NI
17xx Smart Camera to expose the image when the part is in position regardless of changes in
conveyor belt speed. For other applications, a delay specified in milliseconds is sufficient.
If you are strobing a light, there is a short delay while the lighting controller turns on the light.
This delay is represented by the lighting turn-on time in Figure . Table 6-2 lists the lighting
turn-on times.
After the lighting turn-on time, the exposure begins. The width of the exposure pulse determines
how long the sensor is exposed. The exposure time can be adjusted by setting the
Exposure
Time
control in Vision Builder AI, setting the
Exposure Time
attribute in LabVIEW, or by
setting the
Exposure Time
control in MAX. The lighting strobe deasserts at the end of the
exposure pulse. The end of an exposure starts the image readout from the sensor.
The maximum trigger rate is determined by the maximum frame rate for your configuration.
Refer to the
Maximum Frame Rate
section for information about the factors that affect the
maximum frame rate.
Table 6-1.
Trigger Synchronization Variability
S
mart Camera Model
Trigger
S
ynchronization Variability
NI 1712
NI 1732
NI 1752
31.2
μ
s
NI 1754
71.6
μ
s
Table 6-2.
Lighting Turn-On Time
S
mart Camera Model
Lighting Turn-On Time
NI 1712
NI 1732
NI 1752
156
μ
s
NI 1754
143.2
μ
s