National Instruments NI Vision NI 17xx 用户手册

© National Instruments Corporation

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 5-1.

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 smart 
camera on a conveyor belt, a trigger delay will be necessary so that the 
smart camera waits to expose the image until the part to be inspected passes 
in front of the smart camera. In this case, specifying the trigger delay in 
terms of quadrature encoder counts allows the smart camera to expose the 
image when the part is positioned in front of the smart camera regardless of 
changes in speed of the conveyor belt. 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 5-1. Table 5-2 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 property in LabVIEW, or by setting 
the Exposure Time control in MAX. The lighting strobe deasserts at the 

Table 5-1.  Trigger Synchronization Variability

NI 1722
NI 1742
NI 1762

31.2 

μs

NI 1744
NI 1764

71.6 

μs

Table 5-2.  Lighting Turn-On Time

NI 1722
NI 1742
NI 1762

156 

μs

NI 1744
NI 1764

143.2 

μs