AW00123409000 Image Acquisition Control
Basler ace USB 3.0 161
6.8 Acquisition Monitoring Tools
6.8.1 Exposure Active Signal
Exposure Active on Global Shutter Cameras (All Models Except the acA1920-25,
acA2500-14, acA3800-14, acA4600-10)
Cameras with a global shutter imaging sensor can provide an "exposure active" (ExpAc) output
signal. On these cameras, the high state of the signal indicates a logical one on the FPGA output
side (Figure 72, see also Figure 41). This signal can be used as a flash trigger and is also useful
when you are operating a system where either the camera or the object being imaged is movable.
For example, assume that the camera is mounted on an arm mechanism and that the mechanism
can move the camera to view different portions of a product assembly. Typically, you do not want
the camera to move during exposure. In this case, you can monitor the ExpAc signal to know when
exposure is taking place and thus know when to avoid moving the camera.
When you use the exposure active signal, be aware that there is a delay in the rise
and the fall of the signal in relation to the start and the end of exposure (see
Figure 72).
Using a GPIO line, set for output, will bring about shorter delays, compared to
using the opto-isolated output line. The exact delays depend on several factors
See Section 5.10.2 on page 88 for details.
Exposure
Frame N
Exposure
Frame N+1
Exposure
Frame N+2
Exposure
ExpAc
Signal
Opto-coupled OUT: 27 µs to 38 µs (Example Only)
Timing charts are not drawn to scale.
The times stated are
only given as examples. They are only valid
for the operating conditions given in Section 5.10.3.
Fig. 72: Exposure Active Signal on Cameras with a Global Shutter
GPIO OUT: <2.5 µs (Example Only)
Opto-coupled OUT: 3 µs to 6 µs (Example Only)
GPIO OUT: <0.5 µs (Example Only)
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