20.4 Working with triggers 241
Figure 7: Trigger Signal counter is higher than ExposureStart counter
20.4.6 Triggering of an indefinite sequence with precise starting time
20.4.6.1 Scenario
Especially in the medical area, there are applications where a triggered acquisition is started, for example, with a
foot switch. Following challenges have to be solved in combination with these applications:
• The user wants the acquired image immediately (precise starting time).
• It is not known, when the user stops the acquisition (indefinite sequence).
Using AcquisitionStart as the trigger source, it could take between 10 and 40 ms until the camera acquires the first
frame. That's not really an immediately acquisition start. It is recommended to use FrameStart as the trigger source
instead. However, according to the time the trigger event occurs, there will be a timeout during the first frame in
nearly all cases.
You can avoid this using a timer which generates a "high" every 100 us and which is connected to the trigger input
Line4 using a logical AND gate. I.e. if the timer is "high" and there is a trigger signal at Line4 then the logical
conjunction is true. The AND gate result is then connected as TriggerSource of the FrameStart trigger using a
logical OR gate. I.e. as soon as the logical AND conjunction is true, the trigger sourde is true and the image
acquisition will start.
The following figure illustrates the settings:
MATRIX VISION GmbH
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