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Overtrigger Error When Triggering the Sequencer Externally#

You are using the sequencer of a Basler camera to switch between two different exposure times. An external hardware signal is used to toggle between the sequencer sets. You observe that you can't achieve the expected frame rate.

Without external signal, the camera works exactly as you would expect. The reason for this is that the camera is overtriggered.

Let's consider the following diagram where we are toggling between two sequencer sets. Set 1 has a longer exposure than Set 2:

Overtrigger Error in Overlap Mode

Here, the sensor operates in overlap mode. So the exposure of the next image may start during the readout of the previous one. This is fine.

However, the issue is that the second exposure ends when the previous readout is not completed. The second readout must be discarded, the frame is lost. The camera returns the overtrigger error.

To correct this, you have three options:

  • Make sure that the exposure time of the sequencer Set 2 is longer (or equal to) the readout time.

Still, if your trigger frequency is too high, you will get the over-trigger when getting back to Set 1. Check this carefully.

  • More generically, make sure that the exposure time of all of your sequencer sets is longer (or equal to) the readout time.
  • Modify the external trigger signal so that the end of the Set 2 exposure occurs once the readout is completed.

You can determine all values required to adjust the trigger signal. The exposure times and the corresponding readout time is given in the pylon Viewer.

Delay between Readout Phases

Therefore it may be possible to optimize the frame rate by optimizing the sequence of trigger points.

A rough calculation can be done with the known values for sensor readout time and exposure time. An exact calculation (to limit the time without readout as much as possible) would include some sensor times that may be available in the sensor's data sheet.

Note that there must be a delay between the readout phases, as shown in the picture above. The sensor can't immediately jump from one readout to the next.

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