Trigger Overrun Protection Mechanism

This section describes the mechanism that protects the system against missed camera triggers.

Principle

At acquisition channel configuration time:
  • MultiCam checks if the exposure time user setting can be achieved by the camera. If the user setting of the exposure time is out of bound, MultiCam corrects its value. The effective exposure time will be set to the nearest boundary.
  • MultiCam calculates the position on the time-line of the AllowNextTrigger event of P1 and P2 programs. This calculation takes into account the camera operating limits and the user-defined exposure and strobe timing settings for P1 and P2 programs.
At acquisition channel run time, MultiCam reports a “line trigger violation” error if a Line Trigger event is issued before the AllowNextTrigger event during the execution of a program.

Camera Operating Limits

The following camera operating limits are considered:

  • Exposure time range
  • Minimum time interval between two consecutive Exposure
  • Maximum line rate

In MultiCam, the following parameters describe the operating limits of the camera:

  • ExposeMin_us: declares the minimum exposure time, expressed in microseconds (= the minimum duration of a Reset pulse).
  • ExposeMax_us: declares the maximum exposure time, expressed in microseconds (= the maximum duration of a Reset pulse).
  • ResetDur: when the exposure is controlled by the grabber, this parameter declares the minimum time interval between two consecutive Reset pulses.
  • LineRate_Hz: declares the highest line rate supported by the camera (=the reciprocal of the readout time)
  • ExposeOverlap: declares that the camera allows or forbid the next exposure to begin before the completion of the current readout.

Allow Next Trigger Rules

MultiCam applies the following rules when it calculates the position of the AllowNextTrigger event.

RULE 1a – Readout time limitation (Expose Overlapping forbidden)

This rule applies only when ExposeOverlap = FORBID!

The start of exposure of the next cycle may not occur before the end of the camera readout.



Note: If there is any exposure delay (a) in the next cycle, the AllowNextTrigger event may be generated anticipatively
RULE 1b - Readout time limitation (Expose Overlapping allowed)

This rule applies only when ExposeOverlap = ALLOW!

The end of exposure of the next cycle must not occur before the end of the camera readout.



Note: If there is any exposure delay (a) in the next cycle, the AllowNextTrigger event may be generated anticipatively
RULE 2 – Reset interval limitation

The time interval (r) between consecutive Reset pulses may not be shorter than the value specified by ResetDur.



Note: If there is any exposure delay (a) in the next cycle, the AllowNextTrigger event may be generated anticipatively
RULE 3 – Next Cycle

The next cycle after P1 is undetermined, it can be either P2 or P1. The next cycle after P2 is always P1.

For the calculation of the position of the AllowNextTrigger event of P1, MultiCam evaluates both hypothesis (P1 and P2) and keeps the worst case.

For the calculation of the position of the AllowNextTrigger event of P2, MultiCam assumes that the next cycle is P1.

Exposure Delay

By default, MultiCam configures P1 and P2 with the smallest possible value:

  • 0 if StrobeDelay_P<1,2>_us ≥ 0
  • (-StrobeDelay_P<1,2>_us) if StrobeDelay_P<1,2>_us < 0

If required, the exposure delay can be configured using any of the following methods:

Manual Method

This method is invoked when ExposureDelayControl is set to MAN. This is the default method.

With this method, the user may specify the exposure delay for P1 and P2 with:

ExposureDelay_MAN_P1_us and ExposureDelay_MAN_P2_us.

By default, these parameters are set to 0.

MultiCam calculates the smallest possible value for each program separately as follows:

  • ExposureDelay_MAN_P<1,2>_us if

    StrobeDelay_P<1,2>_us ≥ (- ExposureDelay_MAN_P<1,2>_us)

  • (-StrobeDelay_P<1,2>_us) if

    StrobeDelay_P<1,2>_us < (- ExposureDelay_MAN_P<1,2>_us)

Automatic method 1 (Same Start of Exposure)

Select this method by setting ExposureDelayControl to SAME_START_EXPOSURE.

MultiCam calculates, the smallest value ensuring that the start of exposure occurs at the same position on the program time-line.
Automatic method 2 (Same End of Exposure)

Select this method by setting ExposureDelayControl to SAME_END_EXPOSURE.

MultiCam calculates the smallest values ensuring that the end of exposure occurs at the same position on the program timeline.