Delay and Activation

The following figure illustrates the relationship between an external trigger, a lightning strobe, and the exposure time.

1. User-configurable Trigger Delay
2. User-configurable Exposure Delay
3. Beginning of Image Readout

The trigger shown in the figure represents an external trigger, configured to use the rising edge as the active edge. The time between the active edge of the trigger and the assertion of the lighting strobe is a user-configurable trigger delay. The trigger delay can be specified as a duration of time or as a number of edges on an input line.

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 ISC-178x on a conveyor belt, a trigger delay is required to ensure that the image is not exposed until the part to be inspected passes in front of the ISC-178x. In this case, specifying the trigger delay in terms of edge counts allows the ISC-178x to expose the image when the part is in position regardless of changes in conveyor belt speed.

When using an Input line as the trigger source, you must specify the desired activation for your trigger. The activation can be edge-based - rising, falling, or any - or level-based - high or low. When using a level-based activation mode, the ISC-178x only acquires images while the Input line is in the active state. The frame rate in this case is determined by the Acquisition Frame Rate attribute. This is a special case where external and internal timing are blended. When using a level-based activation mode, the trigger delay is ignored.

When using an internally timed acquisition, the activation mode and trigger delay do not apply. When using a software trigger, the activation mode will also be ignored, but the trigger delay is always applied.