Controlled Exposure

In the controlled exposure situation, the CCD sensor is brought into the pixel reset condition before entering the exposure condition. In other words, the electronic shutter is used.

The line-scan camera hosting the sensor experiences a periodical cycle paced by successive instants we will refer to as "trigger pulses". The trigger pulses occur at the line frequency. Each trigger pulse causes the following sequence:

Exposure condition of some known duration,
Transfer gate event,
Readout process,
Return to pixel reset condition.

The trigger pulses are issued by the frame grabber according to rules that will become clear later.

Operational sequence

It can be seen that the exposure duration is not equal to the line period. It can be made independent of the line frequency.

Suppose that we are willing to adjust the aspect ratio by varying the line frequency in order to keep it adequately coupled to the web speed. With the controlled exposure sensor, we can do it without any response variation.

This is the fundamental reason why the industrial vision integrator should specify the electronic shutter feature when selecting a line-scan camera.