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MultiCam Boards Documentation > MultiCam Documentation > MultiCam User Guide > The Channel Class > Understanding the Rate Converter > How to Use an Encoder? > Encoder and Line Triggering

Encoder and Line Triggering

The goal of the industrial vision integrator is to achieve a predictable aspect ratio within the acquired digital image. Usually, but not necessarily, a visual aspect ratio of 1 is desired.

This aspect ratio should be maintained even if the web speed is varying.

The unitary aspect ratio means that the line pitch is equal to the cross web pitch.

We will recall that the line pitch is a function of the web speed and the camera line frequency according to:

Combining this formula with the encoder frequency expression, we easily obtain:

If we can manage to select an encoder having a characteristic pitch equal to the desired line pitch, this simply mean that we just have to impose to the camera a line frequency equal to the encoder frequency.

This is quite simply done by selecting the external line triggering mode and applying the encoder pulses as the line trigger pulses.

For the representative example, we want the line pitch to be 0.39 mm. Consequently, we just have to select an encoder providing a characteristic pitch having the same size.

This impose some mechanical adjustment of the encoder, such as gear wheels swapping.

This burden imposed to the industrial vision integrator can be costly to achieve.