Encoder

Absolute: Digital Input (with as many inputs as the number of bits in the encoder output). You may find a dedicated encoder card, or you may need to convert the encoder output code (probably Gray code) to binary.

Incremental: Quadrature up/down counter for A and B (you can implement this with 2 digital inputs and some ladder logic for low speeds). You may or may not want to include the Z input - many quadrature counters in PLCs have provision for Z.

How Digital Input card gives us the rotation angle when we uses absolute encoder?

Example:

Assume the encoder has 4 bits of resolution - the digital inputs (possibly after converting the code) will give a number between 0 and 15.

0 then represents 0°, and each other number represents (the number x (360/16))°.

So if the number was 8, for example, the shaft angle would be (8 * (360 / 16))° = 180°. OK?

Here's a table which may explain it better:

It may depend on the brand or manufacturer of the PLC you want to use.

Beckhoff Automation uses an EL5151 card as a dedicated encoder interface. Allen Bradley uses a couple of types depending on the model of controller you want to use.

High speed counters will frequently be used with a separate input for reseting to zero.

Happy Hunting!