Encoder for Position Detection

Rotary Encoder is a sensor or device for detecting the direction of rotation, the angle position, and rotational position. 

E6CP-A Absolute
Encoder by Omron

E6B2-C Incremental
Encoder by Omron

There are two types of rotary encoder :

1. Absolute encoder, this encoder uses the code at the time of output the absolute rotation angle, and to read the position of rotation is done by reading that code.
2. Incremental encoder, this encoder output the pulse during the rotation. The number of pulsa used to calculate the rotation number.

Absolute encoder is usually paired with a device called cam positioner. This circuit was used as the signal position of 360 or 720 degree rotation . It is helpfull if a machine requires a complex application or needed more position timing. Try to imagine if the positioning or timing marker used by the sensor/mechanical cam. Surely it would be complicated and difficult.

3F88L-160/162 Cam
Positioner by Omron

For incremental encoder is usually used as detector of rotation, if a rotating device as far as the intended target or not. And through the PLC program can do calculations or conversions about how the number of pule output by the encoder.