Encoder : Part3 Rotary Encoders

Rotary Encoder is an electromechanical device which converts angular motion to analog value or digital code. It is also called Shaft Encoder. Rotary encoders provide value as the shaft or axle of the encoder rotates. An output signal is produced that is proportional to the angle of the rotation. Based on the output signal, there are two types of encoders: incremental and absolute.

The output of an Incremental Encoder is in the form of a square wave and provides information about the motion of the shaft. This information is processed into speed, position, distance and RPM.

The output of absolute encoders is in the form of absolute measure of position, i.e. they indicate the current position of the shaft. This makes them Angle Transducers. Both incremental and absolute encoders are available in two construction designs: optical and mechanical.

In applications where mechanical motion must be processed into digital information, the most popular choice of sensors is incremental encoders.

Incremental encoders provide output of pulse string that is proportional to the rotational displacement of the shaft i.e. it provides output only when the shaft of the encoder is rotated. To determine the amount of rotation, a counter is used that counts the number of output pulses. From a certain input shaft position, for the encoder to detect the amount of rotation, the count in the counter is reset at a reference position and from that position the number of pulses is added by the counter. The reference position can be anywhere and the count can be unlimited.

Incremental encoders are available in two channel types: single channel encoder and quadrature encoder. When the systems rotate in one direction, then single channel encoders are used. These are generally called Tachometers and provide only position and velocity information. Quadrature encoders have two output signals that are phased 900 apart. Hence quadrature encoders provide hi speed bi-directional information for complex motion applications.

Incremental optical encoders are used in applications where high RPM’s with high precision are calculated. Mechanical incremental encoders are generally used as digital potentiometers and require de-bouncing.

Absolute encoders produce a unique binary code output for each distinct angle of the shaft. The code can be gray code, excess gray code or natural binary code. The shaft position is always known in case of absolute encoders even after power failures.

credit :- https://www.electronicshub.org/position-sensors/