Encoders, whether they are rotary encoders or linear encoders, absolute encoders or incremental encoders, usually use one of two measurement principles, optical or magnetic. In the past, optical encoders were the main choice for high-resolution applications, and improvements in magnetic encoder technology now allow them to achieve resolutions as low as 1 micron, thus competing with optical technology in many applications. Magnetic technology is also more durable than optical technology in many ways, which makes magnetic encoders a popular choice in industrial environments.

Magnetic rotary encoder

Magnetic rotary encoder relies on three main components: disk, sensor and adjustment circuit. The magnetic disk has been magnetized and has many magnetic poles on its circumference. The sensor detects the change in the magnetic field when the disk rotates and converts this information into a sine wave. The sensor can be a Hall effect device that induces changes in voltage, or a magnetoresistive device that induces changes in magnetic field. The conditioning circuit multiplies, divides, or interpolates the signal to produce the desired output.

The resolution of a magnetic rotary encoder depends on the number of magnetic poles around the disk and the number of sensors. Incremental encoders (whether magnetic encoders or optical encoders) use quadrature output, and can use X1, X2 or X4 encoding to further improve resolution. The main difference between an incremental encoder and an absolute encoder is that regardless of the sensor technology used, the absolute version assigns a unique binary code or word to each measurement position. This allows them to track the exact position of the encoder even if the power is off.