Whether rotary or linear, incremental or absolute, encoders typically operate on either photoelectric or magnetic principles. Several years ago, photoelectric encoders were the preferred choice for high-resolution encoders, but with the development of magnetic coding technology, magnetic encoders can now achieve micron-level accuracy, challenging the previously dominant market for optical encoders. Furthermore, magnetic coding technology offers greater stability than optical coding in many applications, making it the mainstream encoder in industrial applications.
A magnetic encoder mainly consists of three parts: a magnet, a sensor, and a circuit board. The magnet is a radially magnetized disk, typically fitted with multiple magnetic poles.
The sensor detects the change in the magnetic field caused by the rotation of the magnet and converts it into a sine wave. The sensor can be a Hall effect chip, sensing voltage changes based on the Hall effect principle; or it can be a magnetoresistive sensor, sensing magnetic field changes. The circuit board, composed of various electronic components, processes and outputs the collected signals.
The resolution of a rotary magnetic encoder depends on the number of magnetization levels and the number of sensors. Incremental encoders have quadrature outputs and achieve higher resolution through X1, X2, or X4 encoding. The difference between incremental and absolute encoders lies not in the sensor principle, but in the fact that absolute encoders use certain encoding rules to record each position, allowing the motor to reach a designated position, and even after a power outage and restart, the encoder knows the stopping position.
Linear magnetic encoder
Linear magnetic encoders operate on a similar principle to rotary magnetic encoders, the difference being that linear magnetic encoders use magnetic tracks or magnetic tape and a read head. The read head can also utilize the Hall effect or magnetoresistive principle to determine position by reading magnetic signals. Absolute value linear magnetic encoders determine their specific position by reading specific binary codes on the magnetic tracks.
Incremental type magnetic tracks need to return to their home position after a power outage to continue operating. Linear magnetic tracks can be up to 100m long. The main advantages of magnetic coding are its anti-interference and stability. Unlike optical coding, magnetic coding can be used in environments with dust, liquids, and grease contamination, and it is also vibration-resistant. A certain gap is required between the magnet and the sensor in magnetic coding, similar to optical coding. However, for magnetic coding, this gap does not need to be transparent and pure; as long as there is no magnetically conductive material within the gap, the sensor can correctly detect the magnetic pulse. When installing magnetic coding, attention should be paid to the concentricity of the sensor and magnet, as well as the distance between them.
