Magnetic Encoders VS Optical Encoders

Enrique del Sol - Robotics, Mechatronics & Control Research

Encoders, whether rotary or linear, absolute or incremental, typically use one of two measuring principles—optical or magnetic. While optical encoders were, in the past, the primary choice for high resolution applications, improvements in magnetic encoder technology now allow them to achieve resolutions down to one micron, competing with optical technology in many applications. Magnetic technology is also, in many ways, more robust than optical technology, making magnetic encoders a popular choice in industrial environments.

ParameterOptical Sensor CharacteristicsMagnetic Hall Sensor Characteristics
Principle coded disc/scale, through beam arrangement magnet/tape/polewheel opposed to sensor
Incremental accuracy of target 100 nm – 1 μm

(lithography process)

 5 μm – 30 μm

(magnetisation process)

Energisingby external LED (20 mW) by target (Br>220 mT)
Signal Frequency > 1 MHz possible < 50 kHz
Benefits high code density, high code accuracy robust
Disadvantages sensitive to contamination, high alignment requirements raw code density, medium code…

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