How does a magnetic encoder work?

Magnetic Encoder Working Principle

1. Magnetic Field Generation
A magnetized target (disk for rotation, strip for linear motion) with alternating north-south poles creates a periodic magnetic field. This target attaches to the moving part (e.g., motor shaft or machine slide).

2. Field Detection
Sensor Array: Hall-effect or magnetoresistive sensors (AMR/GMR/TMR) fixed near the target detect field strength changes.
Position Tracking: As the target moves, sensors register magnetic flux variations (peaks at poles, valleys between poles).

3. Signal Conversion
Analog Waveform: Sensors output sinusoidal/cosine voltage signals matching magnetic field transitions.
Digital Processing: Onboard circuitry:
Amplifies weak analog signals
Converts waves to digital square pulses (incremental)
Or decodes absolute position via embedded algorithms

4. Output Generation
Incremental Encoders:
Produce A/B quadrature pulses (90° phase shift) for relative displacement
Index pulse (Z) marks zero position per revolution
Absolute Encoders:
Output unique digital code (e.g., 12-bit binary) for each position
Transmit via protocols like SSI, SPI, or CANopen

5. Direction & Speed Calculation
Direction: Microcontroller compares A/B pulse sequence (A-leads-B = clockwise; B-leads-A = counterclockwise).
Speed: Pulse frequency ÷ poles per revolution = rotational velocity.

6. Error Mitigation
Signal Compensation: Temperature sensors correct thermal drift.
EMI Shielding: Metal housings block external magnetic interference.
Redundancy: Dual sensors cross-verify data to reject outliers.

Critical Design Factors