Magnetic Enc
Reads angular or linear position from a periodically magnetised steel scale (or rotor ring) using on-chip Hall-effect or magnetoresistive sensors, outputting quadrature, ABZ, or absolute serial position with up to 14-bit resolution.
A magnetised pole tape (or ring) carries N/S poles at a fixed pitch (e.g., 2 mm). A magnetoresistive bridge or array of Hall sensors detects the field and decodes the angle of the local magnetic vector to within 0.01° of one pole pair. Multi-pole interpolation extracts continuous position. Absolute parts (e.g., AS5047) include a master reference track plus on-chip CORDIC math for serial absolute output.
In plain terms
Like reading a vinyl record's grooves with a steel needle instead of a laser — slower but immune to fingerprints, dust, and scratched lacquer.
Why designers use it
- Survives dust, oil, coolant — any contaminant that would fog a glass scale doesn't affect a steel scale's magnetic field.
- Robust against shock and vibration — no glass to crack.
- Cost-effective at moderate (10–14-bit) resolution — beats optical for most servo and robotics applications.
- Compact — encoder ring fits on shaft directly with no separate housing or shaft coupling.
Best for
- Robotics
- Servo motors
- BLDC commutation
Key specifications
- Operating limits: Check the exact manufacturer's datasheet (A family name does not establish voltage, current, temperature or timing limits.)
- Pin assignment: Match the complete part and package code (A similar name or function does not guarantee the same wiring.)
- Mechanical fit: Use the exact package drawing (Check pad layout, dimensions and viewing direction before building.)
When not to use it
- When sub-µm linear precision is needed — magnetic encoders top out at ~5 µm; pull glass linear encoder.
- In strong external magnetic fields (e.g., next to MRI or large transformers) — stray fields corrupt readings.
Common mistakes
- Mounting the readhead off-axis or at the wrong air gap — sensitivity collapses outside the spec'd 0.5–1.5 mm window.
- Re-polishing the steel scale to remove rust — abrasion partly demagnetises the pole pattern and the encoder loses absolute accuracy.
Where you will find it
- An ams-OSRAM AS5047P 14-bit magnetic rotary encoder on the rotor of a Maxon EC-i 40 BLDC motor in a Boston Dynamics Spot leg actuator: the encoder reads through the dust and grit Spot kicks up while exploring construction sites, where any optical encoder would have failed within hours.
- A Renishaw RLS LM10 magnetic linear encoder strip runs along the tool magazine of a Mazak QTU 350 turning centre: the readhead reads through coolant mist and metal shavings to deliver tool-position feedback at 10 µm resolution to the CNC controller.
- A Kollmorgen AKM2G servo motor for a packaging-line pick-and-place uses an integrated Renishaw AksIM-2 ring magnetic absolute encoder: the absolute readout means the line restart after a power blip needs no homing cycle, saving minutes of downtime per shift.
A short history
A magnetic encoder detects shaft angle from a changing magnetic field. In a common arrangement, a rotating magnet moves relative to a Hall sensor, and supporting electronics convert the measured field into angle information. This avoids an optical sensing path, which can be useful where contamination would obstruct light.