1. Construction of Magnetic Encoders
Magnetic encoders detect rotational position by measuring magnetic field variations and converting them into electrical signals. A basic configuration consists of a permanent magnet and magnetic sensing IC. The magnet is mounted on a rotating body (e.g., motor shaft), while the sensor IC is positioned on a PCB within the magnet’s field range. As the magnet rotates, the sensor detects changes in magnetic field direction, determining the shaft’s position and speed.
1.1 Hall Elements
Hall elements (magnetic sensors) utilize the Hall effect to output voltage proportional to magnetic flux density. Common semiconductor materials include:
High-sensitivity InSb (Indium Antimonide)
Thermally stable GaAs (Gallium Arsenide)
Balanced InAs (Indium Arsenide)
Si (Silicon) for IC integration
Types: Longitudinal vs. Transverse field detection.
1.2 Permanent Magnets
Typically disc-shaped with radial or axial magnetization. Material/size selection depends on:
- Required flux density
- Operating environment
- Dimensional constraints
2. Operating Principles
2.1 Fundamentals
During shaft rotation, Hall elements detect X-axis (Bx) and Y-axis (By) field components.
2.2 Angle Conversion
Field data → Electrical signals → ADC → Digital processing → Angle calculation via arctan(By/Bx)
Ideal condition: Lissajous curve forms a perfect circle (zero error)
Eccentricity tolerance: <±0.1° error
2.3 Rotary Position Sensor ICs
Integrated components: Magnetic sensor + ADC + Processing core. Enables compact absolute encoders for industrial/automotive applications.
Technical Classification of Magnetic Encoders
Magnetic encoders can be categorized as follows based on operating principles and application scenarios:
1. By Output Signal Type
| Type | Principle | Application Scenario | Representative Model |
| Incremental | Outputs A/B/Z pulses, requires reference point for position calculation | Elevator motors, Conveyor belts | Broadcom AEDR-8700 |
| Absolute | Directly outputs unique position code (Binary/Gray code) | Industrial robot joints, CNC machine tools | AMS AS5048A |
| Multi-turn Absolute | Integrates gear mechanism to record turns (±4096 turns absolute position) | Wind turbine pitch systems, Heavy machinery | RLS AksIM-2 |
2. By Sensing Principle
| Type | Technical Characteristics | Advantages/Limitations |
| Hall Effect | Detects vertical magnetic field component, linear output | Low cost, contamination-resistant (e.g. Allegro A1335) |
| Magnetoresistive | Utilizes resistance change (GMR/TMR), high sensitivity | Resolution up to 0.1° (TDK TAD2141) |
| Inductive | Coil-induced magnetic field variation, strong EMI immunity | Suitable for high EMI environments (SICK ATM60) |
3. By Mechanical Structure
| Type | Mounting Method | Typical Application Scenario |
| Sleeve-type | Directly sleeves onto motor shaft | Servo motors (Maxon ENC series) |
| Modular | Independent PCB module, external magnet ring | Retrofit projects (Renishaw RM08) |
| Hollow Shaft | Lateral magnet mounting, solves axial space constraints | Robot joints (Vishay RAIK060) |
Representative Magnetic Encoder IC Models
1. International Flagship ICs
| Model | Manufacturer | Resolution | Interface | Key Features | Extreme Environment Adaptation |
| AS5047P | AMS | 14-bit | SPI/ABI | Dynamic angle error compensation, ±0.5° accuracy | -40°C ~ 150°C |
| MA730 | Monolithic | 14-bit | SPI/UVW | Integrated PGA, anti-magnetic interference | Vibration resistance 50g |
| TLE5012B | Infineon | 15-bit | SPC | Dual-chip redundancy (Automotive-grade) | AEC-Q100 certified |
| A1335 | Allegro | 14-bit | PWM/Analog | On-chip EEPROM for calibration parameters |