In automated control systems, magnetic encoders act like the "sensory nerves" of equipment, accurately capturing every detail of motion. Choosing the right type is crucial for ensuring efficient system operation.
In modern industrial automation, robotics, and intelligent equipment, magnetic encoders have become core components for position detection due to their unique advantages. Compared to traditional optical encoders, magnetic encoders offer greater environmental adaptability, higher reliability, and a smaller footprint.
Faced with diverse application requirements, magnetic encoders have developed different technical pathways and classification methods, with each type having its own unique performance characteristics and suitable application scenarios.
01 Magnetic Encoders: Working Principle and Technical Advantages
Magnetic encoders are position sensors based on the principle of magnetic induction, measuring rotational or linear displacement by detecting periodic changes in a magnetic field.
The basic components include three parts: a magnetic scale/ring, a magnetic sensor, and a signal processing circuit.
The magnetic scale or ring has evenly arranged N/S magnetic poles, forming a periodic magnetic field distribution. When relative motion occurs between the magnetic scale and the sensor, the magnetic sensing element detects the magnetic field change and outputs a corresponding electrical signal, which is then processed by the circuit to obtain position information.
Compared to optical encoders, magnetic encoders offer multiple advantages: stronger resistance to contamination and vibration; adaptation to a wider temperature range; simple structure and lower cost; ability to work stably in harsh industrial environments.
These characteristics have led to the widespread application of magnetic encoders in fields such as industrial automation, automotive electronics, and aerospace.
02 Classification by Signal Output Type: Incremental, Absolute, and Hybrid
Incremental Magnetic Encoders
Incremental encoders output A and B two-phase pulse signals with a 90° phase difference; some also include a Z-phase index signal (one per revolution).
By counting the number of pulses and judging the sequence of the A and B phases, the relative displacement and direction of movement can be determined.
Advantages: Simple structure, low cost, high response frequency.
Disadvantages: Position information is lost after power loss, requiring re-homing.
Applications: Suitable for continuous rotation, speed control, and occasions with clear reference points.
Absolute Magnetic Encoders
Each position of an absolute encoder corresponds to a unique digital code. It retains position information after power loss and immediately obtains the current position value upon power-up.
Single-Turn Absolute: Within a 360° range, each position has a unique code; the code cycles after exceeding 360°.
Multi-Turn Absolute: Adds revolution counting on the basis of the single-turn, expanding the measurement range.
Advantages: Power-off memory, no need for homing, reliable data.
Disadvantages: Complex structure, higher cost.
Applications: Fields requiring high reliability, such as robot joints, CNC machine tools, and aerospace.
Hybrid Magnetic Encoders
Hybrid encoders combine the features of incremental and absolute types, capable of outputting both absolute position information and high-resolution incremental signals.
This design balances system reliability and precision, and is becoming increasingly popular in high-end servo systems and precision measurement equipment.
03 Classification by Magnetic Detection Principle: Hall Effect, Magnetoresistive
Hall Effect Encoders
Based on the Hall effect, when a current-carrying conductor is placed in a magnetic field, a potential difference is generated in a direction perpendicular to both the current and the magnetic field.
Characteristics: Low cost, good temperature characteristics, long lifespan.
Shortcomings: Relatively low resolution.
Applications: Cost-sensitive applications like automotive motors and home appliances.
Anisotropic Magnetoresistive (AMR) Encoders
Utilize the characteristic that the resistivity of ferromagnetic materials changes in an external magnetic field. Sensitivity is several orders of magnitude higher than Hall elements.
Characteristics: High resolution, wide frequency response, stable temperature characteristics.
Shortcomings: Requires magnetic shielding, higher cost.
Applications: High-precision servo motors, precision instruments.
Giant Magnetoresistive (GMR) and Tunnel Magnetoresistive (TMR) Encoders
GMR and TMR are new-generation magnetic detection technologies, with sensitivity an order of magnitude higher than AMR.
Characteristics: Ultra-high sensitivity, high signal-to-noise ratio, low power consumption.
Shortcomings: Complex process, high cost.
Applications: Ultra-high precision fields like high-end industrial robots and medical equipment.
04 Classification by Structure Type: Solid Shaft, Blind Hollow, Through Hollow
Solid Shaft Magnetic Encoders
The sensor is fixedly connected to the rotating shaft, featuring a compact structure, low torque, and low cost.
Suitable for small motors and micro-robots with space constraints, but installation requires a coupling and demands high alignment accuracy.
Blind Hollow (Semi-Hollow) Magnetic Encoders
The encoder has a blind hole on one side and is directly mounted onto the motor shaft, offering easy installation and good reliability.
This is the most commonly used structure today, balancing performance and cost, and is widely used in servo motors and industrial robots.
Through Hollow (Hollow Shaft) Magnetic Encoders
Have a central through-hole penetrating the entire encoder, allowing for cabling or a shaft to pass through, meeting special installation needs.
Suitable for complex mechanical structures, such as collaborative robot joints and precision turntables.
05 Classification by Accuracy Grade: Commercial, Industrial, Instrument
Commercial Grade Magnetic Encoders
Resolution: Typically below 12 bits (4096 PPR)
Accuracy: ±1° or greater
Operating Temperature: 0°C to +70°C
Applications: Home appliances, consumer electronics, general motors
Industrial Grade Magnetic Encoders
Resolution: 12-16 bits (4096-65536 PPR)
Accuracy: ±0.1° to ±0.5°
Operating Temperature: -40°C to +85°C
Protection Rating: Typically IP54 or above
Applications: Industrial automation, servo motors, power tools
Instrument Grade Magnetic Encoders
Resolution: 16-24 bits (65536-16777216 PPR)
Accuracy: ±0.01° to ±0.05°
Operating Temperature: -40°C to +110°C
Special Features: Shock resistance, vibration resistance, EMC protection
Applications: Aerospace, precision measurement, high-end scientific research
06 Magnetic Encoder Selection Guide
Define Application Requirements
Motion Type: Rotary or linear motion? Continuous or reciprocating?
Control Requirements: Position control, speed control, or both?
Environmental Conditions: Temperature, humidity, vibration, electromagnetic interference?
Determine Key Parameters
Resolution: Select based on control accuracy requirements, not necessarily higher is better.
Accuracy: Consider the overall system error budget.
Response Frequency: Must meet the maximum operating speed requirement.
Output Interface: Parallel, serial, fieldbus.
Consider Installation Conditions
Space Constraints: Determine the allowable installation dimensions and method.
Shaft Connection: Consider alignment requirements and installation convenience.
Protection Rating: Select appropriate protection based on environmental contaminants.
Evaluate Economic Factors
Budget Range: Find a balance point between performance needs and cost.
Lifecycle Cost: Consider long-term costs of maintenance and replacement.
Supply Lead Time: Ensure stability of the supply chain.
07 Special Types of Magnetic Encoders
Linear Magnetic Encoders
Used for linear displacement measurement, consisting of a magnetic scale and a read head.
Advantages: Large measurement range, flexible installation, strong contamination resistance.
Applications: CNC machine tools, coordinate measuring machines, linear motors.
Multi-Turn Absolute Magnetic Encoders
Use Wiegand energy harvesting technology or gear transmission mechanisms to achieve mechanical multi-turn counting.
Characteristics: Can maintain multi-turn position information after power loss without needing a battery.
Applications: Wind turbine pitch systems, port machinery, engineering machinery.
Dual-Track Magnetic Encoders
Have two independent magnetic detection units that can output two signals simultaneously.
Advantages: Redundant design improves reliability; dual signals facilitate error compensation.
Applications: Safety-critical systems, special occasions requiring high reliability.
With advancements in magnetic materials, integrated circuits, and signal processing technologies, magnetic encoders are developing towards higher precision, smaller size, and greater intelligence.
Innovative technologies such as new TMR magnetic sensing elements, intelligent self-diagnostic functions, and integrated drive-control designs are continuously expanding the application boundaries of magnetic encoders.
In the context of the future Industry 4.0 and smart manufacturing, the importance of magnetic encoders as equipment "sensory nerves" will become increasingly prominent, providing more precise and reliable position perception capabilities for intelligent equipment.
