What Is an Encoder?
An encoder is a sensor device that converts physical motion (such as rotation, linear displacement, or speed) into electrical signals, which are used by digital control systems (like PLCs, drivers, or industrial computers) for real-time monitoring, feedback, and control. In fields such as industrial automation, robotics, CNC equipment, medical systems, and aerospace, encoders are key components for achieving closed-loop control and high-precision positioning.
Comprehensive Classification of Encoders
Encoders can be classified from several technical perspectives, including measurement format, signal output type, sensing technology, and communication interface.
1. By Measurement Format
| Type | Description |
|---|---|
| Rotary Encoder | Measures rotational movement (angular displacement), such as motor shafts or turntables |
| Linear Encoder | Measures linear movement, used in machine tools and positioning platforms |
| Draw Wire Encoder | Measures long-distance displacement through the extension of a wire |
| Encoder Kit | Modular design without housing, ideal for compact motor integration |
2. By Signal Output Type
| Type | Description |
|---|---|
| Incremental Encoder | Outputs relative motion signals (A/B/Z phase), requiring continuous counting by the controller |
| Absolute Encoder | Outputs absolute position values, includes single-turn and multi-turn types, retains position after power loss |
| Analog Encoder | Outputs continuous voltage or current signals (e.g., 0–10V, 4–20mA) |
3. By Sensing Technology
| Technology | Features & Applications |
|---|---|
| Optical | High precision and resolution, suitable for clean environments |
| Magnetic | Resistant to dust and oil, suitable for harsh industrial environments |
| Capacitive | Compact, vibration-resistant, and low-power, ideal for precision instruments |
| Inductive | Strong anti-interference, suitable for heavy machinery and high-safety applications |
4. By Communication Interface
| Interface Type | Description |
|---|---|
| A/B/Z Pulse | Standard incremental output, widely compatible |
| Analog Interface | Suitable for legacy systems or basic PLCs |
| Serial Interface (SSI/BiSS) | High accuracy and real-time performance, used in high-end absolute encoders |
| Fieldbus (CANopen/Profibus) | Flexible structure, supports multi-node communication |
| Industrial Ethernet (EtherCAT/Profinet) | High real-time performance, ideal for complex automation networks |
How Encoders Work
Encoders typically consist of the following components:
- Motion Element: Such as a rotating shaft, linear guide, or wire system
- Code Disk / Magnetic Strip: Contains periodic patterns for position detection
- Sensing Component: Includes photoelectric sensors, magnetic sensors, capacitive plates, or inductive coils
- Signal Processing Unit: Converts sensing data into standardized output
- Output Interface: Connects with the controller for real-time data exchange
As the measured object moves, the encoder’s internal detection system captures its position and converts it into an electrical signal. Different encoder types use different methods: optical encoders use light and code disks, magnetic types detect magnetic field changes, capacitive types sense electric field variations, etc.
Key Performance Metrics
| Parameter | Description |
|---|---|
| Resolution | Number of signals per unit movement (e.g., PPR or bits) |
| Accuracy | Maximum deviation between actual and measured values |
| Repeatability | Stability of repeated measurements at the same point |
| Maximum Response Frequency | Maximum supported signal frequency corresponding to input speed |
| Output Logic Level | Standards like TTL, HTL, RS422 |
| Protection Level (IP) | IP ratings (e.g., IP65, IP67) indicating dust and water resistance |
Common Applications
- Industrial Automation: Conveyor positioning, servo control, electric cylinder feedback
- CNC Machines: X/Y/Z axis detection, tool changer feedback
- Robotic Systems: Joint angle detection, mobile platform feedback
- Medical Imaging: Scanning motion control in MRI, CT systems
- Renewable Energy: Wind turbine yaw control, solar tracking systems
- Aerospace and Defense: Missile fin control, flight attitude monitoring
Encoder Structure & Signal Diagrams
Figure 1: General rotary encoder appearance
Figure 2: Encoder internal structure including code disk, sensor, signal processor
Relevant Standards
- IEC 60050-351: International Electrotechnical Vocabulary – Measurement terminology
- ISO 13849: Safety of machinery – Functional safety (includes safety encoders)
- IEC 60529: IP rating – Protection against dust and water
- IEC 61800-5-2: Functional safety of drive systems
- CiA 406: CANopen device profile for encoders
- IEC 61158: Definition of fieldbus communication protocols
Glossary
| Term | Meaning |
|---|---|
| PPR | Pulses Per Revolution |
| CPR | Counts Per Revolution |
| Z Phase | Reference signal output once per revolution by incremental encoders |
| TTL | 5V level digital signal standard |
| HTL | 10–30V level, high noise immunity |
| RS422 | Differential signal standard for high-speed long-distance transmission |
| SSI | Synchronous Serial Interface, used in absolute encoders |
| BiSS | Open high-performance serial communication protocol |
Summary: Encoders serve as a crucial bridge between physical systems and digital control systems. Understanding their classifications, structures, outputs, and standards enables better selection and integration in industrial automation and precision control applications.