Encoder Terminology
This page systematically compiles and explains common and important technical terms in the field of encoders. It covers electrical parameters, signal output, mechanical structures, communication protocols, environmental adaptability, accuracy calibration, functional safety, load limits, and more. Ideal for engineers, system integrators, R&D teams, technical buyers, and users seeking in-depth knowledge of encoders.
Encoder Output & Signal Terminology
| Term | Abbreviation | Definition |
|---|---|---|
| Resolution | Resolution | Number of signals generated per unit movement, indicating measurement accuracy. Measured in PPR, CPR, bit, LPI, CPI, etc. |
| PPR | Pulses Per Revolution | Pulses per revolution, commonly used for incremental rotary encoders. |
| CPR | Counts Per Revolution | Counts per revolution, often with signal multiplication. E.g., CPR = PPR × 4 with 4x decoding. |
| DPI | Dots Per Inch | Number of dots per inch, often used in scanning or high-resolution linear measurement. |
| CPI | Counts Per Inch | Encoder counts per inch of linear travel. |
| LPI | Lines Per Inch | Number of scale lines per inch for linear encoders or scanners. |
| A/B Channels | A/B Channels | Quadrature pulse outputs for incremental encoders; 90° phase shift to determine direction/count. |
| Z Channel | Zero Pulse / Index | One pulse per revolution used for homing or referencing. |
| N Channel | N Channel | Alternative term for the Z channel used by some brands. |
| U/V/W | — | Commutation signals for servo motors, used for electronic commutation and phase detection. |
| TTL | Transistor-Transistor Logic | 5V digital logic signal, ideal for short-distance, high-speed pulse transmission. |
| HTL | High Threshold Logic | 10–30V signal output with high noise immunity, suited for industrial environments. |
| Open Collector | OC | Output mode requiring external pull-up resistor; flexible voltage matching. |
| Push-Pull | — | Bidirectional driver output, no pull-up needed; common in industrial encoders. |
| Line Driver | LD / RS422 | Differential signal output standard for long-distance and noise-resistant transmission. |
| Voltage Output | Voltage Output | Analog signal (e.g., 0–5V, 0–10V) used in simple monitoring applications. |
| Current Output | Current Output | Analog current output (commonly 4–20 mA), robust against noise over long distances. |
| PWM | Pulse Width Modulation | Encodes position or angle information in pulse width; used in specific or customized systems. |
| 1Vpp/11µApp | — | Sine/cosine analog signals, common in high-resolution optical or magnetic encoders. |
Encoder Types, Principles & Sensing Methods
| Term | Definition |
|---|---|
| Incremental Encoder | Outputs continuous pulses representing position changes; absolute position must be calculated by counting. |
| Absolute Encoder | Each position has a unique code; retains position on power loss. Ideal for multi-axis and safety-critical applications. |
| Single-Turn Encoder | Measures position within one revolution, does not track number of turns. |
| Multi-Turn Encoder | Tracks multiple turns via internal gears or magnetic counters; mechanical or electronic variants exist. |
| Optical Encoder | Uses light source, code disk, and photodetectors for non-contact measurement; offers high precision. |
| Magnetic Encoder | Uses Hall or MR sensors to detect magnetic field changes; tolerant to dust/oil, suited for harsh environments. |
| Capacitive Encoder | Detects displacement via electric field changes between plates; compact for space-limited applications. |
| Inductive Encoder | Uses electromagnetic induction to measure motion; excellent resistance to EMI and vibration. |
| Encoder Kit | Also known as Kit Encoder, a frameless design for direct integration into motors or compact robotic joints. |
| Draw Wire Encoder | Measures linear displacement using a retractable cable and reel mechanism. |
| Rotary Encoder | Measures shaft rotation and speed; used in motors, rotary platforms, and servo drives. |
| Linear Encoder | Measures straight-line displacement; common in CNC, CMMs, and semiconductor equipment. |
| Multi-Channel Encoder | Provides various signal outputs (A/B/Z + UVW + serial) for motor commutation, position, and communication. |
| Programmable Encoder | Allows software-based configuration of resolution, direction, and signal format. |
| Code Format | Code formats for absolute encoders such as Gray Code, Binary, BCD, Excess Code. |
Communication Protocols & Industrial Interfaces
| Protocol / Interface | Definition |
|---|---|
| SSI | Synchronous Serial Interface – simple serial transmission used in absolute encoders. |
| BiSS-C | Open-source, high-speed protocol with full-duplex support and daisy-chain capability. |
| EnDat | Bidirectional serial interface from Heidenhain, supports error checking and high resolution. |
| CANopen | Open protocol based on CAN bus; object dictionary structure; widely used in Europe. |
| Profibus-DP | High-speed fieldbus for cyclic data exchange; suited for factory and process automation. |
| DeviceNet | CAN-based protocol by Allen-Bradley for connecting I/O devices and controllers. |
| EtherCAT | Real-time Ethernet protocol from Beckhoff; supports distributed clocks and multi-axis sync. |
| PROFINET | Siemens-backed industrial Ethernet combining IT and real-time communication. |
| IO-Link | Point-to-point protocol for sensors and actuators; supports diagnostics and remote parameterization. |
| Ethernet/IP | Member of CIP protocol family by Rockwell; supports SCADA, drives, and distributed control. |
| Modbus RTU/TCP | Open master-slave protocol for scalable remote I/O and automation systems. |
| UART | Universal asynchronous serial interface (e.g., RS232/RS485), common in low-cost encoder modules. |
| SPI/I²C | Chip-level serial interfaces for miniature or low-power encoders. |
| SERCOS | Real-time fiber/Ethernet motion control protocol for CNC and high-precision servo applications. |
Mechanical Mounting & Shaft Structure Terms
| Term | Definition |
|---|---|
| Solid Shaft | Encoder with a solid center shaft; requires couplings for torque transmission. |
| Hollow Shaft | Hollow design allows direct mounting on a motor shaft; reduces coupling complexity. |
| Blind Hollow Shaft | Partially closed hollow shaft combining compactness and easier installation. |
| Flange Mounting | Uses front or synchro flange according to DIN standards; common round/square interface. |
| Synchro Flange | Standard circular flange for mounting with clamps or bolts. |
| Servo Clamp Flange | Features clamping slots or pin holes for fast alignment and installation on servomotors. |
| Mounting Hole Pitch | Distance between housing screw holes; must match equipment interface. |
| Insertion Depth | Depth the shaft or hollow sleeve must be inserted; affects stability and durability. |
| Coupling | Connects solid shaft encoders to mechanical systems; flexible, bellows, or rigid types. |
| Radial/Axial Load | Maximum force the bearing can withstand in radial or axial directions without performance loss. |
Environmental Adaptability & Reliability
| Term | Definition |
|---|---|
| IP Rating | Ingress Protection rating (e.g., IP65, IP67), defined by IEC 60529; higher numbers mean better protection. |
| Operating Temperature | Temperature range for normal function while maintaining accuracy. |
| Storage Temperature | Permissible temperature range when unpowered. |
| Vibration Resistance | Ability to withstand mechanical vibrations; expressed in g-force. |
| Shock Resistance | Resistance to brief, high acceleration impacts; expressed in g-force. |
| EMC | Electromagnetic compatibility – tolerance to and emission of electromagnetic interference. |
| ESD | Electrostatic discharge immunity – measures sensitivity to static shocks. |
| SIL Level | Safety Integrity Level (e.g., SIL2, SIL3), required in applications like elevators or robotics. |
| MTBF | Mean Time Between Failures – average time the device operates before failure. |
| RoHS / REACH | Compliance standards for hazardous substances and material safety in manufacturing. |
Accuracy, Error & Calibration Terminology
| Term | Definition |
|---|---|
| System Accuracy | Max deviation between actual and measured positions, including encoder, installation, and controller errors. |
| Resolution Ability | Smallest detectable movement step; higher resolution improves motion detection. |
| Repeatability | Consistency of results when returning to the same position repeatedly. |
| Linearity Error | Nonlinear deviation from true position; can be reduced via calibration or compensation. |
| Zero Offset | Misalignment between Z-pulse and actual mechanical zero; corrected by mechanical or software alignment. |
| Encoding Error | Caused by code disk manufacturing defects or misalignment. |
| Calibration Coefficient | Parameters used to calibrate system or linearize output. |
| PID Feedback | Encoder provides feedback in closed-loop servo control systems (Proportional–Integral–Derivative). |
| Hysteresis | Mechanical or transmission lag when changing direction; often in incremental systems. |
Additional Terms & Notes
| Term | Definition |
|---|---|
| Gray Code | Encoding where only one bit changes between adjacent values; reduces switching noise. |
| Binary Code | Outputs binary value directly representing absolute position; easy for controller interpretation. |
| BCD Code | Binary Coded Decimal; each 4-bit group represents a decimal digit. |
| Excess Code | Offset binary used for smooth code transitions; seen in legacy or custom systems. |
| Multi-Turn Gear | Gear mechanism in mechanical multi-turn encoders for turn tracking. |
| Electronic Multi-Turn | Uses electronics/magnetic memory to track turns without mechanical gears. |
| UVW Channels | Motor commutation signals for synchronous three-phase motors. |
| S/N Ratio | Signal-to-noise ratio; reflects output clarity and stability. |
| Max Speed | Maximum safe rotational speed while maintaining accuracy. |
| Max Linear Speed | Highest speed for linear encoders without signal distortion. |
| Redundant Encoder | Dual-sensor or dual-channel for critical safety systems (e.g., SIL3); backup active upon failure. |
Standards & Resources
- IEC 60050-351: Vocabulary for industrial measurement and control
- ISO 13849: Machinery safety function standards (used in safety-certified encoders)
- IEC 60529: Defines IP protection ratings
- IEC 61800-5-2: Functional safety in drive systems, used in servo/safety encoders
- CiA 406: CANopen device profile for encoders
- IEC 61158: Industrial fieldbus protocol standards
- EnDat, BiSS, SERCOS: Key serial communication specifications for encoders
Note: Definitions may vary across brands and standards. Always refer to product-specific manuals for confirmation. This page will be continuously updated to reflect evolving technologies and applications. Contributions and feedback are welcome at Encoder.wiki!