Encoder Fundamentals

Industrial encoders are core sensors that convert rotary motion or linear displacement into electrical signals, widely used in CNC machines, robotics, elevators, wind power, packaging machinery, and other fields. Based on working principle and output method, encoders are primarily divided into two types: incremental encoders and absolute encoders.

The core role of an encoder is to provide precise position, speed, and direction feedback to the control system. Whether for closed-loop control of servo motors or synchronous positioning of conveyor belts, encoders play an indispensable role. Understanding the differences between the two types is the first step in selection.

Structurally, encoders typically consist of a light source, a coded disc, photoelectric receivers, and signal processing circuits. Incremental encoder discs have equally spaced transparent and opaque stripes, while absolute encoder discs have multiple concentric tracks with different encoding patterns. This structural difference directly determines their fundamentally different working principles and application characteristics.

Incremental Encoders in Detail

Working Principle

Incremental encoder discs have evenly distributed transparent and opaque graduation lines. As the encoder shaft rotates, the photoelectric receiver detects changes in light transmission and outputs a series of pulse signals. Typical outputs include Phase A, Phase B (90° phase difference for direction detection), and Phase Z (one reference pulse per revolution). The controller calculates rotation angle, speed, and direction by counting pulses and detecting phase relationships.

Since incremental encoders only output pulses of relative change, they do not store absolute position information internally. After each power-up or power loss, a homing operation is required to establish a position reference. This is the most fundamental difference between incremental and absolute types.

Core Advantages

• Cost Advantage: Relatively simple structure with mature manufacturing processes; typically 30%-50% cheaper than absolute types at the same resolution.
• High Response Speed: Pulse output is naturally suited for high-speed rotation scenarios, supporting speed measurements above 10,000 RPM.
• Compact Size: Some miniature incremental encoders are only 15mm in diameter, suitable for space-constrained installations.
• Good Interface Compatibility: Supports HTL (push-pull), TTL/RS422 (line driver), Sin/Cos, and other output methods, compatible with mainstream PLCs and servo drives.
• Flexible Resolution: Frequency multiplication technology can achieve 2x or 4x equivalent resolution from physical resolution.

Typical Application Scenarios

• Motor speed feedback and control
• Conveyor belt and winder speed synchronization
• Simple angle measurement and positioning (with homing sensor)
• Cost-sensitive batch equipment (e.g., textile machinery, packaging machinery)

Absolute Encoders in Detail

Working Principle

Absolute encoder discs have multiple concentric tracks, each representing a binary bit. At any angular position, the code combination read by the photoelectric receivers is unique — like assigning an "ID number" to each angle. This means even after power loss and restart, the encoder can immediately output the current exact position without needing a homing operation.

Absolute encoders are divided into single-turn and multi-turn types. Single-turn types can only record absolute position within one revolution (360°); multi-turn types use internal gear trains or electronic counting to record the number of turns, covering ranges of thousands of revolutions, particularly suitable for long-stroke linear motion conversion scenarios (e.g., lead screws, lifting platforms).

Core Advantages

• Position Memory After Power Loss: Retains position information after power loss without batteries; immediately obtains absolute position upon restart, eliminating homing errors.
• High Reliability: Each position code is unique with strong anti-interference capability; no cumulative errors from missed pulses like incremental types.
• Safety-Critical Scenarios: In elevators, medical equipment, cranes, and other high-safety scenarios, absolute encoders are mandatory or recommended.
• Multi-Turn Range: Multi-turn absolute encoders can cover measurement ranges exceeding 4,096 turns, eliminating the need for external mechanical reduction mechanisms.
• Digital Interfaces: Supports SSI, BiSS, EnDat, PROFINET, EtherCAT, and other digital protocols for easy integration into industrial Ethernet.

Typical Application Scenarios

• CNC machine tool magazine positioning and spindle orientation
• Robot joint precise position feedback
• Elevator car position detection (safety integrity level requirements)
• Wind turbine pitch angle and yaw control
• Medical imaging equipment scanning positioning

Selection Comparison Table

Comparison Dimension	Incremental Encoder	Absolute Encoder
Resolution	100-10,000 PPR (up to 40,000 with multiplication)	Single-turn 12-25 bit, multi-turn up to 37 bit
Cost	Low, approx. ¥300-2,000 at equivalent resolution	Higher, approx. ¥800-8,000
Power Loss Memory	Not supported; requires homing	Supported; no homing needed
Anti-Interference	Pulse loss may cause cumulative errors	Strong; unique position codes, less susceptible to interference
Max Speed	10,000-12,000 RPM	3,000-6,000 RPM
Output Interface	HTL, TTL/RS422, Sin/Cos	SSI, BiSS, EnDat, PROFINET, EtherCAT
Size	Smaller, min. ~Φ15mm	Larger, typically Φ36mm and above
Application Scenarios	Speed control, relative positioning, cost-sensitive projects	Absolute positioning, safety-critical, long stroke, multi-axis synchronization

Key Selection Parameters

1. Resolution

Resolution determines the positioning accuracy of the encoder. Incremental encoder resolution is typically expressed in PPR (Pulses Per Revolution), with common ranges of 100-10,000 PPR. Through 4x frequency multiplication, actual equivalent resolution can reach 4x. Absolute encoder resolution is expressed in bits, with single-turn 12-17 bit being common specifications, and multi-turn types can provide an additional 12 bits of turn counting.

Selection Recommendation: General servo positioning recommends incremental 1,000-2,500 PPR or absolute 17 bit; high-precision CNC machining recommends absolute 20 bit or above.

2. Output Signal

Common incremental encoder output methods include: HTL (push-pull, 10-30V, strong anti-interference), TTL/RS422 (line driver, 5V, suitable for long-distance transmission), Sin/Cos (analog, 1Vpp, suitable for high-precision interpolation). Absolute encoders primarily use digital interfaces: SSI (synchronous serial, point-to-point), BiSS (open-source high-speed protocol), EnDat (Heidenhain proprietary), and industrial Ethernet interfaces supporting PROFINET/EtherCAT.

Selection Recommendation: Regular applications recommend HTL or RS422 incremental; scenarios requiring industrial network integration or long-distance transmission recommend absolute + PROFINET/EtherCAT.

3. Protection Rating

The encoder's protection rating directly affects its reliability and lifespan in different environments. Common ratings include: IP50 (indoor clean environments), IP64 (dust-proof and splash-proof), IP67 (fully dust-proof, short-term immersion), IP69K (high-pressure high-temperature water wash).

Selection Recommendation: General workshops recommend IP64 or above; food & beverage and outdoor equipment recommend IP67; food processing lines requiring CIP/SIP cleaning recommend IP69K.

4. Mounting Method

Encoder mounting methods are primarily divided into solid shaft (connected via coupling) and hollow shaft/blind bore (directly fitted onto the motor shaft). Solid shaft is suitable for general installation, while hollow shaft offers compact structure and reduced axial space requirements. Additionally, shaft diameter (common 6mm, 10mm, 12mm), flange type (clamping flange, synchro flange), and cable exit direction (radial or axial) should be considered.

Selection Recommendation: Servo motor matching prioritizes hollow shaft type (better compatibility); independent installation or retrofit projects choose solid shaft + flexible coupling.

Ruilianxin Selection Recommendations

In actual projects, encoder selection is not simply an either-or choice, but requires comprehensive decision-making based on specific application scenarios, control requirements, budget, and installation conditions. Here are some practical recommendations we've compiled:

• If the project is cost-sensitive and only requires speed control: Choose incremental encoders for best cost-effectiveness.
• If the equipment needs to retain position information after power loss: Be sure to choose absolute encoders to avoid safety risks and time costs from homing.
• If high-precision multi-axis synchronization is needed: Recommend absolute encoders supporting EtherCAT bus for distributed clock synchronization.
• If installation space is limited: Prioritize miniature incremental or compact hollow-shaft absolute encoders.
• Not sure how to choose? Contact Ruilianxin's technical team with your application scenario and requirements, and we'll recommend the optimal solution.

Ruilianxin Technology maintains long-term partnerships with established European and American encoder brands such as wenglor, SICK, BALLUFF, and Micronor, providing genuine import procurement services for both incremental and absolute encoders. Whether standard models or special customization needs, we offer professional selection advice and competitive pricing.