Encoders-Working Principle, Types, Applications, and Classification

Encoder Types, Working Principles, and Applications in Industrial Automation

Published on Aug 06, 2025 | Category: introduction

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Rotary encoders are essential components in motion control systems, widely used to provide accurate feedback on position, speed, direction, and angular displacement. Their ability to convert mechanical motion into electrical signals makes them critical for automation, robotics, CNC machines, motor drives, and many other industrial and commercial systems.

They play a critical role in various manufacturing and production processes where precise measurement of shaft rotation or linear motion is required. Depending on the application, either rotary encoders (for rotational movement) or linear encoders (for straight-line motion) are used to ensure accurate positioning and movement tracking.

Whether you're selecting an encoder for precision feedback in robotics or high-speed rotation measurement in industrial machinery, this guide will help you understand the working principles, design considerations, and real-world applications of encoders — helping you choose the best solution for your project.

What is an Encoder?

An encoder is an electromechanical device that converts mechanical motion—such as rotation or linear movement—into electrical signals. These signals are used to determine parameters like position, speed, direction, or displacement in control systems. Encoders are essential in automation, robotics, and motor feedback applications.

Types of Encoders

Encoders are commonly classified into two major output types: incremental encoders and absolute encoders. Incremental encoders generate pulses as the object moves, requiring external counters to track position, while absolute encoders provide a unique signal for every position, allowing precise position detection without loss of reference.

Incremental Encoders: These provide relative position information. They generate pulses as the shaft rotates, which are counted to determine movement or speed. However, they do not retain position data after a power loss.
Absolute Encoders: These provide a unique digital code for each shaft position, representing the exact position even after a power interruption. They are ideal for applications requiring precise and consistent position feedback.

The choice between incremental and absolute encoders depends on the application's need for precision, feedback accuracy, and behavior after power loss.

Key Features of Encoders

Rotary encoders typically come with a solid or hollow shaft and are mechanically coupled to the rotating element, whereas linear encoders track displacement along a linear path. Both types of encoders serve as electromechanical devices that convert motion into electrical signals. These signals provide essential feedback to control systems regarding position, distance, velocity, rotational speed, and direction.

Rotational Displacement Output: Encoders provide output signals based on the rotational displacement of the shaft. By linking the encoder to the shaft via a coupling, accurate detection of rotation is achieved.
Category: Safety Components
No Homing Required for Absolute Encoders: Absolute encoders do not require a return-to-origin operation at startup. They output the exact rotational angle as an absolute value.
Category: Relays
Rotation Direction Detection: Both incremental and absolute encoders can detect the direction of rotation. Incremental encoders determine direction based on the phase difference between channels A and B, while absolute encoders determine it by monitoring changes in the output code.
Category: Control Components
Wide Range of Options: Encoders are available in various resolutions, output formats, and electrical interfaces. This allows users to choose the optimal sensor based on system requirements for accuracy, cost, and compatibility.
Category: Automation Systems

Encoder Technologies

Encoders are available in different technologies, each offering unique methods to convert mechanical movement into electrical signals. The choice of encoder technology depends on environmental conditions, required accuracy, resolution, and system cost. Below are the main types of encoder technologies used in industrial and automation systems.

Optical Encoders

Optical encoders track movement by transmitting an optical signal from a source to a receiver, which is then converted into an electrical signal. Optical encoders offer high resolution and are commonly used in precision applications. There are three main types of optical encoders:

1. Transmissive Optical Encoders

These encoders emit a light source (usually LED) through a transparent and opaque line pattern on a rotating disk or linear scale. The alternating lines allow light to pass or be blocked, creating a signal. While reliable, they are sensitive to dust, shock, vibration, and moisture.

2. Reflective Optical Encoders

Reflective optical encoders also use a light source, but both the light emitter and detector are on the same side. The light reflects off a patterned surface back into the sensor. These encoders are more compact and suitable for space-constrained applications.

3. Interferential Optical Encoders

These high-precision encoders use a laser light beam and a diffraction grating pattern on a metal or glass scale. The light forms Talbot planes, which are used to generate high-resolution position signals. They are highly accurate but require clean and stable environments.

Magnetic Encoders

Magnetic encoders detect position by measuring changes in magnetic fields. They use magnets with north and south poles placed on a rotating or linear scale, and sensors such as Hall-effect or magnetoresistive elements measure the change in flux.

Magnetic encoders are available in both incremental and absolute formats. They are compact, cost-effective, and resistant to dust, liquids, and non-metallic contamination. However, they can be affected by external magnetic fields and temperature changes if not properly shielded.

Capacitive Encoders

Capacitive encoders consist of a transmitter, receiver, and sinusoidal rotor. As the rotor moves, it changes the capacitance between the transmitter and receiver by altering the electric field. This change is tracked to determine position.

These encoders are ideal for environments with high EMI (electromagnetic interference), offer high accuracy, low power consumption, and compact size. However, they may be sensitive to electrostatic buildup and condensation.

Inductive Encoders

Inductive encoders are absolute encoders that operate similarly to resolvers but use PCB traces instead of coil windings. This makes them lighter, more compact, and cost-efficient. The PCB-based design also improves resistance to vibration and harsh conditions.

They offer high reliability and environmental stability, making them suitable for rugged industrial applications. Inductive encoders are commonly used where mechanical robustness and noise immunity are critical.

What is an Absolute Encoder?

An absolute encoder is a position sensing device that outputs a unique digital code for each shaft position. Unlike incremental encoders, it provides a specific, repeatable output value that represents the exact rotational angle, even after power loss or startup. It does not require re-homing or referencing every time it is powered on.

Working Principle of Absolute Encoder

Absolute encoders use an optical or magnetic disk with a unique binary or Gray code pattern. As the disk rotates with the shaft, light sensors (in optical types) or magnetic sensors (in magnetic types) read the position-specific code. Each position corresponds to a unique digital output based on the physical code pattern on the disk. The number of output bits determines how many positions can be identified in one revolution.

Accuracy and Resolution

Accuracy: High, as the encoder directly reads a predefined digital code for each position. Errors due to noise or missed pulses are minimized.
Resolution: Depends on the number of bits. For example, a 12-bit encoder can resolve 2¹² = 4096 unique positions per revolution.

Output of Absolute Encoders

The output of an absolute encoder is a multi-bit digital code that represents the exact position of a rotating or moving object. Unlike incremental encoders that generate pulses relative to movement, absolute encoders provide a unique position value for each point in their rotation or travel. This means the encoder's output corresponds directly to a fixed, known mechanical position.

One of the key advantages of absolute encoders is their ability to retain positional data even when power is lost. They feature a built-in reference system that allows them to remember the last known position. So, when power is restored, the system does not require a rehoming process or initial calibration. This feature is especially valuable in automation systems where uptime and accuracy are critical.

Absolute encoders are commonly used in applications where precise position tracking is essential — such as robotics, CNC machines, elevators, and servo systems. Their reliability and non-volatile position data make them ideal for safety-critical and high-performance motion control systems.

Parallel Output: Each bit of the position is sent via a separate wire. Suitable for high-speed systems.
Serial Output: Reduces wiring complexity. Examples include SSI (Synchronous Serial Interface) and BiSS.

Key Features

No need to return to a reference position at startup.
Retains position even after power loss.
Capable of multi-turn position tracking (in advanced versions).
Immune to pulse loss errors, unlike incremental encoders.

Applications of Absolute Encoders

Robotics – to track precise arm or joint angles
CNC machines – for spindle and table positioning
Elevator control systems
Servo motor feedback loops
Automated assembly systems

What is an Incremental Encoder?

An Incremental Encoder is a type of rotary encoder that generates electrical pulses in response to rotational movement of a shaft. It provides relative position information by counting the number of pulses generated as the shaft turns. These pulses do not indicate the exact position, but rather how far and in which direction the shaft has moved.

The encoder disk is typically marked with alternating transparent and opaque segments. As the shaft rotates, an optical or magnetic sensor detects these segments and produces two square wave signals (often called Channel A and Channel B), which are 90 degrees out of phase. This phase difference allows the detection of direction of rotation. A third signal, known as the Index pulse (or Z pulse), is generated once per revolution and can be used as a reference or zero position.

img/encoder-basic/incremental-encoder.webp

To determine position, a counter or PLC must continuously track the number of pulses from a known reference. Since the encoder doesn’t store position data, the system must be re-homed (reset) on startup or power loss unless backup memory is used.

Key Features:

Output: Pulses indicating change in position
Direction: Determined by phase difference between Channel A and B
Resolution: Can be increased using x2 or x4 decoding logic
Reference: Index (Z) pulse indicates one fixed point per revolution
Technology: Optical or magnetic sensing through slotted disc

Output of Incremental Encoders

The output of an incremental encoder consists of a continuous stream of square wave pulses that are generated as the shaft rotates (in rotary encoders) or as the object moves linearly (in linear encoders). These pulses are not tied to an absolute position, but rather represent changes in movement. Each pulse corresponds to a fixed amount of rotation or distance, depending on the encoder's resolution.

By counting the number of pulses over time, the motion control system can calculate key parameters such as position, speed, and direction of movement. The resolution of the encoder—typically expressed as pulses per revolution (PPR) or pulses per millimeter (for linear encoders)—determines how finely the system can measure movement. Higher resolution allows more accurate motion detection and control.

However, incremental encoders do not store position information when power is lost. After a shutdown or restart, the system must perform a homing procedure to re-establish a known reference position. Despite this, incremental encoders are widely used due to their simplicity, low cost, and fast response in applications like conveyor systems, motor feedback, and industrial automation.

How It Works:

As the encoder shaft rotates, the light (in optical encoders) passes through slits on a rotating disk. Photodetectors convert these light signals into electrical pulses. The combination of signal edges from both channels enables higher resolution (e.g., 4x decoding can generate four pulses per slot: rising and falling edges of both A and B).

Important Note:

Since it only provides relative position, an incremental encoder requires a known reference point on startup. If power is lost, the position information is also lost unless continuously stored externally.

Difference Between Incremental and Absolute Encoders

Parameter	Incremental Encoder	Absolute Encoder
Working Principle	Generates pulse signals (A, B, Z channels) based on shaft movement. Only relative position is tracked.	Outputs a unique digital code for each position. Tracks exact position at all times.
Position Detection	Relative – Position is lost on power-down; requires homing on startup.	Absolute – Retains exact position even after power loss; no homing required.
Direction Detection	Based on phase difference between Channel A and B signals.	Determined by increasing or decreasing code values.
Output Type	Pulses (A/B/Z channels) – counted externally to calculate position.	Parallel or serial digital output directly representing position.
Accuracy	Dependent on external electronics and resolution; may accumulate errors over time.	Highly accurate; each position has a unique, consistent code.
Resolution	Can be very high, depending on pulse count per revolution (PPR).	Fixed by the number of bits (e.g., 12-bit = 4096 positions per turn).
Technology	Primarily optical or magnetic sensing with pulse disk.	Uses optical or magnetic sensing with a coded disk and memory.
Startup Behavior	Requires homing to find reference (Z) position.	Ready to use instantly after power-on.
Cost	Lower cost, simple design.	Higher cost due to complex design and electronics.
Applications	Speed monitoring, low-cost motor feedback, general automation.	Robotics, elevators, CNC, safety-critical and precision positioning.