Encoders: types, operating principles, and applications in control systems

Main Types of Encoders

Classification by Operating Principle

Disadvantages:

• Sensitivity to contamination and dust
• Limited performance in extreme operating conditions

2. Magnetic Encoders

Magnetic encoders use the Hall effect or magnetoresistive effect to determine position. They operate by reading changes in the magnetic field generated by a magnetized disc or strip.

Advantages:

• High accuracy and resolution (up to millions of pulses per revolution)
• No mechanical contact between the reading device and the disc
• Wide operating speed range
• Low inertia

Disadvantages:

• Generally lower accuracy compared to optical encoders
• Sensitivity to external magnetic fields

3. Inductive Encoders

Inductive encoders operate on the principle of inductance change when a metal rotor moves relative to a stator with windings.

Advantages:

• Exceptional reliability and durability
• High resistance to extreme temperatures, vibration, and contamination
• Immunity to electromagnetic interference

Disadvantages:

• Relatively low resolution
• Larger dimensions compared to other types


 4. Capacitive Encoders


Capacitive encoders operate on the principle of changing electrical capacitance between plates during their relative movement.

Advantages:

• Low cost
• Resistance to dust and moisture
• Low power consumption

Disadvantages:

• Sensitivity to electromagnetic interference
• Resolution limitations

Classification by Encoder Output Information Type

1. Incremental Encoders


Incremental (relative) encoders generate a sequence of pulses as the shaft rotates. They determine relative displacement, speed, and direction of movement, but not absolute position.
A typical incremental encoder has at least two output channels (A and B) shifted by 90° in phase, allowing the direction of rotation to be determined. A third channel (Z or index) is often added, producing one pulse per full revolution and serving to determine the reference position.

Applications of this sensor:

• Rotation speed control
• Distance measurement
• Systems with initial calibration capability

2. Absolute Encoders


Absolute encoders output a unique code corresponding to a specific angular position of an object at any given moment. They retain position information even when power is turned off.

Absolute encoders can use various encoding methods:

• Binary code
• Gray code (only one bit changes between adjacent positions)
• Serial data transmission formats (SSI, BiSS, EnDat, etc.)

Applications of this sensor:

• Systems where loss of position information is unacceptable
• Equipment with frequent power on/off cycles
• Precision positioning systems

Classification by Encoder Design

1. Hollow Shaft Encoders


Hollow shaft encoders are mounted directly onto the drive shaft, eliminating the need for couplings and reducing displacement measurement errors.

2. Keyed (Solid Shaft) Encoders


A classic solid-shaft design requiring a coupling for torque transmission and accurate displacement measurement.

3. Modular Encoders


Encoder components (disc and reading head) are mounted separately, allowing integration into limited spaces.

How can encoders be found in our store?

Our company "Specialist" supplies incremental encoders that are used with asynchronous motors. For high-precision positioning tasks, we also recommend servo drives — motors with a built-in encoder that can provide highly accurate positioning, for example, in CNC machines.

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+38 0800 210 317

Operating Principle of the Main Types of Encoders

Optical Encoders

The main components of an optical encoder are:

• Light source (usually an LED)
• Coded disc with transparent and opaque sections
• Photodetectors (photodiodes or phototransistors)
• Electronic signal processing circuit

Operating principle of an incremental optical encoder: 

1. The LED emits light directed at the coded disc
2. The disc mounted on the shaft contains radial transparent and opaque sectors
3. As the disc rotates, light periodically passes through transparent areas or is blocked by opaque ones
4. Photodetectors convert changes in the light flux into electrical pulses
5. The presence of several tracks with phase shifts allows determination of the direction and speed of rotation



Operating principle of an absolute optical encoder: 

In an absolute encoder, the coded disc contains several concentric tracks that form a unique binary code for each angular position. The number of tracks determines the encoder resolution. For example, a 10-bit encoder has 10 tracks and can distinguish 2^10 = 1024 positions per revolution.

Magnetic Encoders

Magnetic encoders use the following components:

• Magnetic disc or strip with alternating poles
• Hall sensors or magnetoresistive elements
• Signal processing circuit

Operating principle: 

1. A magnetic disc mounted on the shaft creates a changing magnetic field during rotation
2. Hall sensors or magnetoresistive elements respond to changes in the magnetic field
3. The electronic circuit converts these changes into digital signals

Magnetic absolute encoders often use the principle of position encoding with magnetic fields of different spatial frequencies (the Vernier method)



Encoder Characteristics

Main Parameters

1. Resolution - the number of pulses per full shaft revolution (for incremental encoders) or the number of unique codes per revolution (for absolute encoders)
2. Accuracy - the maximum error in determining angular position
3. Maximum Rotational Speed - the maximum speed at which the encoder operates correctly
4. Output Interfaces:


• TTL/CMOS pulses
• Differential signals (line drivers)
• Serial communication protocols (SSI, BiSS, EnDat)
• Industrial interfaces (Profibus, CANopen, EtherCAT)

5. Operating Temperature Range
6. Protection Class (IP)
7. Mechanical Shaft Load (radial and axial)
8. Rotor Moment of Inertia

Additional Functions

1. Diagnostics - fault detection and transmission of diagnostic information
2. Programmability - the ability to change encoder parameters (resolution, output signal type, etc.)
3. Multi-turn Functionality - counting the number of complete revolutions (for absolute encoders)
4. Electronic Nameplate Function - storing device and calibration information in memory
5. Redundancy - duplication of measurement systems to increase reliability

Applications of Encoders in Control Systems

Industrial Drives and CNC Systems 

In servo drives and CNC systems, encoders provide precise positioning of machine tool components. They are key elements of the closed-loop control system, allowing accurate monitoring of the position, speed, and acceleration of actuators.

Encoder Requirements for CNC Systems:

• High resolution (up to hundreds of thousands of pulses per revolution)
• Minimal errors and long-term stability of characteristics
• Resistance to vibration and cutting fluids



Robotics 

In robotic systems, encoders are used to track joint positions and ensure precise manipulation. They are especially important in collaborative robots working alongside humans, where high precision and motion safety are required.

Application Features:

• Compact size and lightweight design (to reduce joint mass)
• High dynamic accuracy
• Absolute position determination after power-up
• Multi-turn functionality