What are Encoders? Encoder Construction, Working, and Types Explained

Encoders are angular motion sensors, that can detect angular motion, direction, speed, and angles of the rotation. An encoder can also be used for detecting linear displacement. Encoders are primarily used in industrial processes, robotics, automatic guided machines, steppers, servo motors, etc. The encoder that encodes the angle of rotation is called the rotary encoder and is used for linear displacement is called the linear encoder.

Detecting Mechanism of Encoders

Encoders are sensor that measures the physical quantity when a body rotates and convert it into an electrical signal. The electrical signal is processed to obtain the desired information. Different type of encoders measures different physical quantities. Let’s have a look over the different types of encoders.

Mechanical Encoder

This method uses a variable resistor to measure the rotation. Such encoders are called potentiometers. The change in resistance is detected with a change in current.

Mechanical Encoder
Figure 1: Mechanical Encoder Working

Magnetic Encoder

A permanent magnet is attached to the shaft and a magnetic sensor is placed near the magnet. When the shaft moves the magnetic field changes and the sensor detects the changes in the field.

Magnetic Encoders
Figure 2: Magnetic Encoder Construction

Electromagnetic Induction Encoder

The electromagnetic encoder uses induction principles to detect the rotation from inside the motor. The motor consists of a detection coil and an excitation coil. Voltage is induced inside the detection coil using transformer action which helps in detecting the motion.

Electromagnetic Encoders
Figure 3: Electromagnetic Encoder Construction

Optical Encoders

An optical Encoder uses an LED as a light source, a disc with slits, and a photodiode as a light detector. Light pass and blocks through the slits of the disc as the shaft rotates. The light detector converts the rotation into electrical pulses. The rotation can be measured by counting the electrical pulses. These are the latest types of encoders.

Optical Encoders
Figure 4: Optical Encoder Construction

Desired Output of Encoders

An ideal encoder can provide the following information about the rotating shaft.

  1. An encoder can tell us about the angular position of the shaft
  2. The speed of the shaft
  3. Rotational direction, i.e., the rotation is clockwise or counterclockwise
  4. Number of rotations

Uses of Encoders

Industrial processes

Most of the processes in the latest industries are automatic, non-stop, and redundant. Such a process can be controllable with a computer. These processes could be simple and complex like PCB board fabrication, hole drilling, component placement, and testing a PCB board. Each motion of the machine in such industries is measured by encoders.


Robotic arms have increased the productivity of industries and increased the precision of products. A robotic arm is like a human arm that contains multiple joints like the shoulder, elbow, and wrist. The motion of the robotic arm is measured by encoders.

Robotic Arm
Figure 5: Robotic Arm


Motors are commonly used actuators with gear assemblies to increase or decrease the output torque. A simple 3D printer also uses a motor as an actuator in a linear slide by controlling the motion of the electric motor. The motion of the slide is monitored with encoders.

Electric Slider Actuator
Figure 6: Electric Slider Working Diagram


A servo motor is a closed-loop motor. Where the motor is commanded to a certain target angle and speed. With the help of an encoder, it detects if the motor has achieved the target or not. The motor will try unless and until achieves the targeted speed and angle. A servo motor assembles an AC or DC brushless motor, a Servo amplifier or driver, and an encoder.

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