Incremental vs absolute position encoders

Incremental and absolute position encoders are both ideal for specific applications. Incremental encoders provide information about changes in position relative to a reference point whereas absolute position encoders provide a unique position value for each possible position of the encoder shaft. In this article we’ll look at the application specific use of each encoder and the pros and cons of each.

Applications: Incremental

Incremental encoders are widely used in applications that require speed and direction feedback rather than absolute position data. One of the most common uses is in motor control systems, where they help regulate speed and acceleration in industrial automation, robotics, and CNC machinery.

They are also used in conveyor belt systems to monitor and adjust the movement of materials. They can provide real time feedback on velocity and direction and are ideal for applications where changes in position are more important than knowing the absolute position.

In the automotive industry, incremental encoders help manage engine timing and transmission control by monitoring rotational speed. They are also commonly used in consumer electronics, such as printers and scanners, where they track movement for accurate positioning.

Applications: Absolute position

Absolute position encoders are essential in applications where precise and repeatable positioning is required. Unlike incremental encoders, they provide a unique value for every position, ensuring accurate data even after power loss. This makes them ideal for safety critical applications like medical imaging equipment and aerospace navigation systems.

Industrial automation systems, including robotic arms and automated assembly lines, rely on absolute encoders for precise positioning and repeatability. CNC machines and 3D printers also use absolute encoders to ensure exact positioning for high precision manufacturing.

In the energy sector, absolute encoders are used to track the position of wind turbine blades, allowing for optimal angle adjustments to maximize efficiency. They are also used in telescopes and radar systems.

Operation: Incremental

Incremental encoders operate by generating pulses as the shaft rotates. These pulses correspond to the movement of the encoder shaft and are counted by a control system to determine changes in position.

An incremental encoder will consist of a rotating disk with evenly spaced slots and an optical or magnetic sensor that detects these slots as the disk turns. The output signals, usually in quadrature format, allow the system to determine both direction and speed.

To obtain position information the system must count the pulses from a known reference point. However, if power is lost, the encoder does not retain the position, and recalibration is necessary.

Operation: Absolute position

Absolute position encoders work differently by assigning a unique digital code to each position of the encoder shaft. This means that no external reference point is needed, and the encoder can provide precise position data immediately upon startup.

These encoders typically use optical, magnetic, or capacitive technology to determine the position. Optical absolute encoders use a disk with multiple tracks, each corresponding to a bit in the encoder's digital output. By reading the pattern of light passing through or being reflected from the disk, the encoder determines the absolute position.

Absolute encoders can be either single-turn or multi-turn. Single-turn encoders measure position within one complete revolution of the shaft, while multi-turn encoders track multiple revolutions, often using a secondary gear mechanism or battery powered electronic memory.

Advantages: Incremental

Incremental encoders only need to generate pulses rather than store position data. This demands less complexity which makes them generally less expensive than absolute encoders. Another advantage of incremental encoders is their high resolution and ability to provide real time velocity and directional feedback. This makes them ideal for applications requiring rapid adjustments, such as motor control and conveyor systems.

Incremental encoders are available in a wide range of sizes and designs, making them easy to integrate into different industrial and consumer applications.  

Disadvantages: Incremental

Incremental encoders don’t retain their position after power failure. When restarted the system must reference a home position before resuming operation which can cause downtime and require additional hardware like limit switches.

Incremental encoders are susceptible to electrical noise and signal degradation which can occur in high vibration or high EMI environments.

Absolute position encoders have some distinct advantages including instant position feedback, high accuracy and resolution, no loss of position from power failure and a resistance to outside signal interference.

Absolute encoders assign a unique code to each position so they don’t lose their position in the case of power failure. They provide an exact position immediately upon startup as they don’t require a reference move.

Disadvantages: Absolute position

Despite their advantages, absolute encoders have some drawbacks. One major disadvantage is cost. Due to the complexity of their design and the need for more sophisticated electronics, absolute encoders tend to be more expensive than incremental encoders.

Another downside is their increased size and complexity. Because they must store unique position data and often include additional components such as multi-turn tracking mechanisms, they can be bulkier and more difficult to integrate into compact systems.

Absolute encoders also require more sophisticated interfacing and processing, which can add to the overall system cost and complexity. Unlike incremental encoders, which simply output pulse signals, absolute encoders require digital communication protocols, such as SSI, BiSS, or Ethernet based systems, to relay position data accurately.

Absolute vs incremental rotary encoders: which one to choose?

Choosing between an absolute and incremental rotary encoder depends on your specific application needs. Here’s a comparison to help guide your decision:

#Table from ‘What are rotary encoders’ page.

the timken encoder range

Our magnetic encoder range includes incremental, and absolute position.

INCREMENTAL ENCODERS

 M9 Miniature Modular Magnetic Encoder

 M11 Miniature Commutating Modular Magnetic Encoder

 M15 Modular Magnetic Encoder

M15H High Resolution Modular Magnetic Encoder

MPS160 Multiplying Encoder ASIC

 MPS512 Multiplying Encoder ASIC

M15 Modular Encoder 15 Pin Cables

ABSOLUTE POSITION ENCODERS

 100MM High Resolution Absolute Position Magnetic Encoder

80MM High Resolution Absolute Position Magnetic Encoder

 61MM High Resolution Position Magnetic Encoder *

49MM High Resolution Absolute Position Magnetic Encoder

39MM High Resolution Absolute Position Magnetic Encoder

M15A Modular Absolute Position Magnetic Encoder

* Currently in development