Absolute vs Incremental Encoders? Differences between Absolute and Incremental Encoders

Absolute vs Incremental Encoders: What is the real difference

Encoders all do the same core job. They convert mechanical motion into electrical signals that a controller can interpret as position, speed, and direction. The key distinction between absolute encoders and incremental encoders is the way they represent position information, and what happens when power is interrupted.

Incremental encoders, position as change

An incremental rotary encoder does not output a unique position value. Instead, it produces a stream of pulses as the shaft turns. The control system counts these pulses to track movement from a known starting point. Many incremental encoders provide two pulse channels (often called A and B) with a phase offset, which lets the controller determine both speed and direction. Some also include a reference pulse (often called an index) that can be used as a repeatable marker once per revolution.

This approach is efficient and widely used, but it creates a dependency. The controller must maintain a count to know position. If power is lost, the count is lost unless it is stored elsewhere. After power returns, the system typically needs a homing or referencing step to recover the true mechanical position.

Absolute encoders, position as a value

An absolute rotary encoder provides a position value directly. Internally, it uses a coded disc and a sensor to generate a distinct pattern for each shaft angle. Because each position corresponds to a unique code, the encoder can report the shaft angle immediately.

This becomes most visible during power interruptions. If power is removed and the shaft moves while the system is off, an absolute encoder does not rely on any remembered pulse count. When power is restored, it reports the current shaft position straight away based on the code currently detected.

Absolute encoders are often selected when the application cannot tolerate uncertainty at start-up, or when any unintended motion could create a safety or quality risk.

Practical implications in real machines

The choice is usually not about “better” or “worse”. It is about the required behaviour of the machine.

With an incremental encoder, the system is excellent at tracking motion continuously, but it needs a known reference state. With an absolute encoder, the system gains immediate position knowledge after power-up, which can simplify start-up logic and improve fault recovery.

In safety-relevant motion systems, such as lifts, hoists, automated gates, robotics, and critical axes in industrial automation, absolute encoders are commonly preferred because they reduce reliance on homing routines and lower the chance of starting from an incorrectly assumed position.

How to choose quickly

If the application requires a reliable position value immediately after power-up, or if safety and fault recovery are primary drivers, an absolute encoder is usually the more suitable option.

If the application primarily needs speed and direction feedback, has a controlled homing sequence, or prioritises simplicity and cost, an incremental encoder often fits well.