When it comes to motion control and automation, the precise location and movement of the turning shaft are very important. This is where in comes rotary encoders. These powerful, small-sized devices find broad application in the robotics industry, industrial machinery, and automation systems since they do the role of converting mechanical action into digital representation.
Rotary encoders can be of two kinds: absolute and incremental. Although they might appear similar on the surface, they are highly differentiated in regard to the purpose they are made to suit your system needs.
In this paper, we are going to discuss the main distinction between absolute and incremental rotary encoders and assist you in seeing which one is more appropriate to use depending on the application you are going to use it for.
What Are Rotary Encoders?
Rotary encoders are electromechanical devices that convert the angular position or motion of a shaft or axle into digital signals. These signals are sent to control systems like PLCs, microcontrollers, or servo drives to monitor and control movement.
Rotary encoders are commonly used in:
- CNC machines
- Robotics and automation
- Electric motors
- Elevators and conveyor systems
- Printing and packaging equipment
There are two primary categories of rotary encoders: absolute and incremental. Let’s break down each one.
What Is an Absolute Rotary Encoder?
An absolute rotary encoder assigns a unique digital code to every position on its rotating shaft. This means it can report the exact shaft position immediately after powering on—without requiring movement or calibration.
How It Works
The encoder has a disk with multiple concentric tracks. Each track represents a bit of binary code. Light sensors (in optical encoders) or magnetic sensors (in magnetic encoders) read the position of these tracks to determine the shaft’s exact angular position.
There are two subtypes:
- Single-turn absolute encoders: Track position within one 360° rotation
- Multi-turn absolute encoders: Track total rotations as well as shaft position.
Key Benefits
- Immediate position data on startup
- No need for homing or recalibration
- Retains position during power loss (non-volatile)
- Ideal for safety-critical applications
What Is an Incremental Rotary Encoder?
An incremental rotary encoder provides relative position data. It outputs a series of pulses as the shaft rotates, which are counted by the control system to determine speed, direction, or position relative to a starting point.
How It Works
It uses a disk with evenly spaced slots or lines. As the disk spins, it passes between a light source and a sensor, generating electrical pulses. These pulses are interpreted as movement. The direction is determined by comparing two output signals (A and B channels), and some encoders have a third signal (Z channel) to mark the reference position.
Key Benefits
- High resolution and fast response
- Simpler design and lower cost
- Perfect for tracking speed and motion
- Compact and widely compatible with control systems
Key Differences Between Absolute and Incremental Rotary Encoders
Feature
Absolute Rotary Encoder
Incremental Rotary Encoder
Position after power-up
Immediate, accurate position
Unknown until a reference is set
Data retention
Maintains position even after power loss
Loses position without continuous power
Signal output
Unique binary value per position
Continuous pulse stream
Setup complexity
More complex installation
Easier to integrate
Cost
Higher
Lower
Application focus
Precision, safety, multi-turn tracking
Speed, direction, and relative positioning
When to Choose an Absolute Rotary Encoder
Absolute rotary encoders are the best fit when your system needs to remember its position at all times, even after a power outage. They’re especially suited for safety-sensitive or mission-critical systems where restarting and recalibration are not acceptable.
Ideal Use Cases
- Industrial robots
- Medical imaging systems (CT or MRI machines)
- Satellite tracking equipment
- Assembly line automation
- Solar panel tracking systems
These environments demand high reliability, precision, and continuous awareness of position—all of which absolute rotary encoders offer.
When to Choose an Incremental Rotary Encoder
Incremental encoders are great when relative motion is all you need and cost or simplicity is a concern. They’re ideal for tracking speed, distance moved, or rotation direction without needing to know the exact angular position on startup.
Ideal Use Cases
- Electric motor feedback systems
- Packaging and labeling machinery
- Conveyor belts
- Fan and pump speed control
- Robotics with predefined movement patterns
Because of their fast response time and affordability, incremental rotary encoders are widely used in high-volume manufacturing and real-time control systems.
Factors to Consider When Choosing Between the Two
Before choosing between absolute and incremental rotary encoders, ask yourself:
- Do I need an exact position on startup?
- Can I afford downtime for recalibration after power loss?
- Is my system safety-critical?
- What is the budget for the encoder?
- How complex is the installation environment?
- Do I need to track multiple rotations or just one?
Your answers will determine whether precision and reliability (absolute) or speed and simplicity (incremental) are more important for your application.
Conclusion
Both absolute and incremental rotary encoders are essential tools in motion control systems. The best choice depends on your system’s needs:
- Choose absolute rotary encoders if you need accurate, power-independent position tracking and high reliability.
- Choose incremental rotary encoders if your focus is on cost, speed, and simplicity.
By understanding the key differences and practical applications of each type, you’ll be better equipped to build a smarter, more reliable automation system.
