Technical Foundation
What Is a Rotary Encoder?
A rotary encoder converts the angular position or rotational speed of a shaft into an electrical signal a control system can read, using an optical, magnetic, or capacitive sensing element inside the housing. Incremental encoders output a pulse train (commonly quadrature A/B channels, sometimes with an index Z pulse) that a counter tracks to determine relative position and direction — the count resets to an unknown state on power loss, so the system needs a homing routine at startup. Absolute encoders instead output a unique digital code for every shaft position, so the true position is known immediately on power-up without homing.
Resolution — pulses per revolution (PPR) for incremental, or bits of resolution for absolute — determines positioning precision, while output protocol (quadrature, SSI, BiSS, various fieldbus formats) must match what the controller expects. Shaft configuration matters mechanically: solid-shaft encoders couple to a motor or machine shaft via a flexible coupling that must accommodate minor misalignment, while hollow-shaft encoders mount directly over the motor shaft, eliminating coupling alignment issues but requiring the shaft diameter to match precisely.
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| Spec | What It Means | Why It Matters |
|---|---|---|
| Encoder Type | Incremental (pulse output) vs. absolute (unique position code) | Absolute encoders retain true position through power loss; incremental encoders require re-homing |
| Resolution | Incremental in PPR (e.g. 1024, 2500); absolute in bits (e.g. 12-bit = 4096 positions) | Higher resolution gives finer position/speed feedback but generates more data for the controller to process |
| Output Signal/Protocol | Quadrature TTL/HTL, SSI, BiSS, various fieldbus (e.g. EtherCAT) | Must match the controller's supported input protocol exactly, or the signal can't be read |
| Shaft Configuration | Solid shaft with flexible coupling, or hollow/through-bore shaft | Hollow shaft eliminates coupling misalignment but must match the mating shaft diameter precisely |
| Supply Voltage | Commonly 5V, 10-30V DC | Must match the control system's available supply voltage and output driver compatibility |
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Applications
Where Rotary Encoders Get Used
Rotary encoders are specified anywhere a control system needs precise, reliable feedback on shaft position, direction, or rotational speed.
Servo Motor Position Feedback
Encoders mounted on servo motor shafts providing closed-loop position and velocity feedback to drives.
CNC Machine Axis Positioning
High-resolution encoders on machine tool axes enabling precise, repeatable positioning control.
Robotics & Automated Assembly
Absolute encoders on robot joints retaining true position through power cycles without re-homing.
Conveyor & Material Handling Speed Control
Incremental encoders providing speed feedback for synchronized conveyor line control.
Elevator & Hoist Positioning
Absolute encoders tracking car or hoist position reliably, critical where power-loss recovery matters.
Packaging Machinery Synchronization
Encoders synchronizing multiple axes of motion on high-speed packaging and labeling equipment.
FAQ
Rotary Encoders Questions, Answered
What's the difference between an incremental and absolute rotary encoder?
An incremental encoder outputs a pulse train that a controller counts to track relative position and direction, but that count is lost on power interruption, requiring the system to re-home before it knows true position again. An absolute encoder outputs a unique digital code for every shaft position, so the controller reads true position immediately on power-up with no homing routine needed — at a generally higher cost than an equivalent incremental unit.
How do I choose the right resolution for my application?
Resolution should be matched to the positioning precision your application actually needs, not maximized arbitrarily — a higher PPR or bit-count encoder generates proportionally more data the controller must process at a given speed, which can strain fast control loops unnecessarily. Calculate the required resolution from your minimum meaningful position increment and add reasonable margin, rather than defaulting to the highest resolution available.
Solid shaft or hollow shaft — which mounting style should I use?
A hollow (through-bore) shaft encoder mounts directly over the motor or machine shaft, eliminating the alignment concerns of a separate coupling, and is the preferred choice when the mating shaft diameter matches available bore sizes. A solid-shaft encoder uses a flexible coupling to connect to the machine shaft, which accommodates some misalignment but requires careful coupling selection and installation to avoid introducing measurement error or premature bearing wear.
Why does output protocol matter beyond just the resolution number?
The output protocol — quadrature TTL/HTL, SSI, BiSS, or a specific fieldbus format — has to match exactly what your controller or drive is built to read, since a mismatched protocol simply won't communicate regardless of how well the resolution and mechanical fit suit the application. Confirm your controller's supported encoder interface before specifying the encoder's output type.
What happens to an incremental encoder's position count during a power outage?
The pulse count an incremental encoder relies on for relative position tracking is lost the moment power is interrupted, so after power is restored the system doesn't know true position until it runs a homing routine — typically driving to a known reference point or limit switch. This is the main practical reason applications where power-loss recovery matters, like elevators or robots that can't afford to re-home, specify absolute encoders instead.
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