Glossary term
Encoder
A sensor or device that converts position, angle, speed, displacement, or another state into an electrical, optical, magnetic, or digital signal.
Definition
deviceA sensor or device that converts position, angle, speed, displacement, or another state into an electrical, optical, magnetic, or digital signal.
Encoders provide feedback for motion control, robotics, machine tools, drives, vehicles, and instrumentation. Their useful performance depends on resolution, accuracy, repeatability, latency, signal integrity, mounting, reference strategy, and environmental robustness.
An encoder converts mechanical or physical state into a signal that a controller or measurement system can read. In motion systems, the measured state is usually position, angle, displacement, or speed. Encoders may be rotary or linear, incremental or absolute, optical, magnetic, capacitive, inductive, or mechanical.
Engineering role
Encoders are central to closed-loop control because they tell the controller what the machine actually did. They are used in servo motors, robot joints, elevators, machine tools, printers, CNC axes, vehicles, gimbals, medical equipment, and test rigs. Poor encoder selection or installation can make a good actuator and controller perform badly.
Incremental and absolute encoders
Incremental encoders produce pulses as motion occurs. Position is inferred by counting pulses from a reference or home point. Quadrature encoders use two phase-shifted channels to determine direction and improve resolution. Absolute encoders report position directly, often through a digital word or serial protocol, so they can know position after power-up without homing.
Specification
Important specifications include resolution, accuracy, repeatability, maximum speed, output format, index pulse, latency, jitter, electrical interface, environmental sealing, shock and vibration rating, and allowable misalignment. Resolution is not the same as accuracy: a device can report many counts per revolution while still having systematic angle error.
Installation
Mechanical mounting strongly affects performance. Shaft eccentricity, runout, bearing play, coupling compliance, thermal expansion, contamination, cable noise, and grounding can introduce errors or missed counts. In safety-related systems, engineers may use redundant encoders, plausibility checks, or diverse sensing principles.
Common mistakes
Common mistakes include choosing resolution without checking accuracy, ignoring maximum edge rate at high speed, and routing encoder cables near noisy motor leads without shielding or differential signalling. Another error is relying on incremental position after power loss without a reliable homing or reference procedure.