What is an encoder?

An encoder is a feedback device that tells the drive what the motor shaft is doing: position, speed, direction, and motion change.

In closed-loop control, this feedback helps the drive command torque and speed accurately, especially in servo, BLDC, PMSM, robotics, CNC, packaging, and automation systems.

Why are they used?

·    Position feedback

·    Speed measurement

·    Direction detection

·    Closed-loop motor control

1 Incremental feedback

A/B/Z pulse channels show relative motion and direction.

·    Outputs pulses as the shaft moves.

·    Excellent for speed and relative position.

·    Usually needs homing after power loss.

2 Absolute feedback

A unique digital value is assigned to each shaft angle.

·    Knows position immediately after power-up.

·    Useful when homing is slow, unsafe, or impossible.

·    Can be singleturn or multiturn.

Real optical encoder photo

Real absolute encoder photo

Real magnetic/incremental encoder photo

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Start with the function: speed only, position control, safety, or harsh-duty feedback.

1 Optical encoder

Real optical encoder with code disk.

·    Precise speed and position feedback.

·    Coded disk + light sensor.

·    Best for: CNC, robotics, precision servo axes.

·    Environment: clean and dry areas.

2 Magnetic encoder

Real magnetic MiniCoder-style incremental encoder.

·    Robust speed/position feedback.

·    Magnetic target wheel or ring + sensor.

·    Best for: dust, oil, and vibration.

·    Environment: harsh industrial areas.

3 Inductive encoder

Real inductive sensing reference photo.

·    Robust absolute/incremental feedback.

·    Inductive/electromagnetic scanning.

·    Best for: servo drives, robotics, automation.

·    Environment: shock and contamination.

4 Capacitive encoder

Real capacitive encoder principle photo.

·    Compact position and speed feedback.

·    Measures capacitance changes.

·    Best for: compact moderate-precision systems.

·    Environment: moderate dirt/grease if sealed.

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Optical = precision; magnetic/inductive = robustness; capacitive = compact principle-based feedback.

5 Resolver

Real resolver / rotary transformer photo.

·    Purpose: rotor angle and speed feedback.

·    Specificity: electromagnetic analog feedback device.

·    Best for: traction drives, aerospace, heavy-duty motors.

·    Environment: high temperature, shock, vibration.

6 Hall-effect sensors

Real BLDC motor board with Hall sensors.

·    Purpose: simple rotor sector feedback for BLDC commutation.

·    Specificity: normally coarse, low-resolution position.

·    Best for: fans, pumps, simple BLDC drives.

·    Environment: general use where precision is not critical.

Interface

What it carries

Why students should know it

A/B/Z

Incremental pulse channels

Simple, common, low cost

Sin/Cos

Analog sine/cosine signals

Smooth interpolation and fine control

SSI

Serial absolute position

Straightforward point-to-point absolute feedback

BiSS-C

Fast open digital interface

High-speed absolute feedback

EnDat

Digital position + parameters + diagnostics

High-end servo feedback and diagnostics

HIPERFACE DSL

Digital motor feedback over one cable

Reduces cabling in servo systems

Student tip: When reading a motor datasheet, check both the feedback technology and the interface. A high-resolution encoder is only useful if the drive can read its signals correctly.

Page 3                                                         The encoder is not only a sensor; it is part of the drive-control system.