Encoder
Gives precise position or speed feedback by producing pulses (or a coded value) as a shaft turns.
What it is
An encoder reports how far and how fast a shaft has turned, giving a control system precise feedback for positioning and speed control.
How it works
An incremental encoder produces a stream of pulses as it rotates; counting the pulses gives position, and their rate gives speed. An absolute encoder outputs a unique coded value for each shaft position, so it knows where it is even after a power cycle.
Encoders are sensitive to cable damage and electrical noise — both corrupt the counts. A slipping coupling makes the feedback disagree with reality.
Where it's used
Servo and motion systems, precise speed control, and position feedback on drives. Pulses-per-revolution (PPR) and encoder type must match the controller's configuration.
Related faults
Encoder feedback fault (position/speed wrong)
Position or speed feedback from an encoder is wrong — counts drift, position is lost, or a drive faults on encoder loss, so motion control misbehaves.
VSD powered up but won't start the motor
The drive is energised and the display is alive, but it won't run the motor. No fault may be shown — it just sits in 'ready' or 'stopped' and ignores the start command.
Sensor intermittent / drops out randomly
A sensor works most of the time but drops out or false-triggers intermittently, causing random stops, miscounts, or sequence faults that are hard to pin down.
Related definitions
VSD (Variable Speed Drive)
Controls the speed of an AC motor by converting the supply to a variable frequency and voltage.
Induction motor
The workhorse AC motor — a rotating magnetic field in the stator drags the rotor around with it.
Proximity sensor
Detects the presence of a target without contact — inductive, capacitive, or photoelectric.
PLC (Programmable Logic Controller)
An industrial computer that reads inputs, runs a program, and drives outputs to control machinery.