Which device measures position or rotation in a mechanical system?

• A. VFD
• B. PLC
• C. Breaker
• D. Encoder

Answer: (D)

Measuring position or rotation relies on a sensor that turns motion into a readable electrical signal. An encoder is that device. When mounted on a shaft, it generates pulses as the shaft turns. By counting those pulses, the control system can determine how far something has rotated or how far it has moved linearly. There are two common types: incremental encoders, which track relative motion by counting pulses from a reference point, and absolute encoders, which provide a unique position value even after power loss. This makes encoders ideal for precise position feedback in motors and automation systems.

A variable frequency drive controls motor speed and torque, not position measurement. A PLC is a controller that processes inputs and controls outputs, though it can read encoder signals as part of a control loop. A breaker is a protective device that interrupts current; it doesn’t measure position. So the encoder is the device that directly measures position or rotation.