Which statement describes the function of a limit switch in automation?

• A. It senses temperature
• B. It provides a signal when a machine part reaches a set position
• C. It measures pressure
• D. It detects light

Answer: (B)

A limit switch is a position-sensing device used to detect when a moving part has reached a predefined position and to send a signal to the control system. When the part makes contact with or comes within the switch’s actuating element, the switch changes its electrical state, triggering the controller to stop, reverse, or advance to the next step. This helps ensure accurate end-of-travel positioning and safe, coordinated operation in automation. It’s not intended to measure environmental conditions like temperature, pressure, or light—those are handled by other types of sensors.