What is the primary purpose of a limit switch in a machine control system?

• A. To regulate voltage.
• B. To provide a position signal by changing contact state when a moving part reaches a set location.
• C. To detect electrical faults.
• D. To measure current.

Answer: (B)

A limit switch is used to convert a moving part’s physical position into an electrical signal. When the part reaches a predetermined location, the switch changes its contact state—either opening or closing the circuit—providing a clear, discrete signal to the control system. This signal is used to stop, start, or sequence actions, and to implement safety interlocks, ensuring the machine knows exactly when a part has reached its limit. That positional sensing is the key purpose, and it’s why this type of switch is common in end-of-travel applications and automated sequencing. The other options aren’t about detecting position: regulating voltage is the job of power regulators, detecting electrical faults is done by protection devices, and measuring current is done by ammeters or current sensors.