Glossary · Sensors and measurement
Limit switch
Also known as: Position switch, Mechanical limit switch
German: Endschalter
In industrial automation, a limit switch is an electromechanical switch actuated by a moving machine part, usually through a plunger, roller or lever, that signals when a defined position or end of travel is reached.
- Sensors
- Standards
In one sentence
A limit switch is a mechanically actuated switch that signals when a machine part reaches a defined position or the end of its travel.
Example
Limit switches at both ends of a gantry axis stop the drive before the carriage hits the mechanical end stops.
How it applies
- Engineering: Limit switches are robust and simple. Variants with positive opening contacts (direct opening action) force the contacts open mechanically, which is a key property for safety-related use.
- Safety: Whether a limit switch contributes to a safety function depends on the design of the whole function, including fault detection and the control architecture. The switch alone does not make a function safe. Guard interlocking devices are covered by ISO 14119.
- Maintenance: Worn rollers and loose cams change the switching point. Include function checks in maintenance plans.
- Documentation: Distinguish operational limit switches from overtravel or safety limit switches in circuit diagrams and manuals.
Limit switch vs. proximity sensor
A limit switch requires contact and wears mechanically, but its switching state is directly tied to the actuator position. A Proximity sensor works without contact and is suited to high switching frequencies.