Limit switch

Limit switches are used to automatically detect or sense the presence of an object or to monitor and indicate whether the movement limits of that object have been exceeded. The original use for limit switches, as implied by their name, was to define the limit or endpoint over which an object could travel before being stopped. It was at this point that the switch was engaged to control the limit of travel.

A standard limit switch used in industrial applications is an electromechanical device that consists of a mechanical actuator linked to a series of electrical contacts. When an object (sometimes called the target) comes in physical contact with the actuator, the actuator plunger’s movement results in the electrical contacts within the switch to either close (for a normally open circuit) or open (for a normally closed circuit) their electrical connection. Limit switches use the mechanical movement of the actuator plunger to control or change the electrical switch's state. Similar devices, such as inductive or capacitive proximity sensors, or photoelectric sensors, can accomplish the same result without requiring contact with the object. Hence, limit switches are contact sensors in contrast to these other types of proximity sensing devices. Most limit switches are mechanical in their operation and contain heavy-duty contacts capable of switching higher currents than those of alternative proximity sensors.