Limit Switches

Limit switches are devices designed to detect the presence, proximity or absence of an object and to indicate if the movement of the object has exceeded preset limits. Electromechanical limit switches require physical contact to detect the presence of an object, while solid state limit switches can use electric switches, proximity sensors or light sensors to detect an object.

Electromechanical limit switches contain a mechanical actuator connected to a series of electrical contacts. When an object comes into physical contact with the actuator, the movement results in the electrical contacts within the switch to open (for a normally closed circuit) or close (for a normally open circuit) their electrical connection. In an industrial setting, the limit switch begins operating when a moving component of a machine makes contact with an operating lever (or other actuator) that activates the switch. The limit switch then regulates the electrical circuit that controls the machine. They can be used to control standard operations or used as emergency devices to prevent malfunction. They can also be used to start, stop, slow down or accelerate the functions of an electric motor when used as a pilot device for magnetic starter control circuits.

Limit switches can be chosen based on the style of actuator, the object travel orientation and the type of movement. The two most common actuator styles are rotary lever and plunger-type. Rotary levers use lever actuator arms that, when activated, rotate a shaft to operate the switch contacts. Plunger-type actuators can include a roller plunger, lever plunger or metal plunger. They can detect very small machine motion and offer a smaller factor form than rotary lever actuators.