ABB Limit Switches

Limit switches are a contact proximity sensor device that consists of an actuator mechanically linked to a set of output contacts. When an object comes into contact with the actuator, the device operates the contacts to make or break an electrical connection.

Limit Switch Makeup

Limit switches are made up of three key components:

• Actuator Head - The actuator is the part of the switch that makes physical contact with the object. In some limit switches, the actuator is attached to an operating head which translates a rotary, linear, or perpendicular motion to open or close the electrical contacts of the switch.
• Switch Body – The switch body is the component containing the electrical contact mechanism, the contacts within the body open or close the electrical circuit when the actuator is activated.
• Receptacle/Terminals - The component containing the terminal screws or screw/clamp assembly necessary for wiring purposes.

Actuator Types

Limit switches are available with a wide range of actuator types. The type of actuator used can be determined by the mounting position, force required and objects to be detected.

• Rotary Lever - with lever actuators, a cam or plate hits the end of the lever arm which in turn rotates a shaft and operates the contacts in the switch. The rotation may be spring returned (momentary) or maintained.
• Plunger - Plunger types are best where short controlled machine movements are present or where mounting space does not permit a lever type.
• Cat Whisker or Coil Spring – Longer actuators with a coil wire that can be moved/bent in multiple directions. Typically used in conveying applications to count objects as they pass by.
• Forked – Used with maintained contacts, consisting of two roller levers. One roller will trip the switch and when the second is moved to the opposite direction it will reset the switch.