What is a Limit Switch? How does it work?

What is a Limit Switch?

A limit switch is a type of switch used mainly used to detect the pre-defined displacement or movement of any object.

As the name implied, the limit switch is used to define the endpoint or limit over which an object could travel before being stopped. The limit switch engaged to control the travel at this point.


How does a limit switch work?

To better understand the operation of the limit switch, Let’s take some simple examples,

 

Limit Switches installed on the Damper Actuator

limit switch

You can see here limit switches are installed on both upper travel limit and lower travel limit. This will indicate to the operator at the control room about the opening and closing status of the damper as well as limit the travel at this point.

 

Limit Switches installed on the traveling track of trolley

limit switch

Same as the damper actuator here is also limit switches are installed at the left and right endpoint at the traveling track of the trolley. This restricts the trolley travel at right and left endpoints.

Limit switches are used to restrict or limit the mechanical movements and thus used to prevent damage in mechanical equipment. Most limit switches are mechanical in their operation and contain heavy-duty contacts capable of handling higher currents.


Components of a limit switch

The limit switch contains an operating head or arm with a roller, body mechanism, electrical terminals.

Operating Head or Arm ⇒ The operating head or arm is the part of a limit switch that comes in contact with the target. The motion of the target which is either linear, perpendicular, or rotary is directly connected with the operating head which is used to open or close the switch. This is also called an actuator of the limit switch.

Cable Entry ⇒ Maintenance personnel can enter the cable from the cable entry gland which is sealed with a rubber enclosure.

limit switch

Body Mechanism ⇒ The switch body contains the switch contacts mechanism which is operated by the lever or operating head.

Name Plate ⇒ Nameplate contains details like type, contacts, rating, serial number, etc.

limit switch

Electrical Terminals ⇒ The electrical terminals are used to the electrical circuitry used to drive the machine or equipment or PLC to give feedback about the operation.


Selection Criteria

There are several types of limit switches available in the market. User can select the limit switch based on some criteria like,

  • Actuation methods such as lever, plunger, rods, etc.
  • Repeatability
  • Time to operate and reset
  • Force to operate
  • Environment requirements

limit switch wiring

image reference from library.automationdirect.com

You can view different limit switch available in the market and buy it from here.


Advantages or Limitations of Limit Switch

  • Very Simple and Straightforward Design
  • Works well in almost all types of environment
  • High Accuracy and repeatability
  • Rugged and Reliable
  • Heavy-duty electrical contacts

Limit Switches have several limitations like,

  • The limit switch operates on mechanical action, they generally used with equipment that operates on low-speed.
  • They must make physical contact with the target
  • The limit switch has a mechanical design, so they are subject to mechanical wear of fatigue over time.

I hope you like this article what is a limit switch and how does it work? If you have any queries then please comment down below.

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