A limit switch is an electromechanical unit that consists of an actuator that is connected mechanically to the set of contacts.

The limit switch performs the Contacts to make or break an electrical connection mean.. NO/NC.

As the object or target contacts the operator of the switches, it eventually moves the actuator to the “limit” where the contacts change state. 

In a Normally Closed (NC) circuit, this mechanical action opens the electrical contacts and in a Normally Open (NO) circuit, it closes them. The contacts then start or stop the flow of current in the electrical circuit. 

Electrical Limit Switch

Mechanical switches consist of a mounted actuator arm that operates a set of electrical contacts when the arm is dislocated.

Limit switch failures are generally mechanical in nature.

Principle

Automatic operation of a machine requires the use of limit switches that can be activated by the motion of the machine.

A limit switch is used to convert this mechanical motion of the machine to an electrical signal to switches circuits.

The operating position of the Limit Switch is where the limit switch changes from its normal (NO or NC) to its operating state.

The release position is where the contact change from their operating state to their normal state.

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[1]. Limit Switch :- Lever Type

Working of Lever type switch

A lever type crane limit switch works on the principle of a lever attached to a rotating central shaft.

When the moving machinery comes in contact with the lever, the central shaft of the lever rotates ,thereby rotating the coaxial cams which connect or disconnect the electrical contacts.

The rotation of the shaft can be spring returned to its stable normal position.

The length of the lever type crane switch depends on the mounting position of the NO/ NC switch enclosure and the moving crane which needs to stop.

[2]. Limit Switch :- Push Type

The push type switch in the above figure, the contact gets operated from the depression of the contact lever arm.

Based on the type of motion, limit switches are classified as 

1. Rotary motion
2. Linear motion

Advantages

[1] High current capability.
[2] Low cost
[3] Familiar with low technological sensing.

Disadvantages

[1] Wear and tear
[2] Requires physical contact with the target.
[3] Chances of contact bounce.
[4] The response is slow compared with non-contact sensors such as proximity sensors.

Applications

[1] Plant automation or machinery Interlocking applications.
[2] Limit switches are often used in machine tools to limit the travel of a machine axis.
[3] Used in materials handling applications, to indicate the passage of material from one platform to another.
[4] Used in overhead cranes.
[5] Used in control panels to control the lighting.