What is the Advantage and Disadvantage of how many types of limit switch

What are Limit switches? Advantages, disadvantages

What are limit switches?

Limit switches are a type of switch featuring a valve that substitutes a traditional button. They operate similarly to Push ON switches, engaging only when the valve is pressed to a specific pressure limit, and disconnecting when the valve is not pressed.

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Limit switches fall into the mechanical sensor category, designed to produce electrical changes in response to mechanical alterations. Typically, these switches are used as position sensors to detect the movement of objects.

Where Limit switches are used?

Limit switches are generally used to make or break a circuit in response to the presence or movement of an object. They are effective in high-power applications with relatively small actuators and are often utilized to sense the position or condition of an object. Their operation involves pressing a button within a predefined boundary or area, causing the circuit to connect or break. There are two critical contact types in a limit switch: NO (Normally Open) and NC (Normally Close), which change state when the button is pressed. The basic construction and symbols can be seen below:

Mechanical limit switches are contact sensing devices widely used for detecting the presence or position of objects in industrial applications.

Advantages of limit switches:

• Suitable for all industrial environments
• Precise accuracy and repeatability
• Energy-efficient
• Capable of switching loads with high inductance
• Can control multiple loads

Limitations of Limit Switches:

• Generally restricted to equipment operating at relatively low speeds.
• Must make direct contact with the target.
• Mechanical parts are prone to wear and tear.

Types of Limit Switches - Principle, Advantages ...

A limit switch is an electromechanical unit that consists of an actuator connected mechanically to a set of contacts. When the moving object comes into contact with the actuator, the switch connects or disconnects the electrical circuit.

Mechanical limit switches feature an actuator arm that alters the state of electrical contacts when displaced. Such failures are typically mechanical.

Principle: Automatic machine operation relies on limit switches, activated by machine movement. These switches convert mechanical motion into electrical signals for circuit switching. The operating position is where the switch transitions from its normal state (NO or NC) to its active state, and the release position is where it returns to its normal state.

Types of Mechanical Limit Switches

1. Lever-type limit switch
2. Push type limit switch

Lever Type Limit Switch

In a lever-type limit switch, the actuating arm is a rod connected to a lever shaft that rotates when displaced. A return spring restores the lever shaft to its normal position. A roller at the bottom operates a rocker, changing position and actuating electrical contacts which might start as either open or closed. When activated, a normally open switch will close and vice versa.

Push Type Limit Switch

The push type limit switch operates through the depression of the contact lever arm.

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

1. Rotary motion
2. Linear motion

Rotary Motion Limit Switch

Rotary motion limit switches activate through shaft rotation. They are ideal for applications requiring frequent adjustment of travel limits, such as overhead cranes for hoisting and lowering.

Linear Motion Limit Switch

Linear motion limit switches detect and respond to linear motion. They offer limited adjustment post-installation by modifying the lever's position.

Limit Switches are used for

• Momentary contact
• Maintained contact

When a target contacts the actuator arm, it triggers a movement from the free position to the operating position, altering the state of electrical contacts. Upon the target's withdrawal, the actuator and contacts return to normal. In specific applications, actuators and contacts must remain in the actuated state until a force is applied to revert them.

Advantages

• High current capability
• Low cost
• Simple, low-tech sensing

Disadvantages

• Wear and tear
• Requires physical contact with the target
• Possible contact bounce
• Slower than non-contact sensors like proximity sensors

Applications

• Plant automation or machinery interlocking
• Limiting machine axis travel in tools
• Material handling, indicating material movement between platforms
• Overhead cranes
• Control panels for lighting

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