10 Questions You Should to Know about What is a Limit Switch Used For?

1. What is the function of a limit switch?

A limit switch regulates the electrical circuit to control the machine and its moving parts. These switches can be used as pilot devices for magnetic starter control circuits, allowing them to start, stop, slow down, or accelerate the functions of an electric motor.

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2. What is a limit switch used for?

In electrical engineering, a limit switch is a switch operated by the motion of a machine part or the presence of an object. They are used for controlling machinery as part of a control system, safety interlocks, position systems, or for counting objects passing a point.

3. How many types of limit switches are there?

Limit switches are generally composed of five components. The drive mechanism or actuator is an important part of the limit switch and is directly linked to seal performance and operating characteristics. They include plunger, hinge lever, and roller lever. Manufacturers include Omron, Siemens, APT, etc.

4. What is a mechanical limit switch?

A mechanical limit switch is a device used to determine the physical position of equipment. For example, an extension on a valve shaft trips a limit switch as it moves from open to shut or shut to open. The limit switch gives an ON or OFF output that corresponds to the valve position. Normally, limit switches are used to provide full open or full shut indications.

5. Why is the limit switch important?

Limit switches are used in various applications and environments due to their ruggedness, ease of installation, and operation reliability. They can determine the presence or absence, passage, positioning, count, and end of travel of an object.

6. What is the difference between a proximity switch and a limit switch?

A limit switch is an electromechanical device initiated by physical contact of any object using the switch's activator. Proximity switches or sensors are initiated by the physical presence near them, and physical contact is not necessarily required; the distance is the main factor determining their operation.

There’s probably not a day that goes by where you don’t use or encounter a limit switch at home or your workplace.

Types of Limit Switches

There are four general types of limit switches:

1. Whisker

2. Roller

3. Lever

4. Plunger

Depending on the application, a limit switch may be a combination of two of the general types, such as a roller-lever.

What are Limit Switches?

A limit switch is an electromechanical device operated by physical force applied to it by an object. Limit switches are used to detect the presence or absence of an object. These switches were originally used to define the limit of travel of an object, hence the name Limit Switch.

Limit Switch Applications

When you open the fridge door, a light comes on inside. How does that happen? Yes, you guessed it! A limit switch detects if the fridge door is open or closed.

Another application of a limit switch at home is found in many overhead garage doors. A limit switch stops the door's movement when it reaches its fully opened position.

How Do Limit Switches Work?

Now that we’ve looked at a couple of limit switch applications at home, let’s have a closer look at the device itself. Limit switches are electromechanical devices consisting of an actuator mechanically linked to an electrical switch. When an object contacts the actuator, the switch will operate causing an electrical connection to make or break.

Configurations of Limit Switches

Limit switches are available in several switch configurations: Normally Open, Normally Closed, or one of each.

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Symbols of Limit Switches

Depending on the origin of the electrical schematic, you may see limit switches drawn in different ways. The International Electrotechnical Commission (IEC) and the National Electrical Manufacturers Association (NEMA) have slightly different symbols.

Microswitch

Let’s look inside a microswitch, a type of limit switch. A microswitch has two limit switches operating together and sharing a common terminal. One limit switch is normally open, and the other is normally closed. To be technically correct, the switch configuration is Single Pole Double Throw, commonly referred to as SPDT.

The dashed line indicates that both switches are mechanically connected and will operate simultaneously.

Microswitch Simple Circuit

Let’s connect the microswitch to a lamp circuit. In the inactive state, the Red lamp is on as the device is not being operated by an object pushing on the trigger. When the Trigger is pushed, the device will activate, and the Green lamp will come on.

Limit Switches in Action

Now that you’ve seen the limit switch in action, you are probably thinking about some of the applications where you have seen them in use. For example, you might see limit switches operated by a container on an assembly line, by a rotating machine part, or by other moving mechanical objects. Limit switches could be used to count passing objects or determine the position of a hydraulic cylinder.

Proximity Sensor vs. Limit Switch

Limit switches are slowly starting to disappear from many industrial applications and being replaced by proximity sensors. Unlike a limit switch, a proximity sensor has no mechanical moving parts. A proximity sensor performs the switching action with electronic switches. However, limit switches will not completely disappear anytime soon as they outshine their proximity switch counterparts in ruggedness and reliable operation in difficult environments. Generally speaking, limit switches can handle much higher current values than proximity sensors.

You might want to review one of our other articles:

What is a Sensor? Different Types of Sensors, Applications

Summary

OK, let’s review…

– There are four general types of limit switches: whisker, roller, lever, and plunger.

– Limit switches are electromechanical devices operated by a physical force applied to them by an object.

– A limit switch consists of an actuator mechanically linked to an electrical switch.

– Limit switches are available in several switch configurations: Normally Open, Normally Closed, or one of each.

– Depending on the origin of the electrical schematic, you may see limit switches drawn in different ways.

– Limit switches are being replaced by proximity sensors in many applications.

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The RealPars Team

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