- Limit switches are electromechanical devices that detect the presence or absence of an object or the operational limits of machinery, ensuring they don’t go beyond pre-set limits.
- There are four basic types of limit switches: whisker, lever, roller plunger, and plunger type, each serving a specific purpose.
- Limit switches consist of three basic parts: the actuator with an operating head, the switch mechanism, and a series of electrical terminals.
- They are incredibly versatile and can be used in various applications, such as assembly lines, elevators, and even closet lighting.
Have you ever wondered how an elevator knows when to slow down and stop on each floor? Or how your garage doors know when to stop instead of disconnecting from the tracks? It’s all a courtesy of ingenious little devices known as limit switches.
And what are they exactly, you might ask. Well, in this article, we’ll discuss the different types of limit switches. However, before we do, we’ll provide a short introduction. So, without further ado, let’s dive right in.
What Are Limit Switches?
Limit switches are electromechanical devices that are operated by a physical force applied to an object. They’re mostly used to detect the presence or absence of an object or the operational limits of various machinery, thus ensuring they don’t go beyond their pre-set limits.
In simpler terms, the limit switch is operated by the motion of a machine part or the presence of an object. They typically consist of a mechanical actuator, such as a plunger or a lever, which is linked to a series of electrical switches.
When an object actuates the mechanical lever, it forces the switch’s electrical contacts to open or close its electrical connection. Thus, it’s safe to say that limit switches use mechanical force to change the normal operating state of the switch.
4 Types of Limit Switches
There are four basic types, based on their actuator or operating hand — the part that comes into physical contact with another object. Depending on the type of the actuator, the limit switch translates either rotary, linear, or perpendicular motion into switch actuation.
It’s also worth noting that there are more than just four different types of limit switches. However, regardless of their type, all are derived from these four basic ones.
Whisker limit switches, such as the Electrical Buddy ME8169, have a long and fairly strong spring arm that acts as an actuator. Once sufficient force is applied perpendicularly to the spring, it will bend and actuate the switch.
This type of switch is typically used in conveyors and various assembly lines, where they’re usually used to monitor the flow and placement of transported elements.
It’s also worth noting that whisker switches typically actuate at 360°. If you need actuation in one plane, use a typical rod lever or a roller lever limit switch.
If you need a highly responsive limit switch that actuates in one place, the Electrical Buddy ME8104 lever is a good choice. These typically have a lever mounted on a rotating shaft that acts as a limiter. Once the lever has rotated around the shaft to a certain limit, the switch will actuate.
Lever limit switches have a very quick response time, which makes them perfect for shutoffs or triggering signals. This makes it suitable for use in elevators, lifts, door-open switches, and so on.
They come in different varieties, and some feature an adjustable lever length. Others might have a roller at the end of the lever to reduce friction.
3. Roller Plunger
Roller limit switches have a roller on a stationary shaft and are the second most commonly used type of limit switch. They’re designed to transfer the radial force applied by an object to the thrusting force of the plunger. The thrusting movement of the plunger actuates the switch, while the roller is used to reduce friction.
4. Plunger Type
Plunger-type limit switches, such as the Electrical Buddy ME8111, are the most commonly used type. They consist of a plunger that is pushed directly by an object, resulting in electrical switch actuation.
Due to their design, plunger switches require substantially less force to actuate compared to other types. They’re incredibly simple, very durable, quite cost-effective, and incredibly versatile.
A limit switch consists of three basic parts: the actuator with an operating head, the switch mechanism, and a series of electrical terminals. The actuator contains a linear, vertical, or rotary mechanism that’s connected to an operating head.
The operating head transfers an external force exerted by another object into the linear, vertical, or rotary motion of the actuator. The actuator, on the other hand, controls the body switch mechanism. It contains either open or closed electrical contacts, depending on the default state of the switch.
Electrical terminals are connected to the switch and enable wired connections to the circuit, which the limit switch controls. Limit switches are typically exposed to repeated use in manufacturing but also in other applications.
Thus, they have to be reliable and very responsive, which also means that they’re typically made of durable materials. It’s important to note that they vary in size due to their configuration and current rating.
How Do Limit Switches Work?
Let’s say that the whisker switch is used as a counting element in an assembly line. The switch is Normally Open, which means that the current doesn’t flow through the switch when it isn’t mechanically actuated.
Once an object on the conveyor passes next to the switch, it brushes against the spring, which actuates the switch for a brief moment. The current that has passed through the switch will act as a binary signal to the Programmable Logic Controller.
The PLC will then interpret that signal and add one more product to the total product count. Of course, this is an oversimplified explanation of how limit switches work. The intricate details surrounding each specific type differ, but the fundamental function doesn’t change.
This example is just one of their many applications. They are incredibly versatile; for example, you can position them inside your closet so that they power on an LED strip each time you open the closet door.
In the end, limit switches come in a variety of different types, each of which serves a different, specific purpose. However, every type of limit switch is derived from the four basic and commonly used types of limit switches we described above.
The image featured at the top of this post is ©Wongsakorn Napaeng/Shutterstock.com.