Limit Switch Explained | Working Principles

Summary

This video by RealPars introduces viewers to limit switches, highlighting their common presence in everyday life and work environments. Limit switches are electromechanical devices that operate by the physical force applied by an object, detecting its presence or absence. The video details the different types of limit switches—whisker, roller, lever, and plunger—and explains their functions and configurations. Through relatable examples like fridge doors and garage doors, the video illustrates how these switches work. Despite being replaced in some industrial applications by proximity sensors, due to the latter's lack of moving parts, limit switches remain valued for their robustness and ability to handle high current values.

Highlights

• Limit switches are ubiquitous in daily life and workplaces. 🌍
• They come in four types: whisker, roller, lever, and plunger, with combinations like roller-lever. ⛓️
• Their roles span applications like detecting open fridge doors or garage doors. 🚪
• Despite newer tech, limit switches are still preferred for their durability in harsh environments. 🏗️

Key Takeaways

• Limit switches are everywhere! They're likely sneaking around your home or workplace, making things tick smoothly. 🕵️‍♂️
• Four cool types: whisker, roller, lever, and plunger. They're like the fabulous four of the electromechanical world! 🔄
• Despite new tech trends, limit switches remain the tough cookies of the sensor world, handling high currents with ease. 💪

Overview

In the bustling world of electromechanical devices, limit switches have carved a niche for themselves. These little gizmos are present in almost every corner of our daily lives, from the refrigerator light that flicks on when you get a midnight snack, to ensuring your garage door doesn't slam shut. They're the unsung heroes keeping our everyday mechanisms operating smoothly.

Limit switches are categorized into four main types: whisker, roller, lever, and plunger. They are marvels of simple engineering, working tirelessly to detect the presence or absence of objects. Whether you're dealing with a fridge door or the complex workings of an assembly line, these switches ensure everything functions as it should.

Even as proximity sensors start to take over many industries, limit switches stand strong due to their reliability and capability to handle higher current levels. They might be old school, but they're tough and dependable, especially in challenging conditions. If you're intrigued and want to explore further, diving into the world of sensors is your next adventure!

Chapters

• 00:00 - 00:30: Introduction to Limit Switches This chapter introduces the concept of limit switches, devices commonly encountered in daily life either at home or in the workplace. There are four general types of limit switches: whisker, roller, lever, and plunger. Additionally, some applications may require a combination of these types, such as a roller-lever switch.
• 00:30 - 01:00: Basic Functionality of Limit Switches The chapter introduces the basic functionality of limit switches, which are electromechanical devices used to detect the presence or absence of an object. It explains that these switches operate by physical force exerted by an object and were originally named 'Limit Switch' because they defined the limit of travel of an object.
• 01:00 - 01:30: Home Applications of Limit Switches The chapter explains the application of limit switches in home appliances like refrigerators and garage doors. It describes how a limit switch is used to turn on the light inside a refrigerator when the door is opened, and how another application of limit switches is to stop the movement of overhead garage doors when they reach their fully opened position.
• 01:30 - 02:00: Detailed Limit Switch Mechanism The chapter titled 'Detailed Limit Switch Mechanism' provides an in-depth look at limit switches, which are electromechanical devices. These devices consist of an actuator mechanically linked to an electrical switch that changes states (makes or breaks an electrical connection) when contacted by an object. The chapter explains that limit switches can be configured in several ways, including Normally Open, Normally Closed, or with one configuration of each.
• 02:00 - 02:30: Electrical Schematics and Microswitch The chapter discusses the different ways electrical schematics represent limit switches according to two main standards: the International Electrotechnical Commission (IEC) and the National Electrical Manufacturers Association (NEMA). It also provides insights into the internal workings of a microswitch, detailing how it consists of two limit switches operating in tandem.
• 02:30 - 03:00: Circuit Operation Example The chapter titled 'Circuit Operation Example' discusses the configuration and operation of a single pole double throw (SPDT) switch used in a circuit. It explains that one limit switch is normally open while the other is normally closed, and they share a common terminal. These switches are mechanically connected and operate simultaneously. The chapter uses the example of connecting a microswitch to a lamp circuit, where in the inactive state, the Red lamp is illuminated.
• 03:00 - 04:00: Industrial Applications and Proximity Sensors This chapter discusses the industrial applications of limit switches and proximity sensors. It begins by explaining the basic operation of these devices, highlighting how they activate when a trigger is pushed, which subsequently turns on a green lamp. The chapter encourages the reader to think of various real-world applications where they might have encountered such devices, such as in assembly lines where a limit switch is operated by a container or by rotating machine parts.
• 04:00 - 04:30: Ruggedness and Advantages of Limit Switches Limit switches are mechanical devices used in various industrial applications to count objects or determine positions, such as those of hydraulic cylinders. However, their usage is declining, with proximity sensors becoming popular replacements due to their electronic switching capabilities and lack of moving parts.
• 04:30 - 05:00: Conclusion and Further Resources This chapter discusses the durability and reliability of limit switches compared to proximity sensors, especially in challenging environments. It highlights the capability of limit switches to handle higher current values. The chapter suggests exploring further resources on proximity sensors in an additional video.

Limit Switch Explained | Working Principles Transcription

• 00:00 - 00:30 In this video, we're going to introduce you to a device called a Limit Switch. There’s probably not a day that goes by where you don’t use or encounter a limit switch at home, or at your workplace. There are 4 general types of limit switches: whisker, roller, lever, and plunger. Depending on the application, a limit switch may be a combination of 2 of the general types such as roller-lever.
• 00:30 - 01:00 OK….let’s get started. A limit switch is an electromechanical device operated by a physical force applied to it by an object. The limit switch is used to detect the presence or absence of an object. These switches originally used to define the limit of travel of an object, and as a result, they were named "Limit Switch".
• 01:00 - 01:30 When you open the fridge door, a light comes on inside? How does that happen? Yes….you guessed it! A limit switch is used to detect if the fridge door is open or closed. Let’s look at another application of a limit switch that you may encounter at home. On many overhead garage doors, there is a limit switch that stops the movement of the door when it reaches its fully opened position. Alright….now that we’ve looked at a couple of limit switch applications
• 01:30 - 02:00 where you might see them in action at home, let’s have a closer look at the device itself. A limit switch is an electromechanical device 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. Limit switches are available in several switch configurations: Normally Open, Normally Closed, or one of each.
• 02:00 - 02:30 Depending on the origin of the electrical schematic, you may see limit switches drawn in different ways. The International Electrotechnical Commission or IEC and the National Electrical Manufacturers Association or NEMA have slightly different symbols. Let's have a look inside a microswitch that is a type of limit switch. A microswitch has 2 limit switches operating together
• 02:30 - 03:00 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, or commonly referred to as SPDT. The dashed line indicates that both switches are mechanically connected and will operate at the same time. Alright, let's connect the microswitch to a lamp circuit. In the inactive state, the Red lamp is on
• 03:00 - 03:30 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. 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 action. For example, you might see a limit switch operated by a container on an assembly line, or operated by a rotating machine part
• 03:30 - 04:00 or by any number of other moving mechanical objects. A limit switch could be used to count passing objects, or determining the position of a hydraulic cylinder. Limit switches are slowly starting to disappear from many industrial applications. They are 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.
• 04:00 - 04:30 Limit switches will not completely disappear any time soon as they outshine their proximity switch counterpart in their ruggedness and reliable operation in difficult environments. Generally speaking, limit switches are capable of handling much higher current values than proximity sensors. If you want to learn more about proximity sensors and other types of sensors check out our other video called
• 04:30 - 05:00 “What is a Sensor? Different Types of Sensors, Applications”. You can find the link to this video in the description. OK… let’s review what we’ve covered in this video… There are 4 general types of limit switches: whisker, roller, lever, and plunger. A limit switch is an electromechanical device operated by a physical force applied to it by an object.
• 05:00 - 05:30 A limit switch is an electromechanical device consisting 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.
• 05:30 - 06:00 Want to learn PLC programming in an easy to understand format and take your career to the next level? Head on over to realpars.com