Limit Switch Explained - What it is, How it works & How it is used in Manufacturing
Limit Switch Explained - What it is, How it works & How it is used in Manufacturing
Beginner
A limit switch is an electro-mechanical device used to send an electrical signal based on a physical interaction. Limit Switches are used to detect the presence of objects, thus allowing the system to take desired action.
Limit Switches can be found in a number of everyday devices:
Countless limit switches are found in manufacturing. They are used as control devices and safety devices for machinery and personnel. In all cases, the limit switches will send a digital signal to the control system. Based on the hardware and software tied to said switches, the system is able to take appropriate action.
Limit switches are an inexpensive way to create a link between the physical and electrical domains. They have been developed a number of decades ago and the mass adoption of their use significantly lowered their cost for the end user. They thus play an important role in manufacturing due to their simplicity and low cost.
Limit switches can be classified into four main types based on the type of actuator:
In addition to the type of actuator, limit switches can also be classified by their electrical configuration. The two most common electrical configurations are:
Some limit switches also have a double throw (DPDT) electrical configuration, which means that they have two sets of electrical contacts, one NO and one NC. When the actuator is activated, the NO contacts close and the NC contacts open.
Limit switches are available in a wide variety of sizes, shapes, and materials to meet the specific needs of different applications. They are also available in a variety of electrical ratings, so that they can be used to control a wide range of loads.
Here are some examples of how different types of limit switches are used in real-world applications:
Limit switches are a versatile and reliable way to control and monitor machines and processes. They are used in a wide variety of industries, including manufacturing, construction, agriculture, and transportation.
As discussed above, a limit switch is used to translate a change in mechanical state into an electrical signal. How does the device actually accomplish that?
A limit switch is a simple device. The lever is used to close a contact within the switch. When the contact is closed, it allows the electrical signal to go through. The mechanical operation is similar to that of a light switch. However, a spring is added to return the limit switch into its original position.
The critical parameter of a limit switch is at which point it closes the contact within. This parameter will vary between switch types as well as brands. It is important to verify the datasheet to confirm this position. It will influence the system design that will utilize the limit switch.
As discussed previously, once the actuator is displaced a certain distance, the switch is made. At this point, it needs to transmit a signal to an electrical device which may be a Programmable Logic Controller (PLC), relay, control circuit, or an additional limit switch. A limit switch is similar to a relay in the sense that it can be purchased in one of the following configurations:
There is an argument to be made for either configuration. However, when it comes to limit switches being used for safety purposes, it’s always advised to have current circulating in “resting state”. This is important as during a problem in the circuit, the safety should trigger. Should it be set to no-power in the “resting state”, the circuit may fail to prevent injury or damage.
In this section, we’re looking at the Allen Bradley 801 General Purpose Limit Switch configurations. Below, you’ll find the “Contact Arrangement” provided by the manufacturer. Let’s review each section in detail
A - Normally Open (NO) limit switch symbol.
B - Normally Closed (NC) limit switch symbol.
AC - Alternating Current Ratings for light duty limit switches at different voltage levels. It is important to remember that although your application may require a switch to operate within a 24VDC circuit, it’s possible to use these across multiple industries in which voltage level standards are different.
DC - Direct Current Ratings for light duty limit switches.
C - Normally Open (NO) and Normally Closed (NC) set of contacts on a single limit switch.
H - Dual Normally Open (NO) and Normally Closed (NC) set of contacts on a single limit switch.
N - Dual Normally Open (NO) set of contacts on a single limit switch.
O - Dual Normally Closed (NC) set of contacts on a single limit switch.
In the first example of a limit switch we had reviewed, there was a single position at which the switch would trigger the signal. In this case, there are two points at which the signals will be different. These signals can be picked up in discrete logic, but most commonly, this would be done using a PLC. A PLC programmer can utilize such a limit switch to detect a difference between a partial and a full limit switch closure.
Position of Lever = OFF
Position of Lever = Partially Closed
Position of Lever = Fully Closed
Until now, we’ve talked about limit switches that would actuate the same one way or the other. This is the case for most general purpose limit switches. However, it is possible to detect if the switch was pushed in one way or the other through the interlock present in the differential location limit switch. The operation will be as follows.
Position of Lever = OFF
Position of Lever = Closed to the Left
Position of Lever = Closed to the Right
The Normally Closed (NC) variation of the previous switch will operate as follows. The only difference is the state of the contacts in the “Off” position.
Position of Lever = OFF
Position of Lever = Closed to the Left
Position of Lever = Closed to the Right
This variation of a limit switch features four contacts. Two of these contacts can be used as Normally Open (NO) connections and two other as Normally Closed (NC).
Current ratings for regular duty limit switches. Note that these ratings are higher than the ones found in Section 1.
A limit switch is an electromechanical device that consists of an actuator mechanically linked to an electrical switch. When the actuator is moved by an object, it causes the electrical switch to open or close, depending on the type of limit switch.
There are two main types of limit switches: normally open (NO) and normally closed (NC). An NO limit switch is open when the actuator is not activated, and closes when it is activated. An NC limit switch is closed when the actuator is not activated, and opens when it is activated.
Limit Switch | How Does a Limit Switch Work - Example of a Mechanical Limit SwitchLimit switches are used in a wide variety of applications, such as:
Here is a simplified explanation of how a limit switch works:
Here is an example of how a limit switch is used in a real-world application:
A conveyor belt is used to transport products from one area of a factory to another. A limit switch is installed at the end of the conveyor belt to detect the presence of products. When a product reaches the end of the conveyor belt, it activates the limit switch. The limit switch then sends a signal to a controller, which stops the conveyor belt. This prevents the product from falling off the conveyor belt.
A limit switch used in manufacturing is rated for hundreds of thousands of cycles. However, there are various flavors of this device that aren’t as robust for other everyday applications.
Elevator systems commonly require limit switches for a variety of purposes by building codes. They are used for position detection, safety and operational state of the elevator. The types used in this application are rated for an even greater number of cycles as they constantly experience actuator movement through the life of the system.
Limit Switches are used in everyday appliances: fridges, tea kettles, mixers, washers, dryers and more. The limit switches in these appliances are the same in principle, but different in reliability. In other words, they operate the same, but may fail much faster then their manufacturing counterparts.
Using a basic ohmmeter or Digital Multimeter (DMM), it’s possible to determine whether or not a limit switch is bad. Disconnect the limit switch from the system and apply the ohmmeter leads to each terminal. If the limit switch is normally open (NO), the resistance should be very high. If it’s normally closed (NC), the resistance should be close to zero. Toggle the limit switch into the active position and measure the resistance. It should be the opposite in this setting. If the transition does not occur, the limit switch is bad.
Limit Switches are used in a wide array of applications across the production floor as well as our daily lives. A limit switch is one of the most basic mechanical / electronics components on a production floor. They are used for object detection and machine / personnel safety. The limit switch will send a signal to a control circuit once it is in a certain position. Although the function is straight-forward, a wide range of flavors of such switches exist in order to provide flexibility to the end user. In a real-world example, we’ve looked at the datasheet that specifies multiple functions for general purpose allen bradley limit switches.
The following graph indicates the relationship between operating force and stroke or stroke and contact force. In order to operate the Limit Switch with high reliability, it is necessary to use the Limit Switch within an appropriate contact force range. If the Limit Switch is used in the normally closed condition, the dog must be installed so that the actuator will return to the FP when the actuator is actuated by the object. If the Limit Switch is used in the normally open condition, the actuator must be pressed to 80% to 100% of the OT (i.e., 60% to 80% of the TT) and any slight fluctuation must be absorbed by the actuator.
Beginner
A limit switch is an electro-mechanical device used to send an electrical signal based on a physical interaction. Limit Switches are used to detect the presence of objects, thus allowing the system to take desired action.
Limit Switches can be found in a number of everyday devices:
Countless limit switches are found in manufacturing. They are used as control devices and safety devices for machinery and personnel. In all cases, the limit switches will send a digital signal to the control system. Based on the hardware and software tied to said switches, the system is able to take appropriate action.
Limit switches are an inexpensive way to create a link between the physical and electrical domains. They have been developed a number of decades ago and the mass adoption of their use significantly lowered their cost for the end user. They thus play an important role in manufacturing due to their simplicity and low cost.
Limit switches can be classified into four main types based on the type of actuator:
In addition to the type of actuator, limit switches can also be classified by their electrical configuration. The two most common electrical configurations are:
Some limit switches also have a double throw (DPDT) electrical configuration, which means that they have two sets of electrical contacts, one NO and one NC. When the actuator is activated, the NO contacts close and the NC contacts open.
Limit switches are available in a wide variety of sizes, shapes, and materials to meet the specific needs of different applications. They are also available in a variety of electrical ratings, so that they can be used to control a wide range of loads.
Here are some examples of how different types of limit switches are used in real-world applications:
Limit switches are a versatile and reliable way to control and monitor machines and processes. They are used in a wide variety of industries, including manufacturing, construction, agriculture, and transportation.
As discussed above, a limit switch is used to translate a change in mechanical state into an electrical signal. How does the device actually accomplish that?
A limit switch is a simple device. The lever is used to close a contact within the switch. When the contact is closed, it allows the electrical signal to go through. The mechanical operation is similar to that of a light switch. However, a spring is added to return the limit switch into its original position.
The critical parameter of a limit switch is at which point it closes the contact within. This parameter will vary between switch types as well as brands. It is important to verify the datasheet to confirm this position. It will influence the system design that will utilize the limit switch.
As discussed previously, once the actuator is displaced a certain distance, the switch is made. At this point, it needs to transmit a signal to an electrical device which may be a Programmable Logic Controller (PLC), relay, control circuit, or an additional limit switch. A limit switch is similar to a relay in the sense that it can be purchased in one of the following configurations:
There is an argument to be made for either configuration. However, when it comes to limit switches being used for safety purposes, it’s always advised to have current circulating in “resting state”. This is important as during a problem in the circuit, the safety should trigger. Should it be set to no-power in the “resting state”, the circuit may fail to prevent injury or damage.
In this section, we’re looking at the Allen Bradley 801 General Purpose Limit Switch configurations. Below, you’ll find the “Contact Arrangement” provided by the manufacturer. Let’s review each section in detail
A - Normally Open (NO) limit switch symbol.
B - Normally Closed (NC) limit switch symbol.
AC - Alternating Current Ratings for light duty limit switches at different voltage levels. It is important to remember that although your application may require a switch to operate within a 24VDC circuit, it’s possible to use these across multiple industries in which voltage level standards are different.
DC - Direct Current Ratings for light duty limit switches.
C - Normally Open (NO) and Normally Closed (NC) set of contacts on a single limit switch.
H - Dual Normally Open (NO) and Normally Closed (NC) set of contacts on a single limit switch.
N - Dual Normally Open (NO) set of contacts on a single limit switch.
O - Dual Normally Closed (NC) set of contacts on a single limit switch.
For more information, please visit Small Roller Lever Actuator Limit Switch.
In the first example of a limit switch we had reviewed, there was a single position at which the switch would trigger the signal. In this case, there are two points at which the signals will be different. These signals can be picked up in discrete logic, but most commonly, this would be done using a PLC. A PLC programmer can utilize such a limit switch to detect a difference between a partial and a full limit switch closure.
Position of Lever = OFF
Position of Lever = Partially Closed
Position of Lever = Fully Closed
Until now, we’ve talked about limit switches that would actuate the same one way or the other. This is the case for most general purpose limit switches. However, it is possible to detect if the switch was pushed in one way or the other through the interlock present in the differential location limit switch. The operation will be as follows.
Position of Lever = OFF
Position of Lever = Closed to the Left
Position of Lever = Closed to the Right
The Normally Closed (NC) variation of the previous switch will operate as follows. The only difference is the state of the contacts in the “Off” position.
Position of Lever = OFF
Position of Lever = Closed to the Left
Position of Lever = Closed to the Right
This variation of a limit switch features four contacts. Two of these contacts can be used as Normally Open (NO) connections and two other as Normally Closed (NC).
Current ratings for regular duty limit switches. Note that these ratings are higher than the ones found in Section 1.
A limit switch is an electromechanical device that consists of an actuator mechanically linked to an electrical switch. When the actuator is moved by an object, it causes the electrical switch to open or close, depending on the type of limit switch.
There are two main types of limit switches: normally open (NO) and normally closed (NC). An NO limit switch is open when the actuator is not activated, and closes when it is activated. An NC limit switch is closed when the actuator is not activated, and opens when it is activated.
Limit Switch | How Does a Limit Switch Work - Example of a Mechanical Limit SwitchLimit switches are used in a wide variety of applications, such as:
Here is a simplified explanation of how a limit switch works:
Here is an example of how a limit switch is used in a real-world application:
A conveyor belt is used to transport products from one area of a factory to another. A limit switch is installed at the end of the conveyor belt to detect the presence of products. When a product reaches the end of the conveyor belt, it activates the limit switch. The limit switch then sends a signal to a controller, which stops the conveyor belt. This prevents the product from falling off the conveyor belt.
A limit switch used in manufacturing is rated for hundreds of thousands of cycles. However, there are various flavors of this device that aren’t as robust for other everyday applications.
Elevator systems commonly require limit switches for a variety of purposes by building codes. They are used for position detection, safety and operational state of the elevator. The types used in this application are rated for an even greater number of cycles as they constantly experience actuator movement through the life of the system.
Limit Switches are used in everyday appliances: fridges, tea kettles, mixers, washers, dryers and more. The limit switches in these appliances are the same in principle, but different in reliability. In other words, they operate the same, but may fail much faster then their manufacturing counterparts.
Using a basic ohmmeter or Digital Multimeter (DMM), it’s possible to determine whether or not a limit switch is bad. Disconnect the limit switch from the system and apply the ohmmeter leads to each terminal. If the limit switch is normally open (NO), the resistance should be very high. If it’s normally closed (NC), the resistance should be close to zero. Toggle the limit switch into the active position and measure the resistance. It should be the opposite in this setting. If the transition does not occur, the limit switch is bad.
Limit Switches are used in a wide array of applications across the production floor as well as our daily lives. A limit switch is one of the most basic mechanical / electronics components on a production floor. They are used for object detection and machine / personnel safety. The limit switch will send a signal to a control circuit once it is in a certain position. Although the function is straight-forward, a wide range of flavors of such switches exist in order to provide flexibility to the end user. In a real-world example, we’ve looked at the datasheet that specifies multiple functions for general purpose allen bradley limit switches.
The following graph indicates the relationship between operating force and stroke or stroke and contact force. In order to operate the Limit Switch with high reliability, it is necessary to use the Limit Switch within an appropriate contact force range. If the Limit Switch is used in the normally closed condition, the dog must be installed so that the actuator will return to the FP when the actuator is actuated by the object. If the Limit Switch is used in the normally open condition, the actuator must be pressed to 80% to 100% of the OT (i.e., 60% to 80% of the TT) and any slight fluctuation must be absorbed by the actuator.
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