Limit Switch Uses : what is the use of limit switch & how to use limit switch
When it comes to automation, machines, and industrial control, precision and safety go together like bread and butter. One of the most basic and important pieces of equipment in this process is the limit switch. Even though it is a small piece of equipment, a limit switch is a very important tool that controls the movement of machines, prevents damages, and ensures the safety of the operators. In this guide, you will learn about what a limit switch is, applications of a limit switch, and how to use a limit switch.
What Is a Limit Switch?
Limit switch is basically a switch device that can detect the existence, non-existence, or the position of the object. Limit switch converts the physical movement into electrical signal. Limit switch basically comprises of actuators like levers, rollers, or plungers that are coupled to the electrical circuit mechanically. When the actuators get triggered due to physical contact with the moving object, the electrical circuit gets either opened or closed.
Unlike the proximity sensor, which operates by non-contact detection, the limit switch works by physical contact with the moving object.
What Is the Use of a Limit Switch?
Mainly, the use of a limit switch is the supervision and stopping of a machine’s movement at a specific point. In the movement of the machine, the moving part will strike the actuator of the limit switch once it reaches the specific point. An operation will then be performed that will start, stop, reverse, or alter the operation of the machine. These are the various uses of limit switches:
1. Machine Position Control
Limit switches are commonly employed in industrial equipment to monitor the position of moving parts of the equipment. It helps prevent any part of a machine from going out of its required range of movement.
2. Safety Interlocks
Limit switches work as safety interlocks in industrial equipment, where doors, guards and other safety devices are fitted with a limit switch which shuts off electrical supply to a machine when the door or safety device is opened.
3. Elevator and Lift Systems
Limit switches are essential for the smooth functioning of elevator and lift systems where it detects the location of the cabin in the shaft at each level of the building.
4. Conveyor Systems
Limit switches are installed in conveyor belts that detect the presence of an object at certain points on the belt to perform a number of operations including stopping, diverting and packing.
5. Garage Doors and Gate Automation
Automated garage doors and gates have limit switches which sense the position of the doors and gates (open or closed), and thereby de-energize the motor to prevent any sort of damage.
6. Industrial Automation and Robotics
In industrial automation and robotics, limit switches allow the robot or actuator to know whether it has achieved the end of its cycle.
7. Hydraulic and Pneumatic Systems
A limit switch may be applied in connection with a cylinder in either the hydraulic or pneumatic system to know where the piston is located.
8. HVAC and Fluid Level Control
Limit switches may also be utilized in HVAC applications and tanks for measurement of fluid levels and air damper locations.
Types of Limit Switches
Before learning how to use a limit switch, it helps to understand the common types available:
- Lever / Roller Type – Uses the principle of the lever which has a roller attached to its end; works well when detecting objects moving in a horizontal position.
- Plunger Type – Works with vertical force; useful for on/off operation only.
- Whisker / Wobble Stick Type – Flexible rod which may be tripped from different angles.
- Roller Lever with Adjustable Arm – Allows flexibility in mounting.
How to Use a Limit Switch
Being aware of how to operate a limit switch will ensure that the switch functions effectively and has a good lifespan. Here is an overview on how it works:
Step 1: Identify the Application Requirement
To be able to determine what limit switch is ideal for your needs (leverage switch or plunger/ roller switch), you have to determine the movement or position that is needed.
Step 2: Choose the Right Limit Switch
Select a limit switch based on criteria such as type of actuator, contacts normally open or normally closed, electrical ratings and environment (dust, moisture, temperature)
Step 3: Mount the Switch Securely
Install the limit switch at the particular location where you want the triggering event to take place. It must be installed properly to prevent any vibration induced misalignment of the limit switch, which leads to erroneous operations.
Step 4: Adjust the Actuator Position
Adjust the position of the actuator (lever, roller or plunger) so that there is an accurate contact between the actuator and the moving part. Most of the limit switches have adjustable arms and/or plungers for adjustment purposes.
Step 5: Wire the Switch to the Control Circuit
Wiring of the electrical contacts of the limit switch to your control system (PLC, relay, motor controller etc.). It is necessary to use the right terminals for normally open (NO) or normally closed (NC) operation.
Step 6: Test the Operation
The limit switch can now be triggered manually to test its operation.
Step 7: Perform Regular Maintenance
Due to mechanical wear and tear, the performance of limit switches can get affected over a period of time. Inspection and maintenance are needed on regular basis to check actuator, contacts and wiring for wear and tear and loose connections and replacement of the switch if necessary.
Why Limit Switches Remain Essential in Modern Automation
Although modern technology offers such types of devices as proximity switches, photoelectric sensors, and encoders, limit switches continue to be widely used because of their simplicity, strength, and affordability. Limit switches work successfully under any conditions – in dusty, vibrating, and highly heated environment when other electronic sensors may not function properly.
Although the limit switch itself is a tiny element, its role in industrial automatization processes, safety equipment, and mechanisms used in our everyday life is crucial. Knowing the application of the limit switch and how to operate it properly is useful for designing effective and reliable system. It is just a little thing to install a proper limit switch on your belt conveyor, elevator, robot arm, or automatic gate.
Frequently Asked Questions (FAQs)
1. What is the purpose of a limit switch?
A limit switch is used to sense the position or movement of the moving part of a machine and send a signal controlling, stopping or reversing the functions of machines once it gets into the predetermined position.
2. What is the difference between a limit switch and proximity switch?
Limit switches require physical contact to provide an output, but a proximity switch does not require physical contact since it uses the principles of magnetic, capacitive or inductive sensing to detect the presence of an object.
3. How do you distinguish the normally open from normally closed limit switch?
This can be determined by the data sheet and/or wiring diagram of the limit switch. The normally open limit switch maintains an open circuit until it senses the object, whereas normally closed limit switch maintains a closed circuit until it senses the object.
4. Are limit switches used outside?
Yes, there are various types of limit switches with waterproof enclosures and thus suitable for outdoor use.
5. What is the life span of limit switches?
Lifespan differs from one type to another, but generally, industrial limit switches last from hundreds of thousands to even millions of cycles in normal circumstances.
6. What are the reasons behind a limit switch failure?
The common reasons are wear out of the switch components such as the actuator due to vibration, corrosion of contacts, lack of alignment due to vibration, moisture in non-enclosed limit switches, and wear out resulting from continuous cycles.
7. Can limit switches be connected to a PLC?
Yes, limit switches can be used with PLCs, and the switch is wired directly to the PLC input module.
8. How can you adjust the sensitivity of a limit switch?
The sensitivity can be set by moving the actuator arm or the plunger, or by using a model having an adjustable roller lever.
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