Feb. 06, 2023
If you work with electric motors, then you may have heard the term "limit switch" before. But what exactly is it? What does a limit switch do? Below, we provide a basic overview of what limit switches are, where they are used and how to use them.
Limit switches are used to automatically detect or sense the presence of an object, or to monitor and indicate whether the movement limits of that object have been exceeded. As the name implies, the original purpose of a limit switch was to define the limit or end point at which an object could move before it stopped. It is at this point that the switch is engaged to control the travel limit.
TZ-8108 Adjustable Roller Lever Limit Switch
In most cases the limit switch starts to operate when a moving machine or a moving part of a machine comes into contact with the actuator or operating lever that initiates the switch. The limit switch then regulates the circuit that controls the machine and its moving parts. These switches can be used as guides for the control circuits of magnetic starters, allowing them to start, stop, slow down or speed up the function of the motor. Limit switches can be installed into machinery as control instruments for standard operation or as emergency devices to prevent mechanical failure. Most switches are either maintained contact or momentary contact models.
Step1 Mounting: Securely mount the limit switch in a position where it will come into contact with the object whose movement you want to detect. Make sure it is properly aligned and securely fastened to prevent movement during operation.
Step2 Wiring: Connect the limit switch to a power source and the device or circuit you want to control. Typically, limit switches have two or more terminals for electrical connections. Consult the manufacturer's instructions or datasheet to determine the appropriate wiring configuration for your specific application.
Step3 Adjustment: Some limit switches allow you to adjust the position of the actuator or the sensitivity of the switch to customize its operation. Follow the manufacturer's instructions to make any necessary adjustments based on your specific requirements.
Step4 Testing: Test the limit switch to ensure that it functions correctly. Manually move the object or mechanism that the limit switch is intended to detect, and observe the response of the switch. It should activate (or deactivate) as the object reaches the predefined position or threshold.
Step5 Integration: Integrate the limit switch into your overall system or control circuit. Depending on the application, the limit switch may be used to stop or start a motor, control the movement of a mechanical arm, activate an alarm, or trigger other actions based on the position of the object it detects.
Step6 Maintenance: Regularly inspect and maintain the limit switch to ensure proper operation. Clean the switch and its surroundings to remove any debris or obstructions that could interfere with its function. Replace any worn or damaged components as needed to prevent malfunctions.
By following these steps, you can effectively use a limit switch to detect the position or movement of objects in various industrial, commercial, or residential applications.
The control schematic for limit switches usually shows a limit switch symbol to indicate the status of the switch contacts. The most common contact symbols indicate whether the device has a normally open or normally closed limit switch contact. The "normally open held closed" symbol indicates that the contacts have been wired as normally open contacts, but that part of the machine holds the contacts closed when the circuit enters its normal closed state. Similarly, a limit switch designated as "normally closed held open" will have a closed wiring design but will remain open. Other types of contacts, such as those used in pressure and flow switches, can be configured in a similar way.
Miniature limit switches or microswitches are another type of limit switch commonly found in control circuits. These switches are much smaller than standard switches and can therefore be installed in tight spaces where other switches are normally inaccessible. Microswitches usually have an actuating plunger that can be moved only a short distance to trigger a contact sequence. The actuating plunger is usually located at the top of the microswitch and must be pressed a predetermined amount before it can be activated. Since the spring loading mechanism causes the moveable contact to move rapidly between alternate positions, a small movement is all that is required to change the contact position. Microswitches can be designed to have a range of different activation arms.
Very similar to micro limit switches, ultra-compact micro switches are intended for applications requiring compact design and limited space availability. They have a similar contact arrangement with a spring loaded mechanism to microswitches, but are often one-half to one-quarter the size of a normal microswitch. Depending on the particular model, the electrical ratings of the contacts of the subminiature switches range from approximately 1 to 7 amps due to the reduced size of the switch itself.
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