Different Types Of Door Limit Switches And Their Methods Of Testing

In the world of engineering, a door limit switch is a switch that is operated by the motion of a machine part or by the presence of an object. Door limit switches are used to control pieces of machinery as a part of a control system, as a safety interlock, or for counting objects passing through a point. A good example of a door limit switch can be a refrigerator, where a door limit switch is used to check whether the door of the fried is opened or closed. As when you open the door of a refrigerator a light pops up, this is because of a door limit switch.

For better understanding, we can take another example of the garage door opener, as a limit switch prevents a garage door to crash into the ground and also limits the opening of the door to an extent while sliding upwards.

What are the different types of Door Limit Switches?

There are namely 4 different kinds of door limit switch namely:

• Whisker
• Rollers
• Plunger, and
• Lever

This switch gets combined with two of its general categories for example roller-lever, depending on the customer’s requirement.

The testing of a Door Limit Switch :

To test a door limit switch we usually use three methods as follows:

1. The preferred method by Philip Armstrong (Test method 1) — Here connects a digital voltmeter across the two connections of the limit switch, with the furnace in full operation. The voltage drop should be less than or maximum to 0.1 VDC. If the voltage is dropped to 0.2 VDC, then the switch should immediately get suspected.
2. Using an Ohmmeter (Test method 2) — When the two leads are shorted together, the verification of Ohmmeter will read to “0” or between “0” and “0.1” Ohms. Remove or disconnect the wires and then connect an Ohmmeter set to the lowest possible range across the switch. Further, depress or release the snap action surface of the switch a dozen or so times. With every press, the switch should go from open to close with each being a reliable 0.1 Ohms or less than that.
3. Using a battery-operated continuity tester (Test method 3) — The continuity tester comes with a built-in battery and lamp, this is the one we used that has two AA cells and when the batteries are new, the current that passes through the switch have about 0.29 Amps. When the continuity tester is connected across the limit switch, the light should be as bright as when the continuity tester leads are shorted together. The test light method is the least preferred procedure for testing because a minute variation with the light is hard to detect than the variation with a meter.

These are the three methods of testing a door limit switch.

There are many leading manufacturers of door limit switch in India like JIGO India, BCH Electric Limited, Salzer, to name a few. These companies will provide you with the perfect door limit switches as per your requirement.