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Selection of Electro-mechanical Limit Switches

Posted by Phillip Warwick

Apr 3, 2014 2:26:21 PM

Limit switches are used to convert a mechanical motion into an electrical control signal. The mechanical motion is usually in the form of a comma machine component, or an object moving toward a predetermined position. The cam engages the limit switch lever or plunger and this in turn makes or breaks an electrical contact inside the switch. This electrical control signal is then used to limit position or reverse the machine travel, or to initiate another operating sequence. It can also be used for counting, sorting or as a safety device. 

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Typical limit switch applications are in the control circuits of solenoids, control relays and motor starters which control the motion of machine tools, conveyors, hoists, elevators and practically every type of motor driven machine. 

Experience has shown that most limit switch failures are the fault of the installation. In some cases an installation that is not perfect cannot be avoided, but in the majority of cases, proper application of the limit switch would have prevented failure.

When selecting a limit switch, there a some key things to keep in mind:

  1. What is the voltage and current that you want to switch?
  2. How many contacts?
    1. Normally Open?
    2. Normally closed?
  3. What is the environment?
    1. Relatively clean?
    2. Dusty, dirty, smoky, wet, hot, cold, etc?
  4. How close can you get to the target?
  5. Where can you mount it?
  6. What is best way to activate the switch? 
    1. Lever type
    2. Plunger type
    3. Cat whisker
    4. Other

I found a useful resource that expounds on this subject. Take a look at this video:  http://www.youtube.com/watch?v=igg2LKPurd8.

There are several general categories or classifications of limit switches on the market, the most common are electromechanicalswitches, non-contact proximity switches and photoelectric switches. Because electro-mechanical switchesare suitable for the vast majority of applications and are generally the most economic to use, the electro-mechanical limitswitch should be the first choice. This application section will deal predominantly with the proper application of electromechanicallimit switches.

Selection of the proper electro-mechanical limit switch for an application generally breaks down into two major decisions, choosing the proper actuator (lever) and choosing the proper enclosure. There are other considerations, such as whatoperating sequences are available, temperature rating and electrical rating. These vary from switch type to switch type.

Selection of Limit Switch Actuator – Selection of a suitable actuator depends on the shape, speed, direction and totaltravel of the cam or part being used to trip the limit switch and the accuracy desired.

I hope you found this article helpful. Please contact me if you have any additional questions or a specific application need.

Topics: NAMCO, Power Generation, Limit Switch, Utilities, SNAP-LOCK

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Written by Phillip Warwick

Phillip has a long history with Danaher Specialty Products. In his most recent role as Applications Support, he is the SME on all things that time and count for Eagle Signal and Veeder-Root. He's no stranger to supporting our other brands as well. You'll find he's always willing to help!

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