Are Limit Switches Obsolete?


Being the “product guy” for mechanical or limit switches I am often told that I have the obsolete products. Well I am here to say that mechanicals are still around and definitely have their place in automation.

Mechanical switches, at least the ones I deal with, are precision limit switches. How can a mechanical switch be a precise device? These switches use a cam or trip dog and once the switch and cam are secured in the application, the repeatability, with a chisel plunger, can be .002mm – that’s two microns. Applications for these switches include actuators for automatic controls, positioning and end of travel for machine tools, transfer lines, transport equipment, and gantries.

Limit switches are often used for end of travel or in some cases a home position of a machine tool. The advantage these devices offer over a proximity switch is they are more precise and usually have a dry contact or a contact closure that is easily integrated into servo controlled positioning systems or emergency stop strings. In addition, with the multiple position switches you can have up to twelve switches in an industrially rated enclosure in a smaller space than 12 proximity sensors due to the possibility of cross talk.

One of the disadvantages of a limit switch is that they are typically more expensive than a proximity sensor, however they usually are used in conjunction with a DC power supply where mechanical switches do not require an external supply. Moreover, contrary to one engineer’s belief that being a mechanical device they do wear out, he actually said that they should last forever.

Even though they are “old school” consider mechanical switches. They are still a viable solution to some tough applications and environments.

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