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About limit switches
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How do position switches work?
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Design and types of limit switches
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Protection types of limit switches
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FAQ - frequently asked questions about limit switches
How does a position switch work?
A button on the end position switch mechanically registers the position of a moving object. This can be a door or a machine part, for example. The switch then generates a signal that is transmitted electrically and initiates an automatic response in certain events.
Simple limit switches connect and disconnect circuits. For example, when the refrigerator door is opened, an end-position switch can turn on the light or stop a garage door motor when the floor is touching and the door is closed.
In sequence controls, limit switches take over the function of detecting the completion of a work step and initiating the next step in the workflow. For example, you can register a tilted transport container at the end of a conveyor belt and then switch on the packaging line. Complex control processes are implemented in mechanical engineering by means of such functions of the position switches.
Tree shape and types of limit switches
Limit switches can be normally open, normally closed or changeover contacts, which generate a signal for the controller based on a position detection sensor. Position switches are available with several operating types:
The sensor of the limit switch is often a roller lever. Other limit switches, for example, operate with cable, plunger, spring rod or mechanical levers to register the movement and convert it into a shift operation.
Special subgroups of the limit switches are:
- Pull-pull switches are actuated manually by pull. Common applications of cable pull switches are the starting of machines or the closing or opening of electrically driven barriers, doors and gates.
- Safety switches are electromechanical equipment for closing or disconnecting circuits. They are used to protect people or to protect machinery against external influences. They often have a separate actuator for mechanically recording, evaluating and initiating a switching process for defined events.
Our practical tip: Emergency stop switch
Emergency stop switches are always designed as NC contacts to ensure wire break safety. This means that the system is stopped immediately if a wire break occurs in an off function and a restart is not possible on the affected component before repair.
Protection types of limit switches
Limit switches are often used to secure process sequences and should therefore be protected against external influences.
There are protection types for electronic equipment that are defined in both DIN EN 60529 and ISO 20653:2013. IP codes are English for International Protection or Ingress Protection (protection against intrusion).
Example: A limit switch with degree of protection IP65 is therefore dust-proof and completely protected against contact and offers protection against jet water from any angle (Figure 3).
FAQ - frequently asked questions about limit switches
Are limit switches programmable?
No. But they can be connected by wiring to a programmable logic controller.
Can ich find light barriers and motion detectors in the limit switches?
No. Limit switches are electromechanical components while light barriers use optical detection mechanisms. Motion detectors are also usually addressed optically rather than mechanically. In this respect, you can find the light barriers and motion detectors in our shop under the sensors for the active components.
What was to be ich when using position switches with metal housing?
Metal enclosure limit switches are popular for use in harsh operating environments. In order to ensure contact security, such a housing must be ground at all times!