Inductive proximity switch
An inductive proximity switch (initiator, proximity switch, proximity sensor, position sensor ) is a sensor that can detect metallic (electrically conductive) objects without contact when approached .
A binary signal, "Object recognized / not recognized", is made available.
Structure and functionality
An inductive proximity switch mainly consists of three functional units: an oscillator , an evaluation unit and an output stage. As soon as a supply voltage is applied to the inductive proximity switch, the oscillator begins to oscillate. The resulting electromagnetic field is directed forward to the active surface by means of a ferrite core (half a pot core ), in which the coil of the oscillator's resonant circuit is located. An approaching object or an actuating element removes energy from the resonant circuit, whereupon the oscillator voltage decreases. The downstream comparator detects this and controls the output switching amplifier at the set switching distance or vibration level. For the functional principle, see also metal detector .
Reduction factor
Inductive proximity switches have reduction factors for metals that differ from the reference material (usually iron or ST37). For example, the switching distance for brass is reduced to approx. 40%, i.e. brass has a reduction factor of 0.4. In order to avoid this, so-called factor 1 sensors have been developed which have the same switching distances for different metals.
Designs
The size ranges from cylindrical sensors with a diameter of 3 mm to square sensors with an edge length of 180 mm. The outputs are potential-free mechanical switching contacts , transistor outputs (PNP, NPN or push-pull output ). There are also variants with a fieldbus interface . Devices with an analog output (0/4… 20 mA) see inductive distance sensor .
The switching distance of inductive proximity switches is physically limited by the range of the field. Large sensor designs have large switching distances. For applications in road traffic, see also induction loop .
Systematization
The rated switching distances for all types of inductive proximity switches - except for slot and ring-shaped designs - are defined by EN 60947-5-2.
IEC 60947-6-1 applies to low-voltage switchgear.
application
The area of application for the inductive proximity switch includes industries such as machine and plant engineering , factory automation , the automotive industry , storage and conveyor technology , packaging technology , the printing and paper industry and chemical and process engineering, as well as road traffic.
See also
Individual evidence
- ↑ http://www.maschinenmarkt.vogel.de/reduktionsffekt-1-sensoren-detektieren-völker-metalle-mit-gleichem-schaltstange-a-65232/ magazine Maschinenmarkt May 10, 2007