In brief
An inductive proximity sensor is a non-contact proximity switch that detects metal objects by means of a high-frequency alternating electromagnetic field.
Contents
What is Inductive proximity sensor?
An inductive sensor generates an alternating field at its active face. When a metal part approaches, eddy currents arise in it that draw energy from the oscillator; the electronics evaluate this damping and switch the output. Because it works without contact and without moving parts, it is resistant to dirt, oil and vibration and is suitable for position detection on machines, end positions or speed monitoring. Typical applications are end-position detection on cylinders, cam detection and counting metal parts on conveyors.
Key ratings are the rated sensing distance, the housing style (cylindrical with thread or rectangular), flush or non-flush mounting, output type (PNP, NPN, normally closed or normally open, analogue), supply voltage, switching frequency and degree of protection. The real sensing distance depends on the material and is usually smaller for non-ferrous metals than for steel. Basic requirements for proximity switches are described in IEC 60947-5-2.
Failures are often caused by mechanical damage, cable breakage or chips on the active face. Inductive sensors are typical wear parts and stock items that can be kept on hand with little effort. For welding applications, versions with a coating against weld spatter and immunity to magnetic fields are used.
In practice: maintenance and procurement
For a replacement, the manufacturer part number or housing style with thread size, sensing distance, mounting type, output type, contact function, voltage and connector are usually sufficient. Where many variants are in use, it is worth standardising on a few standard types.
Synonyms and abbreviations: inductive proximity switch · inductive sensor · proximity sensor · prox switch
Frequently asked questions
What is the difference between an inductive and a capacitive sensor?
An inductive sensor only responds to metal, because it evaluates eddy currents in the object. A capacitive sensor, by contrast, detects changes in an electric field and therefore also responds to plastic, wood, liquids or bulk materials. For pure metal detection, the inductive sensor is usually less susceptible to interference.
What do PNP and NPN mean for sensors?
PNP and NPN describe the type of transistor output. A PNP output switches the positive supply voltage to the output, an NPN output switches to ground. Which variant fits depends on the input card of the controller. When replacing, the output type must match, otherwise the signal will not be recognised.
What information is needed to replace an inductive proximity sensor?
Housing style and size, sensing distance, flush or non-flush mounting, PNP or NPN output type, normally closed or normally open, supply voltage, connection type with connector type and degree of protection are needed. If the manufacturer part number is legible, this is usually sufficient to identify a suitable spare part.