Proximity switches usually sense the presence of a target without physical contact.

• A. True
• B. False
• C. Only for metal targets
• D. Only in an electrical field

Answer: (A)

Proximity switches detect the presence of a target without physical contact by sensing changes in an energy field around the sensor. When a target enters that field, the sensor registers the change and changes its output accordingly. This non-contact operation is why such devices are valued: there’s no wear from touching targets, and switching can be very fast.

There are several sensing technologies that fit this idea. Inductive proximity sensors detect metal targets through a magnetic field. Capacitive sensors respond to changes in capacitance caused by nearby objects, which can be metal or nonmetal. Optical or infrared proximity sensors detect presence by interrupting or detecting reflected light, all without contact.

Because proximity sensing covers metal and nonmetal targets and uses magnetic, electric, or optical methods, it isn’t limited to metal targets or to sensing only via an electrical field.