Which sensor type senses metallic objects by induction?

• A. Inductive proximity sensor
• B. Capacitive sensor
• C. Photoelectric sensor
• D. Magnetic reed switch

Answer: (A)

Inductive proximity sensing works by creating an alternating magnetic field with a coil inside the sensor. When a metal object comes into that field, eddy currents are induced in the metal. Those currents generate their own magnetic field, which disturbs the original field and changes the coil’s impedance. The sensor detects this change and switches its output, signaling that a metal object is present. This noncontact method is specifically suited to metals and is robust in dirty or harsh environments.

Capacitive sensors detect changes in capacitance caused by nearby materials, including nonmetals, so they aren’t limited to metals. Photoelectric sensors use light to detect objects, not metal induction. Magnetic reed switches respond to a magnetic field; they’re triggered by magnets or electromagnets, not by metal objects entering an induction field.