An inductive proximity sensor uses the principle of which to sense metal objects?

• A. Capacitance
• B. Resistance
• C. Inductance
• D. Voltage

Answer: (C)

Inductive proximity sensors sense metal objects through changes in inductance caused by eddy currents in the metal. The sensor has a coil that creates a magnetic field; when a metal object enters that field, eddy currents are induced in the metal and produce their own opposing magnetic field. This interaction alters the coil’s inductance and disturbs the oscillator or sensing circuit, which the electronics detect and then produce a switching output.

Capacitance would involve changes in a dielectric or the distance to a non-metal object, not metal itself. Resistance and voltage are not the fundamental sensing mechanisms for detecting nearby metal in this type of sensor.