Which sensor type detects metallic objects at greater distances than nonmetallic objects?

• A. Capacitive proximity sensor
• B. Inductive proximity sensor
• C. Photoelectric sensor
• D. Ultrasonic sensor

Answer: (A)

Capacitive sensing works by detecting changes in the electric field around the sensor as objects come near. It responds to both metals and nonmetals, but the amount of field disturbance—and thus the detectable change in capacitance—is typically larger for metallic objects than for nonmetallic ones. That stronger perturbation lets the sensor pick up metals at a greater distance than it does nonmetals. Inductive sensors are tuned for metal but have relatively short ranges and don’t apply to nonmetals, while photoelectric and ultrasonic sensors rely on light or sound and aren’t inherently biased toward metal over nonmetal in terms of detection distance. So the capacitive proximity sensor best fits the idea of detecting metallic objects at greater distances than nonmetallic ones.