What are the two types of prox sensors?

• A. Ultrasonic and Optical
• B. Inductive and Capacitive
• C. Magnetic and Capacitive
• D. Inductive and Magnetic

Answer: (B)

Proximity sensing means detecting the presence of nearby objects without making contact. The two fundamental prox sensor types are inductive and capacitive.

Inductive sensors generate a magnetic field with a coil; when a metal object enters that field, the interaction changes the coil’s impedance and the sensor switches. They’re great for metal parts, fast, and rugged, but they don’t sense nonmetals well.

Capacitive sensors form an electrical field between two conductors; any material that changes the dielectric around the sensor—metal or nonmetal—alters the capacitance and triggers the output. They’re versatile for detecting plastics, liquids, powders, and other nonmetals, though they’re more sensitive to environmental conditions.

Ultrasonic and optical sensors also detect presence or distance, but they do so by measuring sound or light under different principles, not by the field-based proximity methods described above.