A capacitive proximity sensor uses the principle of what to sense objects?

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

Answer: (C)

Capacitive proximity sensors rely on changes in capacitance caused by the nearby object altering the electric field around the sensing electrode. The electrode and the object form a capacitor, and as the object approaches, the effective dielectric between the plates increases, raising the capacitance. The sensor’s electronics detect this change (often by a shift in oscillation frequency or charging time) and signal when the object is close enough. This non-contact method is distinct from inductive sensing, which uses magnetic fields to detect metal objects, resistance-based sensing that needs a current path, or reflectivity-based sensing that relies on light.