CAPACITANCE SENSOR

Capacitance Sensor It is based on the capacitance of a parallel plate capacitor. Variable Capacitance type It varying distance between two or more parallel electrodes. Variable area between the electrodes. Variable dielectric constant materials.

Parallel Plate Capacitance Sensor the ability of a substance to store electrical energy in an electric field. Relative permittivity is the factor by which the electric field between the charges is decreased relative to vacuum.

Capacitance Value

Equivalent Circuit of Capacitance Transducer

Parallel plate Capacitive sensor

Serrated Plate Capacitive Sensor

Variable Permittivity or Variable Thickness Dielectric Capacitive Sensor

Advantage Extremely sensitive Good frequency response High input impedance Loading effects are minimum Small forces to operate them use in small systems.

Disadvantage Metallic parts must be insulated each other (reduce the effect of stray capacitances), frame must be earthed. Non linear behavior many a times on account of edge effects. (guard ring used eliminate this effect) Cable connecting the sensor to the measuring point is also a source of error.

Applications Measurement of both linear and angular displacement. Force and pressure Humidity in gases Volume, density, liquid level, weight.