Capacitive transducers are capacitors that change their capacity under the influence of the input magnitude, which can be linear or angular movement. The capacity of a flat capacitor, composed of two electrodes with sizes a´b, with area of overlapping s, located at a distance δ from each other (in d << а/10 and d << b/10) is defined by the formula
C=ε0 ε s/d
where: ε0=8,854.10-12 F/m is the dielectric permittivity of vacuum;
ε - permittivity of the area between the electrodes (for air e= 1,0005);
S=a.b – overlapping cross-sectional area of the electrodes. The capacity can be influenced by changing the air gap d, the active area of overlapping of the electrodes s and the dielectric properties of the environment.
Capacitive sensors have found wide application in automated systems that require precise determination of the placement of theobjects, processes in microelectronics, assembly of precise equipment associated with spindles for high speed drilling machines, ultrasonic welding machines and in equipment for vibration measurement. They can be used not only to measure displacements (large and small), but also the level of fluids, fuel bulk materials, humidity environment, concentration of substances and others Capacitive sensors are often used for non-contact measurement of the thickness of various materials, such as silicon wafers, brake discs and plates of hard discs. Among the possibilities of the capacitive sensors is the measurement of density, thickness and location of dielectrics.
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