Importance

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Abstract

A capacitive force responsive transducer provides a linear relationship between electrical output and input force variations while protecting the sensing diaphragm from damage during extremely high overload forces. In one example differential pressures or forces are applied to opposite sides of a diaphragm interposed between two supporting plates, such that the diaphragm deflects toward one supporting plate and away from the other. Electrodes on opposite sides of the diaphragm are moved oppositely toward or away from facing electrodes on the supporting plates. A fourth order deflection curve machined into both surfaces of the diaphragm assures very linear capacitance variations (l/c) with the input differential pressures. Other electrodes are disposed in positions to provide invariant reference capacitors. At overload differential pressures, the diaphragm surface becomes flat and engages a supporting plate. A method of forming the fourth order 'deflection curve' surfaces into the diaphragm uses a precision flat grinder in combination with fixtures that cause the diaphragm to deflect under internal pressure into the grinding or lapping surfaces. Successive grinding steps remove surface areas of the deflected diaphragm until a flat condition is achieved in the curved surface. On removal of the diaphragm from the fixture and release of internal pressure, the diaphragm assumes a final 'fourth order' shape.

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First Claim