Force responsive transducer

Abstract

A differential capacitive force responsive transducer provides a substantially linear relationship between transducer output and input variations. A pressure or load to be measured is applied to one surface of a deflectable diaphragm, the opposite surface of which includes at least a pair of electrodes at different positions, such that when the diaphragm flexes there is a differential deflection of the electrodes. A substantially rigid electrode-bearing plate is secured to the electrode-bearing face of the diaphragm by a spacer or spacers in an intermediate flexure region of the diaphragm, to define separate capacitive elements with the diaphragm electrodes. The plate thus moves with the diaphragm, maintaining a fixed spacing at the spacer elements, but with the spacings between the elements varying in opposite senses. With this construction, the transducer can be of low cost, small size, precision manufacture, and use readily deposited thick or thin film electrodes. Moreover the circuits may automatically be adjusted to provide selected nominal zero and range values, so that the transducer can be utilized interchangeably with other transducers in mass production systems. Furthermore, the differential capacitance values obtained from a single transducer can directly provide digital values to a processor, by oppositely varying two variable frequency oscillators, and using the difference frequency to generate pulse counts during successive time intervals.