Thermometrics

Philip C Demarest

An improved miniature, in vivo, pressure sensor is disclosed which comprises a housing having an internal chamber adapted to be connected to a conduit for varying the pressure therein; a piezoresistive element positioned in the chamber and adapted to be connected to a circuit for sensing changes in the resistance of the piezoresistive element; a pressure responsive element carried by the housing and having an inner portion and an outer portion, the inner portion being exposed to the pressure extant in the interanl chamber and the outer portion being exposed to ambient pressure conditions outside of the housing; and a coupling device releasably coupling the pressure responsive element to the piezoresistive element in such a manner that when equal pressures are concurrently applied to the inner and outer portions of the pressure responsive element, the pressure responsive element applies a predetermned load to thre piezoresistive element and when unequal pressures are concurrently applied to the inner and outer portions of the pressure responsive element, the load applied by the pressure responsive element to the piezoresistive element correspondingly changes. A method fo checking the calibration of the pressure sensor and recalibrating it, when necessary, while it remains in an in vivo measurement site, is also disclosed. The method includes, inter alia, the steps of applying a gradually increasing unloading pressure to the pressure responsive element to decrease the predetermined load on, and output of, the piezoresistive element, and establishing the value of the unloading pressure at which the output of the piezoresistive element ceases to decrease.

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Pine Brook, NJ, United States of America

Philip C Demarest