Bourns Instruments, Inc.

International Telephone and Telegraph Corporation

Itt Corporation

Gurnam Singh

A dual differential pressure/static pressure unit including a housing and three approximately parallel diaphragms sealed therewith forming low and high pressure compartments. Incompressible fluid then fills the respective spaces between the center diaphragm and that on each side thereof. Differential pressure/static pressure sensors are then provided. The housing is provided with passageways to conduct each of said fluids to the respective high and low pressure sides of said sensors.

Transducer

Differential and static pressure transducers are provided with piezoresistive elements connected in Wheatstone bridges on the 100 surface of a silicon chip over a diaphragm etched into the chip from the back. A thin disk diaphragm is used for differential pressure (DP) and a thicker annular diaphragm around the disk diaphragm is used for static pressure (SP) measurements. Two of the elements opposite each other in each bridge are produced along one crystallographic direction (110), and the other two are produced along an orthogonal crystallographic direction (110). Extra elements are produced for each pair to permit selection of a more closely matched set of four elements. A plurality of DP diaphragms with different diameters and respective bridges are provided along with a multiplexer for selecting a DP bridge in order to provide different ranges of sensitivity for the differential pressure measurements.

Integral differential and static pressure transducer

An apparatus which utilizes solid state piezoresistive strain sensing means to measure the static pressure as well as the differential pressure across a primary element, such as an orifice plate, venturi tube, nozzle or wedge. In a preferred embodiment, the apparatus includes a dual pressure sensing transducer comprising a body, means for applying two different pressures to the body, first and second pressure diaphragms respectively, hermetically sealed to the body at first and second spaced apart portions of the body with a back wall of the second diaphragm forming one wall of a chamber which contains a desired reference pressure, a compliant cantilever beam fixedly mounted at one end thereof to the body, a strut wire coupled between the beam and the first diaphragm to cause deflection of the beam in response to movement of the first diaphragm due to an applied differential pressure, a first plurality of piezoresistive strain elements contained on a thinned portion of the beam for deflection therewith so that movement of the first diaphragm will result in changes in the electrical resistance of the first plurality of elements that are indicative of the differential pressure applied across the first diaphragm, a second plurality of piezoresistive strain elements contained on a front wall of the second diaphragm for deflection therewith so that movement of the second diaphragm in response to the static (line) pressure will result in changes in the electrical resistance of the second plurality of elements that are indicative of the static pressure with respect to the reference pressure.

Pressure measuring apparatus

An apparatus which utilizes solid state piezoresistive strain sensing means to measure the static pressure as well as the differential pressure across a primary element, such as an orifice plate, venturi tube, nozzle or wedge. In a preferred embodiment, the apparatus includes a dual pressure sensing transducer comprising a body, means for applying two different pressures to the body, first and second pressure diaphragms respectively, hermetically sealed to the body at first and second spaced apart portions of the body with a back wall of the second diaphragm forming one wall of a chamber which contains a desired reference pressure, a compliant cantilever beam fixedly mounted at one end thereof to the body, a strut wire coupled between the beam and the first diaphragm to cause deflection of the beam in response to movement of the first diaphragm due to an applied differential pressure, a first plurality of piezoresistive strain elements contained on a thinned portion of the beam, a second plurality of piezoresistive strain elements contained on a front wall of the second diaphragm.

In a differential pressure transducer, of the type having a cantilever beam mechanically linked to a pressure-sensitive diaphragm, and piezoelectric strain gauges diffused into or bonded onto the beam, the beam has a relatively high compliance as compared with the diaphragm to facilitate operation in low pressure ranges and to increase the overall operating range of the unit. In addition, the beam is constructed so that the total bending energy is transmitted to the area of the strain gauges so as to achieve near-perfect operating efficiencies.

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Riverside, CA, United States of America

Gurnam Singh