US 4,382,385 A · Digital differential pressure transducer

Abstract

A digital differential pressure transducer with relatively low sensitivity to common mode line pressure errors. The transducer includes an airtight enclosure having a pair of pressure ports through which pressure is coupled to opposite sides of a pressure-sensing diaphragm or bellows. The force generated by the pressure differential across the diaphragm or bellows is coupled to a stress-sensitive resonator either directly or through a force-transmitting structure. A first bellows extends from the diaphragm or a bellows end cap. The first bellows has an effective area which is substantially smaller than the effective area of the pressure-sensing diaphragm or bellows so that it applies substantially less pressure-induced stress to the resonator than does the pressure-sensing diaphragm or bellows. A second bellows has an effective area and a mounting position chosen to counteract the effect of the first bellows on the pressure-sensing diaphragm or bellows. The common mode line pressure error of the transducer resulting from a mismatch between the forces generated by the first and second bellows is thus proportional to the ratio of the effective area of the first bellows to the effective area of the pressure-sensing diaphragm or bellows. This ratio can be minimized to minimize the common mode line pressure error. The first and second bellows encapsulate or surround either the resonator or a portion of the force-transmitting structure to isolate the resonator from the pressure ports, thereby optimizing the performance of the resonator.

Claims16

Dependent claims

A digital differential pressure sensor, comprising:

a stress-sensitive resonator;
an enclosure having first and second pressure ports;
a force-generating member isolating said first pressure port from said second pressure port, said force-generating member being mechanically coupled to said resonator and moving in a direction which applies a stress to said resonator responsive to forces induced by the pressure differential across said member;
and;
first and second bellows mechanically coupled to said resonator and having respective areas and positions selected so that the forces imparted to said resonator by said first and second bellows responsive to a predetermined pressure applied to said first and second pressure ports are substantially equal and opposite to each other and substantially less than the force applied to said resonator by said force-generating member responsive to a differential pressure equivalent to said predetermined pressure applied to said first and second pressure ports, at least one of said first and second bellows being positioned to isolates said resonator from said first and second pressure ports, whereby the common mode line pressure error of said sensor as a ratio of full scale differential pressure range is proportional to the ratio of the difference in the forces generated by said first and second bellows to the force generated by said force generating member and said resonator is isolated from said first and second pressure ports.

2 more elements

A digital differential pressure sensor, comprising:

an airtight enclosure having first and second pressure ports;
a force-generating member having a generally planar surface isolating said first pressure port from said second pressure port, said force-generating member moving in a direction perpendicular to said planar surface responsive to forces induced by the pressure differential across said force-generating member;
a first bellows having an effective area substantially smaller than the effective area of said force-generating member, said bellows being concentrically mounted with said force-generating member and having respective ends connected to said force-generating member and a portion of said housing;
a second bellows having an area substantially equal to the area of said first bellows, said second bellows extending concentrically along the axis of said first bellows and having respective ends secured to the opposite face of said force-generating member and to a portion of said housing;
a pivotally mounted lever arm;
a rod extending through one of said bellows, said rod having one end secured to said force-generating member and the other end secured to said lever arm;
and
a stress-sensitive resonator having respective ends secured to said lever arm and a portion of said housing such that forces induced by pressure differentials between said first and second pressure ports are transmitted from said force-generating member to said resonator through said rod and said lever arm while said first and second bellows isolate said resonator from said pressure ports.

5 more elements

Dependencies are inferred from the claim text.

Digital differential pressure transducer

Life of this patent

Digital differential pressure transducer

Life of this patent

Abstract

Claims16