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Abstract

A liquid filled differential pressure detector comprises two pressure sensors. Each sensor is constructed of one or more capsules, which are pairs of diaphragms sealed at their peripheries. The innermost diaphragms are interconnected by a tube which contains a rod assembly. The interior of the sensors and interconnection tube form a sealed volume filled with a incompressible liquid. The rod assembly contacts the outermost diaphragm of the sensors and is displaced by expansion and contraction of the capsules caused by a differential pressure change against the outer surface of the sensors. The motion of the rod assembly is transformed into an electrical signal to indicate the pressure measurement. The apparatus is symmetrical about the center point of the tube to reduce error caused by the fluid's thermal expansion by causing equal and opposite forces to cancel, thereby preventing motion of the rod assembly. An overpressure condition results with one sensor completely collapsing with one diaphragm bottoming out against the other, but causes no damage to the capsules due to complementary facing of the diaphragm pairs. The compliance of the diaphragms is chosen to be small enough to cause any gaseous bubbles to be driven into solution during the initial prepressurization of the fluid, ensuring its incompressibility. In a second embodiment, the rod assembly is replaced with a core assembly located at the midpoint of the tube, suspended in a magnetic fluid which separates the incompressible fluid into two identical volumes. The motion of the core assembly, which is due purely to the displacement of the incompressible fluid, is transformed into an electrical signal to indicate a pressure measurement.

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First Claim