Pressure sensor useable in oil wells

A pressure sensor comprising:

• a cell having an outside surface which is subjectable to a pressure to be measured, said cell having two portions of the same material joined together at a join plane, at least one of said cell portions having a deformable outside plane surface parallel to said join plane;
• a hermetically sealed chamber, located inside said cell, in which a predetermined pressure is contained;
• and
• a strain-measuring device integrally deposited on said outside plane surface;
• wherein at least one of said cell portions comprises a peripheral wall and a central cap portion having said strain-measuring device deposited thereon, wherein said cap portion is substantially deformable to the exclusion of said peripheral wall and has an internal surface in the form of a flattened ellipsoid.

A sensor for use in a borehole containing fluid, said sensor to measure the pressure of the borehole fluid, said sensor comprising:

• a sensor including a housing having a deformable outside surface subjectable to the pressure of the borehole fluid and an internal cavity, a channel to permit fluid communication between the exterior of said housing and said internal cavity, and a flexible membrane therebetween;
• a measurement cell defining a join plane that parallels the deformable outside surface and which is located in said internal cavity, said cell including a hermetically sealed internal chamber having a predetermined reference pressure therein;
• and
• a strain gauge mounted on an external portion of said measurement cell, said gauge mounted substantially parallel to said membrane;
• wherein said measurement cell comprises monocrystalline sapphire and the crystal axis of the sapphire is perpendicular to said external portion of said measurement cell on which said strain gauge is mounted.