Gauge for remotely indicating the pressure of a subterranean formation

DETAILED DESCRIPTION Referring to the drawings and first to FIG.
1, the portion of the gauge which is lowered into a subterranean formation through a bore hole is shown.
This may be termed the "down hole" portion.
The gauge includes a tubular housing 10 including a lower portion 12.
Coupling the upper portion 10 and lower portion 12 is an isolation plug 14.
The housing lower portion 12 includes a diaphragm portion 16 which includes the lower end of the housing, the external surface 16A of the diaphragm being exposed to the ambient pressure in which the gauge is positioned.
Formed in the interior of the housing lower portion 12 is a reduced diameter portion 18 which provides a ledge 20 on the interior surface of the tubular body portion 12.
Positioned within the lower tubular body portion 12 is a cup shaped stator element 22, best shown in FIG.
2.
The stator element has a lower surface generally indicated by the numeral 24 which, when positioned in the tubular body 12, is parallel to the interior surface 16B of the diaphragm.
The side walls 26 of the stator element are of external diameter less than the internal diameter of the body reduced diameter portion 18.
In the preferred arrangement, the side walls have notches 28 therein, which permit the stator element to flex to compensate for differences in the coefficient of expansion of the stator element 22 and tubular lower body portion 12.
Formed on the upper open end of the stator element 22 is an enlarged external diameter lip 30 which engages the ledge 20 in lower tubular body 12.
The engagement of lip 30 with ledge 20 serves to accurately position the stator lower surface 24 relative to diaphragm 16.
The stator 22 is preferably formed of ceramic material.
In the embodiment of the invention illustrated in FIGS.
1 and 2, the stator lower surface 24 includes an integral circular ridge 32 which divides the lower surface 24 into an inner circular capacitive surface 34 and an outer ring shaped capacitive surface 36.
The surfaces 34 and 36 are formed of a conductive material and in a preferred arrangement are formed by coating the ceramic stator element 24 in these areas with a metallicized surface