Capacitive pressure sensor cells or differential pressure...

Details Capacitive pressure sensor cells or differential pressure... Capacitive pressure sensor cells or differential pressure...

2000-02-16

2001-07-31

Fuller, Benjamin R. (Department: 2855)

Measuring and testing

Fluid pressure gauge

Diaphragm

C073S724000, C361S283400

Reexamination Certificate

active

06267009

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to capacitive ceramic pressure sensor cells or differential pressure sensor cells and to methods for manufacturing the same.
BACKGROUND OF THE INVENTION
A capacitive ceramic pressure sensor cell commonly comprises a ceramic substrate and a ceramic diaphragm which covers the substrate and is spaced from the latter to form a sensing chamber between the diaphragm and a surface of the substrate facing the diaphragm. The facing surfaces of the substrate and the diaphragm are provided with electrodes which together form a capacitor that provides an electric signal which corresponds to a pressure of a process medium acting on and deforming the diaphragm. Under overload conditions, the substrate serves as a limiter for the movement of the diaphragm.
To measure a difference between two pressures (differential pressure), two sensing chambers are commonly used, one for each pressure, the sensing chambers being spatially and mechanically connected with one another and being provided with one sensing capacitor each. In this manner it is possible to produce an electric signal which corresponds to the difference between a pressure acting on one of the sensing chambers and a pressure acting on the other sensing chamber.
A particular problem encountered with ceramic pressure sensor cells is to fasten and join the diaphragm in its edge area to the substrate in such a manner that the joint is gasu and liquid-tight and can withstand high tensile and compressive loads. In addition, the joint is to be long-term-stable and free of relaxation effects.
Glass-frit joints used in conventional ceramic pressure sensor cells do not fully meet the above requirements. Therefore, a joint produced by means of an active brazing solder has been used.
U.S. Pat. No. 5,050,034, for example, discloses a capacitive pressure sensor cell comprising
a ceramic substrate having
a cylindrical surface and,
at a first major surface, a central area which
is provided with a first electrode and
has an electrical connection from the first electrode through the substrate to a second major surface, and
a ceramic diaphragm
which is joined to the substrate using a plane-parallel ring of active brazing solder to form a high-vacuum-tight sensing chamber,
with a second electrode being provided on a planar inner surface of the diaphragm facing the substrate.
The joint produced by means of active brazing solder meets the above-mentioned requirements for high stability, but in certain cases where the diaphragm is subjected to overpressure, it has turned out that the diaphragm cannot be supported on the substrate in a satisfactory manner. Because of the “angular” shape of the ring of active brazing solder, which serves as a spacer between the substrate and the diaphragm, tensile stresses may occur, particularly in the edge region of the diaphragm, which result in a failure of the diaphragm.
U.S. Pat. No. 4,329,826 discloses a capacitive differential pressure sensor cell comprising:
a substrate having
an edge area and,
at a first major surface, a concave first central area which
is provided with a first electrode,
has a first electrical connection to the first electrode, and,
in the direction of the edge area, merges into a convex first surface
which has a first vertex line intersecting the edge area and
forms a first planar ring surface in the area of the first vertex line,
said substrate further having, at a second major surface opposite the first major surface, a concave second central area
which is provided with a second electrode,
has a second electrical connection to the second electrode, and,
in the direction of the edge area, merges into a convex second surface which
has a second vertex line intersecting the edge area and
forms a second planar ring surface in the area of the second vertex line,
the substrate being provided with a connecting channel between the first central area and the second central area;
a first ceramic diaphragm
which rests on and is fixed to the first ring surface of the substrate,
with a third electrode being provided on a planar inner surface of the first diaphragm facing the substrate; and
a second ceramic diaphragm
which rests on and is fixed to the second ring surface of the substrate,
with a fourth electrode being provided on a planar inner surface of the second diaphragm facing the substrate.
In the case of this prior-art differential pressure sensor cell, the ring surfaces, which serve exclusively to join the respective diaphragms to the substrate, extend up to the cylindrical surface of the substrate. The way the joint is produced is not explained.
It has turned out that the joint produced solely by means of the ring surfaces is insufficient, particularly if great axially parallel forces act on these surfaces. In addition, such a joint is not high-vacuum-tight and not long-term-stable.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide capacitive pressure sensor cells or capacitive differential pressure sensor cells in which the joint between the substrate and the diaphragms is both pressure- and/or tension-proof and high-vacuum-tight and long-term-stable.
To attain this object, a first variant of the invention provides a capacitive pressure sensor cell comprising:
a ceramic substrate having
a cylindrical surface,
a first major surface and
a second major surface,
said second major surface being opposite said first major surface,
said first major surface including a concave central area which, in the direction of and up to said cylindrical surface, merges into a convex surface having a vertex line,
said convex surface forming a planar ring surface in the area of said vertex line,
a first electrode located in said concave central area of said first major surface, and
an electrical connection extending from said first electrode through said substrate to said second major surface; and
a ceramic diaphragm having a planar inner surface,
a second electrode located on said planar inner surface of said diaphragm,
said planar inner surface of said diaphragm resting on said planar ring surface of said first major surface of said substrate,
said diaphragm being joined to said substrate by an active brazing solder
which forms a circumferential wedge zone between said diaphragm and said substrate in the area of said substrate between said planar ring surface and said cylindrical surface,
a high-vacuum-tight sensing chamber being formed between said planar inner surface of said diaphragm and said first major surface of said substrate, and
electrical connection to said second electrode being made through said circumferential wedge zone.
To attain the above object, a second variant of the invention provides a capacitive differential pressure sensor cell comprising:
a ceramic substrate having
a cylindrical surface and,
at a first major surface, a concave first central area which
is provided with a first electrode,
has a first electrical connection from the first electrode through the substrate to a second major surface, and,
in the direction of and up to the cylindrical surface, merges into a convex first surface having a first vertex line,
said convex first surface forming a first planar ring surface in the area of the first vertex line,
which substrate further has, at a second major surface opposite the first major surface, a concave second central area which
is provided with a second electrode,
has a second electrical connection from the second electrode through the substrate to the cylindrical surface, and,
in the direction of and up to the cylindrical surface, merges into a convex second surface having a second vertex line,
said convex second surface forming a second planar ring surface in the area of the second vertex line,
said substrate further having a connecting channel between the first central area and the second central area;
a first ceramic diaphragm
which rests on the first ring surface of the substrate, and
which is joined to the substrate on the first ring surface and between the cylindrical surface and the first ring surface by

Affiliated with

Also associated with

Rating

Capacitive pressure sensor cells or differential pressure... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Capacitive pressure sensor cells or differential pressure..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Capacitive pressure sensor cells or differential pressure... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2553892