Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
2000-08-11
2003-05-27
Williams, Hezron (Department: 2855)
Measuring and testing
Fluid pressure gauge
Diaphragm
Reexamination Certificate
active
06568274
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to capacitive pressure transducers.
BACKGROUND OF THE INVENTION
FIG. 1A
shows a partially sectional side view of an assembled prior art capacitive pressure transducer assembly
100
.
FIG. 1B
shows an exploded sectional side view of transducer assembly
100
. For convenience of illustration,
FIGS. 1A and 1B
, as well as other figures in the present disclosure, are not drawn to scale. U.S. Pat. No. 4,823,603 discloses a capacitive pressure transducer assembly of the general form of transducer assembly
100
.
Briefly, transducer assembly
100
includes a body that defines a first sealed interior chamber
110
, and a second sealed interior chamber
112
. Chambers
110
and
112
are isolated from one another by a relatively thin, flexible, conductive diaphragm
120
. As will be discussed in greater detail below, diaphragm
120
is mounted so that it flexes, or deflects, in response to pressure differentials in chambers
110
and
112
. Transducer assembly
100
provides a parameter that is indicative of the amount of diaphragm flexure and this parameter is therefore indirectly indicative of the differential pressure. The parameter provided by transducer assembly
100
indicative of the differential pressure is the electrical capacitance between diaphragm
120
and an electrode
130
.
Transducer assembly
100
includes a P_x cover
140
and a P_x body
150
(as will be discussed below, the term “P_x” refers to an unknown pressure).
FIG. 2A
shows a top view of P_x body
150
. P_x body
150
has a tubular shape and defines a central interior aperture
152
(shown in FIG.
2
A and indicated by lines
153
in FIG.
1
B). The upper surface of P_x body
150
is stepped and provides a shoulder
154
that extends around the perimeter of aperture
152
. P_x body
150
also includes a lower surface
156
. P_x cover
140
is a circular metallic sheet and is provided with a pressure tube
142
that defines a central aperture
144
. P_x cover
140
is rigidly affixed to the lower surface
156
of P_x body
150
(e.g., by welding). Diaphragm
120
is normally a thin, circular, flexible sheet of conductive material (e.g., stainless steel). As stated above,
FIGS. 1A and 1B
are not drawn to scale, and diaphragm
120
is normally much thinner than illustrated in comparison to the other components of transducer assembly
100
. Diaphragm
120
contacts shoulder
154
of P_x body
150
as indicated in FIG.
1
A. The outer perimeter of diaphragm
120
is normally welded to P_x body
150
to rigidly hold the outer perimeter of diaphragm
120
to shoulder
154
of P_x body
150
.
P_x cover
140
, P_x body
150
, and diaphragm
120
cooperate to define interior sealed chamber
110
. P_x cover
140
defines the bottom, P_x body
150
defines the sidewalls, and diaphragm
120
defines the top of chamber
110
. Fluid in tube
142
may flow through aperture
144
, and through central aperture
152
(shown in
FIG. 2A
) into chamber
110
. So, fluid in tube
142
is in fluid communication with the lower surface of diaphragm
120
.
Transducer assembly
100
also includes a P_r body
160
and a P_r cover
170
(as will be discussed below, the term “P_r” refers to a reference pressure).
FIG. 2B
shows a top view of P_r body
160
. P_r body
160
has a tubular shape and defines a central aperture
162
(shown in FIG.
2
B and indicated by lines
263
in FIG.
1
B). The upper surface of P_r body
160
is stepped and provides a lower shoulder
164
and an upper shoulder
166
. Lower shoulder
164
extends around the perimeter of aperture
162
, and upper shoulder
166
extends around the perimeter of lower shoulder
164
. P_r body
160
also includes a lower surface
168
opposite to shoulders
164
,
166
. Lower surface
168
of P_r body
160
is rigidly affixed to the upper surface of the outer perimeter of diaphragm
120
(e.g., by welding). P_r cover
170
is a circular metallic sheet and is provided with a pressure tube
172
which defines a central aperture
174
. P_r cover
170
is rigidly affixed to P_r body
160
(e.g., by welding) so that the outer perimeter of P_r cover
170
is in contact with upper shoulder
166
of P_r body
160
.
P_r cover
170
, P_r body
160
, and diaphragm
120
cooperate to define interior sealed chamber
112
. Diaphragm
120
defines the bottom, P_r body
160
defines the sidewalls, and P_r cover
170
defines the top of chamber
112
. Fluid in tube
172
may flow through aperture
174
, and through central aperture
162
(shown in
FIG. 2B
) into chamber
112
. So, fluid in tube
172
is in fluid communication with the upper surface of diaphragm
120
. As will be discussed below, electrode
130
is housed in, and does not interfere with the fluid flow in, chamber
112
.
Electrode
130
is normally fabricated from a non-conducting (or insulating) ceramic block and has a cylindrical shape.
FIG. 2C
shows a bottom view of electrode
130
. The lower surface of electrode
130
is stepped and includes a central face
135
and a shoulder
136
that extends around the outer perimeter of central face
135
. Electrode
130
also defines an aperture
132
(shown in FIG.
2
C and indicated by lines
133
in FIG.
1
B). Electrode
130
further includes a relatively thin conductor
134
that is deposited (e.g., by electroplating) onto central face
135
. Conductor
134
is explicitly shown in
FIGS. 1B and 2C
, and for convenience of illustration, conductor
134
is not shown in FIG.
1
A. Electrode
130
is clamped between P_r cover
170
and lower shoulder
164
of P_r body
160
as shown in FIG.
1
A. Aperture
132
(shown in
FIG. 2C
) in electrode
130
permits fluid to freely flow through electrode
130
between the upper surface of diaphragm
120
and pressure tube
172
. Clamping electrode
130
to P_r body
160
holds conductor
134
in spaced relation to diaphragm
120
. Electrode
130
is normally positioned so that the space between conductor
134
and diaphragm
120
is relatively small (e.g., on the order of 0.0002 meters).
Conductor
134
and diaphragm
120
form parallel plates of a capacitor
138
. As is well known, C=Ae/d, where C is the capacitance between two parallel plates, A is the common area between the plates, e is a constant based on the material between the plates (e=1 for vacuum), and d is the distance between the plates. So, the capacitance provided by capacitor
138
is a function of the distance between diaphragm
120
and conductor
134
. As diaphragm
120
flexes up and down, in response to changes in the pressure differential between chambers
110
and
112
, the capacitance provided by capacitor
138
also changes. Because electrode
130
(and conductor
134
) preferably remains stationary relative to the housing, electrode
130
may be referred to as the “reference electrode.” At any instant in time, the capacitance provided by capacitor
138
is indicative of the instantaneous differential pressure between chambers
110
and
112
. Known electrical circuits (e.g., a “tank” circuit characterized by a resonant frequency that is a function of the capacitance provided by capacitor
138
) may be used to measure the capacitance provided by capacitor
138
and to provide an electrical signal representative of the differential pressure.
Transducer assembly
100
includes an electrically conductive feedthrough
180
to permit measurement of the capacitance provided by capacitor
138
. One end
182
of feedthrough
180
contacts electrode
130
. Feedthrough
180
extends through an aperture in P_r cover
170
so that the other end
184
of feedthrough
180
is external to transducer assembly
100
. The aperture in P_r cover
170
through which feedthrough
180
extends is sealed, for example by a melted glass plug
185
, to maintain the pressure in chamber
112
and to electrically insulate feedthrough
180
from P_r cover
170
. Feedthrough
180
is electrically connected to conductor
134
. Electrode
130
normally includes an electroplated through hole (not shown) to permit electrical c
Denner John
Grudzien Chris P.
Lischer Jeff
Lucas Paul D.
Weight Kristen
Ferguson Marissa
Hale and Dorr LLP
MKS Instruments Inc.
Williams Hezron
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