Pressure transducer assembly with thermal shield

Details Pressure transducer assembly with thermal shield Pressure transducer assembly with thermal shield

2000-12-28

2003-09-02

Williams, Hezron (Department: 2855)

Measuring and testing

Fluid pressure gauge

With pressure and/or temperature compensation

Reexamination Certificate

active

06612176

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to capacitive pressure transducers. More particularly, the present invention relates to capacitive pressure transducers with improved thermal properties.
BACKGROUND OF THE INVENTION
FIG. 1
shows a sectional view of a prior art heated capacitive pressure transducer
100
. Transducer
100
includes several major components such as an external shell
110
, a heater shell
120
, a heater
130
, a capacitive pressure sensor
140
, a front end electronics assembly
160
, a heater control electronics assembly
170
, and an input/output (I/O) electronics assembly
180
. As will be discussed in greater detail below, transducer
100
generates an output signal indicative of a pressure measured by sensor
140
.
For convenience of illustration, many mechanical details of transducer
100
, such as the construction of sensor
140
and the mounting of sensor
140
and electronics assemblies
170
,
180
, have been omitted from FIG.
1
. However, heated capacitive pressure transducers such as transducer
100
are well known and are described for example in U.S. Pat. Nos. 5,625,152 (Pandorf); 5,911,162 (Denner); and 6,029,525 (Grudzien).
Briefly, external shell
110
includes a lower enclosure
112
, an upper electronics enclosure
114
, and a joiner
116
that holds enclosures
112
,
114
together. Heater shell
120
is disposed within the lower enclosure
112
and includes a lower enclosure or can
122
and a cover
124
. Heater
130
includes a barrel heater
132
and an end heater
134
. Barrel heater
132
is wrapped around the external cylindrical sidewall of can
122
and end heater
134
is disposed on the bottom of can
122
. Barrel heater
132
and end heater
134
are electrically connected via wires
136
so the two heaters
132
,
134
may be simultaneously controlled via a single electrical signal. Sensor
140
and front end electronics assembly
160
are disposed within heater shell
120
. Mounting posts
162
support front end electronics assembly
160
over sensor
140
and wires
164
electrically connect front end electronics assembly
160
and sensor
140
. Heater control electronics assembly
170
and I/O electronics assembly
180
are disposed within the upper electronics enclosure
114
. A temperature sensor (e.g., a thermistor)
190
is fixed to an internal surface of heater shell
120
.
Sensor
140
includes a metallic, flexible, diaphragm
142
and a pressure tube
144
. Tube
144
extends from an area proximal to the diaphragm through the heater shell
120
, and through the lower sensor enclosure
112
. The lower, or external, end of tube
144
is generally coupled to a source of fluid (not shown). Pressure of fluid in the source is communicated via tube
144
to the lower surface of diaphragm
142
and the diaphragm
142
flexes up or down in response to changes in pressure within tube
144
. Diaphragm
142
and a reference conductive plate of sensor
140
form a capacitor, and the capacitance of that capacitor varies in accordance with movement or flexion of the diaphragm. Accordingly, that capacitance is indicative of the pressure within tube
144
. Front end electronics assembly
160
and I/O electronics assembly
180
cooperatively generate an output signal representative of the capacitance of sensor
140
which is, of course, also representative of the pressure within tube
144
. I/O electronics assembly
180
makes that output signal available to the environment external to transducer
100
via an electronic connector
182
.
FIG. 2
shows one example of how a capacitive pressure sensor
140
can be constructed. Capacitive pressure sensors of the type shown in
FIG. 2
are discussed in greater detail in U.S. Pat. No. 6,029,525 (Grudzien). The sensor
140
shown in
FIG. 2
includes a circular, conductive, metallic, flexible diaphragm
142
, a pressure tube
144
, and an electrode
246
. Electrode
246
and diaphragm
142
are mounted within a housing
248
. Electrode
246
includes a ceramic block
250
and a conductive plate
252
. The ceramic block
250
is rigidly mounted to the housing
248
so that a bottom face of block
250
is generally parallel to, and spaced apart from, the diaphragm. The bottom face of block
250
is normally planar and circular. The conductive plate
252
is deposited onto the bottom face of block
250
and is also generally parallel to, and spaced apart from, the diaphragm. Conductive plate
252
and diaphragm
142
form two plates of a variable capacitor
254
. The capacitance of capacitor
254
is determined in part by the gap, or spacing, between the diaphragm
142
and the conductive plate
252
. Since the diaphragm flexes up and down (thereby changing the spacing between diaphragm
142
and conductive plate
252
) in response to pressure changes in tube
144
, the capacitance of capacitor
254
is indicative of the pressure within tube
144
.
FIG. 2
shows only one of the many known ways of configuring a capacitive pressure sensor
140
. However, capacitive pressure sensors
140
generally include one or more conductors that are held in spaced relation to a flexible, conductive, diaphragm. The diaphragm and the conductors form plates of one or more variable capacitors and the capacitance of those capacitors varies according to a function of the pressure in tube
144
.
Capacitive pressure sensors often include additional features such as a tube
260
and a getter
262
as shown in FIG.
2
. When sensor
140
is being constructed, tube
260
is initially open and is used to establish a reference pressure (e.g., vacuum) in the portion of housing
248
above diaphragm
142
. Once the desired reference pressure is established (e.g., by attaching a vacuum pump to tube
260
), the upper portion of tube
260
is closed, or “pinched off”, so as to maintain the desired reference pressure inside the upper portion of housing
248
. Getter
262
is often included to absorb gas molecules that get into the upper portion of housing
248
after tube
260
has been pinched off (e.g., via outgasing of electrode
250
).
Returning to
FIG. 1
, in operation, front end electronics assembly
160
measures the capacitance (or capacitances) of sensor
140
and generates a voltage signal representative of that capacitance (e.g., the voltage signal may vary linearly with changes in capacitance). I/O electronics assembly
180
typically amplifies and further conditions that voltage signal to generate the output signal of transducer
100
.
In high performance transducers, front end electronics assembly
160
must be capable of resolving very small changes in the capacitance of sensor
140
(e.g., in a sensor that measures pressures in the range of one Torr, a delta pressure of 0.1 Torr typically corresponds to a change of only two picofarads in the capacitance of sensor
140
). Accordingly, it is important to minimize any stray capacitances associated with measurement of the capacitance of sensor
140
. One method of minimizing these stray capacitances is to locate front end electronics assembly
160
closely to sensor
140
and thereby minimizing the length of the wires
164
that electrically connect assembly
160
and sensor
140
.
Ideally, the output signal of transducer
100
varies only according to changes in the pressure of the fluid in tube
144
. However, changes in the temperature of transducer
100
, or temperature gradients within transducer
100
, can affect the output signal. This is primarily due to the different coefficients of thermal expansion of different materials used to construct the sensor
140
. A secondary effect relates to the temperature sensitive performance of front end electronics
160
. Accordingly, the accuracy of transducer
100
can be adversely affected by temperature changes in the ambient environment.
To minimize the adverse effect of changing ambient temperature, the temperature sensitive components of transducer
100
(i.e., sensor
140
and front end electronics
160
) are disposed within heater shell
120
, and in operation the heater
130
attempts to heat th

Affiliated with

Also associated with

Rating

Pressure transducer assembly with thermal shield does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Pressure transducer assembly with thermal shield, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pressure transducer assembly with thermal shield will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3058344