Umted States Patent [191
`Jenkins
`
`[11] Patent Number:
`[45] Date of Patent:
`
`4,555,952
`Dec. 3, 1985
`
`[54] DIFFERENTIAL PRESSURE SENSOR
`
`.
`
`0.:
`
`Patrick A. Jenkins, Decatur, Ill.
`[75] Inventor:
`[73] Assignee: Borg-Warner Corporation, Chicago,
`I11_
`[21] A l N 618 667
`_pp
`’
`[22] Flled:
`Jun- 8’ 1984
`[51] Int. GL4 .............................................. .. G01F 1/38
`[52] US. Cl. ................................. .. 73/86L47; 73/718;
`73/ 861.61
`[58] Field of Search _______________ " 73/717’ 718’ 719, 720,
`73/721’ 861.47’ 86148’ 861.61’ 86165. 92/97
`_
`’
`References Cited
`U_5_ PATENT DOCUMENTS
`73 7
`w_
`St‘e‘iind """"""""""""" " 94/913 52
`i’ggg’égé
`3’245'266 4/1966 Mitten":
`73/720
`3,859,575 1/1975 Lee et a1.
`317/246
`4,089,036 5/1978 Geronime
`361/283
`4,125,027 11/1978 Clark ................................... .. 73/274
`
`[561
`
`4,382,377 5/1983 Kleinschmidt et a]. .............. .. 73/35
`4,382,385 5/1983 P
`................................... .. 73/702
`arcs
`1
`OTHER PUBLICATIONS
`Speci?cation Sheets—Everett/Charles Marketing Ser
`vices, Inc. Force Transducers—Model FT655.
`Primary Examiner—Herbert Goldstein
`Attorney, Agent, or Firm-Florian S. Gregorczyk
`[57]
`ABSTRACT
`
`_
`_
`_
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`A differential pressure sensor assembly 1s disclosed,
`_
`which includes a transducer and a differential pressure
`sensor. The sensor responds to a fluid pressure change
`across an ori?ce of a known size and transfers this
`sensed pressure differential to the transducer. The elec
`tronic elements of the transducer are not exposed to the
`?uid which may be at an elevated temperature or have
`entrained particulates. The fluid flow can be determined
`by noting the ?uid pressure change across the ori?ce of
`knOwn 5118
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`5 Claims, 1 Drawing Figure
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`. US. Patent
`
`Dec. 3, 1985'
`
`4,555,952 ‘
`
`//5
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`1
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`DIFFERENTIAL PRESSURE SENSOR
`
`4,555,952
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`2
`compared may be atmosphere or a vacuum, but it is not
`a pressure drop across‘ an ori?ce.
`A differential pressure transducer is taught in U.S.
`Pat. No. 4,382,385 (Paros). This transducer includes an
`air tight enclosure with a pair of pressure ports coupled
`to opposite sides of a pressure-sensing diaphragm or
`bellows. The force generated by the pressure differen
`tial is coupled to a stress-sensitive resonator either di
`rectly or through a force-transmitting structure. This
`structure teaches the use of bellows operators in coop
`eration with a resonator member or resonant sensitive
`member to provide a measured signal. In U.S. Pat. No.
`4,089,036 (Geronime) a capacitive type load cell is dis
`closed having a diaphragm member mounted to a sup
`port for movement relative thereto. However, there is
`no indication of communication of a pressure or differ
`ential pressure across the diaphragm face to provide the
`force for moving such diaphragm. Further, the relation
`ship of the diaphragm and support button is provided to
`reduce radial bending stresses in the diaphragm during
`loading, which implies that all loading is provided ex
`ternal to the electronic structure. Therefore, Geronime
`’036 recognizes the need to provide protective environ
`ments for electronic components.
`The objective of the above devices is to provide a
`variable capacitance type signal to measure applied
`force. This measurement is proportional to, or a func
`tion of, a change in distance between capacitor plates.
`Some of the references identi?ed above recognized the
`problem associated with the introduction of electronic
`components into harsh environments, but did not pro
`pose effective solutions. In the case of Kleinschmidt et
`al. ‘377, the sensor has been partially encapsulated with
`an expensive electronic structure to overcome the intr0~
`duction of the device into a harsh environment. A simi
`lar device for force measurement is taught by Everett/
`Charles Marketing Services, Inc. Their model FT655
`includes a force transducer in contact with a mechanical
`arm to move a pressure transducer diaphragm. This
`device is advertised speci?cally for use in an environ
`ment exposed to compression forces. The present inven
`tion provides a means for measurement of a differential
`pressure across an ori?ce in a harsh environment which
`may include ?uids at elevated temperatures and en
`trained particulates. It utilizes a pressure sensor, partic
`ularly a capacitive pressure sensor, without exposing
`the electronic circuitry thereof to either heat, corrosion
`or dielectric degradation. Therefore, the pressure drop
`across an ori?ce is continuously provided, and as the
`ori?ce is of a known size it provides a means to measure
`flow rate.
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The present invention relates to pressure sensors used
`in the measurement of pressure in ?uid mediums, which
`mediums may be either liquid or gas.
`'
`2. Prior Art
`Pressure sensors known in the prior art generally
`teach a pressure or force responsive diaphragm forming
`one plate or electrode of a capacitor. This electrode or
`capacitor plate is subject to deformation, the extent of
`which is compared to a second electrode means or
`capacitive plate that is not displaced. As the deforma
`tion varies the distance between such capacitor plates,
`an electrical or electrically translatable signal is pro
`duced which can be calibrated to relate the deformation
`to the deforming force. The production of such capaci
`tor sensors or transducers is well known in the art. .
`An inherent part of the capacitive sensor structures
`available today is a ceramic diaphragm operator. How
`ever, the deformation of any diaphragm operator results
`from the differential force acting on both sides of such
`a diaphragm. This differential force is then translated
`into an electrical analog signal through an electrode
`means or capacitive plate sensor which in fact measures
`the deformation or displacement of such diaphragm
`operator. These analog signals are thereafter calibrated
`or related to the measured or sensed parameter. Such a
`variable capacitance sensor is illustrated in U.S. Pat.
`No. 3,859,575 (Lee et a1) wherein a rod and plate are
`provided to react to a force and apply it to capacitive or
`separated electrode plates calibrated to measure the
`force applied to the rod. More speci?cally, the embodi
`ment taught at FIG. 4 provides a force applied to rod 90
`to increase the separation between electrode plates 5
`and 23. Diaphragm or plate 96 is primarily provided to
`ensure centering of rod 90 and may be provided with
`pressure relieving holes or apertures. Thus, the forces
`communicated to the electrodes for measurement are
`provided through rod member 90. Alternatively, pres
`sure forces may be communicated to rod 9 as in FIG. 1
`through chamber 31 which forces act on the lower
`surface of the diaphragm. However, such force is mea
`sured as a difference between the pressure on either side
`of surface 5.
`A means for indicating pressure in subterranean for
`mations is taught in U.S. Pat. No. 4,125,027 (Clark).
`This patent discloses a variable capacitance sensor re
`sponsive to changes in ambient pressure, not to a differ
`ential pressure across an ori?ce. Further, it uses an arm
`extending from its diaphragm operator as a centering
`means to maintain location of its electrode or stator 24.
`However, there is no means provided to measure a
`differential pressure across an ori?ce nor is there any
`means disclosed to provide such measurement in a re
`mote setting to protect, or provide a protective environ
`ment for, the electrodes associated with this sensor.
`U.S. Pat. No. 4,382,377 (Kleinschmidt et al.) teaches a
`piezoelectric pressure sensor for detecting knock and
`ping. This-sensor is designed to be secured in a cylinder
`head for an internal combustion engine with the mem
`brane diaphragm located within a cylinder. The forces
`being measured are provided at membrane 15. Again
`there is no provision in the structure to provide a differ
`ential pressure across an ori?ce in a ?ow passage. The
`reference pressure against which the sensed pressure is
`
`35
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`40
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`45
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`BRIEF DESCRIPTION OF THE DRAWING
`The single FIGURE of the drawing illustrates a dia
`grammatic cross-section of the present invention.
`
`SUMMARY OF THE INVENTION
`The present invention encompasses a differential
`pressure sensor assembly for remotely measuring the
`pressure drop of a ?uid across an ori?ce in a fluid flow
`passage to sense fluid ?ow or pressure drop and com
`municate the differential pressure to an electrode trans
`ducer means such as a capacitive pressure sensor, with
`out introducing extremes in heat or corrosive atmo
`sphere to the transducer. This sensor assembly includes
`two elements, that is, a transducer and a pressure sens
`ing transfer means to communicate a pressure differen
`
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`20
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`4,555,952
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`transducer assembly and, as the size of ori?ce 16 is
`tial to the transducer. This arrangement provides ease
`of assembly, protects the sensitive electronic elements,
`known, the ?ow through such ori?ce can also be deter
`mined.
`and a means to retain the dielectric atmosphere sur
`rounding the electronic elements of the transducer.
`It can now be appreciated that the transducer 12 will
`Therefore, the electronic pressure sensor is being uti
`measure a differential pressure across an ori?ce 16 of a
`known size without coming into contact with the fluid
`lized to sense a differential pressure but is insulated from
`a potentially destructive environment.
`transferred through ?uid passage 18. Such measurement
`in the past would require the ?uid to be communicated
`DETAILED DESCRIPTION OF THE
`to either side of diaphragm 20. Direct contact of the
`INVENTION
`?uid, which may be at an elevated temperature or have
`entrained particulates, with the capacitive plate
`The relationship of the parts of an assembly of a dif
`ferential pressure sensor assembly 10 utilized for the
`mounted side of diaphragm 20 would introduce heat
`measurement of pressure of a ?uid medium is illustrated
`and corrosive atmosphere into this sensitive area. Heat,
`in the drawing. As there shown, a sensor‘ assembly 10
`corrosive atmospheres or particulate laden ?uids would
`includes three distinct elements: a transducer means 12;
`severely deteriorate, either through corrosion or by
`a sensing and pressure-response transfer means 14; and,
`disturbing the dielectric constant within such enclosed
`an ori?ce 16 in a ?uid passage 18. Transducer means 12
`chamber, the monitoring or calibration of the electronic
`has a first diaphragm operator 20, a cover or housing 22
`means. Consequently, it has been the practice to utilize
`and a capacitance plate 24 which is positioned in cham
`force measurement sensors balanced against atmo
`ber 26 de?ned by cover 22 and diaphragm 20. Capacitor
`spheric pressure or a pressure within an enclosed cham
`plate 24 has a lower surface 28 and an upper surface 30.
`ber such as 26 of transducer assembly 12. This would
`The transducer means, preferably a capacitive pressure
`not provide effective measurement of a differential pres
`transducer, is shown in the reference position with no
`sure.
`de?ection of its diaphragm 20. In this reference position
`Those skilled in the art will recognize that certain
`capacitor plate 24 has an electrode or capacitance plate
`variations can be made in the illustrative embodiment.
`(not shown) mounted on surface 28 and parallel to a
`While only a speci?c embodiment of the invention has
`capacitor plate (not shown) mounted on the facing sur
`been described and shown, it is apparent that various
`face 32 defined by diaphragm 20. As diaphragm 20 is
`alterations amd modi?cations can be made therein. It is,
`deflected, the capacitance changes between the plates
`therefore, the intention in the appended claims to cover
`on surfaces 28 and 32. These plates 28 and 32 comprise
`all such modi?cations and alterations as may fall within
`an electronic signal means which cooperates with any
`the true scope of the invention.
`suitable electrical circuit (not shown). The capacitance
`I claim:
`varies with changes in diaphragm deformation produc
`1. A differential pressure sensor assembly for measur
`ing a correspondingly varying signal which, as known
`ing the pressure drop across an ori?ce in a ?uid flow
`in the art, can be related to the force producing the
`passage at a location displaced from the ori?ce and
`deflection of diaphragm 20.
`passage, comprising:
`Transfer means 14 includes a wall structure 34 de?n
`a transducor means including a housing, a ?rst dia
`ing an enclosure 36. Positioned in enclosure 36 is a
`phragm operator, and an electronic signal means
`second diaphragm operator 38 which cooperates with
`sealed in said housing and operable in response to
`wall structure 34 to de?ne an inlet chamber 40 and an
`movement of said ?rst diaphragm operator;
`outlet chamber 42. Wall structure 34 further de?nes an
`a sensing and pressure-response transfer means, in
`40
`inlet port 44, an outlet port 46, and a stem port 48. A
`cluding a wall structure de?ning an enclosure, a
`stem 50 is positioned in chamber 42 as shown, and is
`second diaphragm operator postioned in said en
`connected to and operable by second diaphragm opera
`closure to de?ne an inlet chamber and an outlet
`tor 38. Stem 50 extends through stem port 48 to contact
`chamber therein, said wall structure de?ning a
`?rst diaphragm operator 20. A seal means 52 is pro
`stem port, an inlet port communicating between
`vided to seal fluid ?ow through port 48. Inlet port 44
`45
`said inlet chamber and said ?uid passage upstream
`communicates between fluid passage 18 (upstream of
`of said ori?ce, and an outlet port communicating
`ori?ce 16) and inlet chamber 40, and outlet port 46
`between said outlet chamber and said ?uid passage
`communicates between ?uid passage 18 (downstream of
`downstream of said ori?ce;
`ori?ce l6) and outlet chamber 42.
`a stem connected to and operable by said second
`In operation assembly 10 measures the pressure drop
`diaphragm operator, which stem extends through
`of fluid ?ow in passage 18 as the fluid passes through
`said stem port to contact said ?rst diaphragm oper
`ori?ce 16, which passage 18 may be an exhaust gas
`ator; and
`recirculation passage of an automobile engine. The
`seal means to seal ?uid ?ow through said stem port,
`upstream pressure is communicated to inlet chamber 40
`the pressure drop across said ori?ce being moni
`through inlet port 44. The downstream pressure is com
`tored by said pressure-response transfer means and
`municated to chamber 42 of the transfer means through
`transmitted by said stem to said transducer means.
`outlet port 46, such downstream fluid pressure being
`2. A differential pressure sensor assembly as claimed
`lower than the upstream ?uid pressure. Second dia
`in claim 1 wherein said transducer means is a capacitive
`phragm operator 38, which may be an elastomeric ma
`pressure transducer.
`terial for greater response, is displaced in response to
`3. A differential pressure sensor assembly as claimed
`the pressure differential. This diaphragm 38 movement
`in claim 1 wherein said ori?ce is a square edged ori?ce.
`will in turn move stem 50. Stem 50, in contact with ?rst
`4. A differential pressure sensor assembly as claimed
`diaphragm 20, communicates this diaphragm 38 move
`in claim 1 wherein said second diaphragm operator is of
`ment to the transducer assembly 12 causing diaphragm
`an elastomeric material.
`20 and its associated capacitive plate means to de?ect
`5. A differential pressure sensor assembly as claimed
`and vary the capacitance and thus vary an electrical
`signal related to the pressure drop through ori?ce 16.
`in claim 1 wherein said ?uid ?ow passage is an exhaust
`gas recirculation passage of an automobile engine.
`Therefore, the pressure drop across ori?ce 16, which is
`preferably a square-edged ori?ce, can be measured by a
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