WO1997040350A1 - Differential pressure device - Google Patents

Differential pressure device Download PDF

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Publication number
WO1997040350A1
WO1997040350A1 PCT/SE1997/000690 SE9700690W WO9740350A1 WO 1997040350 A1 WO1997040350 A1 WO 1997040350A1 SE 9700690 W SE9700690 W SE 9700690W WO 9740350 A1 WO9740350 A1 WO 9740350A1
Authority
WO
WIPO (PCT)
Prior art keywords
servomedium
pressure
sensors
measuring
liquids
Prior art date
Application number
PCT/SE1997/000690
Other languages
French (fr)
Inventor
Hans Persson
Original Assignee
Hans Persson
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hans Persson filed Critical Hans Persson
Priority to AU27204/97A priority Critical patent/AU2720497A/en
Priority to EP97921056A priority patent/EP0895582A1/en
Publication of WO1997040350A1 publication Critical patent/WO1997040350A1/en

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/14—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measurement of pressure
    • G01F23/16—Indicating, recording, or alarm devices being actuated by mechanical or fluid means, e.g. using gas, mercury, or a diaphragm as transmitting element, or by a column of liquid
    • G01F23/164—Indicating, recording, or alarm devices being actuated by mechanical or fluid means, e.g. using gas, mercury, or a diaphragm as transmitting element, or by a column of liquid using a diaphragm, bellow as transmitting element
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/05—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects
    • G01F1/34—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by measuring pressure or differential pressure
    • G01F1/36—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by measuring pressure or differential pressure the pressure or differential pressure being created by the use of flow constriction
    • G01F1/38—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by measuring pressure or differential pressure the pressure or differential pressure being created by the use of flow constriction the pressure or differential pressure being measured by means of a movable element, e.g. diaphragm, piston, Bourdon tube or flexible capsule
    • G01F1/383—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by measuring pressure or differential pressure the pressure or differential pressure being created by the use of flow constriction the pressure or differential pressure being measured by means of a movable element, e.g. diaphragm, piston, Bourdon tube or flexible capsule with electrical or electro-mechanical indication
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L11/00—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00
    • G01L11/004—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by the use of counterbalancing forces
    • G01L11/006—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by the use of counterbalancing forces hydraulic or pneumatic counterbalancing forces
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N9/00—Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity
    • G01N9/26—Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity by measuring pressure differences

Definitions

  • the present invention relates to a device for measuring differential pressures with the aid of pressure sensors that have separate control circuits.
  • measuring devices that measure pressure with the aid of electric sensors, strain gauges or like indicators.
  • a common feature of such devices is that the majority include a membrane or diaphragm whose movements in response to pressure changes can be registered, e.g., piezoelectrically, by resistivity changes in response to axial stresses on metal wire, by changes in induction caused by positional shifts, etc.
  • the conditions in the fluid whose pressure changes are to be registered are substantially favourable in this respect, a measuring result of acceptable reliability will also be obtained.
  • the device, or apparatus, fundamental to the present invention has the advantage of constantly registering a pressure difference in the form of an absolute value, i.e. error sources resulting from more or less inexact conversion numbers are eliminated. Because the pressure difference is an absolute value within a specific path from the measuring points, the measured pressure gradient will be independent of fluctuations in the total pressure. Measuring of the fluid pressure in a system at two points located at mutually different depths in the system is an example in this regard. If the absolute value of the pressure is not measured, the result obtained with respect to the pressure gradient will be significantly unreliable, not least when the level of liquid varies. U.S.
  • Patent Specification 4,614,118 describes a pressure measuring cell in which movements of a diaphragm are registered by a sensor, which delivers a signal that, after being amplified via a control device, actuates a valve for a servomedium which is pumped into the cell so as to adjust the diaphragm to zero deflection. Certain intrinsic errors of the measuring cell are eliminated thereby, for instance such errors as the lack of linearity as the diaphragm stretches, etc.
  • the inner pressure of the cell is established on the basis of the pressure of the servomedium, this pressure corresponding to the pressure of the medium outside the cell.
  • this prior publication suggests no method with which there is obtained an outgoing measuring signal which is directly proportional to the pressure gradient to be measured and which is independent of pressure fluctuations or other variables, e.g. temperature.
  • SE Published Specification 395188 teaches a measuring device that includes a venturi tube between two pressure sensors. Each sensor is supplied with a pressure controlled fluid and includes a fluid inlet and two fluid outlets. The fluid outflows from the sensor are also pressure controlled. One outlet is controlled by a flap which is connected to the pressure sensing membrane of the sensor. The other outlet undergoes a pressure reduction subsequent to passage of the fluid through a cavity in the sensor. The pressure sensing movements via the membrane will thereby be very small. It is stated on page 8 of the published specification that the sensors can be used for, e.g., sensing pressure and liquid levels in reservoirs, for instance. Distinct from the inventive device, however, the prior publication makes no reference to mamtaining a constant pressure within respec ⁇ tive sensors, which excludes the use of measuring devices that include differential pressure sensors or indicators.
  • the sensors used in die present measuring system are balanced-out during a measuring operation by means of a servomedium in separate control circuits and, distinct to earlier techniques, a pressure difference between two measuring points can be registered via a measuring device subsequent to regulating to equilibrium between outer and inner pres- sures of respective sensor membranes.
  • Deflection of the membrane i.e. the initial inward bulging of the membrane in normal cases, is controlled on the basis of inductance from a sensing element in the sensor, although other sensing possibilities are feasible, such as piezoelectric sensors and strain-gauge related resistivity.
  • the control is preferably effected to zero deflection, even though other degrees of deflection are feasible for achieving equilibrium.
  • the servomedium used to balance-out the sensors may be an inert gas or a low viscous liquid that are not electrically conductive.
  • the servomedium may conveniently comprise an inert thinly fluid oil, particularly a hydrocarbon based oil.
  • the servomedium may comprise an inert, thinly fluid oil, preferably a hydrocarbon based oil.
  • the membrane is relatively insensitive to the build-up of foreign material that changes the mass of the sensor elements.
  • the membrane can be considered to be rigid, i.e. non-resilient in operation, which counteracts errors due to creepage.
  • FIG 1 is a schematic illustration of the inventive measuring system, and shows the functional principles in broad outlines.
  • Each measuring sensor (7, 8) is fixedly mounted at a fixed distance between the two measuring points. It is assumed that a pressure difference exists over this constant distance.
  • Respective sensor membranes (9, 10) are balanced-out by separate pressure regulators (11, 12) with the aid, for instance, of an hydraulic valve in the regulator, and the pressure difference dP between the servomedia in respective circuits is registered by a measuring device (13).
  • the pressure regulators are, in principle, supplied with a pressurized servomedium from a common connection (1).
  • the sensors are balanced with respect to one another, i.e. after achieving equilibrium between the pressure in the servo medium (2) and the pressure on the outside of the sensor, the counterpressure in each sensor will correspond to the pressure prevailing on the outside of the membrane.
  • the measuring device for differential pressure (13) to the servomedium (2) in respective sensors, there is obtained an output signal which is directly proportional to the pressure level at each measuring point subsequent to balancing-out the sensors.
  • the pressure in respective sensors is registered by separate movement sensors (5, 6) and respective signals (3, 4) are used to control the pressure regulators (11, 12).
  • the measuring device enables primarily the densities of liquids to be measured under severe conditions, e.g. corrosive conditions or of liquids whose properties cannot be readily handled, such as liquids of high viscosity, tacky liquids, liquids that have high sedimentation tendencies, etc., with which different types of mass-flow measuring devices, weighing apparatus, etc., function less well.
  • the inventive device has no open intakes, which contributes towards why drawbacks relating to clogged flow passageways and pressure absorbing zones can be greatly reduced, thereby lengthening the periods between which inspection is necessary.
  • the adjustment needs of the structurally very simple measuring system are minimal in comparison with known density measuring apparatus.
  • the inventive device can be used advantageously in fields other those concerned with measuring the density of liquids.
  • the device can be used to measure rates of flow through venturi tubes, liquid levels in systems, investigation of aerodynamic and hydrodynamic flow sequences, etc.

Abstract

There is described a device that is useful in determining pressure gradients in liquids, for instance. Pressure sensing is effected with the aid of two sensors (7, 8) mounted at a predetermined distance apart, wherein the membranes (9, 10) of respective sensors are in connection with a servomedium. The device includes separate servomedium pressure regulators (11, 12) which balance out each of the membranes to equilibrium with liquid outside the sensors in response to control signals (3, 4) delivered by conventional detectors in the sensors. The servomedium in respective sensors is connected to a common differential pressure measuring device (13). The structurally simple measuring system is particularly suitable for determining the intensity of liquids under difficult conditions, for instance in systems having varying liquid levels, in corrosive environments, in cases when the liquids are heavily contaminated, under fluctuating pressures and temperatures, and so on.

Description

DIFFERENTIAL PRESSURE DEVICE
The present invention relates to a device for measuring differential pressures with the aid of pressure sensors that have separate control circuits.
There are many types of measuring devices that measure pressure with the aid of electric sensors, strain gauges or like indicators. A common feature of such devices is that the majority include a membrane or diaphragm whose movements in response to pressure changes can be registered, e.g., piezoelectrically, by resistivity changes in response to axial stresses on metal wire, by changes in induction caused by positional shifts, etc. Provided that the conditions in the fluid whose pressure changes are to be registered are substantially favourable in this respect, a measuring result of acceptable reliability will also be obtained.
Unfortunately, the measuring conditions are very seldom ideal. Examples of typical error sources are temperature variations, pressure fluctuations, chemically aggressive fluids, contaminated fluids, and coatings on the pressure sensors. The conditions can be particularly unfavourable for obtaining correct results when registering pressure gradi¬ ents, since two measuring positions are normally used and occurrent measuring errors thus stand the risk of being summated.
The device, or apparatus, fundamental to the present invention has the advantage of constantly registering a pressure difference in the form of an absolute value, i.e. error sources resulting from more or less inexact conversion numbers are eliminated. Because the pressure difference is an absolute value within a specific path from the measuring points, the measured pressure gradient will be independent of fluctuations in the total pressure. Measuring of the fluid pressure in a system at two points located at mutually different depths in the system is an example in this regard. If the absolute value of the pressure is not measured, the result obtained with respect to the pressure gradient will be significantly unreliable, not least when the level of liquid varies. U.S. Patent Specification 4,614,118 describes a pressure measuring cell in which movements of a diaphragm are registered by a sensor, which delivers a signal that, after being amplified via a control device, actuates a valve for a servomedium which is pumped into the cell so as to adjust the diaphragm to zero deflection. Certain intrinsic errors of the measuring cell are eliminated thereby, for instance such errors as the lack of linearity as the diaphragm stretches, etc. The inner pressure of the cell is established on the basis of the pressure of the servomedium, this pressure corresponding to the pressure of the medium outside the cell. However, this prior publication suggests no method with which there is obtained an outgoing measuring signal which is directly proportional to the pressure gradient to be measured and which is independent of pressure fluctuations or other variables, e.g. temperature.
SE Published Specification 395188 teaches a measuring device that includes a venturi tube between two pressure sensors. Each sensor is supplied with a pressure controlled fluid and includes a fluid inlet and two fluid outlets. The fluid outflows from the sensor are also pressure controlled. One outlet is controlled by a flap which is connected to the pressure sensing membrane of the sensor. The other outlet undergoes a pressure reduction subsequent to passage of the fluid through a cavity in the sensor. The pressure sensing movements via the membrane will thereby be very small. It is stated on page 8 of the published specification that the sensors can be used for, e.g., sensing pressure and liquid levels in reservoirs, for instance. Distinct from the inventive device, however, the prior publication makes no reference to mamtaining a constant pressure within respec¬ tive sensors, which excludes the use of measuring devices that include differential pressure sensors or indicators.
The sensors used in die present measuring system are balanced-out during a measuring operation by means of a servomedium in separate control circuits and, distinct to earlier techniques, a pressure difference between two measuring points can be registered via a measuring device subsequent to regulating to equilibrium between outer and inner pres- sures of respective sensor membranes. Deflection of the membrane, i.e. the initial inward bulging of the membrane in normal cases, is controlled on the basis of inductance from a sensing element in the sensor, although other sensing possibilities are feasible, such as piezoelectric sensors and strain-gauge related resistivity. The control is preferably effected to zero deflection, even though other degrees of deflection are feasible for achieving equilibrium. The servomedium used to balance-out the sensors may be an inert gas or a low viscous liquid that are not electrically conductive. The servomedium may conveniently comprise an inert thinly fluid oil, particularly a hydrocarbon based oil. In particularly, the servomedium may comprise an inert, thinly fluid oil, preferably a hydrocarbon based oil.
Small area membranes are preferred, since the membrane is relatively insensitive to the build-up of foreign material that changes the mass of the sensor elements. The membrane can be considered to be rigid, i.e. non-resilient in operation, which counteracts errors due to creepage.
Figure 1 is a schematic illustration of the inventive measuring system, and shows the functional principles in broad outlines. Each measuring sensor (7, 8) is fixedly mounted at a fixed distance between the two measuring points. It is assumed that a pressure difference exists over this constant distance. Respective sensor membranes (9, 10) are balanced-out by separate pressure regulators (11, 12) with the aid, for instance, of an hydraulic valve in the regulator, and the pressure difference dP between the servomedia in respective circuits is registered by a measuring device (13).
The pressure regulators are, in principle, supplied with a pressurized servomedium from a common connection (1). When the sensors are balanced with respect to one another, i.e. after achieving equilibrium between the pressure in the servo medium (2) and the pressure on the outside of the sensor, the counterpressure in each sensor will correspond to the pressure prevailing on the outside of the membrane. By connecting the measuring device for differential pressure (13) to the servomedium (2) in respective sensors, there is obtained an output signal which is directly proportional to the pressure level at each measuring point subsequent to balancing-out the sensors. The pressure in respective sensors is registered by separate movement sensors (5, 6) and respective signals (3, 4) are used to control the pressure regulators (11, 12).
The measuring device enables primarily the densities of liquids to be measured under severe conditions, e.g. corrosive conditions or of liquids whose properties cannot be readily handled, such as liquids of high viscosity, tacky liquids, liquids that have high sedimentation tendencies, etc., with which different types of mass-flow measuring devices, weighing apparatus, etc., function less well. The inventive device has no open intakes, which contributes towards why drawbacks relating to clogged flow passageways and pressure absorbing zones can be greatly reduced, thereby lengthening the periods between which inspection is necessary. The adjustment needs of the structurally very simple measuring system are minimal in comparison with known density measuring apparatus.
It will be understood, however, that the inventive device can be used advantageously in fields other those concerned with measuring the density of liquids. For instance, the device can be used to measure rates of flow through venturi tubes, liquid levels in systems, investigation of aerodynamic and hydrodynamic flow sequences, etc.

Claims

1. A device for measuring differential pressure in a fluid by sensing pressure with the aid of two measuring sensors, characterized in that each sensor (7, 8) is fixedly mounted at a predetermined distance between the two measuring points; in that each sensor membrane (9, 10) is connected to a separate pressure regulator (11, 12) via a servomedium, whereby respective sensor membranes can be balanced-out to equilibrium between surrounding fluid and the servomedium in response to a control signal indicating deflection of the membrane, wherein respective measuring sensors are connected to a common differential pressure measuring device (13) by means of said servomedium.
2. A device according to Claim 1, characterized in that the device is connected to a computer having control and logic functions for establishing the density of the fluid.
3. A device according to Claim 1, characterized in that the servomedium is a gas.
4. A device according to Claim 1, characterized in that the servomedium is an inert liquid of low electrical conductivity.
5. A device according to Claim 4, characterized in that the servomedium is an inert, thinly fluid oil, particularly a hydrocarbon based oil.
6. A device according to any one of the preceding Claims, characterized in that the membranes are rigid, i.e. non-resilient, and have a small pressure area.
7. The use of a device according to any one of the preceding Claims to measure the density of liquids in cisterns in which the liquid level varies.
PCT/SE1997/000690 1996-04-25 1997-04-24 Differential pressure device WO1997040350A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
AU27204/97A AU2720497A (en) 1996-04-25 1997-04-24 Differential pressure device
EP97921056A EP0895582A1 (en) 1996-04-25 1997-04-24 Differential pressure device

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE9601581A SE506368C2 (en) 1996-04-25 1996-04-25 Device for differential pressure measurement as well as use of the device for density measurement
SE9601581-3 1996-04-25

Publications (1)

Publication Number Publication Date
WO1997040350A1 true WO1997040350A1 (en) 1997-10-30

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/SE1997/000690 WO1997040350A1 (en) 1996-04-25 1997-04-24 Differential pressure device

Country Status (4)

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EP (1) EP0895582A1 (en)
AU (1) AU2720497A (en)
SE (1) SE506368C2 (en)
WO (1) WO1997040350A1 (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1064042A1 (en) * 1998-03-17 2001-01-03 Resmed Limited An apparatus for supplying breathable gas
US10677622B2 (en) 2016-01-22 2020-06-09 Elvesys System for measuring flow of a liquid in a microfluidic circuit by determining gas and liquid pressures
FR3126773A1 (en) 2021-09-08 2023-03-10 Elvesys LIQUID FLOW MEASUREMENT SYSTEM IN A MICRO-FLUID PIPELINE

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4489613A (en) * 1982-02-10 1984-12-25 Ennio Valletti Transmitting device for measuring the operating pressure in a system
US4561307A (en) * 1984-01-26 1985-12-31 Smith George E Liquid differential pressure measurement using a vertical manifold
US4614118A (en) * 1985-02-12 1986-09-30 Chevron Research Company Non-compliant pressure cell
US4625553A (en) * 1985-04-12 1986-12-02 Dresser Industries, Inc. System to determine the level and weight of liquid in a tank or the like

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4489613A (en) * 1982-02-10 1984-12-25 Ennio Valletti Transmitting device for measuring the operating pressure in a system
US4561307A (en) * 1984-01-26 1985-12-31 Smith George E Liquid differential pressure measurement using a vertical manifold
US4614118A (en) * 1985-02-12 1986-09-30 Chevron Research Company Non-compliant pressure cell
US4625553A (en) * 1985-04-12 1986-12-02 Dresser Industries, Inc. System to determine the level and weight of liquid in a tank or the like

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1064042A1 (en) * 1998-03-17 2001-01-03 Resmed Limited An apparatus for supplying breathable gas
EP1064042A4 (en) * 1998-03-17 2002-07-17 Resmed Ltd An apparatus for supplying breathable gas
US6899100B2 (en) 1998-03-17 2005-05-31 Resmed Limited Apparatus for supplying breathable gas
US7571725B2 (en) 1998-03-17 2009-08-11 Resmed Limited Apparatus for supplying breathable gas
US10677622B2 (en) 2016-01-22 2020-06-09 Elvesys System for measuring flow of a liquid in a microfluidic circuit by determining gas and liquid pressures
FR3126773A1 (en) 2021-09-08 2023-03-10 Elvesys LIQUID FLOW MEASUREMENT SYSTEM IN A MICRO-FLUID PIPELINE
WO2023036482A1 (en) 2021-09-08 2023-03-16 Elvesys System for measuring the flow rate of liquid in a microfluidic pipe

Also Published As

Publication number Publication date
EP0895582A1 (en) 1999-02-10
SE9601581L (en) 1997-10-26
AU2720497A (en) 1997-11-12
SE9601581D0 (en) 1996-04-25
SE506368C2 (en) 1997-12-08

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