WO1999060343A1 - Flow resistance of air flow flowtransducer - Google Patents

Flow resistance of air flow flowtransducer Download PDF

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Publication number
WO1999060343A1
WO1999060343A1 PCT/FI1999/000368 FI9900368W WO9960343A1 WO 1999060343 A1 WO1999060343 A1 WO 1999060343A1 FI 9900368 W FI9900368 W FI 9900368W WO 9960343 A1 WO9960343 A1 WO 9960343A1
Authority
WO
WIPO (PCT)
Prior art keywords
flow resistor
flow
air
holes
current
Prior art date
Application number
PCT/FI1999/000368
Other languages
French (fr)
Inventor
Mikko Eloranta
Original Assignee
Medikro Oy
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 Medikro Oy filed Critical Medikro Oy
Priority to AU39341/99A priority Critical patent/AU3934199A/en
Publication of WO1999060343A1 publication Critical patent/WO1999060343A1/en

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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/08—Detecting, measuring or recording devices for evaluating the respiratory organs
    • A61B5/087—Measuring breath flow
    • 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
    • G01F1/40—Details of construction of the flow constriction devices
    • 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
    • G01F1/40—Details of construction of the flow constriction devices
    • G01F1/42—Orifices or nozzles
    • 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
    • G01F1/40—Details of construction of the flow constriction devices
    • G01F1/44—Venturi tubes

Definitions

  • the present invention relates to a flow resistor for a current transducer which measures air current by converting the air current into a differential pressure signal, and which has of two or more holes Furthermore, the current transducer comprises a frame which transfers the differential pressure signal to the pressure gauging element
  • the flow resistors producing the differential pressure signal are usually made either of cockle finished metallic film (Fleish current transducer) or of a fine and thin metal or plastic mesh (Lilly current transducer) They may be equipped with heating and a heat regulation element, which tends to keep the current transducer's flow resistor at the same temperature as the air flowing through it
  • the holes of the fine mesh have to be very small in order to be able to attain a signal free from interference, whereby the moisture condensing when breathing obstructs the holes of the mesh and vastly transforms the signal
  • the present invention seeks to provide a flow resistor, which eliminates the disadvantages of the present air-flow current transducers
  • the invention seeks to provide a mesh for a flow resistor which can be produced of plastic by means of die-casting technology
  • the invention seeks to provide a flow resistor, in which condensation does not obstruct the holes, and whose structure is simple and economical to produce
  • a flow resistor according to the invention is produced of plastic by means of die- casting technology, and its geometrical properties have been formed such that the proportion of the thickness of the flow resistor to the diameter of the hole is over 3 It is essential that the geomet ⁇ cal characte ⁇ stics of the mesh for the measurement be such that the mesh of the flow resistor can be produced out of plastic by means of die- casting
  • the holes must be big enough
  • the flow resistor together with the current transducer can be produced economically
  • its structure is simple and its operation is reliable
  • the thickness of the mesh linearizes and increases the signal, thus making big holes possible
  • Another advantage is also that condensation does not obstruct the holes while measurements are being taken
  • Figure 1 illustrates a block diagram of an air current transducer according to the invention
  • Figure 2 illustrates the geometrical structure of a flow resistor according to Figure 1 , as seen from above
  • Figure 3 illustrates a cross-section of a flow resistor according to Figure 2
  • part 1 shows the flow resistor that converts the current of the air into differential pressure
  • Part 2 shows the frame of the current transducer which conducts the pressure signal from the flow resistor to the cu ⁇ ent transducer
  • Figures 2 and 3 illustrate one flow mesh embodiment of a flow resistor
  • the proportion of the flow resistor's thickness a to the diameter ot the flow mesh hole b is over 3
  • different values in which the said proportion is over 3 can be used This value will not be limited to any precise value
  • the thickness of the mesh both linearizes and increases the signal, thus making it possible to enlarge the holes
  • the flow mesh has several holes

Abstract

The present invention relates to a flow resistor (1) for a current transducer which is designed such that it converts air current into a differential pressure signal, and which has two or more holes, characterized in that the flow resistor is produced of plastic by means of die-casting technology, and the geometrical properties of which have been formed such that the proportion of thickness (a) of the flow resistor (1) to the diameter of the hole (b) is over 3.

Description

FLOW RESISTANCE OF AIR FLOW FLOWTRANSDUCER
The present invention relates to a flow resistor for a current transducer which measures air current by converting the air current into a differential pressure signal, and which has of two or more holes Furthermore, the current transducer comprises a frame which transfers the differential pressure signal to the pressure gauging element
The flow resistors producing the differential pressure signal are usually made either of cockle finished metallic film (Fleish current transducer) or of a fine and thin metal or plastic mesh (Lilly current transducer) They may be equipped with heating and a heat regulation element, which tends to keep the current transducer's flow resistor at the same temperature as the air flowing through it
These known solutions have the following disadvantages.
1 A metallic current transducer is both expensive and the manufacturing is complicated
2 The signal of a flow resistor made of fine mesh is strongly non-linear, and the signal is very weak when the flow is minimal Therefore, the separating capacity of this kind of transducer is poor with weak currents
3 The holes of the fine mesh have to be very small in order to be able to attain a signal free from interference, whereby the moisture condensing when breathing obstructs the holes of the mesh and vastly transforms the signal
4 The temperature of a heat conductive flow resistor and that of the air of the current to be measured have to have the same value, since even a small difference in the temperature causes a considerable error This kind of an error happens, for example, when the inhalation and exhalation of a person is being measured with a conventional flow resistor made of cockle finished metal film, in which the flow resistor has been kept as warm as the air being exhaled When inhaling, the air is considerably colder than the flow resistor, and the signal will thus be incorrect Correction coefficients are generally used to eliminate this error Thus, the error can be reduced but not totally eliminated
5 Unheated metallic flow resistors do not yield a correct signal for either inhaling or exhaling, since when cooling the exhaled air, the heat conductive flow resistor becomes warm at the same time Thus the flow resistor warms the inhaled air while at the same time it is being cooled down The average temperature of the flow resistor uses while the measurement is being taken, which increases the pressure signal from the current in the transducer Thus, the error changes depending on how many phases of inhalation and exhalation are measured
The present invention seeks to provide a flow resistor, which eliminates the disadvantages of the present air-flow current transducers In particular, the invention seeks to provide a mesh for a flow resistor which can be produced of plastic by means of die-casting technology In addition, the invention seeks to provide a flow resistor, in which condensation does not obstruct the holes, and whose structure is simple and economical to produce
The object of the invention is accomplished by means of a flow resistor of a current transducer, the charactenstics of which are presented in the claims
A flow resistor according to the invention is produced of plastic by means of die- casting technology, and its geometrical properties have been formed such that the proportion of the thickness of the flow resistor to the diameter of the hole is over 3 It is essential that the geometπcal characteπstics of the mesh for the measurement be such that the mesh of the flow resistor can be produced out of plastic by means of die- casting The holes must be big enough Thus, the flow resistor together with the current transducer can be produced economically In addition, its structure is simple and its operation is reliable In this kind of structure, the thickness of the mesh linearizes and increases the signal, thus making big holes possible Another advantage is also that condensation does not obstruct the holes while measurements are being taken
In the following, the invention will be described in more detail with reference to the accompanying drawings in which
Figure 1 illustrates a block diagram of an air current transducer according to the invention, Figure 2 illustrates the geometrical structure of a flow resistor according to Figure 1 , as seen from above, and Figure 3 illustrates a cross-section of a flow resistor according to Figure 2
In the block diagram according to Figure 1, part 1 shows the flow resistor that converts the current of the air into differential pressure Part 2 shows the frame of the current transducer which conducts the pressure signal from the flow resistor to the cuπent transducer
Figures 2 and 3 illustrate one flow mesh embodiment of a flow resistor In the embodiment, the proportion of the flow resistor's thickness a to the diameter ot the flow mesh hole b is over 3 In different solutions, different values in which the said proportion is over 3 can be used This value will not be limited to any precise value The thickness of the mesh both linearizes and increases the signal, thus making it possible to enlarge the holes In this embodiment the flow mesh has several holes
The invention is not limited to the advantageous embodiment set forth in this application The invention is versatile and can vary within the frame of the idea of the invention put forth in the claim

Claims

CLAIM
1 A flow resistor (1) for a current transducer which is designed such that it converts air current into a differential pressure signal, and which has two or more holes, characterized in that the flow resistor is produced of plastic by means of die-casting technology, and the geometrical properties of which have been formed such that the proportion of thickness (a) of the flow resistor ( 1) to the diameter of the
Figure imgf000006_0001
PCT/FI1999/000368 1998-05-04 1999-05-04 Flow resistance of air flow flowtransducer WO1999060343A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU39341/99A AU3934199A (en) 1998-05-04 1999-05-04 Flow resistance of air flow flowtransducer

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI980988A FI980988A (en) 1998-05-04 1998-05-04 Airflow flow sensor flow resistance
FI980988 1998-05-04

Publications (1)

Publication Number Publication Date
WO1999060343A1 true WO1999060343A1 (en) 1999-11-25

Family

ID=8551650

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/FI1999/000368 WO1999060343A1 (en) 1998-05-04 1999-05-04 Flow resistance of air flow flowtransducer

Country Status (3)

Country Link
AU (1) AU3934199A (en)
FI (1) FI980988A (en)
WO (1) WO1999060343A1 (en)

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3129587A (en) * 1960-10-11 1964-04-21 Honeywell Regulator Co Flow sensing device
CH495744A (en) * 1968-08-22 1970-09-15 Siemens Ag Breathing tube for pneumotachographs
US3838598A (en) * 1969-03-28 1974-10-01 Brunswick Corp Capillary flow meter
US4040293A (en) * 1975-12-22 1977-08-09 Airflow Developments Limited Fluid flow measuring device
GB2123564A (en) * 1982-03-29 1984-02-01 Furness Controls Ltd Fluid flow measurement
US4884459A (en) * 1987-06-16 1989-12-05 Institute Po Technicheska Kibernetika I Robotika Flow rate converter
US4884460A (en) * 1988-12-01 1989-12-05 Northgate Research, Inc. Device for sensing air flow

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3129587A (en) * 1960-10-11 1964-04-21 Honeywell Regulator Co Flow sensing device
CH495744A (en) * 1968-08-22 1970-09-15 Siemens Ag Breathing tube for pneumotachographs
US3838598A (en) * 1969-03-28 1974-10-01 Brunswick Corp Capillary flow meter
US4040293A (en) * 1975-12-22 1977-08-09 Airflow Developments Limited Fluid flow measuring device
GB2123564A (en) * 1982-03-29 1984-02-01 Furness Controls Ltd Fluid flow measurement
US4884459A (en) * 1987-06-16 1989-12-05 Institute Po Technicheska Kibernetika I Robotika Flow rate converter
US4884460A (en) * 1988-12-01 1989-12-05 Northgate Research, Inc. Device for sensing air flow

Also Published As

Publication number Publication date
AU3934199A (en) 1999-12-06
FI980988A0 (en) 1998-05-04
FI980988A (en) 1999-11-05

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