Flow meter

• US 4,240,294 A
• Filed: 12/15/1978
• Issued: 12/23/1980
• Est. Priority Date: 12/16/1977
• Status: Expired due to Term

• Current Assignee: Per-Olof Grande
• Original Assignee: Per-Olof Grande
• Inventors: Grande, Per-Olof
• Primary Examiner(s): Goldstein, Herbert
• Application Number:
  US05/970,091
• Time in Patent Office: 739 Days
• Field of Search: 73/205 R, 73/707, 73/182
• US Class Current: 73/861.47
• CPC Class Codes: G01F 1/38 the pressure or differential pressure being measured by means of a movable element, e.g. diaphragm, piston, Bourdon tube or flexible capsule

Abstract

A flow meter for the registration of pulsating liquid flows, and preferably for registration of small blood flows. The flow is measured by means of a differential pressure measurement over a first flow resistance (I) having a resistance R₁. The flow meter includes a high pressure part in the form of a flow resistance (II) and a lower pressure part in the form of a flow resistance (III), and these have the resistances R₂ and R₃, respectively. The resistances R₁, R₂ and R₃ are selected so as to adjust the pressures on each side of the differential pressure meter in phase with each other independent of the frequency of the flow pulsations. Each resistance has a corresponding modulus of elasticity, and the resistances and moduli of elasticity are so related as to fulfill certain formulas.

Claims

1. A flow meter for the registration of pulsating liquid flows, preferably for registration of small blood flows, the flow being measured by means of a differential pressure measurement over a first flow resistance (I) with the resistance R₁, and the flow meter comprising, besides the flow resistance I, also a high pressure part in the form of a flow resistance (II) and a lower pressure part in the form of a flow resistance (III) with the resistances R₂ and R₃, respectively, wherein the resistances R₁, R₂ and R₃ are selected so as to adjust the pressures on each side of the differential pressure meter in phase with each other independent of the frequency of the flow pulsations, the flow resistances (I), (II) and (III) with the resistances R₁, R₂ and R₃, respectively, having moduli of elasticity k₁, k₂ and k₃, respectively, said factors being adapted to fulfill the following formula

View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)

2. A flow meter according to claim 1, including an outer receptacle and a differential pressure meter mounted therein, both the outer receptacle and the interior of the pressure meter containing an inert not electrically conductive liquid having a low viscosity.

3. A flow meter according to claim 2, wherein the inert liquid has another density than water.

4. A flow meter according to claim 2 or 3, wherein the outer receptacle has an elastic wall portion which alters its shape with volume alterations so that the pressure in the outer receptacle remains constant.

5. A flow meter according to claim 2 or 3, wherein the outer receptacle also contains a smaller quantity of gas which compensates for the volume alteration of the liquid by which the pressure in the outer receptacle remains approximately constant.

6. A flow meter according to claim 1, 2 or 3 wherein the high pressure part (II) in the main has a volume which is equal to that of the low pressure part (III).

7. A flow meter according to claim 6, wherein the equal volume of the high pressure part and low pressure part (II, III) has been obtained by means of intermediate pieces with a large and a smaller, respectively, inner volume, the pressure part originally having the largest volume moreover having been reduced by means of a pierced insert mounted in a coupling tube of that part, which tube extends to the pressure meter, said insert preferably having a good heat conductivity.

8. A flow meter according to claim 1, 2 or 3 wherein the desired resistances are obtained by means of intermediate pieces which have depressions for membranes in contact with the flow, the pressure of which should be measured.

9. A flow meter according to claim 8, wherein the membranes transferring the pressure from the flow path to the differential pressure meter are double-walled, the membrane wall contacting the blood vessel being a part of the flow resistance (I).

10. A flow meter according to claim 8, wherein the membranes are elastic and at measurement of the blood flow the membrane walls positioned in the blood flow also consist of a blood-minded material, such as for instance siliconized-rubber.

11. A flow meter according to claim 1, 2 or 3 wherein the flow meter is for measurement of blood flow and wherein the inner surface of flow resistance (I) comprises a blood-minded material, for instance silicon-rubber, and is shaped without unevenesses damaging to the blood during the flowing thereof.

12. A flow meter according to claim 11, wherein flow resistance (I) forms a mountable part thereof.

13. A flow meter according to claim 2 wherein the receptacle is heat insulating and has a reflecting surface.

14. A flow meter according to claim 2, wherein the inert liquid in the outer receptacle has a temperature buffer capability.

15. A flow meter for the registration of pulsating liquid flows, preferably for registration of small blood flows, the flow being measured by means of differential pressure measurement over a first flow resistance (I) with the resistance R₁, and the flow meter comprising, besides the flow resistance (I), also a high pressure part in the form of a flow resistance (II) and a low pressure part in the form of a flow resistance (III) with the resistances R₂ and R₃, respectively, and wherein the resistances R₁, R₂ and R₃ are selected so as to adjust the pressures on each side of the differential pressure meter in phase with each other independent of the frequency of the flow pulsations the flow resistances (I), (II) and (III), with the resistances R₁, R₂ and R₃, respectively, having moduli of elasticity k₁, k₂ and k₃, respectively which are adapted to fulfill the formula