METHOD AND APPARATUS FOR MEASURING THE FLOW RATE OF A LIQUID

• US 20140116128A1
• Filed: 06/21/2012
• Published: 05/01/2014
• Est. Priority Date: 06/23/2011
• Status: Active Grant

• Current Assignee: RenalSense Ltd.
• Original Assignee: RenalSense Ltd.
• Inventors: Mantinband, Jack Yehoshua, Adler, Michael
• Granted Patent: US 9,857,210 B2
• Time in Patent Office: Days
• US Class Current: 73/204.11
• CPC Class Codes: A61B 5/208 adapted to determine urine quantity, e.g. flow, volume
• CPC Class Codes: G01F 1/68 by using thermal effects
• CPC Class Codes: G01F 1/6847 where sensing or heating elements are not disturbing the fluid flow, e.g. elements mounted outside the flow duct
• CPC Class Codes: G01F 1/69 of resistive type
• CPC Class Codes: G01F 1/6965 comprising means to store calibration data for flow signal calculation or correction
• CPC Class Codes: G01F 1/6986 with pulsed heating, e.g. dynamic methods

Abstract

The invention is an apparatus and method for measuring the flow rate of a liquid through a conduit. The apparatus is based on a flow rate meter which is adapted to accurately measure the volumetric flow rate of a liquid using a simple, cost and energy effective, and accurate method using only one temperature sensor. The method is based on applying a pulse of thermal energy to the flowing liquid and measuring the temperature increase as a function of time and energy input. By comparing these measurements to a calibration table made by performing similar measurements for known flow rates, the rate of flow can be determined. One application, which will be described to illustrate the features of the method and apparatus of the invention, is measurement of the flow rate of urine excreted by a catheterized patient.

Claims

1. An apparatus for measuring the volumetric rate of flow of a liquid through a conduit, said apparatus comprising the following components:

a) a heating element in thermal contact with said liquid in said conduit, said heating element adapted to deliver a known quantity of heat to said flowing liquid;

b) a temperature sensor adapted to measure the instantaneous temperature of said heating element; and

c) a control system that comprises at least one of the following components;

a processor, input means, a memory unit, display devices, and output means, wherein said components of said control system are configured to;

i) activate said heating element to deliver said known quantity of heat;

ii) receive said measurements of the instantaneous temperature of said heating element from said temperature sensor;

iii) retrieve from said memory unit pre-stored calibration data relating changes in the temperature of said heating element to known flow rates of said liquid; and

iv) use said known quantity of heat, said measurements of the instantaneous temperature of said heating element, and said pre-stored calibration data to determine the volumetric flow rate.

2. The apparatus of claim 1, wherein the components of said control system are configured to carry out at least one of the following:

a) to store and display to a user information related to the operation of said apparatus and the properties of said liquid that are measured or determined by components of said apparatus;

b) to send instantaneous or historical values of measured temperatures and other information relative to said liquid and said apparatus to remote locations;

c) to send signals that can be used as input to other systems; and

d) to send alarms if there are predetermined changes in the flow rate or other measured properties of said liquid.

3. The apparatus of claim 1 comprising at least one of:

a) a bubble trap located upstream of the measurement location;

b) a gas-permeable membrane located upstream of said measurement location;

4. The apparatus of claim 1, wherein said apparatus is adapted to be either connected to or an integral part of a conduit.

5. The apparatus of claim 4, wherein said conduit is a catheter or drainage tube leading from a patient.

6. The apparatus of claim 5 wherein the control system is configured to detect risk of acute kidney injury and stages thereof.

7. A method for real-time measuring the volumetric rate of flow of a liquid through a conduit by use of an apparatus comprising a heating element in thermal contact with said flowing liquid and adapted to deliver a known quantity of heat to said flowing liquid, a temperature sensor adapted to measure the instantaneous temperature of said heating element, and a control system comprising a processor and a memory unit;

said method comprising the following steps;

i) measuring the temperature T_i of said heating element;

ii) activating said heating element to deliver a known quantity of heat to said flowing liquid;

iii) measuring the temperature Tj of said heating element immediately after said known quantity of heat has been delivered to said flowing liquid;

iv) determining from the measurements the value of Δ

T=Tj−

T_i;

v) recalling from a memory a calibration table, graph, or mathematical relationship that was constructed for said known quantity of heat and determining from said table, graph, or mathematical relationship the value of the flow rate that corresponds to said measured value of Δ

T.

8. The method of claim 7, wherein said method is adapted to measure the volumetric flow rate of a liquid through a catheter or a drainage tube leading from a patient.

9. The method of claim 8, wherein the liquid is urine.

10. The method of claim 9, wherein the measurements are used to detect risk of acute kidney injury and stages thereof.

11. A method of using a heating element in thermal contact with liquid flowing through a conduit and adapted to deliver a known quantity of heat to said flowing liquid and a temperature sensor adapted to measure the instantaneous temperature of said heating element to construct a calibration table, graph, or mathematical relationship that can be used to determine the value of the flow rate that corresponds to a measured value of Δ

T for a known quantity of heat delivered by said heating element, said method comprising the following steps;

a) adjusting the flow rate to a known constant value;

b) measuring the temperature T_i of said heating element;

c) activating said heating element to deliver said known quantity of heat to said flowing liquid;

d) measuring the temperature Tj of said heating element immediately after said known quantity of heat has been delivered to said flowing liquid;

e) determining Δ

T=Tj−

T_i;

f) storing the values of said flow rate, said quantity of heat, and Δ

T in a memory unit; and

g) repeating steps a to f for different known values of flow rate.