Flow measurement system

• US 4,827,430 A
• Filed: 05/11/1987
• Issued: 05/02/1989
• Est. Priority Date: 05/11/1987
• Status: Expired due to Term

• Current Assignee: Baxter Travenol Laboratories Incorporated (Baxter International Inc.)
• Original Assignee: Baxter International Inc.
• Inventors: Hartranft, Thomas P., Cameron, Norman F., Aid, James D.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US07/048,307
• Time in Patent Office: 722 Days
• Field of Search: 364/509, 364/510, 364/415, 364/416, 340/603, 340/606, 73/861.04, 73/195-197, 73/202, 73/203, 128/637, 128/638
• US Class Current: 700/285
• CPC Class Codes: A61M 1/16 with membranes
• CPC Class Codes: A61M 1/1601 Control or regulation
• CPC Class Codes: A61M 1/1647 with flow rate measurement of the dialysis fluid, upstream and downstream of the dialyser
• CPC Class Codes: A61M 2205/3334 Measuring or controlling the flow rate
• CPC Class Codes: A61M 2205/3365 Rotational speed
• CPC Class Codes: A61M 2205/50 with microprocessors or computers
• CPC Class Codes: G01F 1/00 Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow measuring a proportion of the volume flow G01F5/00
• CPC Class Codes: G01F 1/08 Adjusting, correcting or compensating means therefor
• CPC Class Codes: G01F 1/125 with electric, electro-mechanical or electronic means

Abstract

A flow rate measurement system and method suitable for monitoring filtrate flow in a hemodialysis apparatus, provides a pair of flow meters in series at the input of a dialyzer for producing electrical signals indicative of dialysate flow rate and a pair of flow meters in series at the output of the dialyzer for producing electrical signals indicative of dialysate plus filtrate flow rate. A computer receives the flow rate signals and is programmed to calibrate each flow meter during a calibration phase to correct for any variations in each pair to thereby produce corrective scale factors. During an operational phase of the apparatus, the program monitors the flow meters and provides an alarm if any changes between the readings of either of the pairs of flow meters occurs.

Claims

1. In a flow rate measurement and monitoring system having flow rate transducers, said transducers having inherent inaccuracies, said system having a calibration phase and an operational phase, the improvement comprising:

a first flow rate transducer for producing a first electrical signal proportional within a first inherent error to a rate of flow of a fluid therethrough;

a second flow rate transducer connected in tandem with said first flow rate transducer for producing a second electrical signal proportional within a second inherent error to said rate of flow of said fluid therethrough;

a computer connected to said first and second flow rate transducers for receiving said first and second electrical signals;

program means resident in said computer, said program means including a calibration algorithm for calculating, during said calibration phase of operation of said system, a difference between said first and second signals due to said first and second inherent errors, and to calculate a scale factor and an average of said first and second electrical signals;

said program means thereafter applying said scale factor to said first and second signals during said operational phase of said system; and

said program means including a monitoring algorithm for monitoring said difference and for indicating a fault, during said operational phase of said system, when said difference between said first and second electrical signals changes.

2. In a system having first flow rate transducers for measuring a rate of flow of a first fluid in a first part of said system and having second flow rate transducers for measuring a rate of flow of a second fluid flow combined with said first fluid flow in a second part of said system, a subsystem for measuring said rate of flow of said second fluid from a rate of flow measurement of said first fluid prior to such combination of said fluid flows and a rate of flow measurement of said first fluid in combination with said second fluid, said system having a calibration period and an operational period, comprising:

a first flow rate transducer, having an inherent inaccuracy, for producing a first electrical signal proportional within a first inherent error to a rate of flow of said first fluid therethrough;

a second flow rate transducer, having an inherent inaccuracy, connected in series with said first flow rate transducer for producing a second electrical signal proportional within a second inherent error to said rate of flow of said first fluid therethrough;

a third flow rate transducer, having an inherent inaccuracy, connected to receive said combined flow of said first and second fluids for producing a third electrical signal proportional within a third inherent error to a rate of flow of said combined flow of said first and second fluids;

a fourth flow rate transducer, having an inherent inaccuracy, connected in series with said third transducer for producing a fourth electrical signal proportional within a fourth inherent error to said rate of flow of said combined flow of said first and second fluids;

means for temporarily causing said first fluid only to flow through said third and fourth transducers during said calibration period of said system and for causing said combined fluids to flow through said third and fourth transducers during said operational period of said system;

a computer connected to said first, second, third, and fourth flow rate transducers for receiving said first, second, third, and fourth electrical signals;

program means resident in said computer, said program means including a calibration algorithm for calculating first scale factors from a difference between said signals from said first, and second transducers during said calibration period of said system, said first scale factors applied to said first and second signals during said operational period of said system for correcting for the difference therebetween, said calibration algorithm for calculating second scale factors from a difference between said signals from said third and fourth transducers during said calibration period of said system, said second scale factors applied to said third and fourth signals during said operational period of said system for correcting for the difference therebetween; and

said program means including a monitoring algorithm for monitoring said difference between said first and second electrical signals, and said difference between said third and fourth electrical signals during said operational period and for indicating a fault when at least one of said differences varies from the corresponding difference measured during said calibration period.

3. The system as recited in claim 2 in which said calibration algorithm includes means for indicating a fault when any of said differences exceeds a preselected amount.

4. The system as recited in claim 2 in which said calibration algorithm defines a calibration phase, and a test and update phase.

5. The system as recited in claim 4 in which said calibration algorithm produces a set of plurality of samples of values of said electrical signals and calculates an average value for each set and a standard deviation for each set.

6. The system as recited in claim 5 in which said calibration algorithm includes means for indicating a fault when the standard deviation of a set of signals from any one of said transducers exceeds a preselected percentage of said average value of said set.

7. A method of monitoring and calibrating a pair of tandem connected electrical transducers for measuring a rate of flow of a fluid through a system, the pair of transducers connected to a computer, the computer for receiving electrical signals from the transducers essentially proportional to the rate of flow of the fluid therethrough, comprising the steps of:

8. (a) producing a constant rate of flow of the fluid through each of the pair of transducers;

(b) initiating a calibration phase of the system;

(c) recording a set of samples of the fluid flow rate signals in the computer;

(d) calculating an average fluid flow rate signal level from each set of samples;

(e) comparing an average of each of the set of samples and calculating a scale factor to produce equal flow measurement values from each transducer;

(f) initiating an operational phase of the system;

(g) comparing calculated flow measurement values from each transducer during the operational phase; and

(h) initiating a fault indication when such compared calculated values differ from each other by a preselected percentage.