Thermal Flow Meter

• US 20100116048A1
• Filed: 10/07/2009
• Published: 05/13/2010
• Est. Priority Date: 10/11/2007
• Status: Active Grant

• Current Assignee: Fresenius Medical Care Holdings Incorporated (Fresenius Medical Care AG)
• Original Assignee: Xcorporeal, Inc.
• Inventors: Fulkerson, Barry Neil, Smith, Mark F.
• Granted Patent: US 8,040,493 B2
• Time in Patent Office: Days
• US Class Current: 73/204.110
• CPC Class Codes: A61M 1/152 Details related to the interface between cassette and machine
• CPC Class Codes: A61M 1/153 the cassette being adapted for heating or cooling the treating fluid, e.g. the dialysate or the treating gas
• CPC Class Codes: A61M 1/154 with sensing means or components thereof
• CPC Class Codes: A61M 1/155 with treatment-fluid pumping means or components thereof
• CPC Class Codes: A61M 1/1562 Details of incorporated reservoirs
• CPC Class Codes: A61M 1/15632 the filter being a dialyser
• CPC Class Codes: A61M 1/1565 Details of valves
• CPC Class Codes: A61M 1/3401 Cassettes therefor
• CPC Class Codes: A61M 1/36222 Details related to the interface between cassette and machine
• CPC Class Codes: A61M 1/36224 with sensing means or components thereof
• CPC Class Codes: A61M 1/36225 with blood pumping means or components thereof
• CPC Class Codes: A61M 1/362264 the filter being a blood filter
• CPC Class Codes: A61M 1/362265 Details of valves
• CPC Class Codes: A61M 1/362266 Means for adding solutions or substances to the blood
• CPC Class Codes: A61M 1/3663 Flow rate transducers; Flow integrators
• CPC Class Codes: G01F 1/667 Arrangements of transducers for ultrasonic flowmeters; Circuits for operating ultrasonic flowmeters
• CPC Class Codes: G01F 1/6842 with means for influencing the fluid flow
• CPC Class Codes: G01F 1/6986 with pulsed heating, e.g. dynamic methods
• CPC Class Codes: G01F 1/699 by control of a separate heating or cooling element
• CPC Class Codes: G01F 1/7084 using thermal detecting arrangements

Abstract

A thermal flow meter for use in dialysis is described, that uses a thermal wave to generate a signal in the fluid for which the flow rate is to be measured. The phase angle of the thermal wave signal changes when traversing downstream. The phase difference between the signals received downstream, compared with a reference excitation source signal is measured, and used to determine the flow rate of the fluid.

Claims

1. A flow rate sensor for sensing the flow rate of a fluid passing through a channel, comprising:

a. An excitation probe having a body and a contact surface, wherein said excitation probe is physically positioned within said channel;

b. A receiver probe having a body and a contact surface, wherein said receiver probe is physically positioned within said channel and wherein said receiver probe senses a thermal wave within said fluid;

c. A reference signal generator, wherein said reference signal generator outputs a reference signal;

d. A heat source, wherein said heat source receives said reference signal from said reference signal generator, is configured to thermally engage with said excitation probe, and generates a first thermal signal, having a frequency derived from said reference signal;

e. A temperature sensor, wherein said temperature sensor is configured to thermally engage with said receiver probe, and generates a second thermal signal, having a frequency derived from said thermal wave;

f. A multiplier for receiving an input signal from said reference signal generator, for receiving said second thermal signal and for outputting a third signal; and

g. A filter for receiving a fourth signal, wherein said fourth signal is a function of the third signal, and for receiving an input signal from said reference signal generator, wherein said low pass filter modulates its cutoff frequency based upon the input signal from said reference signal generator.

2. The flow rate sensor of claim 1 wherein said receiver probe is separated from said excitation probe by a distance of less than two inches.

3. The flow rate sensor of claim 1 further comprising an amplifier for amplifying said third signal and generating said fourth signal.

4. The flow rate sensor of claim 1 wherein said channel area is in the range of 3 mm² to 65 mm².

5. The flow rate sensor of claim 1 wherein the body of said receiver probe or excitation probe has a diameter in the range of 0.03 inches to 0.15 inches.

6. The flow rate sensor of claim 1 wherein the contact surface of said receiver probe or excitation probe has a diameter in the range of 0.025 inches to 0.2 inches.

7. The flow rate sensor of claim 1 wherein the excitation probe and receiver probe are embedded into a manifold and wherein the contact surfaces of said receiver probe or excitation probe are externally exposed.

8. The flow rate sensor of claim 1 wherein said filter is a low pass filter.

9. The flow rate sensor of claim 8 wherein the low pass filter generates a filtered signal and wherein the reference signal generator generates said reference signal based, at least in part, on said filtered signal.

10. The flow rate sensor of claim 1 wherein the flow rate sensor has an operative sensing range between 20 mL/min to 600 mL/min.

11. The flow rate sensor of claim 1 wherein said flow rate sensor dynamically adjusts said reference signal in order to maintain a constant phase.

12. A manifold comprising a flow rate sensor for sensing a flow rate of a fluid passing through a channel having a hydraulic diameter in a range of 1.5 mm to 7.22 mm, comprising:

a. At least two probes, each having a body embedded into a first surface of said manifold and positioned within said channel and each probe having a contact surface positioned on a surface of said manifold, wherein a first of said at least two probes generates a thermal wave within said fluid in response to a first thermal signal and a second of said at least two probes senses said thermal wave within said fluid;

b. A reference signal generator, wherein said reference signal generator outputs a reference signal;

c. A heat source, wherein said heat source receives said reference signal from said reference signal generator, is configured to thermally engage with the first of said at least two probes, and generates said first thermal signal, having a phase derived from said reference signal;

d. A temperature sensor, wherein said temperature sensor is configured to thermally engage with said second probe, and generates a second thermal signal, having a phase derived from said thermal wave;

e. A multiplier for receiving an input signal from said reference signal generator and for receiving said second thermal signal and for outputting a third signal; and

f. A low pass filter for receiving a signal derived from said third signal, and for receiving the reference signal from said reference signal generator, wherein said low pass filter modulates its cutoff frequency based upon the reference signal.

13. The manifold of claim 12 wherein said second probe is separated from said excitation probe by a distance of less than two inches.

14. The manifold of claim 12 further comprising an amplifier for amplifying said third signal and generating the signal derived from said third signal.

15. The manifold of claim 12 wherein the body of each of said at least two probes has a diameter in the range of 0.03 inches to 0.15 inches.

16. The manifold of claim 12 wherein the contact surface of each of said at least two probes has a diameter in the range of 0.025 inches to 0.2 inches.

17. The manifold of claim 12 wherein said second probe comprises a thermistor.

18. The manifold of claim 12 wherein the low pass filter generates a filtered signal and wherein the reference signal generator generates said reference signal based, at least in part, on said filtered signal.

19. The manifold of claim 12 wherein said flow rate sensor dynamically adjusts said reference signal in order to maintain a constant frequency.

20. The manifold of claim 12 wherein said flow rate sensor dynamically adjusts said reference signal in order to maintain a constant phase.