Method and apparatus for measuring fluid flow

• US 6,530,286 B1
• Filed: 05/09/2000
• Issued: 03/11/2003
• Est. Priority Date: 05/09/2000
• Status: Expired due to Fees

• Current Assignee: Reflect Scientific Inc.
• Original Assignee: David R. Carver, Thomas A. Tait
• Inventors: Carver, David R., Tait, Thomas A.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Mull, Fred H
• Application Number:
  US09/568,871
• Time in Patent Office: 1,036 Days
• Field of Search: 356/28, 738/619.5, 732/041.4
• US Class Current: 73/861.95
• CPC Class Codes: G01F 1/7084 using thermal detecting arrangements
• CPC Class Codes: G01F 1/7086 using optical detecting arrangements

Abstract

The present invention relates to methods and apparatus useful for detecting and measuring flow of a fluid along a flow path. In a method according to the invention, the temperature of a flowing fluid is altered at a selected location for a selected duration so as to generate a pulse in the fluid moving in a downstream direction along a flow path, and the fluid is monitored at a sensing region to detect the pulse passing therethrough. An apparatus according to the present invention may comprise a conduit, a sensor element disposed therein, an energy source proximate to the conduit, and a controller operative to generate an on signal and an off signal respectively operative to activate and deactivate the energy source. The present invention also relates to a liquid chromatography device having a fluid flow detecting and measuring apparatus according to the present invention.

Claims

1. An apparatus for detecting and measuring a flow rate of a fluid, comprising:

(a) a conduit sized and adapted to receive a selected volume of the fluid, said conduit defined by a surrounding sidewall having a portion thereof that is transparent to electromagnetic radiation of a frequency in the visible spectrum;

(b) a sensor element disposed in said conduit;

(c) an energy source proximate to said conduit and operative to transmit electromagnetic radiation of a frequency in the visible spectrum through said portion of said sidewall at a spaced apart location from said sensor element; and

(d) a controller operative to generate an on signal and an off signal, said on signal operative to activate said energy source for a first selected duration, and said off signal operative to deactivate said energy source for a second selected duration.

2. An apparatus according to claim 1 wherein said energy source is selected from the group consisting of a light emitting diode, a LASER and a tungsten bulb.

3. An apparatus according to claim 2 wherein said energy source includes a lens operative to focus said electromagnetic radiation.

4. An apparatus according to claim 1 wherein said surrounding sidewall includes an energy-absorbing portion thereof that is proximate to said spaced apart location.

5. An apparatus according to claim 4 wherein said surrounding sidewall includes an energy-reflecting portion adjacent said energy-absorbing portion.

6. An apparatus according to claim 1 wherein said sensor element is a thermistor.

7. An apparatus according to claim 1 wherein said controller is operative to intermittently generate said on signal and said off signal.

8. A method for detecting and measuring flow of a fluid along a flow path, comprising:

(a) moving the fluid in a downstream direction along a flow path;

(b) altering the temperature of the fluid at a selected location for a selected duration so as to generate a pulse in the fluid, said pulse having a leading edge forming a first temperature gradient and a trailing edge forming a second temperature gradient, said pulse moving in a downstream direction along said flow path;

(c) monitoring the fluid at a sensing region that is spaced apart and downstream of said selected location, thereby to detect said pulse passing through said sensing region; and

(d) wherein the step of altering the temperature occurs at a first time and said pulse is detected passing through said sensing region at a second time, and wherein said selected duration is between 10% and 20% of a time Interval between said first time and said second time.

9. A method according to claim 8 wherein the step of altering the temperature of the fluid is accomplished by heating the fluid at said selected location.

10. A method according to claim 8 wherein the step of altering the temperature of the fluid is accomplished by transmitting electromagnetic radiation of a selected frequency into the fluid at said selected location.

11. A method according to claim 10 wherein said electromagnetic radiation is of a frequency in the visible spectrum.

12. A method according to claim 8 wherein the step of altering the temperature is accomplished by passing electrical current through a resistive element that is proximate to said selected location.

13. A method according to claim 8 wherein the step of altering the temperature is accomplished by acoustically vibrating the fluid at said selected location.

14. An apparatus for detecting and measuring a flow rate of a fluid, comprising:

(a) a conduit sized and adapted to receive a selected volume of the fluid, said conduit defined by a surrounding sidewall having a portion thereof that is transparent to electromagnetic radiation;

(b) a sensor operative to detect a temperature gradient of the fluid at a selected location in said conduit;

(c) a light emitting diode proximate to said conduit and operative to transmit electromagnetic radiation through said portion of said sidewall at a spaced apart location from said sensor;

(d) an energy-absorbing band disposed on an interior surface of said surrounding sidewall of said conduit at a location aligned with said light-emitting diode and said portion of said sidewall, wherein said energy-absorbing band is operative to increase in temperature when said electromagnetic radiation passes through said portion of said sidewall; and

(e) a controller operative to generate an on signal and an off signal, said on signal operative to activate said light emitting diode for a first selected duration, and said off signal operative to deactivate said light emitting diode for a second selected duration.

15. An apparatus according to claim 14 wherein said portion of said sidewall is transparent to electromagnetic radiation of a frequency in the visible spectrum and wherein said light emitting diode is operative to transmit electromagnetic radiation of a frequency in the visible spectrum.

16. An apparatus according to claim 14 including a lens disposed between said light emitting diode and said portion of said sidewall, said lens being operative to focus said electromagnetic radiation through said portion of said sidewall towards a region inside said conduit.

17. An apparatus according to claim 14 wherein said energy-absorbing band is formed of a material selected from glassy carbon and ceramic deposited on said interior surface.

18. An apparatus according to claim 14 wherein said surrounding sidewall includes an energy-reflecting band disposed adjacent said energy-absorbing band.

19. An apparatus according to claim 18 wherein said energy-reflecting band is formed by polishing said interior surface of said conduit.

20. An apparatus according to claim 19 including a lens disposed between said light-emitting diode and said portion of said sidewall, said lens being operative to focus said electomagnetic radiation through said portion of said sidewall towards said energy-absorbing band, whereby said light-emitting diode, said lens, said energy-absorbing band and said energy-reflecting band cooperate to heat said fluid in a region adjacent said energy-absorbing band.

21. An apparatus according to claim 20 wherein said light-emitting diode, said lens, said energy-absorbing band and said energy-reflecting band cooperate to heat the fluid by 0.01°

C.

22. An apparatus for detecting and measuring a flow rate of a fluid, comprising:

(a) a first panel of a selected dimension, said first panel formed of a material operative to transmit visible light therethrough;

(b) a second panel of a selected dimension;

(c) a gasket disposed between said first and second panel, said gasket having a channel formed therethrough thereby to form a conduit defined by said first panel, said second panel and said gasket, wherein said conduit is sized and adapted to receive a selected volume of the fluid;

(d) an inlet and an outlet adapted to be placed in fluid communication with said conduit, thereby to permit fluid to flow through said inlet, along said conduit and out said outlet;

(e) a light emitting diode proximate to said first panel and operative to transmit visible light therethrough; and

(f) a sensor operative to detect a temperature gradient of the fluid at a selected location in said conduit.

23. A method for detecting and measuring flow of a fluid along a flow path, comprising:

(a) moving the fluid in a downstream direction along a flow path;

(b) heating the fluid at a selected location for a selected duration so as to raise the temperature thereof at the selected location by about 0.01°

C., thereby to generate a heat pulse in the fluid, said pulse having a leading edge forming a first temperature gradient and a trailing edge forming a second temperature gradient, said pulse moving in a downstream direction along said flow path; and

(c) monitoring the fluid at a sensing region that is spaced apart and downstream of said selected location, thereby to detect said heat pulse passing through said sensing region.

24. An apparatus for detecting and measuring a flow rate of a fluid, comprising:

(a) a conduit sized and adapted to receive a selected volume of the fluid, said conduit defined by a surrounding sidewall having a portion thereof that is capable of passing energy therethrough;

(b) a sensor element disposed in said conduit;

(c) an energy source proximate to said conduit and operative to transmit energy through said portion of said sidewall at a spaced apart location from said sensor element; and

(d) wherein said surrounding sidewall includes an energy-absorbing portion thereof that is proximate to said spaced apart location.

25. An apparatus according to claim 24 wherein said surrounding sidewall includes an energy-reflecting portion adjacent said energy-absorbing portion.