Time lag approach for measuring fluid velocity

• US 6,234,016 B1
• Filed: 12/31/1997
• Issued: 05/22/2001
• Est. Priority Date: 12/31/1997
• Status: Expired due to Term

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell International Inc.
• Inventors: Matthys, Robert J., Schuldt, Spencer B., Bonne, Ulrich, Kubisiak, David
• Primary Examiner(s): Fuller, Benjamin R.
• Assistant Examiner(s): THOMPSON, JEWEL VERGIE
• Application Number:
  US09/002,157
• Time in Patent Office: 1,238 Days
• Field of Search: 732/042.6, 732/042.5, 732/041.5
• US Class Current: 73/204.26
• CPC Class Codes: G01F 1/6845 Micromachined devices
• CPC Class Codes: G01F 1/6884 making use of temperature dependence of optical properties
• CPC Class Codes: G01F 1/692 Thin-film arrangements
• CPC Class Codes: G01F 1/696 Circuits therefor, e.g. constant-current flow meters
• CPC Class Codes: G01F 1/7084 using thermal detecting arrangements
• CPC Class Codes: G01P 5/10 by measuring thermal variables
• CPC Class Codes: G01P 5/22 using auto-correlation or cross-correlation detection means

Abstract

A method and apparatus for measuring the velocity of a fluid relatively independently of the physical properties of the fluid. This is preferably accomplished by spacing two sensor elements at different distances from a heater element. The present invention also contemplates minimizing the effects of the non-zero heater time lag and/or the non-zero sensor time lag for increased accuracy. This is preferably accomplished by either measuring the time lags and subtracting the values thereof from an uncorrected transit time measurement, forcing the sensor elements to track the thermal disturbance in the fluid thereby minimizing the effects of the sensor time lags, or measuring the transit time using sensors that have substantially zero thermal mass.

Claims

1. Apparatus for determining the fluid velocity, V, of a fluid of interest, comprising:

heater means in thermal communication with the fluid of interest, said heater means having a resistance that changes with temperature;

heater energizing means connected to said heater means for energizing said heater means, said heater energizing means providing a transient elevated temperature condition in said heater means;

at least two sensor means in thermal communication with the fluid of interest, each of the at least two sensor means spaced a different distance from said heater means, and each having a resistance that changes with temperature;

time lag means for determining at least two time lag values each corresponding to the delay between said heater means and a corresponding sensor means; and

determining means for determining the fluid velocity, v, of the fluid of interest using the at least two time lag values.

2. Apparatus according to claim 1 wherein the at least two time lag values each corresponding to the delay between the transient elevated temperature condition of said heater means and a transient elevated temperature response of a corresponding one of said sensor means.

3. Apparatus according to claim 2 wherein there are two sensor means, and said determining means determines the fluid velocity based on the relation:

4. Apparatus according to claim 1 wherein each of the sensor means has a corresponding sensor energizing means for energizing the corresponding sensor means with in input power signal, the input power signals having a phase relative to the periodic time-varying input signal of said heater energizing means such that substantially no heat is transferred from the fluid of interest to the at least two sensor means during the transient elevated temperature condition.

5. Apparatus according to claim 1 wherein said heater energizing means provides a periodic time-varying input signal to said heater means to induce the transient elevated temperature condition in said heater means, said apparatus further comprising first output means for providing a first output signal that is proportional to the resistance of said heater means.

6. Apparatus according to claim 5 wherein each of the sensor means has a corresponding sensor energizing means for energizing the corresponding sensor means, each of said sensor energizing means providing a periodic time-varying input signal to the corresponding sensor means that is out of phase relative to the periodic time-varying input signal of said heater energizing means.

7. Apparatus according claim 6 wherein each of the sensor means has a corresponding output means for providing a number of second output signals, each of the second output signals being proportional to the resistance of the corresponding sensor means, and wherein each of the sensor means has a corresponding second time lag means for determining a second time lag value for each of the at least two sensor means, the second time lag values representing the time from the corresponding input power signal provided by the corresponding sensor energizing means to the corresponding second output signal.

8. Apparatus according to claim 7 wherein each of the sensor energizing means comprise a phase shifter for shifting the phase of the periodic time-varying input signal provided by said heater energizing means by an amount which causes each of said second time lag values to be substantially equivalent to a corresponding predetermined value.

9. Apparatus according to claim 8 wherein the predetermined value is equivalent to the second time lag for the corresponding sensor means when measured with the sensor means in a vacuum.

10. Apparatus according to claim 9 wherein the input power signal provided by each of said sensor energizing means has an amplitude that is selected to provide a power-resistance ratio in each of the corresponding sensor means that is substantially identical to the power-resistance ratio in the corresponding sensor means when measured under a vacuum.

11. Apparatus according to claim 1 wherein each of the at least two sensor means comprise a wire.

12. Apparatus according to claim 1 wherein each of the at least two sensor means comprise a film.

13. Apparatus according to claim 1 wherein at least one of the sensor means is positioned upstream from the heater means and at least one of the sensor means is positioned downstream of said heater means.

14. Apparatus according to claim 1 wherein at least two of the sensor means are positioned downstream of said heater means, with a first sensor means positioned closer to the heater means than a second sensor means.

15. Apparatus according to claim 14 wherein the first sensor means is used to measure a first fluid velocity, while the second sensor means is used to measure a second fluid velocity, wherein the second fluid velocity is lower than the first fluid velocity.

16. Apparatus according to claim 1 wherein at least two of the sensor means are positioned upstream of said heater means, with a first sensor means positioned closer to the heater means than a second sensor means.

17. Apparatus according to claim 16 wherein the first sensor means is used to measure a first fluid velocity, while the second sensor means is used to measure a second fluid velocity, wherein the second fluid velocity is lower than the first fluid velocity.

18. Apparatus according to claim 1 wherein said heater energizing means provides an input signal to said heater means to produce the transient elevated temperature condition in said heater means, said heater energizing means providing a first amplitude input signal to said heater means when measuring a first fluid velocity and a second amplitude input signal for measuring a second fluid velocity, wherein the second fluid velocity is lower than the first fluid velocity.

19. Apparatus according to claim 1 wherein said heater energizing means provides a periodic time-varying input signal to said heater means during a measurement period, and subsequently providing a relatively static input signal to said heater means during a wait period.

20. Apparatus according to claim 19 wherein said wait period is longer than said measurement period.

21. Apparatus for determining the fluid velocity, v, of a fluid of interest, comprising:

heater means in thermal communication with the fluid of interest, said heater means having a resistance that changes with temperature;

heater energizing means connected to said heater means for energizing said heater means, said heater energizing means providing a heater input signal to said heater means to provide a transient elevated temperature condition in said heater means;

first sensor means in thermal communication with the fluid of interest, said first sensor means spaced a first distance from said heater means and having a resistance that changes with temperature;

second sensor means in thermal communication with the fluid of interest, said second sensor means spaced a second distance from said heater means wherein said second distance is different from said first distance, and having a resistance that changes with temperature;

first sensor energizing means connected to said first sensor means for providing a first sensor input signal to said first sensor means;

second sensor energizing means connected to said second sensor means for providing a second sensor input signal to said second sensor means;

first sensor time lag means for determining a first sensor time lag between the first sensor input signal and the resulting resistance change of said first sensor means;

second sensor time lag means for determining a second sensor time lag between the second sensor input signal and the resulting resistance change of said second sensor means;

said first input power signal being out of phase relative to the input signal provided by said heater energizing means by a sufficient amount to cause said first sensor time lag to be substantially equivalent to a first predetermined time value;

said second input power signal being out of phase relative to the input signal provided by said heater energizing means by a sufficient amount to cause said second sensor time lag to be substantially equivalent to a second predetermined time value;

output time lag means for determining a first output time lag, Δ

z₁, between the heater and the first sensor, and a second output time lag, Δ

z₂, between the heater and the second sensor; and

determining means for determining the fluid velocity, v, of the fluid of interest using the relation;

22. Apparatus according to claim 21 wherein the first output time lag, Δ

z₁, corresponds to the delay between the heater input signal and the first sensor output signal, and the second output time lag, Δ

z₂, corresponds to the delay between the heater input signal and the second sensor output signal.

23. Apparatus according to claim 21 further comprising heater time lag means for determining a heater time lag between the heater input signal and the resulting resistance change of said heater means during the transient elevated temperature condition.

24. Apparatus according to claim 23 wherein the heater time lag is subtracted from the time lag between the heater input signal and the first sensor input signal to provide the first output time lag, Δ

z₁, and the heater time lag is subtracted from the lag between the heater input signal and the second sensor input signal to provide the second output time lag, Δ

z₂.

25. Apparatus according to claim 21 wherein said first predetermined value is equivalent to the first sensor time lag when measured under a vacuum condition.

26. Apparatus according to claim 25 wherein said second predetermined value is equivalent to the second sensor time lag when measured under a vacuum condition.

27. Apparatus according to claim 26 wherein the first sensor input signal has an amplitude that is selected to provide a power-resistance ratio in said first sensor means that is substantially identical to a power-resistance ratio of said first sensor means when measured under a vacuum condition.

28. Apparatus according to claim 27 wherein the second sensor input signal has an amplitude that is selected to provide a power-resistance ratio in said second sensor means that is substantially identical to a power-resistance ratio of said second sensor means when measured under a vacuum condition.

29. A method for determining the fluid velocity, v, of a fluid of interest using a heater element and at least two spaced sensor elements, the method comprising the steps of:

providing a first one of the sensor elements a first distance from the heater element, and a second one of the sensor elements a second distance from the heater element, wherein the second distance is greater than the first distance;

energizing said heater element to providing a transient elevated temperature condition in said heater element;

determining a first time lag value between the heater element and the first one of the sensor elements;

determining a second time lag value between the heater element and the second one of said sensor elements;

determining the fluid velocity, v, of the fluid of interest using the first and second time lag values.

30. A method according to claim 29 wherein the first time lag value corresponds to the delay between the heater input signal and the first sensor output signal, and the second time lag value corresponds to the delay between the heater input signal and the second sensor output signal.

31. A method according to claim 29 wherein said determining step determines the fluid velocity, v, of the fluid of interest using the relation:

32. A method according to claim 29 further comprising the steps of:

energizing said first sensor element with a first sensor input signal having a phase and amplitude such that substantially no heat is transferred from the fluid of interest to the first sensor element during the transient elevated temperature condition; and

energizing said second sensor element with a second sensor input signal having a phase and amplitude such that substantially no heat is transferred from the fluid of interest to the second sensor element during the transient elevated temperature condition.

33. A method for measuring the velocity of a fluid of interest using a heater element and a number of spaced sensor elements, the method comprising the steps of:

providing a first one of the sensor elements a first distance from the heater element, and a second one of the sensor elements a second distance from the heater element, wherein the first distance is greater than the second distance;

providing a time-varying heater input signal to said heater element to provide a transient elevated temperature condition in said heater element;

providing a first sensor input signal to said first sensor element;

providing a second sensor input signal to said second sensor element;

determining a first sensor time lag between the first sensor input signal and the resulting resistance change of said first sensor element;

determining a second sensor time lag between the second sensor input signal and the resulting resistance change of said second sensor element;

changing the phase of the first sensor input signal relative to the heater input signal by a sufficient amount to cause said first sensor time lag to be substantially equivalent to a first predetermined time value.

changing the phase of the second sensor input signal relative to the heater input signal by a sufficient amount to cause said second sensor time lag to be substantially equivalent to a second predetermined time value.

determining a first output time lag, Δ

z₁, by determining the lag between the heater and the first sensor;

determining a second output time lag, Δ

z₂, by determining the lag between the heater and the second sensor;

determining the fluid velocity, v, of the fluid of interest using the relation;

34. A method according to claim 33 further comprising the steps of:

determining a heater lag time between the heater input signal and the resulting resistance change of said heater element;

determining the first output time lag, Δ

z₁, by determining the lag between the heater and the first sensor input signal and subtracting the heater lag time; and

determining a second output time lag, Δ

z₂, by determining the lag between the heater input and the second sensor input signal and subtracting the heater lag time.

35. A method for determining a time lag between a transient elevated temperature condition of a heater element and the transient elevated temperature response of a sensor element through a fluid of interest, the method comprising the steps of:

energizing the heater element to providing a transient elevated temperature condition in said heater element and thus the fluid of interest;

energizing the sensor element with a sensor input signal, wherein said sensor input signal has a phase and an amplitude that causes substantially no heat to be transferred from the fluid of interest to the sensor element during the transient elevated temperature condition; and

measuring the time lag between said heater element and the sensor element.

36. Apparatus for determining a time lag between a first location and a second location for a transient elevated temperature condition in a fluid, comprising:

energizing means for energizing a heater element that is thermally coupled to the fluid, thereby providing the transient elevated temperature condition in the fluid;

first optical means for optically detecting the transient elevated temperature condition at a first location;

second optical means for optically detecting the transient elevated temperature condition at a second location, wherein the second location is spaced from the first location; and

determining means for determining the time lag between the detected temperature response at the first location and the detected temperature response at the second location.

37. A method for determining a time lag between a first location and a second location for a transient elevated temperature condition in a fluid, comprising the steps of:

energizing a heater element that is thermally coupled to the fluid, thereby providing the transient elevated temperature condition in the fluid;

optically detecting the transient elevated temperature condition at a first location using a first optical device;

optically detecting the transient elevated temperature condition at a second location using a second optical device, wherein the second location is spaced from the first location; and

determining the time lag between the detected temperature response at the first location and the detected temperature response at the second location.