Microsensor for measuring velocity and angular direction of an incoming air stream

• US 6,502,459 B1
• Filed: 09/01/2000
• Issued: 01/07/2003
• Est. Priority Date: 09/01/2000
• Status: Expired due to Term

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.), Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Weeres, Steve R., Satren, Ernie A., Bonne, Ulrich, Kubisiak, David
• Primary Examiner(s): OEN, WILLIAM L
• Application Number:
  US09/653,399
• Time in Patent Office: 858 Days
• Field of Search: 731/700.1, 731/700.2, 731/700.7, 731/700.8, 732/041--20, 738/610.5, 738/619.5, 731/701.1, 731/701.2, 731/701.3, 731/701.4, 731/701.5
• US Class Current: 73/170.11
• CPC Class Codes: G01F 1/6845 Micromachined devices
• CPC Class Codes: G01F 1/699 by control of a separate heating or cooling element

Abstract

A rugged microsensor assembly is disclosed that measures both the velocity and angular direction of an incoming air stream. The microsensor assembly includes at least two flow sensors, each orientated to measure a different velocity component of the incoming air stream. The velocity components are related by the geometry between the sensors, and the angular direction and velocity of the incoming air stream are determined by examining the measured velocity components. The preferred sensor is a fully passivated thermal differential microanemometer with back contacts, designed to operate in harsh environments.

Claims

1. A sensor assembly for detecting the angular direction of an incoming fluid stream having a velocity, the sensor assembly comprising:

a first sensor having a first sensor axis for providing an output signal that is related to the component of the velocity of the incoming fluid stream that extends along the first sensor axis;

a second sensor having a second sensor axis for providing an output signal that is related to the component of the velocity of the incoming fluid stream that extends along the second sensor axis;

the first sensor and the second sensor positioned such that the first sensor axis intersects the second sensor axis at a point; and

determining means for determining the angular direction of the incoming fluid stream from the output signal of the first sensor and the output signal of the second sensor.

2. A sensor assembly according to claim 1, wherein the determining means further determines the velocity of the incoming fluid stream from the output signal of the first sensor and the output signal of the second sensor.

3. A sensor assembly according to claim 1, wherein the first sensor axis and the second sensor axis intersect at an angle of about 90 degrees.

4. A sensor assembly according to claim 3, wherein the determining means determines the velocity of the incoming fluid stream from the output signal of the first sensor and the output signal of the second sensor using the relation:

5. A sensor assembly according to claim 4, where n is about equal to 1.

6. A sensor assembly according to claim 4, wherein the determining means determines the angular direction of the incoming fluid stream from the output signal of the first sensor and the output signal of the second sensor using the relation:

$\mathrm{\varphi <br><br>}=\frac{A-B}{2}$

where, $A=\arccos <br><br>\text{\hspace{1em}<br><br>}\left[{\left(\frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>G_A}{v}\right)}^{1/n}\right];<br><br>$

B=90−

A; and

v=the velocity of the incoming fluid stream.

7. A sensor assembly according to claim 1, wherein the angular direction of the incoming fluid stream is related to the flight attitude of an aircraft by mounting the sensor assembly along a vertical plane.

8. A sensor assembly according to claim 2, wherein the velocity of the incoming fluid stream is related to the air speed of an aircraft.

9. A sensor assembly according to claim 1, wherein the first sensor axis and the second sensor axis intersect at an angle of less than 90 degrees.

10. A sensor assembly according to claim 9, wherein the first sensor axis and the second sensor axis intersect at an angle of 90-X degrees, where X is greater than zero.

11. A sensor assembly according to claim 9, where the determining means determines the velocity of the incoming fluid stream from the output signal of the first sensor and the output signal of the second sensor using the relation:

12. A sensor assembly for detecting the angular direction of an incoming fluid stream having a velocity, the sensor comprising:

a first microbridge flow sensor having at least one elongated heater strip and at least one elongated sensor strip both in thermal communication with the incoming fluid stream, the at least one elongated sensor strip laterally spaced from the at least one elongated heater strip, both the at least one elongated heater strip and the at least one elongated sensor strip extending at least substantially perpendicular to a first sensor axis, the first microbridge flow sensor providing an output signal that is related to the component of the velocity of the incoming fluid stream that extends along the first sensor axis;

a second microbridge flow sensor having at least one elongated heater strip and at least one elongated sensor strip both in thermal communication with the incoming fluid stream, the at least one elongated sensor strip laterally spaced from the at least one elongated heater strip, both the at least one elongated heater strip and the at least one elongated sensor strip extending at least substantially perpendicular to a second sensor axis, the second microbridge flow sensor providing an output signal that is related to the component of the velocity of the incoming fluid stream that extends along the second sensor axis;

the first microbridge flow sensor and the second microbridge flow sensor positioned such that the first sensor axis intersects the second sensor axis at a point; and

determining means for determining the angular direction of the incoming fluid stream from the output signal of the first microbridge flow sensor and the output signal of the second microbridge flow sensor.

13. A sensor assembly according to claim 12, wherein the determining means further determines the velocity of the incoming fluid stream from the output signal of the first microbridge flow sensor and the output signal of the second microbridge flow sensor.

14. A sensor assembly according to claim 13, wherein the first sensor axis and the second sensor axis intersect at an angle of about 90 degrees.

15. A sensor assembly according to claim 14, wherein the determining means determines the velocity of the incoming fluid stream from the output signal of the first microbridge flow sensor and the output signal of the second microbridge flow sensor using the relation:

$v={\left[\frac{\left(\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>G_A^{2/n}+\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>G_B^{2/n}\right)}{2}\right]}^{n/2}$

where,

Δ

G_A=the first microbridge flow sensor output signal;

Δ

G_B=the second microbridge flow sensor output signal; and

n=scaling factor.

16. A sensor assembly according to claim 15, where n=2.

17. A sensor assembly according to claim 16, wherein the determining means determines the angular direction of the incoming fluid stream from the output signal of the first microbridge flow sensor and the output signal of the second microbridge flow sensor using the relation:

$\mathrm{\varphi <br><br>}=\frac{A-B}{2}$

where, $A=\arccos <br><br>\text{\hspace{1em}<br><br>}\left[{\left(\frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>G_A}{v}\right)}^{1/n}\right];<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}$

18. A sensor assembly according to claim 13, wherein the first sensor axis and the second sensor axis intersect at an angle of less than 90 degrees.

19. A sensor assembly according to claim 18, wherein the first sensor axis and the second sensor axis intersect at an angle of 90-X degrees, where X is greater than zero.

20. A sensor assembly according to claim 19, where the determining means determines the velocity of the incoming fluid stream from the output signal of the first sensor and the output signal of the second sensor using the relation:

21. A sensor assembly according to claim 12, wherein the first microbridge flow sensor includes a heater means connected to each of the at least one elongated heater strip for providing a transient elevated temperature condition in each of the at least one elongated heater strips.

22. A sensor assembly according to claim 21, wherein the at least two elongated sensor strips of the first microbridge flow sensor have a resistance that changes with temperature.

23. A sensor assembly according to claim 22, wherein the first microbridge flow sensor further comprises:

time lag means for determining at least two time lag values each corresponding to the delay between a transient elevated temperature condition in a selected elongated heater strip and the resulting transient elevated temperature condition in at least two corresponding elongated sensor strips; and

determining means for determining the component, Δ

G_A, of the velocity of the incoming fluid stream that extends along the first sensor axis using the at least two time lag values.

24. A sensor assembly according to claim 23, wherein the second microbridge flow sensor includes a heater means connected to each of the at least one elongated heater strips for providing a transient elevated temperature condition in each of the at least one elongated heater strips.

25. A sensor assembly according to claim 24, wherein the at least two elongated sensor strips of the second microbridge flow sensor have a resistance that changes with temperature.

26. A sensor assembly according to claim 25, wherein the second microbridge flow sensor further comprises:

time lag means for determining at least two time lag values each corresponding to the delay between a transient elevated temperature condition in a selected elongated heater strip and the resulting transient elevated temperature condition in at least two corresponding elongated sensor strips; and

determining means for determining the component, Δ

G_B, of the velocity of the incoming fluid stream that extends along the second sensor axis using the at least two time lag values.

27. A sensor assembly according to claim 12, wherein the first microbridge sensor has a substrate and a bridge, the bridge carrying the at least one elongated heater strip and the at least one elongated sensor strip, the substrate having a cavity formed therein below the bridge to separate the bridge from the substrate.

28. A sensor assembly according to claim 27, wherein the bridge is at least partially thermally isolated from the substrate.

29. A sensor assembly according to claim 28, wherein the bridge has a thickness that is in the range of 1 to 15 microns.

30. A sensor assembly according to claim 27, wherein the cavity is at least substantially filled with a filler.

31. A sensor assembly according to claim 30, wherein the filler has a substantially similar thermal coefficient of expansion as the substrate.

32. A sensor assembly according to claim 30, wherein the filler is a poor thermal conductor.

33. A sensor assembly according to claim 30, wherein the filler is a UV curable epoxy.

34. A sensor assembly according to claim 30, wherein the filler is in a honeycomb configuration.

35. A sensor assembly according to claim 30, wherein the filler is in a ribbed or embossed configuration.

36. A sensor assembly according to claim 30, wherein the sensor and heater strips are deposited on a solid substrate of a low thermal conductivity material such as glass.

37. A sensor assembly according to claim 12, wherein the first microbridge sensor has a protective coating over the at least one elongated heater strip and at least one elongated sensor strip.

38. A sensor assembly according to claim 12, wherein contact is made to the at least one elongated heater strip and at least one elongated sensor strip of the first microbridge sensor via through-the-wafer (TTW) contacts.

39. A sensor assembly according to claim 38, wherein the through-the-wafer (TTW) contacts mate with corresponding mating contact posts on a header.

40. A sensor assembly according to claim 39, wherein the header includes a seal.

41. A sensor assembly according to claim 12, wherein contact is made to the at least one elongated heater strip and at least one elongated sensor strip of the first microbridge sensor via wire bonds.

42. A sensor according to claim 12, wherein the fluid is a gas.

43. A sensor according to claim 12, wherein the fluid is air.

44. A method for detecting the angular direction of an incoming fluid stream having a velocity, the method comprising the steps of:

measuring a first component of the velocity of the incoming fluid stream that extends along a first axis;

measuring a second component of the velocity of the incoming fluid stream that extends along a second axis;

the first axis intersecting the second axis at a point; and

determining the angular direction of the incoming fluid stream from the first component and the second component of the velocity of the incoming fluid stream.

45. A method according to claim 44, further comprising the step of determining the velocity of the incoming fluid stream.

46. A method according to claim 45, wherein the first axis and the second axis intersect at an angle of about 90 degrees.

47. A method according to claim 46, wherein the velocity of the incoming fluid stream is determined using the relation:

$v={\left[\frac{\left(\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>G_A^{2/n}+\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>G_B^{2/n}\right)}{2}\right]}^{n/2}$

where,

Δ

G_A=the first thermal microanemometer output signal;

Δ

G_B=the second thermal microanemometer output signal; and

n=curve fit factor.

48. A method according to claim 46, where n is about equal to 1.

49. A method according to claim 46, wherein the angular direction of the incoming fluid stream is determined using the relation:

50. A method according to claim 44, wherein the first sensor axis and the second sensor axis intersect at an angle of less than 90 degrees.

51. A method according to claim 49, wherein the first sensor axis and the second sensor axis intersect at an angle of 90−

X degrees, where X is greater than zero.

52. A method according to claim 50, where the determining means determines the velocity of the incoming fluid stream from the output signal of the first sensor and the output signal of the second sensor using the relation: