Strain gauge with moisture barrier and self-testing circuit

• US 20060213278A1
• Filed: 03/28/2005
• Published: 09/28/2006
• Est. Priority Date: 03/28/2005
• Status: Active Grant

• Current Assignee: Lord Corporation (Parker-Hannifin Corporation)
• Original Assignee: MicroStrain, Inc. (Spectris PLC)
• Inventors: Arms, Steven W., Townsend, Christopher P., Churchill, David L., Mundell, Steven W.
• Granted Patent: US 7,461,560 B2
• Time in Patent Office: Days
• US Class Current: 73/781
• CPC Class Codes: G01B 7/16 for measuring the deformation in a solid, e.g. by resistance strain gauge
• CPC Class Codes: G01B 7/20 formed by printed-circuit technique
• CPC Class Codes: G01L 1/2268 Arrangements for correcting or for compensating unwanted effects
• CPC Class Codes: G01L 1/26 Auxiliary measures taken, or devices used, in connection with the measurement of force, e.g. for preventing influence of transverse components of force, for preventing overload
• CPC Class Codes: G01M 5/0083 by measuring variation of impedance, e.g. resistance, capacitance, induction
• CPC Class Codes: G01N 27/223 for determining moisture content, e.g. humidity rain detectors on vehicle windows B60S1/0825
• CPC Class Codes: G01N 33/442 Resins, plastics

Abstract

A structure includes a structure surface and a protective cover. The protective cover includes a circuit having a component, a moisture detector, and a radio frequency transmitter. The component is adhesively connected to the structure surface with an adhesive connection. The moisture detector is positioned to provide information about moisture in the protective cover. The circuit is for providing data derived from the component and from the moisture detector to the radio frequency transmitter for external transmission. The component may be a strain sensor. The moisture detector may be a capacitor. A moisture barrier may also be provided.

Claims

1. A device, comprising a strain sensing device and a moisture detector, wherein said strain sensing device is integral with said moisture detector.

2. A device, as recited in claim 1, wherein said strain sensing device and said moisture detector or both mounted on the same thin flexible substrate.

3. A device, as recited in claim 2, wherein said thin flexible substrate includes an insulative material including at least one from the group polyimide and fiberglass.

4. A device, as recited in claim 1, wherein said moisture detector extends on three sides of said strain sensing device.

5. A device, as recited in claim 1, wherein said moisture detector includes a capacitor.

6. A device, as recited in claim 1, wherein said capacitor includes a dielectric having a dielectric constant that varies with moisture.

7. A device, as recited in claim 1, wherein said strain gauge includes a material having a resistance that varies with changes in strain.

8. A device, as recited in claim 1, further comprising a metal carrier, wherein said integral strain gauge and moisture detector are mounted on said metal carrier, wherein said metal carrier can be welded to a structure.

9. A device, as recited in claim 1, wherein said integral strain gauge and moisture detector include an adhesive, wherein said integral strain gauge and moisture detector can be bonded to a structure with said adhesive.

10. A device, as recited in claim 1, wherein said integral strain gauge and moisture detector includes a plurality of strain gauges.

11. A device for mounting on a structure surface comprising a protective cover, said protective cover including a circuit having a component, a moisture detector, and a radio frequency transmitter, said component for bonding to the structure surface with a bond susceptible to damage from moisture, said moisture detector positioned to provide information about moisture in said protective cover, said circuit for providing data derived from said component and from said moisture detector to said radio frequency transmitter for external transmission.

12. A device as recited in claim 11, wherein said component comprises a sensor.

13. A device as recited in claim 12, wherein said sensor comprises a strain gauge.

14. A device as recited in claim 11, wherein said moisture detector comprises a capacitor.

15. A device as recited in claim 14, wherein said capacitor includes a dielectric that has a dielectric constant that varies with the presence of moisture.

16. A device as recited in claim 15, wherein said dielectric includes one from the group air, polyimide, and epoxy.

17. A device as recited in claim 14, wherein said capacitor is located adjacent said component.

18. A device as recited in claim 14, wherein said component includes component capacitance and a component dielectric, wherein said component capacitance and said component dielectric serve as said moisture detector.

19. A device as recited in claim 11, wherein said circuit further comprises a microprocessor connected to receive data from said component and from said moisture detector.

20. A device as recited in claim 11, wherein said protective cover further comprises a moisture barrier.

21. A device as recited in claim 20, wherein said moisture barrier comprises a wax material.

22. A device as recited in claim 21, wherein said wax material substantially fills said protective cover.

23. A device for mounting on a structure surface, comprising a protective cover, said protective cover including a component, a circuit, and a moisture barrier, said component for bonding to the structure surface with a bond susceptible to damage from moisture, said circuit including a radio frequency transmitter, said circuit for providing data derived from said component to said radio frequency transmitter for external transmission.

24. A structure as recited in claim 23, wherein said moisture barrier comprises wax.

26. A structure as recited in claim 24, wherein said sensor comprises a strain sensor.

27. A structure as recited in claim 23, wherein said protective cover includes two ports for filling said protective cover with said wax and providing an exhaust for while filling.

28. A structure as recited in claim 23, wherein said circuit further comprises a microprocessor and signal conditioning.

29. A method of monitoring, comprising the steps of:

a) providing a circuit including a moisture sensor, a second electronic component, and a radio frequency transmitter, said second electronic component having a function different from detecting moisture, wherein said moisture sensor is located to provide information about moisture in or around said second electronic component;

b) providing data derived from said second electronic component to said radio frequency transmitter for external transmission; and

c) monitoring said moisture sensor.

25. A structure as recited in claim 33, wherein said component comprises a sensor.

30. A method as recited in claim 29, wherein said moisture detector comprises a capacitor.

31. A method as recited in claim 30, wherein said capacitor includes a dielectric that has a dielectric constant that varies with the presence of moisture.

32. A method as recited in claim 31, wherein said dielectric includes one from the group air, polyimide, and epoxy.

33. A method as recited in claim 30, wherein said capacitor is located adjacent said component.

34. A method as recited in claim 30, wherein said component includes component capacitance and a component dielectric, wherein said component capacitance and said component dielectric serve as said moisture detector.

35. A method as recited in claim 30, wherein said capacitor dielectric comprises a curable material and wherein capacitance of said capacitor is sensitive to amount of curing of said material, further comprising the step of monitoring curing by monitoring said capacitance.

36. A method as recited in claim 29, wherein said second electronic component comprises a sensor.

37. A method as recited in claim 36, wherein said sensor comprises a strain gauge.

38. A method as recited in claim 29, further comprising rejecting data from said second electronic component while moisture level determined from said moisture sensor is outside a specification.

39. A method as recited in claim 29, wherein said circuit further comprises a microprocessor and signal conditioning connected to receive data from said second component and from said capacitor.

40. A method as recited in claim 29, further comprising providing a protective cover and enclosing said moisture sensor, said second electronic component, and said radio frequency transmitter within said protective cover.

41. A method as recited in claim 40, further comprising providing a moisture barrier within said protective cover.

42. A method as recited in claim 41, wherein said moisture barrier comprises a wax material.

43. A method as recited in claim 42, further comprising substantially filling said protective cover with said wax material.

44. A method as recited in claim 41, wherein said moisture barrier comprises a thin layer on said moisture sensor and on said second component.

45. A method as recited in claim 41, wherein said moisture barrier comprises a foam material.

54. A method as recited in claim 43, wherein said moisture barrier comprises a wax material.

46. A method of mounting a strain gauge to a structure surface, comprising the steps of:

a) providing a strain sensor, a capacitor, an adhesive and a transmitter, wherein said capacitor has a capacitance subject to change with curing or with moisture;

b) mounting said strain sensor on said structure surface with said adhesive;

c) mounting said capacitor on said structure surface;

d) providing data derived from said strain sensor to said transmitter and transmitting said data;

e) monitoring a parameter of said capacitor to detect problems with curing or moisture.

47. A method as recited in claim 46, wherein said capacitor includes a dielectric that is sensitive to presence of moisture.

48. A method as recited in claim 47, wherein said dielectric has a dielectric constant that varies with the presence of moisture.

49. A method as recited in claim 46, further comprising the step of rejecting data from said strain sensor while said capacitance is outside a specification.

50. A method as recited in claim 46, wherein said capacitor is located adjacent said strain sensor.

51. A method as recited in claim 46, wherein said strain sensor includes a strain sensor capacitance and said strain sensor serve as said capacitor.

52. A method as recited in claim 46, wherein said circuit further comprises a microprocessor and signal conditioning connected to receive data from said strain sensor and from said capacitor.

53. A method as recited in claim 46, further comprising a protective cover and a moisture barrier.

55. A method as recited in claim 46, wherein said parameter is RC delay of an RC circuit including said capacitor.

56. A method as recited in claim 46, wherein said parameter is capacitance of said capacitor.

57. A structure, comprising a structure surface and a protective cover, said protective cover mounted on said structure surface, an energy providing device within said protective cover, said protective cover having a protective cover outer surface, said protective cover outer surface having a convex shape with a curvature extending from said structure surface to transfer impact loads into compression loads.

58. A structure as recited in claim 57, wherein said energy providing device includes a battery.

59. A structure as recited in claim 58, wherein said battery is sealed within said protective cover.

60. A structure as recited in claim 58, wherein said battery is replaceably sealed within said protective cover.

61. A structure as recited in claim 60, wherein said replaceable seal includes an o-ring.

62. A structure as recited in claim 57, wherein said energy providing device includes an energy harvesting device.

63. A structure as recited in claim 57, further comprising a sensor and a transmitter within said protective cover.

64. A structure as recited in claim 63, wherein said sensor includes a strain sensor.

65. A structure as recited in claim 63, wherein said strain sensor is adhesively mounted on said structure surface within said protective cover.

66. A structure as recited in claim 57, further comprising a moisture sensor within said protective cover.

67. A structure as recited in claim 57, further comprising a moisture barrier within said protective cover.

68. A structure as recited in claim 67, wherein said moisture barrier comprises a wax material.

69. A structure as recited in claim 68, wherein said wax material substantially fills said protective cover.

70. A structure as recited in claim 67, wherein said moisture barrier comprises a thin layer of material.

71. A structure as recited in claim 67, wherein said moisture barrier comprises a foam material.

72. A structure as recited in claim 57, wherein said protective cover is adhesively mounted on said structure surface.

73. A structure, comprising a structure surface, a strain sensor, a transmitter, a battery, and a protective cover, said protective cover adhesively mounted on said structure surface, said battery replaceably sealed within said protective cover, said strain sensor adhesively mounted on said structure surface within said protective cover, and said transmitter within said protective cover, a moisture barrier on said strain sensor within said protective cover, said protective cover having a protective cover outer surface, said protective cover outer surface having a convex shape with a curvature extending from said structure surface to transfer impact loads into compression loads.