Wireless vibrating strain gauge for smart civil structures

• US 7,591,187 B2
• Filed: 05/10/2006
• Issued: 09/22/2009
• Est. Priority Date: 05/10/2005
• Status: Expired due to Fees

• Current Assignee: MicroStrain, Inc. (Spectris PLC)
• Original Assignee: MicroStrain, Inc. (Spectris PLC)
• Inventors: Hamel, Michael John
• Primary Examiner(s): Caputo; Lisa M
• Assistant Examiner(s): DAVIS, OCTAVIA L
• Application Number:
  US11/431,194
• Publication Number:
  US 20060254365A1
• Time in Patent Office: 1,231 Days
• Field of Search: 737/78
• US Class Current: 73/778
• CPC Class Codes: G01B 17/04 for measuring the deformation in a solid, e.g. by vibrating string

Abstract

A gauge includes a wire, a housing, a coil, a processor, and a power supply. The wire is mounted in the housing to vibrate at a natural frequency. The coil is magnetically coupled to the wire. The processor is connected to provide a digital signal to the coil and the processor is further connected to detect when the wire is vibrating. An embodiment provides an efficient technique to excite the wire into vibration. Another embodiment enables long term operation from a small battery. Another embodiment enables wireless communications to be used, eliminating the need for cable runs.

Claims

1. A gauge, comprising a wire, a coil, and a source of excitation current pulses, wherein said wire is mounted to vibrate at natural frequency of said wire, wherein said coil is magnetically coupled to said wire, wherein said source of excitation current pulses includes a programmable processor and a memory, wherein said source of excitation current pulses is connected to provide a train of excitation current pulses to said coil, wherein each excitation current pulse of said train of excitation current pulses has an excitation time, wherein said train of excitation current pulses has a period and a time between excitation current pulses, wherein said excitation time is less than said time between excitation current pulses, wherein said memory includes a program to automatically vary said period of said train of pulses to reach a period that stimulates said wire to vibrate at said natural frequency.

2. A gauge as recited in claim 1, wherein said programmable processor includes an input connected to receive a signal from said coil.

3. A gauge as recited to claim 1, further comprising a second coil magnetically coupled to said wire, wherein said programmable processor is connected to receive a signal from said second coil.

4. A gauge as recited in claim 1, wherein said coil is part of a circuit, wherein said circuit includes a variable reactance for adjusting resonance of said circuit and for providing said circuit at resonance at any frequency within a range of frequencies to provide efficient electromagnetic radiation from said coil to said wire.

5. A gauge as recited in claim 1, wherein said circuit includes a variable capacitance.

6. A gauge as recited in claim 1, wherein said wire and said coil are mounted in a housing.

7. A gauge as recited in claim 6, wherein said source of excitation current pulses includes a programmable processor and a memory, wherein said programmable processor and said memory are mounted in said housing.

8. A gauge as recited in claim 7, further comprising a wireless transmitter and a power supply mounted in said housing, wherein power for operating said wireless transmitter is derived from said power supply, further wherein said wireless transmitter is connected to transmit data derived from said wire.

9. A gauge as recited in claim 7, further comprising a wireless transmitter and a power supply, said wireless transmitter mounted in said housing, wherein power for operating said wireless transmitter is derived from said power supply, wherein said power supply is external to said housing, further comprising a wired connection for providing power from said power supply to said coil, said processor, said memory and said wireless transmitter.

10. A gauge as recited in claim 1, further comprising a temperature sensor, wherein said temperature sensor is positioned to provide a temperature of said wire, wherein said temperature sensor is connected to said programmable processor.

11. A gauge as recited in claim 1, further comprising a power supply and a switch, wherein said switch is connected to said power supply and to said coil to provide an excitation current pulse of said train of excitation current pulses to said coil when said switch is closed, wherein said switch has a control terminal, wherein said programmable processor is connected to said control terminal, wherein timing of closing and opening said switch is controlled by a digital signal from said programmable processor.

12. A gauge as recited in claim 11, wherein said coil emits a train of magnetic pulses for stimulating said wire to vibrate, wherein said magnetic pulses have a magnetic pulse period equal to said period.

13. A gauge, as recited to claim 12, wherein said programmable processor is further connected to receive a signal between pulses of said train of pulses indicating that said wire is vibrating.

14. A gauge as recited in claim 1, wherein said programmable processor is further connected to receive a signal indicating that said wire is vibrating.

15. A gauge as recited in claim 14, wherein said connection for detecting when said wire is vibrating includes a signal conditioning circuit.

16. A gauge as recited in claim 15, wherein said signal conditioning circuit includes a capacitor and an amplifier.

17. A gauge as recited in claim 1, further comprising a wired connection for providing power and for communicating data.

18. A gauge as recited in claim 1, further comprising a wireless transmitter and a power supply.

19. A gauge as recited in claim 18, wherein said wireless transmitter is part of a wireless transceiver.

20. A gauge as recited in claim 19, wherein operation of said wireless transceiver is programmable.

21. A gauge as recited in claim 20, further comprising a first housing, an electronic switch, a temperature sensor, wherein said programmable processor, said power supply, said electronic switch, said temperature sensor, and said wireless transceiver are mounted within said first housing.

22. A gauge as recited in claim 20, further comprising a first housing, a second housing, a temperature sensor, wherein said coil and said temperature sensor are mounted in said first housing, wherein said programmable processor, said power supply, and said wireless transceiver are mounted in said second housing.

23. A gauge as recited in claim 20, further comprising a first housing, a second housing, a temperature sensor and a switch, wherein said coil, said programmable processor, said switch, and said temperature sensor are mounted in said first housing, wherein said wireless transceiver is mounted in said second housing.

24. A gauge as recited in claim 23, wherein said power supply is mounted in said second housing.

25. A gauge as recited in claim 18, further comprising a base station, wherein said wireless transmitter transmits to said base station.

26. A gauge as recited in claim 18, wherein said power supply includes a battery.

27. A gauge as recited in claim 18, wherein said power supply includes an energy harvesting circuit.

28. A gauge as recited in claim 1, further comprising a transient voltage suppressor circuit.

29. A gauge as recited in claim 1, further comprising a housing, a temperature sensor, and a switch, wherein said coil, said programmable processor, said switch, and said temperature sensor are mounted in said housing.

30. A gauge as recited in claim 29, further comprising a cable and a reader, said cable for hard wired connection to said reader.

31. A gauge as recited in claim 30, wherein said reader includes said power supply.

32. A gauge as recited in claim 1, wherein said programmable processor includes a program to receive a signal between each pulse of said train of pulses.

33. A gauge as recited in claim 1, comprising just one coil.

34. A gauge as recited in claim 1, wherein said memory includes a program to control provision of said excitation to said coil, wherein said program provides a train of pulses with a gradually changing period until a signal is received indicating that said wire is vibrating.

35. A gauge as recited in claim 34, wherein said train of pulses has an excitation time that is less than or equal to one quarter of said period.

36. A gauge as recited in claim 34, wherein said memory includes a program to correct said period for changes in temperature.

37. A gauge as recited in claim 1, wherein said wire is connected to at least one from the group consisting of a spring, a pressure sensitive diaphragm, and a weight.

38. A gauge as recited in claim 1, further comprising a plurality of nodes and a base station, wherein each node includes at least one said wire, coil, processor, and memory, wherein said plurality of nodes are in network communication with said base station.

39. A gauge as recited in claim 38, wherein said network communication with said base station is wireless.

40. A gauge as recited in claim 38, wherein said base station further includes a device for communicating to a remote server.

41. A gauge as recited in claim 38, wherein said base station further includes an energy harvesting element.

42. A gauge as recited in claim 1, further comprising a variable capacitance.

43. A gauge as recited in claim 42, wherein said variable capacitance includes a switched array of fixed value capacitors.

44. A gauge as recited in claim 42, wherein said variable capacitance is connected for dynamically tuning said coil to match frequency of said wire.

45. A gauge as recited in claim 1, wherein said memory includes a program for determining frequency of vibration of said wire from number of zero crossings in a measured time.

46. A gauge as recited in claim 1, wherein said programmable processor is capable of sleep mode and wherein said memory includes a program to enter said processor into sleep mode.

47. A gauge as recited in claim 1, wherein said wire is mounted to a structure for measuring changes in strain of the structure.

48. A method of making a measurement, comprising:

a. providing a wire, a coil, and a source of excitation current pulses, wherein said wire is mounted to vibrate at natural frequency of said wire, wherein said coil is magnetically coupled to said wire, wherein said source of excitation current pulses includes a programmable processor and a memory, wherein said source of excitation current pulses is connected to provide a train of excitation current pulses to said coil;

b. providing said train of excitation current pulses to said coil, wherein each excitation current pulse of said train of excitation current pulses has an excitation time, wherein said train of excitation current pulses has a period and a time between excitation current pulses, wherein said excitation time is less than said time between excitation current pulses, wherein said memory includes a program for running on said processor to automatically vary said period of said train of pulses to reach a period that stimulates said wire to vibrate at said natural frequency;

c. using said processor to automatically vary said period to reach a period that stimulates said wire to vibrate at said natural frequency; and

d. receiving a response signal derived from said vibration of said wire.

49. A method as recited in claim 48, further comprising determining that said wire is vibrating from presence of said response signal above a threshold.

50. A method as recited in claim 49, further comprising determining a parameter characteristic of frequency of vibration of said wire.

51. A method as recited in claim 49, further comprising storing and transmitting frequency of vibration of said wire when wire vibration is detected.

52. A method as recited in claim 51, further comprising measuring a temperature related to temperature of said wire, further comprising storing and transmitting said temperature.

53. A method as recited in claim 48, further comprising:

a. providing a switch and a power supply, wherein said switch includes a control terminal, wherein said control terminal is connected to said programmable processor, wherein said switch is connected to said power supply and to said coil to provide current to said coil when said switch is closed; and

b. providing a digital control signal from said programmable processor to said control terminal to repeatedly close and to open said switch to provide said train of excitation current pulses from said power supply to said coil, wherein said digital control signal has a first frequency, wherein said train of excitation current pulses has said first frequency, and wherein said coil emits a train of magnetic pulses at said first frequency for stimulating said wire to vibrate.

54. A method as recited to claim 48, wherein said response signal includes an analog signal, wherein said analog signal is received between excitation current pulses of said train of excitation current pulses.

55. A method as recited in claim 54, further comprising determining that said wire is vibrating from presence of said analog signal above a predetermined threshold.

56. A method as recited in claim 55, further comprising determining a parameter characteristic of frequency of vibration of said wire.

57. A method as recited in claim 48, further comprising providing at least one housing, wherein said wire, said coil, said programmable processor, and said memory are mounted in said at least one housing.

58. A method as recited in claim 57, wherein said wire, said coil, said programmable processor, and said memory are mounted in one housing.

59. A method as recited in claim 48, further comprising measuring a temperature related to temperature of said wire.

60. A method as recited in claim 59, further comprising providing a digital excitation signal from said programmable processor, wherein said digital excitation signal is in a frequency range based on a previous measurement as corrected for said measured temperature.

61. A method as recited in claim 48, further comprising providing a signal conditioning circuit for detecting when said wire is vibrating.

62. A method as recited in claim 61, wherein said signal conditioning circuit includes a capacitor and an amplifier.

63. A method as recited in claim 48, further comprising providing a wireless transmitter linked to receive and transmit data derived from vibration of said wire.

64. A method as recited in claim 63, wherein said wireless transmitter is part of a wireless transceiver.

65. A method as recited in claim 64, wherein power provided to said transceiver is under control of said programmable processor.

66. A method as recited in claim 48, further comprising providing a transient voltage suppressor circuit.

67. A method as recited in claim 48, further comprising measuring current in said coil at two times between said current pulses in said coil.

68. A method as recited in claim 67, wherein said two times are set to provide approximately a maximum difference if said wire is vibrating.

69. A method as recited in claim 68, further comprising repeatedly measuring current in said coil, further comprising averaging differences of said repeated two measurements.

70. A method as recited in claim 48, further comprising providing said programmable processor in sleep mode.

71. A method as recited in claim 48, further comprising performing a calculation in said programmable processor and transmitting a calculated result to provide at least one from the group including strain, pressure, inclination, temperature, displacement, and level.

72. A method as recited in claim 48, further comprising a base station, further comprising providing wirelessly transmitting data to said base station.

73. A method as recited in claim 48, comprising just one coil.

74. A method as recited in claim 48, further comprising providing a train of excitation current pulses with a gradually changing period.

75. A method as recited in claim 74, wherein said train of excitation current pulses has an excitation time that is less than or equal to one quarter of said period.

76. A method as recited in claim 48, further comprising correcting period for changes in temperature.

77. A method as recited in claim 48, further comprising connecting said wire to at least one from the group consisting of a spring, a pressure sensitive diaphragm, and a weight.

78. A method as recited in claim 48, further comprising providing a plurality of nodes and a base station, wherein each node includes at least one said wire coil, processor, and memory, and further comprising providing said plurality of nodes in network communication with said base station.

79. A method as recited in claim 78, wherein said network communication with said base station is wireless and wirelessly communicating with said base station.

80. A method as recited in claim 78, wherein said base station further includes a device for communicating to a remote server and communicating with said remote server.

81. A method as recited in claim 78, wherein said base station further includes an energy harvesting element and providing energy from said energy harvesting element to each of said plurality of nodes.

82. A method as recited in claim 48, further comprising a power supply.

83. A method as recited in claim 82, wherein said power supply includes a battery.

84. A method as recited in claim 82, wherein said power supply includes an energy harvesting circuit.

85. A method as recited in claim 48, further comprising determining frequency of vibration of said wire while said wire is vibrating.

86. A method as recited in claim 48, further comprising attaching said wire to a structure for measuring changes in strain of the structure.

87. A gauge comprising a wire, a coil, a programmable processor, a memory, a wireless transmitter, and an energy harvesting circuit, wherein said wire is mounted to vibrate at natural frequency of said wire, wherein said coil is magnetically coupled to said wire, wherein said programmable processor provides a digital signal, wherein said programmable processor is connected to provide a train of excitation current pulses to said coil, wherein said train of excitation current pulses is derived from said digital signal, wherein each excitation current pulse of said train of excitation current pulses has an excitation time, wherein said train of excitation current pulses has a period and a time between excitation current pulses, wherein said excitation time is less than said time between excitation current pulses, wherein said memory includes a program to automatically vary said period of said train of pulses to reach a period that stimulates said wire to vibrate at said natural frequency, wherein said coil, said programmable processor, said memory and said wireless transmitter receive all power for their operation derived from said energy harvesting circuit.