Absolute property measurement with air calibration

• US RE39,206 E1
• Filed: 02/13/2003
• Issued: 07/25/2006
• Est. Priority Date: 10/29/1997
• Status: Expired due to Term

• Current Assignee: Jentek Sensors, Inc.
• Original Assignee: Jentek Sensors, Inc.
• Inventors: Goldfine, Neil J., Schlicker, Darrell E., Washabaugh, Andrew P.
• Primary Examiner(s): PATIDAR, JAY M
• Application Number:
  US10/366,306
• Time in Patent Office: 1,258 Days
• Field of Search: 324/202, 324/207.17, 324/207.18, 324/207.19, 324/225, 324/207.26, 324/227, 324229-233, 324239-243, 324/262, 340/870.32
• US Class Current: 324/243
• CPC Class Codes: G01N 27/023 where the material is placed in the field of a coil
• CPC Class Codes: G01N 27/72 by investigating magnetic variables

Abstract

An instrument and method for providing accurate and reproducible measurement of absolute properties of a material under test without using conductivity or crack calibration standards. The instrument has a sensor designed to minimize unmodeled parasitic effects. To accomplish this, the sensor has one or more of the following features: dummy secondary elements located at the ends of a primary winding meandering, setting back of the sensing element from a connecting portion of the primary winding, or various grouping of secondary elements. The sensing elements of the sensor can be connected individually or in differential mode to gather absolute or differential sensitivity measurements. In addition, the instrumentation is configured such that a significant portion of the instrumentation electronics is placed as close to the sensor head to provide independently controllable amplification of the measurement signals therein reducing noise and other non-modeled effects.

Claims

1. A sensor comprising:

a primary wincing meandering in a back and forth square wave-like pattern and having a plurality of parallel legs, a half wavelength defined by the space between a pair of adjacent parallel legs;

a plurality of sensing elements, the sensing elements interposed between the legs of the primary winding,

dummy sensing elements located in half wavelengths at ends of the primary winding for maintaining the periodicity of the field for the sensing elements.

2. The sensor of claim 1 wherein sensing elements opening to one side of the primary winding are connected in series to one another and sensing elements opening to the other side of the primary winding are connected to one another.

3. The sensor of claim 2 further comprising at least one additional sensing element near the end of the primary winding and defining a small pixel for detection of the edge of a material under test.

4. The sensor of claim 1 wherein each of the sensing elements has a pair of distinct leads.

5. The sensor of claim 1 wherein the primary winding has a plurality of connecting portions for connecting the plurality of parallel legs and wherein each of the sensing elements has an end which is spaced from a connection portion of primary winding within a range of one-quarter and one-half of wavelength.

6. The sensor of claim 1 further comprising leads to the sensing elements, the leads shouldered in from the sensing elements to minimize coupling of the leads of the sensing elements to the primary winding.

7. A sensor comprising:

a primary winding meandering in a back and forth square wave-like pattern and having a plurality of parallel legs, a half wavelength defined by the space between a pair of adjacent parallel legs; and

a plurality of sensing elements, the sensing elements interposed between the legs of the primary winding, the sensing elements opening to one side of the primary winding being connected in a plurality of distinct groups and the sensing elements opening to the other side of the primary winding being connected in a plurality of distinct groups.

8. The sensor of claim 7 wherein at least one group of the one side overlaps a plurality of groups on the other side.

9. The sensor of claim 8 wherein the gap between the sensing element and the parallel legs of the primary winding is approximately an eighth of a wavelength for minimizing coupling of shorter wavelength modes.

10. The sensor of claim 8 wherein the primary winding has a plurality of connecting portions for connecting the plurality of parallel legs and wherein each of the sensing elements has an end which is spaced from a connection portion of primary winding within a range of one-quarter and one-half of wavelength.

11. The sensor of claim 8 further comprising leads to the sensing elements, the leads shouldered in from the sensing elements to minimize coupling of the leads of the sensing elements to the primary winding.

12. The sensor of claim 7 wherein at least one group on the one side has less sensing elements than the at least one group on the other side and all the sensing elements of the one group on the one side are interposed between sensing elements of the one group of the other side.

13. The sensor of claim 12 wherein the gap between the sensing element and the parallel legs of the primary winding is approximately an eighth of a wavelength for minimizing coupling of shorter wavelength modes.

14. The sensor of claim 12 wherein the primary winding has a plurality of connecting portions for connecting the plurality of parallel legs and wherein each of the sensing elements has an end which is spaced from a connection portion of primary winding within a range of one-quarter and one-half of wavelength.

15. The sensor of claim 12 further comprising leads to the sensing elements, the leads shouldered in from the sensing elements to minimize coupling of the leads of the sensing elements to the primary winding.

16. A sensor comprising:

a primary winding meandering in a back and forth square wave-like pattern and having a plurality of parallel legs, a half wave length defined by the space between a pair of adjacent parallel legs;

a plurality of sensing elements, the sensing elements interposed between the legs of the primary winding; and

a gap between the sensing element and the parallel legs of the primary winding is approximately an eighth of a wavelength for minimizing coupling of shorter wavelength modes.

17. The sensor of claim 16 further comprising a pair of dummy sensing elements, each dummy sensing element located at an end of the primary winding in the last half wavelength of primary winding for maintaining the periodicity of the field for the sensing element.

18. The sensor of claim 16 wherein the primary winding has a plurality of connecting portions for connecting the plurality of parallel legs and wherein each of the sensing elements has an end which is spaced from a connection portion of primary winding within a range of one-quarter and one-half of wavelength.

19. The sensor of claim 16 further comprising leads to the sensing elements, the leads shouldered in from the sensing element to minimize coupling of the leads of the sensing elements to the primary winding.

20. An instrument for measuring property of a material comprising

a sensor having

a primary winding meandering in a square wave pattern and having a plurality of parallel legs, a half wave length defined by the space between a pair of adjacent parallel legs;

and

a plurality of sensing elements, the sensing elements interposed between the legs of the primary winding;

a probe head for holding the sensor;

an impedance analyzer for inputting an input current or voltage source at a temporal excitation frequency and measuring the output from the sensing elements, the analyzer having remote analog components; and

a property analyzer for analysis of the measured output.

21. The instrument of claim 20 wherein the probe head contains a differential amplifier therein minimizing unmodeled change in the sensor behavior.

22. The sensor of claim 21 further comprising a pair of dummy sensing elements, each dummy sensing element located at an end of the primary winding in the last half wavelength of primary winding for maintaining the periodicity of the field for the sensing element.

23. The sensor of claim 21 wherein the primary winding has a plurality of connecting portions for connecting the plurality of parallel legs and wherein each of the sensing elements has an end which is spaced from a connection portion of primary winding between a range of one-quarter and one-half of wavelength.

24. The instrument of claim 21 further comprising a grid model in the property analyzer.

25. The instrument of claim 20 further comprising a remote instrument module spaced from the property analyzer and containing an analog portion of the impedance analyzer for increasing the signal to noise ratio.

26. The sensor of claim 25 further comprising a pair of dummy sensing elements, each dummy sensing element located at an end of the primary winding in the last half wavelength of primary winding for maintaining the periodicity of the field for the sensing element

27. The sensor of claim 25 wherein the primary winding has a plurality of connecting portions for connecting the plurality of parallel legs and wherein each of the sensing elements has an end which is spaced from the connection portion of primary winding between a range of one-quarter and one-half of wavelength.

28. The instrument of claim 25 further comprising a grid model in the property analyzer.

29. The instrument of claim 20 further comprising a remote instrument module spaced from the property analyzer and containing the independently controllable amplifiers for the input current and measurement voltage for optimizing or tuning the electronics to a representative range in properties for the material under test.

30. The sensor of claim 29 further comprising a pair of dummy sensing elements, each dummy sensing element located at an end of the primary winding in the last half wavelength of primary winding for maintaining the periodicity of the field for the sensing element.

31. The sensor of claim 29 wherein the primary winding has a plurality of connecting portions for connecting the plurality of parallel legs and wherein each of the sensing elements has an end which is spaced from the connection portion of primary winding between a range of one-quarter and one-half of wavelength.

32. The instrument of claim 29 further comprising a grid model in the property analyzer.

33. A method of calibration of a sensor comprising the following steps:

providing a sensor having a primary winding meandering in a square wave pattern with a plurality of parallel legs and a plurality of sensing elements with the sensing elements interposed between the legs of the primary winding;

connecting the sensor to an impedance analyzer;

placing the sensor in the air away from a material under test;

introducing a current into the primary winding;

measuring the voltage resulting on the sensing elements using the impedance analyzer; and

aligning the phase and magnitude of the impedance to a measurement grid.

34. The method of claim 33 wherein the step of aligning comprises shifting and scaling the measured impedance.

35. The method of claim 33 wherein the step of aligning comprises shifting the measurement grid.

36. The method of claim 33 further comprising varying a known property to verify and tune calibration.

37. The method of claim 36 wherein the property is lift-off.

38. The method of claim 36 wherein the property is conductivity.

39. The method of claim 36 wherein the property is permeability.

40. A method of measuring a property of a material comprising the following steps:

providing a sensor having a primary winding meandering in a square wave pattern with a plurality of parallel legs and a plurality of sensing elements with the sensing elements interposed between the legs of the primary winding;

connecting the sensor to an impedance analyzer;

placing the sensor in the air away from a material under test;

introducing a current into the primary winding;

measuring the voltage resulting on the sensing elements using the impedance analyzer;

aligning the phase and magnitude of the impedance to a measurement grid;

moving the sensor in proximity to the material under test;

introducing a current into the primary winding;

measuring the voltage resulting on the sensing elements using the impedance analyzer; and

converting the phase and magnitude of the impedance using the measurement grid to determine at least one unknown property of interest.

41. A method of measuring a property of a material comprising the following steps:

providing a sensor having a primary winding meandering in a square wave pattern with a plurality of parallel legs and a plurality of sensing elements with the sensing elements interposed between the legs of the primary winding, wherein the sensor elements opening to one side of the primary winding are connected in a plurality of distinct groups and sensing elements opening to the other side of the primary winding are connected in a plurality of distinct groups and each of the groups of the one side having at least one sensing element located interposed between sensing elements of a group on the other side; and

at least one sensing element located interposed between sensing elements of a second group on the other side, therein the groups overlapping;

connecting the sensor to an impedance analyzer;

moving the sensor in proximity to a material under test;

introducing a current into the primary winding;

measuring the voltage resulting on the sensing elements using the impedance analyzer; and

converting the phase and magnitude of the impedance using the measurement grid to determine at least one unknown property of interest.

42. A method of measuring a property of a material comprising the following steps:

providing a sensor having a primary winding meandering in a square wave pattern with a plurality of parallel legs and a plurality of sensing elements with the sensing elements interposed between the legs of the primary winding, wherein the sensor elements opening to one side of the primary winding are connected in a plurality of distinct groups and sensing elements opening to the other side of the primary winding are connected in a plurality of distinct groups and at least one group on the one side has less sensing elements that the at least one group on the other side and all the sensing elements of the one group on the one side are interposed between sensing elements of the one group of the other side;

connecting the sensor to an impedance analyzer;

moving the sensor in proximity to a material under test;

introducing a current into the primary winding;

measuring the voltage resulting on the sensing elements using the impedance analyzer; and

converting the phase and magnitude of the impedance using the measurement grid to determine at least one unknown property of interest.

43. A method of measuring a property of a material comprising the following steps:

providing a sensor having a primary winding meandering in a square wave pattern with a plurality of parallel legs and a plurality of sensing elements with the sensing elements interposed between the legs of the primary winding;

connecting the sensor to an impedance analyzer;

moving the sensor in proximity to a material under test;

introducing a current into the primary winding;

measuring the voltage resulting on the sensing elements using the impedance analyzer; and

converting the abase and magnitude of the impedance using a measurement grid wherein all the sensing elements are grouped together for absolute measurements.

44. A method of measuring a property of a material comprising the following steps:

providing a sensor having a primary winding meandering in a square wave pattern with a plurality of parallel legs and a plurality of sensing elements with the sensing elements interposed between the legs of the primary winding;

connecting the sensor to an impedance analyzer;

moving the sensor in proximity to a material under test;

introducing a current into the primary winding;

measuring the voltage resulting on the sensing elements using the impedance analyzer; and

converting the chase and magnitude of the impedance using a measurement grid of at least one sensing element to determine the absolute measurement of at least one property and measuring the differences between sensing elements to increase the sensitivity to at least one unknown property.

45. A sensor comprising:

a primary winding of at least three parallel conducting segments, a half wavelength defined by the space between a pair of adjacent parallel segments having current flowing in opposite directions;

a plurality of sensing elements, the sensing elements interposed between the segments of the primary winding;

dummy sensing elements located in half wavelengths at ends of the primary winding for maintaining the periodicity of the field for the sensing elements.

46. The sensor of claim 45 wherein sensing elements opening to one side of the primary winding are connected in series to one another and sensing elements opening to the other side of the primary winding are connected to one another.

47. The sensor of claim 46 further comprising at least one additional sensing element near the end of the primary winding and defining a small pixel for detection of the edge of a material under test.

48. The sensor of claim 45 wherein each of the sensing elements has a pair of distinct leads.

49. The sensor of claim 45 wherein the primary winding has a plurality of connecting portions for connecting the at least three parallel segments and wherein each of the sensing elements has an end which is spaced from a connection portion of primary winding within a range of one-quarter and one-half of wavelength.

50. The sensor of claim 45 further comprising leads to the sensing elements, the leads shouldered in from the sensing elements to minimize coupling of the leads of the sensing elements to the primary winding.

51. A sensor comprising:

a primary winding of at least three parallel conducting segments, a half wavelength defined by the space between a pair of adjacent parallel segments having current flowing in opposite directions and;

a plurality of sensing elements, the sensing elements interposed between the segments of the primary winding, the sensing elements opening to one side of the primary winding being connected in a plurality of distinct groups and the sensing elements opening to the other side of the primary winding being connected in a plurality of distinct groups.

52. The sensor of claim 51 wherein at least one group of the one side overlaps a plurality of groups on the side.

53. The sensor of claim 52 wherein the gap between the sensing element and the parallel segments of the primary winding is approximately an eighth of a wavelength for reducing coupling of shorter wavelength modes.

54. The sensor of claim 52 wherein the primary winding has a plurality of connecting portions for connecting the at least three parallel segments and wherein each of the sensing elements has an end which is spaced from a connection portion of primary winding within a range of one-quarter and one-half of wavelength.

55. The sensor of claim 52 further comprising leads to the sensing elements the leads shouldered in from the sensing elements to minimize coupling of the leads of the sensing elements to the primary winding.

56. The sensor of claim 51 wherein at least one group on the one side has less sensing elements than the at least one group on the other side and all the sensing elements of the one group on the one side are interposed between sensing elements of the one group of the other side.

57. The sensor of claim 56 wherein the gap between the sensing element and the parallel segments of the primary winding is approximately an eight of a wavelength for reducing coupling of shorter wavelength modes.

58. The sensor of claim 56 wherein the primary winding has a plurality of connecting portions for connecting the at least three parallel segments and wherein each of the sensing elements has an end which is spaced from a connection portion of primary winding within a range of one-quarter and one-half wavelength.

59. The sensor of claim 56 further comprising leads to the sensing elements, the leads shouldered in from the sensing elements to minimize coupling of the leads of the sensing elements to the primary winding.

60. A sensor comprising:

a primary winding of at least three parallel conducting segments, a half wavelength defined by the space between a pair of adjacent parallel segments having current flowing in opposite directions;

a plurality of sensing elements, the sensing elements interposed between the segments of the primary winding; and

a gap between the sensing element and the parallel segments of the primary winding for reducing coupling of shorter spatial wavelength field modes.

61. The sensor of claim 60 wherein the gap is approximately an eighth of a wavelength.

62. The sensor of claim 60 further comprising a pair of dummy sensing elements, each dummy sensing element located at an end of the primary winding in the last half wavelength of primary winding for maintaining the periodicity of the field for the sensing element.

63. The sensor of claim 60 wherein the primary winding has a plurality of connecting portions for connecting the at least two parallel segments and wherein each of the sensing elements has an end which is spaced from a connection portion of primary winding within a range of one-quarter and one-half of wavelength.

64. The sensor of claim 60 further comprising leads to the sensing elements, the leads shouldered in from the sensing element to minimize coupling of the leads of the sensing elements to the primary winding.

65. An instrument for measuring property of a material comprising:

a sensor having

a primary winding of at least three parallel conducting segments, a half wavelength defined by the space between a pair of adjacent parallel segments having current flowing in opposite directions; and

a plurality of sensing elements, the sensing elements interposed between the segments of the primary winding;

a probe head for holding the sensor;

an impedance analyzer for inputting an input current or voltage source at a temporal excitation frequency and measuring the output from the sensing elements, the analyzer having remote analog components; and

a property analyzer for analysis of the measured output.

66. The instrument of claim 65 wherein the probe head contains a differential amplifier for minimizing unmodeled changes in the sensor behavior.

67. The sensor of claim 66 further comprising a pair of dummy sensing elements, each dummy sensing element located at an end of the primary winding in the last half wavelength of primary winding for maintaining the periodicity of the field for the sensing element.

68. The sensor of claim 66 wherein the primary winding has a plurality of connecting portions for connecting the at least three parallel segments and wherein each of the sensing elements has an end which is spaced from a connection portion of primary winding within a range of one-quarter and one-half of wavelength.

69. The instrument of claim 66 further comprising a measurement grid in the property analyzer.

70. The instrument of claim 66 further comprising a model for the sensor response in the property analyzer.

71. The instrument of claim 65 further comprising a remote instrument module spaced from the property analyzer and containing an analog portion of the impedance analyzer for increasing the signal to noise ratio.

72. The sensor of claim 71 further comprising a pair of dummy sensing elements, each dummy sensing element located at an end of the primary winding in the last half wavelength of primary winding for maintaining the periodicity of the field for the sensing element.

73. The sensor of claim 71 wherein the primary winding has a plurality of connecting portions for connecting the at least three parallel segments and wherein each of the sensing elements has an end which is spaced from a connection portion of primary winding within a range of one-quarter and one-half of wavelength.

74. The instrument of claim 71 further comprising a measurement grid in the property analyzer.

75. The instrument of claim 71 further comprising a model for the sensor response in the property analyzer.

76. The instrument of claim 65 further comprising a remote instrument module spaced from the property analyzer and containing the independently controllable amplifiers for the input current and measurement voltage for optimizing or tuning the electronics to a representative range in properties for the material under test.

77. The sensor of claim 76 further comprising a pair of dummy sensing elements, each dummy sensing element located at an end of the primary winding in the last half wavelength of primary winding for maintaining the periodicity of the field for the sensing element.

78. The sensor of claim 76 wherein the primary winding has a plurality of connecting portions for connecting the at least three parallel segments and wherein each of the sensing elements has an end which is spaced from a connection portion of primary winding within a range of one-quarter and one-half of wavelength.

79. The instrument of claim 76 further comprising a measurement grid in the property analyzer.

80. The instrument of claim 76 further comprising a model for the sensor response in the property analyzer.

81. A method of calibration of a sensor comprising:

a primary winding of at least three parallel conduct in segments and a plurality of sensing elements with the sensing elements interposed between the segments of the primary winding;

connecting the sensor to an impedance analyzer;

placing the sensor in the air away from a material under test;

introducing a current into the primary winding;

measuring the voltage resulting on the sensing segments using the impedance analyzer; and

aligning impedance to match a prediction for the sensor response.

82. The method of claim 81 wherein the phase and magnitude of the impedance are aligned.

83. The method of claim 81 wherein the prediction is based upon a model calculation for the sensor response.

84. The method of claim 81 wherein the prediction is based upon a measurement grid.

85. The method of claim 81 wherein the step of aligning comprises shifting and scaling the measured impedance.

86. The method of claim 81 wherein the step of aligning comprises shifting the prediction for the sensor response.

87. The method of claim 81 further comprising measuring the impedance with the sensor on a test material of known properties to verify the calibration.

88. The method of claim 87 wherein the property is lift-off.

89. The method of claim 87 wherein the property is conductivity.

90. The method of claim 87 wherein the property is permeability.

91. The method of claim 81 further comprising measuring the impedance with the sensor on a test material with a varied property to verify calibration.

92. The method of claim 81 further comprising measuring the impedance with the sensor on a test material with a varied property to tune calibration.

93. A method of measuring a property of a material comprising the following steps:

providing a sensor having a primary winding of at least three parallel conducting segments and a plurality of sensing elements with the sensing elements interposed between the segments of the primary winding;

connecting the sensor to an impedance analyzer;

placing the sensor in the air away from a material under test,

introducing a current into the primary winding;

measuring the voltage resulting on the sensing elements using the impedance analyzer;

aligning impedance to a prediction of the sensor response;

moving the sensor in proximity to the material under test;

introducing a current into the primary winding;

measuring the voltage resulting on the sensing elements using the impedance analyzer; and

converting the impedance to a prediction of the sensor response to determine at least one unknown property of interest.

94. The method of claim 93 further comprising using the phase and magnitude of the impedance.

95. The method of claim 93 wherein the prediction is based upon a model calculation for the sensor response.

96. The method of claim 93 wherein the prediction is based upon a measurement grid.

97. A method of measuring a property of a material comprising the following steps:

providing a sensor having a primary winding of at least three parallel conducting segments and a plurality of sensing elements with the sensing elements interposed between the segments of the primary winding, wherein the sensor elements opening to one side of the primary winding are connected in a plurality of distinct groups and sensing elements opening to the other side of the primary winding are connected in a plurality of distinct groups and each of the groups of the one side having at least one sensing element located interposed between sensing elements of a group on the other side and at least one sensing element located interposed between sensing elements of a second group on the other side, therein the groups overlapping;

connecting the sensor to an impedance analyzer;

moving the sensor in proximity to the material under test;

introducing a current into the primary winding;

measuring the voltage resulting on the sensing elements using the impedance analyzer; and

converting impedance using a prediction of the sensor response to determine at least one unknown property of interest.

98. The method of claim 97 wherein the phase and magnitude of the impedance are converted into the at least one unknown property of interest.

99. The method of claim 97 wherein the prediction is based upon a model calculation for the sensor response.

100. The method of claim 97 wherein the prediction is based upon a measurement grid.

101. A method of measuring a property of a material comprising the following steps:

providing a sensor having a primary winding of at least three parallel conducting segments and a plurality of sensing elements with the sensing elements interposed between the segments of the primary winding, wherein the sensor elements opening to one side of the primary winding are connected in a plurality of distinct groups and sensing elements opening to the other side of the primary winding are connected in a plurality of distinct groups and at least one group on the one side has less sensing elements than the at least one group on the other side and all the sensing elements of the one group on the one side are interposed between sensing elements of the one group on the other side;

connecting the sensor to an impedance analyzer;

moving the sensor in proximity to the material under test;

introducing a current into the primary winding;

measuring the voltage resulting on the sensing elements using the impedance analyzer; and

converting impedance using a prediction of the sensor response to determine at least one unknown property of interest.

102. The method of claim 101 wherein the phase and magnitude of the impedance are converted into the at least one unknown property of interest.

103. The method of claim 101 wherein the prediction is based upon a model calculation for the sensor response.

104. The method of claim 101 wherein the prediction is based upon a measurement grid.

105. A method of measuring a property of a material comprising the following steps:

providing a sensor having a primary winding of at least three parallel conducting segments and a plurality of sensing elements with the sensing interposed between the segments of the primary winding,

connecting the sensor to an impedance analyzer;

moving the sensor in proximity to the material under test;

introducing a current into the primary winding;

measuring the voltage resulting on the sensing elements using the impedance analyzer; and

converting impedance using a prediction of the sensor response wherein all the sensing elements are grouped together for absolute measurements.

106. The method of claim 105 wherein the phase and magnitude of the impedance are converted into the property of the material.

107. The method of claim 105 wherein the prediction is based upon a model calculation for the sensor response.

108. The method of claim 105 wherein the prediction is based upon a measurement grid.

109. A method of measuring a property of a material comprising the following steps:

providing a sensor having a primary winding of at least three parallel conducting segments and a plurality of sensing elements with the sensing elements interposed between the segments of the primary winding,

connecting the sensor to an impedance analyzer;

moving the sensor in proximity to the material under test;

introducing a current into the primary winding;

measuring the voltage resulting on the sensing elements using the impedance analyzer, and

converting impedance using a prediction of the sensor response of at least one sensing element to determine the absolute measurement of at least one property and measuring the differences between sensing elements to increase the sensitivity to at least one unknown property.

110. The method of claim 109 wherein the phase and magnitude of the impedance are converted into the property of the material.

111. The method of claim 109 wherein the prediction is based upon a model calculation for the sensor response.

112. The method of claim 109 wherein the prediction is based upon a measurement grid.