Method for digitally measuring electrical impedance

2- The device of claim 1 wherein said convolving means includes means, operatively coupled to said sampling means, for digitally multiplying each of said digitized voltages with a digitized sine wave and a digitized cosine wave.

3- The device of claim 2 wherein said digitized sine wave and said digitized cosine wave are pulled from a memory means operatively coupled to said convolving means.

4- The device of claim 3 wherein said convolving means further includes means for transforming the results of multiplying each of said digitized voltages with said digitized sine wave and said digitized cosine wave into orthogonal DC components which define a real component magnitude and an imaginary component magnitude for each of said first complex number and said second complex number correlative to said first voltage impressed across said network and said second voltage impressed across said second component.

5- The device of claim 4 wherein said determining means includes a digital signal processor operatively coupled to said convolving means for determining said ratio of said second complex number to said difference between said first and said second complex number, and wherein said calculating means includes said processor for calculating said unknown electrical impedance of said second component by multiplying said ratio by said know value of said first component.

6- The device of claim 5 wherein said signal generating means includes at least one frequency/phase programmable signal generator operatively coupled to said digital signal processor and said network for receiving digital commands from said digital signal processor for generating a frequency/phase programmable signal for driving said current through said serially connected components at a digitally programmed frequency/phase defined by said digital signal processor.

7- The device of claim 6 further including a timing control means for triggering said sampling means to sample said first voltage and said second voltage at a rate which maintains a substantially constant phase relationship between said programmable signal and the sampled voltages

8- The device of claim 1 wherein said first electrical component includes a resistance means having a known resistance value.

9- The device of claim 8 wherein said second electrical component includes a proximity probe comprising a sensing coil and a probe cable operatively coupled to said sensing coil, said proximity probe having an unknown impedance value and located proximate a conductive target material to be monitored for position.

10- The device of claim 9 wherein said means for calculating said electrical impedance of said second component by multiplying said ratio by said value of said first component includes calculating the electrical impedance of the proximity probe by multiplying said ratio by said know resistance value wherein said unknown electrical impedance of said proximity probe is digitally measured.

11- A device of claim 10 further including means for correlating the digitally measured impedance value of the proximity probe to a value defining a gap between said proximity probe and said metallic target being monitored.

13- The method of claim 12 wherein the step of convolving each of the digitized voltages with the digital waveform includes the step of multiplying each of the digitized voltages with a digital sine waveform and a digital cosine waveform and then accumulating and averaging each multiply for forming the first complex number and the second complex number including the real and the imaginary magnitudes correlative of the voltage impressed across the network and across the second electrical component respectively.

14- The method of claim 13 wherein the step of convolving each of the digitized voltages with the digital waveform includes the step of selecting from a memory means the digital sine waveform and the digital cosine waveform.

15- The method of claim 14 wherein the step of driving the network with the dynamic signal for impressing the voltage across the network and each component further includes the step of digitally programming a frequency of the dynamic waveform.

16- The method of claim 15 wherein the step of digitizing the voltage across the network and across the second electrical component includes the step of sampling the voltage across the network and across the second electrical component at a rate which maintains a substantially constant phase relationship between the dynamic signal and the sampled voltages.

17- The method of claim 12 wherein the step of forming the network including providing the first electrical component includes the step of providing the first electrical component in the form of a resistance means having a known resistance value.

18- The method of claim 17 wherein the step of forming the network including providing the second electrical component includes the step of providing the second electrical component in the form of a proximity probe including a sensing coil and a probe cable operatively coupled to said sensing coil, the proximity probe having an unknown impedance.

19- The method of claim 18 further including the step of locating the proximity probe proximate a metallic target to be monitored.

20- The method of claim 19 wherein the step of calculating the electrical impedance of the second electrical component by multiplying the ratio by the know value of the first electrical component includes calculating the electrical impedance of the proximity probe by multiplying the ratio by the know resistance value wherein the unknown electrical impedance of the proximity probe is digitally measured.

21- A method of claim 20 further including the step of correlating the digitally measured impedance value of the proximity probe to a value defining a gap between the proximity probe and the metallic target being monitored.

23- The apparatus of claim 22 wherein said processing means further includes means for calculating a complex electrical impedance value of said proximity probe from said voltage ratio and processing said impedance value into said gap value correlative to said gap between said proximity probe and said conductive target material.

24- The apparatus of claim 23 further including means for outputting a signal as a function of said gap value which is correlative to said gap between said proximity probe and said conductive target material.

25- The apparatus of claim 22 wherein said processing means further includes means for calculating a complex electrical impedance value of said proximity probe from said voltage ratio and normalizing said complex electrical impedance value into said gap value correlative to said gap between said proximity probe and said conductive target material.

26- The apparatus of claim 25 further including means for outputting a signal as a function of said gap value which is correlative to said gap between said proximity probe and said conductive target material.

28- The apparatus of claim 27 wherein said processing means further includes means for calculating a complex electrical impedance value of said proximity probe from said voltage ratio by digitally compensating for an impedance of said extension cable and processing said complex electrical impedance value into said gap value correlative to said gap between said proximity probe and said conductive target material.

29- The apparatus of claim 28 further including means for outputting a signal as a function of said gap value which is correlative to said gap between said proximity probe and said conductive target material.

30- The apparatus of claim 27 wherein said processing means further includes means for calculating a complex electrical impedance value of said proximity probe from said voltage ratio by digitally compensating for an impedance of said extension cable and normalizing said complex electrical impedance value into said gap value correlative to said gap between said proximity probe and said conductive target material.

31- The apparatus of claim 30 further including means for outputting a signal as a function of said gap value which is correlative to said gap between said proximity probe and said conductive target material.

32- The apparatus of claim 27 further including means for storing proximity probe and extension cable serials numbers for identifying said proximity probe and said extension cable in said network.

33- The apparatus of claim 32 further including a portable check out device operatively coupled to said storing means and including a bar code reader for recording into said storing means serial numbers on probes and extension cables for identifying which probe is coupled to which extension cable.

34- The apparatus of claim 33 wherein said serial numbers of probes and extension cables coded to indicate machine location and orientation.

35- The apparatus of claim 32 further including a portable check out device operatively coupled to said storing means for receiving stored probe and extension cable serials numbers and including a bar code reader for scanning probes and extension cables for identifying a match to the stored probe and extension cable serials numbers.

36- The apparatus of claim 27 further including means for determining intermittent connections on said probe and said extension cable by monitoring rates of change of said analog voltage signals sampled by said sampling means and determining if said rates of change are greater than a rate that said conductive target material can move.

37- The apparatus of claim 27 further including means for determining an intermittent on input power wiring to the apparatus by determining if power to said apparatus has caused said apparatus to reset over a certain period of time and means for communicating this information to a host computer operatively coupled to said processing means.

38- The apparatus of claim 27 further including a memory means operatively coupled to said processing means which in turn is operatively coupled to a host computer wherein a maintenance request stored in said memory means is communicated to said host computer from said apparatus.

39- The apparatus of claim 27 further including a memory means operatively coupled to said processing means for storing checkout information following installation in order to communicate to a host computer operatively coupled to said processing means wherein the host computer can discern whether said apparatus has been subject to a loop check, when the check occurred and results of the check.

40- The apparatus of claim 27 further including a memory means operatively coupled to said processing means which in turn is operatively coupled to a host computer for allowing remote access to the apparatus for determining configuration errors and needed repairs wherein required replacement components can be obtained without having to go to the location of said apparatus.

41- The apparatus of claim 40 wherein a timestamped event list is maintained in said memory means to document configuration changes.

42- The apparatus of claim 27 wherein said sampling and digitizing means samples and digitizes an analog voltage impressed across said serial connection of said extension cable and said proximity probe into digitized voltages without being driven by said alternating current and processing said voltages by said processing means for determining signals correlative to ground loops or radio frequency interference.

43- The apparatus of claim 27 wherein said processing means measures a wideband RMS voltage from said digitized voltages and compares that to a frequency of the signal driving the probe to determine if noise is being injected into the signal driving the probe.

45- The apparatus of claim 44 wherein said means for establishing dynamic voltage signals correlative to dynamic gaps between said proximity probe and said conductive target material includes a network including a first electrical component and said proximity probe serially connected, and a signal generating means operatively coupled to said network for driving a current through said serial connection wherein a first analog voltage is impressed across said network and a second analog voltage is impressed across said proximity probe for establishing said dynamic voltage signals.

46- The apparatus of claim 45 wherein said sampling means for digitizing said established dynamic voltage signals into digital voltage signals includes means for sampling and digitizing said first analog voltage impressed across said network and said second analog voltage impressed across said proximity probe into first and second digitized voltages respectively

47- The apparatus of claim 46 wherein said digital multiplier multiplies each of said first and second digitized voltages by said digital sine signal and said digital cosine signal for forming first complex number and second complex number pairs.

48- The apparatus of claim 47 wherein said means for processing each multiply for obtaining said complex voltage representations correlative to said dynamic gaps between said proximity probe and said conductive target material includes means for determining voltage ratios of each said complex number pair by determining a ratio of said second complex number to a difference between said first complex number and said second complex number for each said pair and processing with said processing means said voltage ratios into values correlative to said dynamic gaps between said proximity probe and said conductive target material.

50- The method of claim 49 further including the step of outputting a signal as a function of said gap value which is correlative to said gap between said proximity probe and said conductive target material.

51- The method of claim 49 wherein said processing step further includes the step of calculating a complex electrical impedance value of said proximity probe from said voltage ratio and processing said impedance value into said gap value correlative to said gap between said proximity probe and said conductive target material.

52- The method of claim 51 further including the step of outputting a signal as a function of said gap value which is correlative to said gap between said proximity probe and said conductive target material.

53- The apparatus of claim 49 wherein said processing step further includes the steps of calculating a complex electrical impedance value of said proximity probe from said voltage ratio, normalizing said complex electrical impedance value into a normalized value and processing said normalized value into said gap value correlative to said gap between said proximity probe and said conductive target material.

54- The apparatus of claim 53 further including means for outputting a signal as a function of said gap value which is correlative to said gap between said proximity probe and said conductive target material.

56- The method of claim 55 further including the step of storing digital values in a memory means for defining a plurality different gap values.

57- The method of claim 56 wherein the correlating step further includes the step of correlating the determined impedance to at least one stored digital value for determining the gap between the proximity probe and the conductive target material.

59- The method of claim 58 wherein said processing step further includes the step of calculating a complex electrical impedance value of the proximity probe from the voltage ratio by digitally compensating for an impedance of the extension cable and processing the complex electrical impedance value into said gap value correlative to said gap between said proximity probe and said conductive target material.

60- The method of claim 59 further including the step of outputting a signal as a function of said gap value which is correlative to said gap between said proximity probe and said conductive target material.

61- The method of claim 58 wherein said processing step further includes the steps of calculating a complex electrical impedance value of the proximity probe from the voltage ratio by digitally compensating for an impedance of said extension cable and normalizing the complex electrical impedance value into said gap value correlative to said gap between said proximity probe and said conductive target material.

62- The apparatus of claim 61 further including means for outputting a signal as a function of said gap value which is correlative to said gap between said proximity probe and said conductive target material.

63- The method of claim 58 wherein said processing step further includes the step of determining a complex electrical impedance of the serial connection of the extension cable and proximity probe by multiplying the voltage ratio by a value of the electrical component, the determined value defining a measured value of the electrical impedance of the serial connection of the extension cable and proximity probe.

64- The method of claim 63 further including the step of performing open, short and load measurements on the extension cable for determining compensation parameters and storing the parameters in a memory means, the compensation parameters including a measured open impedance of the extension cable, a measured short impedance of the extension cable, a measured impedance of a load coupled to the extension cable in place of the proximity probe, the load having a known impedance value.

66- The method of claim 65 wherein said processing step further includes the step of processing the complex electrical impedance of the proximity probe into said gap value correlative to said gap between said proximity probe and said conductive target material.

67- The method of claim 66 further including the step of outputting a signal as a function of said gap value which is correlative to said gap between said proximity probe and said conductive target material.

68- The method of claim 65 wherein said processing step further includes the steps of normalizing the complex electrical impedance value of the probe into a normalized impedance value and processing the normalized impedance value into said gap value correlative to said gap between said proximity probe and said conductive target material.

69- The apparatus of claim 68 further including means for outputting a signal as a function of said gap value which is correlative to said gap between said proximity probe and said conductive target material.

70- The method of claim 58 further including the step of storing electrical parameters for a plurality of different proximity probes and extension cables and retrieving the electrical parameters of the proximity probe that is disposed adjacent the conductive target material and the electrical parameters of the extension cable coupled to that probe for use in the step of processing the voltage ratio into a gap value correlative to a gap between the proximity probe and the conductive target material.

71- The method of claim 58 further including the step of storing electrical parameters for a plurality of different target materials and retrieving the electrical parameters of the target material in which the proximity probe is disposed adjacent to and using the retrieved parameters in the step of processing the voltage ratio into a gap value correlative to a gap between the proximity probe and the conductive target material.

73- The method of claim 72 further including the steps of normalizing the calculated electrical impedance of the proximity probe and comparing the normalized impedance to a plurality of previously compiled representations of normalized impedance curves for different conductive target materials for identifying the conductive target material prior to correlating the calculated electrical impedance to the gap between the proximity probe and the conductive target material.

74- The method of claim 72 wherein the correlating step further includes the steps of normalizing the calculated electrical impedance of the proximity probe and comparing the normalized impedance to a previously compiled representation of a plurality of gap locus lines, each defining a single gap value for different conductive target materials, for identifying a gap line for use in correlating the calculated electrical impedance to a gap between the proximity probe and the conductive target material.

75- The method of claim 70 further including the step of storing electrical parameters for a plurality of different proximity probes and retrieving the electrical parameters of the proximity probe that is disposed adjacent the conductive target material for use in the step of calculating the electrical impedance of the proximity probe.

76- The method of claim 70 further including the step of storing electrical parameters for a plurality of different target materials and retrieving the electrical parameters of the target material in which the proximity probe is disposed adjacent and using the retrieved parameters in the step of calculating the electrical impedance of the proximity probe.

78- The method of claim 77 wherein the correlating step further includes the steps of comparing the normalized electrical impedance to a plurality of previously compiled representations of normalized impedance curves for different conductive target materials for identifying the conductive target material prior to correlating the normalized electrical impedance to the gap between the proximity probe and the conductive target material.

79- The method of claim 77 wherein the correlating step further includes the step of comparing the normalized impedance to a previously compiled representation of a plurality of gap locus lines, each defining a single gap value for different conductive materials, for identifying a gap line for use in determining the gap between the proximity probe and the conductive target material.

81- The method of claim 80 wherein the correlating step further includes the steps of comparing the normalized electrical impedance to a plurality of previously compiled representations of normalized impedance curves for different conductive target materials for identifying the conductive target material prior to correlating the normalized electrical impedance to the gap between the proximity probe and the conductive target material.

82- The method of claim 81 wherein the correlating step further includes the step of comparing the normalized impedance to a previously compiled representation of a plurality of gap locus lines, each defining a single gap value for different conductive materials, for identifying a gap line for use in determining the gap between the proximity probe and the conductive target material.

83- A method for measuring a gap between a proximity probe and a conductive target material, said method including the steps of:

• digitally measuring an electrical impedance of a proximity probe located adjacent a conductive target material;
• combining a predetermined digitized impedance with the digitally measured impedance of the proximity probe;
• correlating the combined impedance to a gap interposed between the proximity probe and the conductive target material being monitored.

84- The method of claim 83 wherein the step of combining the predetermined digitized impedance with the measured impedance of the proximity probe includes combining an equivalent digitized impedance of an analog circuit with the digitally measured impedance of the proximity probe.

85- The method of claim 83 wherein the step of correlating the combined impedance to the gap interposed between the proximity probe and the conductive target material being monitored includes the step of correlating both the combined impedance and a measured frequency of a signal driving the proximity probe to the gap interposed between the probe and the conductive target material being monitored.

86- The method of claim 85 further including the step of adjusting the frequency of the signal driving the proximity probe as a function of the combined impedance and the measured frequency for correcting any anomalous phase error and subsequently driving the proximity probe at the adjusted frequency.

87- The method of claim 83 further including the step of compensating the digitally measured impedance of the proximity probe by using compensation coefficients for eliminating probe cable effects included in the proximity probe.

88- The method of claim 87 wherein the step of compensating the digitally measured impedance of the proximity probe by using compensation coefficients includes the steps of performing an open, a short and a load measurement on the probe cable for determining the compensation coefficients.

89- A method for measuring a gap between a proximity probe and a conductive target material, said method including the steps of:

• digitally measuring an electrical impedance of an a proximity probe and an extension cable connected thereto, the proximity probe is located adjacent a conductive target material;
• combining a predetermined digitized impedance with the digitally measured impedance;
• correlating the combined impedance to a gap interposed between the proximity probe and the conductive target material being monitored.

90- The method of claim 89 wherein combining the predetermined digitized impedance with the digitally measured impedance further includes the step of compensating the digital impedance of the proximity probe and extension cable by using compensation coefficients for eliminating the extension cable effects on the digitally measured impedance of the proximity probe and extension cable for forming the combined impedance.

91- The method of claim 90 wherein the step of compensating the digitally measured impedance of the proximity probe and extension cable by using compensation coefficients includes the steps of performing an open, a short and a load measurement on the extension cable for determining compensation coefficients and storing the coefficients in a memory means, the compensation coefficients including a measured open impedance of the extension cable, a measured short impedance of the extension cable and a measured impedance of a load coupled to the extension cable in place of the proximity probe, the load having a known impedance value.

93- The method of claim 92 wherein the step of combining the predetermined digitized impedance with the digitally measured impedance includes combining the predetermined digitized impedance with the compensated digitally measured impedance for forming the combined impedance.

94- The method of claim 93 wherein the step of correlating the combined impedance to the gap interposed between the proximity probe and the conductive target material being monitored further includes the steps of normalizing the combined impedance into a normalized impedance value and processing the normalized impedance value into a gap value correlative to the gap between said proximity probe and the conductive target material.

96- The method of claim 94 wherein the correlating step further includes the steps of comparing the normalized impedance value to a plurality of previously compiled representations of normalized impedance curves for different conductive target materials for identifying the conductive target material prior to processing the normalized impedance value into a gap value correlative to the gap between said proximity probe and the conductive target material.

97- The method of claim 94 wherein the correlating step further includes the step of comparing the normalized impedance value to a previously compiled representation of a plurality of gap locus lines, each defining a single gap value for different conductive materials, for identifying a gap line for use in the step of processing the normalized impedance value into a gap value correlative to the gap between the proximity probe and the conductive target material.

98- The method of claim 89 wherein the step of combining the predetermined digitized impedance with the digitally measured impedance includes combining an equivalent digitized impedance of an analog circuit with the digitally measured impedance.

100- The method of claim 99 wherein the step of combining the predetermined impedance with the measured impedance includes combining an equivalent impedance of an analog circuit with the digitally compensated impedance.

102- The method of claim 101 wherein the step of providing a database of normalized impedance curve representations for different conductive target materials includes providing at least one lookup table storing values of each normalized impedance curve for each different target material.

103- The method of claim 102 wherein the step of providing a database of normalized impedance curve representations for different conductive target materials includes providing at least one equation in the database to represent normalized impedance curves for different target materials.

105- The method of claim 104 wherein the step of providing the representation of the defined series of gap locus that represent the same gap for different target materials includes using a lookup table to represent the series of gap locus.

106- The method of claim 104 wherein the step of providing the representation of the defined series of gap locus that represent the same gap for different target materials includes using at least one equation to represent the series of gap locus.

107- The method of claim 104 wherein the determining step further includes comparing the normalized probe impedance with the representation of the defined series of gap locus in the database for determining a gap locus which defines the gap value between the proximity probe and the conductive target material wherein the gap value is substantially correct for any conductive target material adjacent the proximity probe thereby providing the material insensitive method for measuring gap values between the proximity probe and different conductive target materials.

109- The method of claim 108 wherein the determining step further includes comparing the normalized coil impedance with the representation of the defined series of gap locus in the database for determining a gap locus that corresponds to the normalized impedance value of the coil for defining the gap value between the proximity probe and the conductive target material wherein the gap value is substantially correct for different conductive target materials adjacent the proximity probe thereby providing the material insensitive method for measuring gap values between the proximity probe and different conductive target materials.

113- The method of claim 112 wherein the step of compensating the measured impedance by mathematically eliminating the extension cable residuals includes the steps of determining a first impedance of the extension cable with the first end opened for defining an open impedance, determining a second impedance of the extension cable with the first end shorted for defining a short impedance, and determining a third impedance of the extension cable with the first end coupled to a load having a known value for defining a load impedance.

114- The method of claim 113 wherein the step of compensating the measured impedance by mathematically eliminating the extension cable residuals from the measured impedance further includes the step of determining the proximity probe impedance as a function of the measured impedance, the open impedance, the short impedance and the load impedance for defining the proximity probe impedance of the proximity probe.

115- The method of claim 112 wherein the step of compensating the measured impedance by mathematically eliminating the extension cable residuals includes the step of using compensation coefficients stored in a memory means for defining the proximity probe impedance as a function of the compensation coefficients.

116- The method of claim 115 wherein the step of using compensation coefficients stored in a memory means includes the steps of determining a first impedance of the extension cable with the first end opened for defining an open impedance coefficient, determining a second impedance of the extension cable with the first end shorted for defining a short impedance coefficient, and determining a third impedance of the extension cable with the first end coupled to a load having a known value for defining a load impedance coefficient wherein the opened impedance coefficient, the short impedance coefficient and the load impedance coefficient are included in the compensation coefficients stored in the memory means for defining the proximity probe impedance.

118- The method of claim 117 wherein the step of determining the impedance of the proximity probe as a function of the short impedance, the open impedance and the measured impedance for defining the proximity probe impedance includes the step of calculating the impedance of the proximity probe from compensation coefficients representative of the short impedance, the open impedance and the measured impedance for defining the proximity probe impedance.

120- The method of claim 119 wherein the step of determining an impedance of the proximity probe as a function of the short impedance, the open impedance, the load impedance and the measured impedance for defining the proximity probe impedance includes the step of calculating the impedance of the proximity probe from compensation coefficients representative of the short impedance, the open impedance, the load impedance and the measured impedance for defining the proximity probe impedance.

122- The method of claim 121 further including the step of determining a third load impedance of the extension cable with one of the two ends coupled to a third load, the third load having an impedance that is less than the impedance of the first load and greater than the impedance of the second load.

123- The method of claim 122 wherein the step of calculating the proximity probe impedance of the proximity probe as the function of the measured impedance, the first load impedance, and the second load impedance for compensating for extension cable residuals includes calculating the proximity probe impedance of the proximity probe as a function of the measured impedance, the first load impedance, the second load impedance, and the third load impedance for compensating for extension cable residuals.

125- The method of claim 124 further including the step of determining a third impedance of the cable with the first end coupled to a load having a known value for defining a load impedance.

126- The method of claim 125 wherein the step of calculating the proximity probe impedance as a function of the measured impedance, the open impedance, and the short impedance for compensating for cable length residuals includes calculating the proximity probe impedance as a function of the measured impedance, the open impedance, the short impedance, and the load impedance for compensating for cable length residuals.