Bridgeless system for directly measuring complex impedance of an eddy current probe
First Claim
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1. An eddy current measuring system comprising:
- an eddy current measuring probe having an electromagnetic coil;
a reference resistor connected in series with said electromagnetic coil for producing a reference resistor value;
means for applying a first driving signal to said coil;
means for producing second and third voltage signals respectively representing a probe current in said coil and a probe voltage across said coil, said second and third signals being produced during the time said driving signal is applied to said coil;
means for analog-to-digital converting said second and third signals;
means for determining a plurality of magnitude and phase angle values representing the complex impedance of said probe from said converted second and third signals; and
storing means connected to said determining means for receiving and storing said plurality of magnitude and phase angle values from said determining means wherein said converted values from said second signals represent probe current values and said converted values from said third signals represent probe voltage values and for storing said reference resistance value received from said reference resistor and for providing said reference resistance value to said determining means;
wherein said means for determining produces a plurality of digital signal values representing probe current by dividing sample values of said second voltage signal by said reference resistance value wherein each said second voltage sample is represented by a voltage V2 across said reference resistance R as I=V2/R and for producing a plurality of digital values representing said third voltage signal where each said third voltage value is represented by a voltage (V1 -V2), wherein V1 is the voltage across a serial interconnection of said coil and said reference resistance, said voltages V1 and V2 being said voltage signals representative of the instantaneous current (I) through said coil and the instantaneous voltage (V1 -V2) across said coil.
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Abstract
An all digital eddy current measurement system is described and illustrated in which an eddy current probe is driven by a driving signal and voltage signals representing the current through and voltage across the probe coil are used to calculate the magnitude and phase angle of a complex probe impedance. Digitization of the voltage signals is controlled by a control logic system which is run separately from but initiated by a microprocessor, the latter of which functions to analyze the acquired data and calculate impedance magnitude and phase angle values therefrom.
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Citations
24 Claims
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1. An eddy current measuring system comprising:
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an eddy current measuring probe having an electromagnetic coil; a reference resistor connected in series with said electromagnetic coil for producing a reference resistor value; means for applying a first driving signal to said coil; means for producing second and third voltage signals respectively representing a probe current in said coil and a probe voltage across said coil, said second and third signals being produced during the time said driving signal is applied to said coil; means for analog-to-digital converting said second and third signals; means for determining a plurality of magnitude and phase angle values representing the complex impedance of said probe from said converted second and third signals; and storing means connected to said determining means for receiving and storing said plurality of magnitude and phase angle values from said determining means wherein said converted values from said second signals represent probe current values and said converted values from said third signals represent probe voltage values and for storing said reference resistance value received from said reference resistor and for providing said reference resistance value to said determining means; wherein said means for determining produces a plurality of digital signal values representing probe current by dividing sample values of said second voltage signal by said reference resistance value wherein each said second voltage sample is represented by a voltage V2 across said reference resistance R as I=V2/R and for producing a plurality of digital values representing said third voltage signal where each said third voltage value is represented by a voltage (V1 -V2), wherein V1 is the voltage across a serial interconnection of said coil and said reference resistance, said voltages V1 and V2 being said voltage signals representative of the instantaneous current (I) through said coil and the instantaneous voltage (V1 -V2) across said coil. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A probe impedance measuring system comprising:
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a probe comprising an electromagnetic coil; means for generating a probe driving signal; means for applying said driving signal to said probe coil; means for receiving signals representing a voltage across said coil and a current passing through said coil when said coil is driven by said driving signal; means for sampling and analog-to-digital converting said signals representing coil voltage and coil current to produce digital samples of said signals representing coil voltage and current; means for storing said digital samples; control logic means for controlling the sampling and converting means to produce said digital samples; and processor means for controlling said generating means and applying means so that said driving signal is generated and applied to said probe coil, for initializing operation of said control logic means so that said signals representing coil current and coil voltage are converted to said digital samples, and for calculating a complex probe impedance from said stored digital samples of said signals representing coil voltage and current.
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11. A system for directly measuring the magnitude and phase angle of a complex coil impedance comprising:
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a probe comprising an electromagnetic coil; a reference resistor connected in series to said electromagnetic coil for producing a reference resistor value; a driving signal generator adapted to apply a probe driving signal to said coil; means operative when said driving signal is applied to said coil for obtaining voltage signals representative of the instantaneous current through said coil and the instantaneous voltage across said coil; analog to digital converter means for converting said voltage signals representative of instantaneous current through said coil and said instantaneous voltage across said coil respectively into first and second digital signals, each comprising a plurality of digital samples; means for determining a value of a magnitude and phase angle of a complex impedance of said coil from said first and second digital signals, said means for determining a value of the magnitude and phase angle of said complex impedance doing so by extracting a plurality of sets of digital samples, one from each of said first and second digital signals, and using each said set of extracted digital samples to form a respective magnitude value and a respective phase angle value, thereby forming a plurality of magnitude and phase angle values corresponding to said plurality of sets of digital samples; and storing means connected to said determining means for storing said plurality of magnitude and phase angle values representing said first and second digital signals received from said determining means and for receiving and storing said reference resistance value and for providing said reference resistance value to said determining means; wherein said determining means produces said second digital signals by dividing sample values of said second digital signal representing said probe current by said reference resistance value wherein each said probe current value is represented by a voltage V2 across a reference resistance R as I=V2/R and said second digital signals are represented by a voltage (V1 -V2), where V1 is the voltage across a serial interconnection of said electromagnetic coil and said reference resistor, wherein said voltages V1 and V2 being said voltage signals representative of the instantaneous current (I) through said coil and the instantaneous voltage (V1 -V2) across said coil. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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Specification