Inline current sensor

Abstract

An immittance instrument system is disclosed, featuring a sensor with a drive conductor and a sense element connected to the instrument by a cable that includes an inline current sensor. The sensor may be used to measure responses of a test object while the inline current sensor is used to measure a current driving the sensor. In some embodiments, the sensor is inductive with a multi-turn sense element. The inline current sensor may have a current sense element such as an inductive loop or magnetoresistive sensor. The inline current sensor may have a drive element which may be connected in series with a drive lead in the cable (the drive lead connecting the instrument to the drive conductor of the sensor). The inline current sensor may be positioned nearer the end of the cable proximal the sensor.

Description

[0001] INLINE CURRENT SENSOR

[0002] CROSS-REFERENCE TO RELATED APPLICATION

[0003] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 695,312, filed September 16, 2024, the entirety of which is hereby incorporated by reference.

[0004] TECHNICAL FIELD

[0005] The technical field of this invention is that of nondestructive materials characterization, particularly quantitative, model-based characterization of surface, near-surface, and bulk material condition for flat and curved parts or components.

[0006] BACKGROUND

[0007] The subject matter discussed in the background section should not be considered prior art merely because of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be considered to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves, may also correspond to claimed embodiments.

[0008] Characterization of bulk material condition includes (1) measurement of changes in material state, i.e., degradation / damage caused by fatigue damage, creep damage, thermal exposure, or plastic deformation; (2) assessment of residual stresses and applied loads; and (3) assessment of processing-related conditions, for example from aggressive grinding, shot peening, roll burnishing, thermal-spray coating, welding or heat treatment. It also includes measurements characterizing material, such as alloy type, and material states, such as porosity and temperature. Characterization of surface and near-surface conditions includes measurements of surface roughness, displacement or changes in relative position, coating thickness, temperature and coating condition. Each of these includes detection of electromagnetic property changes associated with either microstructural and / or compositional changes, or electronic structure (e.g., Fermi surface) or magnetic structure (e.g., domain orientation) changes, or with single or multiple cracks, cracks or stress variations in magnitude, orientation or distribution.

[0009] A common technique for material characterization is eddy-current testing. Conventional eddy-current sensing involves the excitation of a conducting winding, the primary, with an electric current source of prescribed frequency. This produces a time-varying magnetic field, which in turn is detected with a sensing winding, the secondary. The spatial distribution of the magnetic field and the field measured by the secondary is influenced by the proximity and physical properties (electrical conductivity and magnetic permeability) of nearby materials. When the sensor is intentionally placed in close proximity to a test material, the physical properties of the material can be deduced from measurements of the impedance between the primary and secondary windings. In some cases, only the self-impedance of the primary winding is measured. Traditionally, scanning of eddy-current sensors across the material surface is then used to detect features, such as cracks.

[0010] Eddy current inspection typically involves placing a sensor proximate to a test material, exciting the sensor with an electrical signal to create a magnetic field that can be used to interrogate the test material, measuring at least one response from the sensor to assess the condition of the test material, and the appropriate instrumentation for creating the excitation or drive signal and for measuring the response or sense element signal. Often the sensor array has a drive winding to create a magnetic field when driven by an electric current and secondary elements to sense the responses of the material under test (MUT) to the imposed magnetic field. A time-varying current is applied to the primary winding, which creates a magnetic field that penetrates into the MUT and induces a voltage at the terminals of the secondary elements. This terminal voltage reflects the properties of the MUT.

[0011] U.S. Patent No. 6, 188,218, Absolute Property Measurement with Air Calibration, Goldfine et al., issued February 13, 2001, describes calibration of an eddy current sensor “in air” and is herein incorporated by reference in its entirety (the ‘218 patent).

[0012] U.S. Patent No. 10,324,062, Method and apparatus for measurement of material condition, Denenberg et al., issued June 18, 2019, describes a fully parallel, multi-channel impedance instrument and is herein incorporated by reference in its entirety (the ‘062 patent).

[0013] U.S. Patent No. 6,784,662, Eddy current sensor arrays having drive windings with extended portions, by Schlicker et al., issued August 31, 2004, describes an eddy current sensor array and is herein incorporated by reference in its entirety (the ‘662 patent).

[0014] In U.S. Patent No. 7,467,057, issued December 16, 2008, which is herein incorporated by reference in its entirety, Sheiretov et al. describe material property estimation using non- orthogonal responsive databases (the ’057 patent).

[0015] In U.S. Patent No. 11,435,317, issued September 6, 2022, which is incorporated herein by reference in its entirety, Goldfine et al. describe a process for enhancing detection of defects having characteristic shapes provided in a signature library (the ’317 patent). In International Publication No. WO 2025 / 102007 having an International Filing Date of November 8, 2024, which is incorporated herein by reference in its entirety, Goldfine et al. further describe the use of signature libraries (the ’007 publication).

[0016] FIG. 1 provides a schematic 400 of some of the basic components of a transimpedance measurement system. A drive signal 404, typically in the form of a time-varying excitation current, h, is used to create the excitation signal inside the drive winding 403 of the sensor array 406. It is common to measure the drive signal current with a current sensor in instrument 401. Current sensor in instrument 401 is either a series resistor or an inductive pick-up coil, proximate to the electronic circuitry used to generate drive signal 404. The sensor array is typically physically located at some distance away from where the drive signal is generated. The electrical coupling between these locations is represented by cable 402, which represents the series inductance and resistance along the connecting conductors as well as the parallel capacitance and resistance between the conductors. Multiple sense elements 406 are shown adjacent to the drive winding. The induced voltage on these sense elements is due to the mutual inductance 405 between each sense element 406 and the drive winding 403; this mutual inductance 405 varies with the properties of the test material adjacent to the sensor array.

[0017] SUMMARY

[0018] One aspect relates to a system comprising an immittance instrument having first and second measurement channels; a sensor having a drive conductor and a sense element; and a cable operably connecting the drive conductor and the sense element of the sensor to the immittance instrument, and having a current sense element, wherein the first and second measurement channels are operably connected to measure responses of the current sense element and the sense element, respectively.

[0019] In some embodiments of the system, the sensor is an inductive sensor and the sense element is a coil comprising five or more turns.

[0020] In some embodiments of the system, the cable is operably connected to the immittance instrument via a first coupling interface comprising an instrument-side connector and a first cable-side connector, the cable is operably connected to the sensor via a second coupling interface comprising a sensor-side connector and a second cable-side connector, the instrumentside connector is mated with the first cable-side connector, the sensor-side connector is mated with the second cable-side connector, the instrument further includes the instrument-side connector, the sensor further includes the sensor-side connector, and the cable comprises the first and second cable-side connectors. In some embodiments of the system, the cable comprises an immittance-instrument end that is operably connected to the immittance instrument and a sensor end that is operably connected to the sensor, and the current sense element is closer to the sensor end than the immittance-instrument end.

[0021] In some embodiments of the system, the current sense element is located within a length portion of the cable that is closest to the sensor end and is less than 25% of an entire length of the cable.

[0022] In some embodiments of the system, the current sense element is part of a current sensor, the current sensor further comprising a drive element that is operably connected in series with a drive lead of the cable that connects the drive conductor of the sensor to the immittance instrument.

[0023] In some embodiments of the system, the current sense element comprises a sense coil, the drive element comprises a drive coil, and the drive coil and sense coil are wrapped around a core having a magnetic permeability greater than 2po.

[0024] In some embodiments of the system, the current sense element is a magnetoresistive sensor.

[0025] In some embodiments of the system, the sensor is permanently installed on a test object.

[0026] In some embodiments the system further comprises a scanner, wherein the sensor is integrated into the scanner for scanning measurements.

[0027] In some embodiments of the system, the sense element is among a plurality of sense elements forming a sensor array, the second measurement channel is among a plurality of second measurement channels, and the cable operably connects each of the plurality of sense elements to a respective member of the plurality of second measurement channels.

[0028] Another aspect relates to a system comprising a sensor having a drive conductor and a sense element; and a cable integral with or connectable to the sensor. The cable comprises a drive lead integral with or connectable to the drive conductor; a sense lead integral with or connectable to the sense element; and a current sensor comprising a current sense element.

[0029] In some embodiments of the system, the current sensor further comprises a drive element that is inserted in series with the drive lead of the cable.

[0030] In some embodiments of the system, the current sense element comprises a sense coil, the drive element comprises a drive coil, and the drive coil and sense coil are wrapped around a core having a magnetic permeability greater than 2po.

[0031] In some embodiments of the system, the current sense element is a magnetoresistive sensor.

[0032] In some embodiments of the system, the sensor is an inductive sensor and the sense element is a coil comprising five or more turns.

[0033] In some embodiments, the system further comprises an immittance instrument having first and second measurement channels, wherein the first and second measurement channels are operably connected to the sensor via the cable to measure responses of the current sense element and the sense element, respectively.

[0034] In some embodiments, the system further comprises an immittance instrument having a measurement channel, the immitance instrument operably connected to the sensor via the cable to measure responses of the current sense element and the sense element, respectively.

[0035] In some embodiments of the system, the instrument comprises a multiplexor to switch the measurement channel between the sense element and the current sense element.

[0036] The foregoing is a non-limiting summary of the invention, which is defined by the attached claims.

[0037] BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:

[0039] FIG. l is a block diagram of a conventional system;

[0040] FIG. 2 is a block diagram of a system reproduced from Patent Application Publication No. 2025 / 0216360, Remote Current Sense, published July 3, 2025;

[0041] FIG. 3 is a block diagram of a system for inspecting a test object, according to some embodiments;

[0042] FIG. 4 is a block diagram of instrument 110 with a specific focus on illustrating data collection and analysis, according to some embodiments;

[0043] FIG. 5 is a block diagram of a system 300 utilizing a cable with an inline current sense, according to some embodiments;

[0044] FIG. 6A is a perspective view of a simplified illustration of an inline current sense, according to some embodiments;

[0045] FIG. 6B is an exploded view of the inline current sense illustrated in FIG. 6A, according to some embodiments; and FIG. 7 is a flow diagram of a method for calibrated measurement of a test object using an eddy current sensor and an inline current sensor, according to some embodiments.

[0046] DETAILED DESCRIPTION

[0047] The inventors have recognized and appreciated that a substantial measurement performance limitation with the schematic of FIG. 1 is that the drive current IA into the drive winding 403 can be different from the imposed drive current h. This is a result of the electrical impedance between the ends of the terminals of cable 402 being dependent upon the excitation frequency and length of cable. Generally the impedance effect of the cable increases with frequency and length of the cable. Consequently, these cable effects create a limit for the upper bound for the excitation frequencies or the cable length that can be used.

[0048] In U.S. Patent Application Publication No. 2025 / 0216360, Remote Current Sense, published July 3, 2025, and herein incorporated by reference in its entirety (the ’360 publication), the inventors (T. Dunford and A. Washabaugh) disclosed a remote current sense (a current sensor) on an electromagnetic sensor. FIG. 2 of the ’360 publication, reproduced here as FIG. 2, shows a schematic of a system 500 having a remote current sense 507 as part of the eddy current sensor that is connected to cable 502. System 500 generates a drive signal 504 which produces a current / ;. The current / ; may be measured locally by local current sense 501 within the instrumentation. The current passes through cable 502 and connects to a sensor array drive 503. Remote current sense 507 utilizes a sense element for measuring the current through sensor array drive 503, IA. Because of the impedance of cable 502, current / ; measured on the sensor, may be different from current / ; measured within the instrument. The current measurement is used with sense voltages measured on the sensor array 506 (induced due to inductive coupling 505) to determine the transimpedance of each sensing element of the sensor array.

[0049] The inventors have recognized and appreciated that there are many applications where it is impractical to implement a remote current sense as part of the electromagnetic sensor. For example, an application may demand an existing sensor that cannot be retrofitted or redesigned; the application may have severe spatial constraints that would not permit the addition of the remote current sense disclosed in the ’360 publication; or the sensor fabrication process may be amenable to the inclusion of the remote current sense disclosed in the ’360 publication.

[0050] The inventors have recognized and appreciated that in circumstances where a current sensor cannot be made part of the electromagnetic sensor, significant performance improvements over the prior art system 400 may still be achieved by providing an inline current sensor along the electrical path between the instrumentation and sensor. For example, in some embodiments, an inline current sensor is integrated into an electrical cable connecting the instrumentation to the sensor.

[0051] Accordingly, aspects of some embodiments relate to the use of a system 100 shown as a block diagram in FIG. 3. System 100 may be used for inspecting a test object 130. System 100 includes an instrument 110 and a sensor cartridge 140.

[0052] In some embodiments, instrument 110 is an immittance instrument. As used herein, the term “immittance” refers generally to an electrical transfer property between voltage and current, and encompasses impedance, admittance, or equivalent linear parameters that characterize such relationships. An “immittance instrument” therefore denotes any device configured to measure, derive, or report an immittance quantity, whether expressed as impedance, admittance, or in a related form.

[0053] Instrument 110 may be housed in a housing 107; in some embodiments the housing is substantially cylindrical in shape such as that described in U.S. Patent No. 10,416,118, Measurement system and method of use, by Goldfine et al. issued September 17, 2019 and herein incorporated by reference in its entirety (the ’ 118 patent). Sensor cartridge 140 may have a rigid connector which interfaces both mechanically and electrically with an instrument side connector 105.

[0054] In some embodiments, sensor cartridge 140 is connected to instrument side connector 105 via cable 150. Cable 150 may be of arbitrary length in accordance with the requirements of the application. Although cable 150 is shown with only excitation signals 121 and response signals 123 passing through it, it should be appreciated that cable 150 may also convey other signals (including power). For example, power and / or measurement signals for position encoder 103 may be conveyed through cable 150. Similarly, power and / or control signals for actuator 101 may be conveyed through cable 150. Cable 150 may have an inline current sensor 125 used for estimating the current through drive winding 122 of sensor 120.

[0055] Sensor cartridge 140 in some embodiments includes a sensor 120, and a mechanical support 141 to which the sensor is attached. Sensor 120 may be attached to mechanical support 141 with glue, tape, double sided tape, or in any suitable way. In some other embodiments, sensor cartridge 140 does not include mechanical support 141. Instrument 110 is configured to provide excitation signals 121 to sensor 120 and measure the resulting response signals 123 of sensor 120. Response signals 123 may be measured and processed to estimate properties of interest, such as electromagnetic properties (e.g., electrical conductivity, permeability, and permittivity), geometric properties (e.g., layer thickness, sensor liftoff), material condition (e.g., fault / no fault, crack size, layer to layer bond integrity, porosity, residual stress level, temperature), or any other suitable property or combination thereof including properties of the fabricated part and the powder. (Sensor liftoff is a distance between the sensor and the closest surface of the test object for which the sensor is sensitive to the test object’s electrical properties.)

[0056] Instrument 110 may include a processor 111, a user interface 113, memory 115, an immittance analyzer 117, and a network interface 119. Though, in some embodiments of instrument 110 may include other combinations of components. While instrument 110 is drawn with housing 107, it should be appreciated that instrument 110 may be physically realized as a single mechanical enclosure; multiple, operably-connected mechanical enclosures, or in any other suitable way. For example, in some embodiments it may be desired to provide certain components of instrument 110 as proximal to sensor 120 as practical, while other components of instrument 110 may be located at greater distance from sensor 120. In one such embodiment, immittance analyzer 117, including instrument side connector 105, is housed separately from components such as processor 111, user interface 113, memory 115, and network interface 119 (which may be housed, for example, in a laptop computer), and immittance analyzer 117 communicates digitally with the other components of instrument 110.

[0057] Processor 111 may be configured to control instrument 110 and may be operatively connected to memory 115. Processor 111 may be any suitable processing device such as for example and not limitation, a central processing unit (CPU), digital signal processor (DSP), controller, addressable controller, general or special purpose microprocessor, microcontroller, addressable microprocessor, programmable processor, programmable controller, dedicated processor, dedicated controller, or any suitable processing device. In some embodiments, processor 111 comprises one or more processors, for example, processor 111 may have multiple cores and / or be comprised of multiple microchips. Processing of sensor data and other computations such as for control may be performed sequentially, in parallel, or by some other method or combination of methods.

[0058] Memory 115 may be integrated into processor 111 and / or may include “off-chip” memory that may be accessible to processor 111, for example, via a memory bus (not shown). Memory 115 may store software modules that when executed by processor 111 perform desired functions. Memory 115 may be any suitable type of non-transitory computer-readable storage medium such as, for example and not limitation, RAM, a nanotechnology-based memory, optical disks, volatile and non-volatile memory devices, magnetic tapes, flash memories, hard disk drive, circuit configurations in Field Programmable Gate Arrays (FPGA), or other semiconductor devices, or other tangible, non-transitory computer storage medium.

[0059] Instrument 110 may have one or more functional modules 109. Modules 109 may operate to perform specific functions such as processing and analyzing data. Modules 109 may be implemented in hardware, software, or any suitable combination thereof. Memory 115 of instrument 110 may store computer-executable software modules that contain computerexecutable instructions. For example, one or more of modules 109 may be stored as computerexecutable code in memory 115. These modules may be read for execution by processor 111. Though, this is just an illustrative embodiment and other storage locations and execution means are possible.

[0060] Instrument 110 provides excitation signals for sensor 120 and measures the response signal from sensor 120 using immittance analyzer 117. Immittance analyzer 117 may contain a signal generator 112 for providing the excitation signal to sensor 120. Signal generator 112 may provide a suitable voltage and / or current waveform for driving sensor 120. For example, signal generator 112 may provide a sinusoidal signal at one or more selected frequencies, a pulse, a ramp, or any other suitable waveform. Signal generator 112 may provide digital or analog signals and include conversion from one mode to another. The ‘062 patent provides a discussion of an immittance analyzer that may be used in some embodiments. See, for example, the discussion in connection with FIG. 19a which provides a discussion on how immittance analyzer 117 can take a measurement. The ‘218 patent provides further discussion on how such immittance measurements may be calibrated to remove certain systematic bias from the measurements.

[0061] In some embodiments, immittance analyzer 117 has a current sensor 108 that is used to measure a current leaving signal generator 112. Current sensor 108 may be any suitable sensor for measuring such current. For example, current sensor 108 may include a known series resistance in the drive current signal path and current sensor 108 may measure the voltage across such known resistance such that the current may be calculated using Ohm’s Law. As another example, current sensor 108 may measure the voltage induced on an inductive pick-up coil having a well known transimpedance.

[0062] Sense hardware 114 may comprise multiple sensing channels for processing multiple sensing element responses in parallel. As there is generally a one to one correspondence between sense elements and instrumentation channels these terms may be used interchangeably. It should be appreciated that care should be used, for example, when multiplexing is used to allow a single channel to measure multiple sense elements. For sensors with a single drive and multiple sensing elements such as the MWM®-Array eddy current array available from JENTEK® Sensors, Inc., the sensing element response may be measured simultaneously at one or multiple frequencies including simultaneous measurement of real and imaginary parts of the transimpedance (or mathematically equivalent measurements / representations such as the magnitude and phase of the transimpedance or the in-phase and quadrature components of the transimpedance). Though, other configurations may be used. For example, sense hardware 114 may comprise multiplexing hardware to facilitate serial processing of the response of multiple sensing elements and for eddy current arrays. Some embodiments of sensor 120 use certain MWM-Array formats to take advantage of the linear drive and the ability to maintain a consistent eddy current pattern across the part using such a linear drive.

[0063] Sense hardware 114 may have dedicated sensing channels for measuring each of the current sensors (e.g., current sensor 108, current sensor 125). In some embodiments, sense hardware 114 allows a single sensing channel to be switched between the available current sensors such that a current sensor selected for a particular measurement may be used. In some embodiments the sensing channel used to measure a current sensor is also used for measuring other sensing elements. For example, immittance analyzer 117 may serially measure one or more current sensors and one or more sense elements. Whether multiplexing the current sensor measurement will be adequate is application specific, with some applications (e.g., permanently mounted sensors) being more likely to yield adequate results than some other applications (e.g., scanning applications). Here “adequate” means the current sensor response provides a current measurement that is sufficiently representative of the current provided at the time the sensing element responses were recorded such that an immittance with acceptable accuracy can be calculated. Of course, adequacy will depend on the specific requirements of an application.

[0064] Sense hardware 114 may measure sensor transimpedance for one or more excitation signals at one or more sense elements 124 of sensor 120. It should be appreciated that while transimpedance (sometimes referred to simply as impedance), may be referred to as the sensor response, the way the sensor response is represented is not critical and any suitable representation may be used. In some embodiments, the output of sense hardware 114 is stored along with temporal information (e.g., a time stamp) to allow for later temporal correlation of the data, and positional data correlation to associate the sensor response with a particular location on test object 130. Instrumentation may also operate in a pulsed mode with time gates used to provide multiple sensing outputs and multiple channels used to acquire data from multiple sensing elements. If these sensing elements 124 have different drive-sense gaps (distance between a drive winding 122 and the sense elements 124, then this is referred to as a segmented field sensor. Thus, sensor operation can be at a single frequency, multiple frequencies, or in a pulsed mode where the drive is turned on and off in a prescribed manner or switched between two or more modes of excitation.

[0065] Sensor 120 is shown as an eddy-current sensor, though other sensor types may be used with system 100. Sensor 120 has a drive winding 122 and a sense element 124 (or multiple sense elements) which is discussed further herein. In some embodiments sensor 120 provides temperature measurement, voltage amplitude measurement, strain sensing or other suitable sensing modalities or combination of sensing modalities. In some embodiments, sensor 120 is an eddy-current sensor such as an MWM, MWM-Rosette, or MWM- Array sensor available from JENTEK Sensors, Inc., Marlborough, MA. A discussion of some MWM-Array sensors may be found, for example, in the ‘662 patent. Sensor 120 may be a magnetic field sensor or sensor array such as a magnetoresistive sensor (e.g., MR-MWM-Array sensor available from JENTEK Sensors, Inc.), a segmented field MWM sensor, and the like. Segmented field sensors have sensing elements at different distances from the drive winding to enable interrogation of a material to different depths at the same drive input frequency. Sensor 120 may have a single or multiple sensing and drive elements. Sensor 120 may be scanned across, mounted on, or embedded into test object 130.

[0066] Some sensor designs may be characterized by spatial wavelength. As used herein, the term “spatial wavelength” (denoted ) refers to the spatial periodicity or the longest dominant spatial mode of the drive-sense field structure of the sensor. In sensors having a periodic drive / sense pattern, is the physical periodic spacing between repeating elements (e.g., distance between adjacent drive conductors, or between drive and sense conductors of repeating units). In sensors without strict periodicity, X is the largest spatial wavelength component obtained when the spatial distribution of the applied magnetic field (or other field as applicable) is represented in the spatial frequency domain (e.g., via Fourier decomposition), such that the largest component that meaningfully contributes to the measured response is taken. Example values may be derived from drive winding geometry or drive-sense gap.

[0067] In some embodiments, the computer-executable software modules 109 may include a sensor data processing module that, when executed, estimates properties of test object 130. The sensor data processing module may utilize multi-dimensional precomputed databases that relate one or more frequency transimpedance measurements to properties of test object 130 to be estimated. The generation of suitable databases and the implementation of suitable multivariate inverse methods are described, for example, in U.S. Patent No. 7,467,057, issued on December 16, 2008 (the ‘057 patent), and U.S. Patent No. 8,050,883, issued on November 1, 2011 (the ‘883 patent), both of which are herein incorporated by reference in their entirety. The sensor data processing module may take the precomputed database and sensor data and, using a multivariate inverse method, estimate material properties for the processed part or the powder. Though, the material properties may be estimated using any other analytical model, empirical model, database, look-up table, or other suitable technique or combination of techniques.

[0068] User interface 113 may include devices for interacting with a user. These devices may include, by way of example and not limitation, keypad, pointing device, camera, display, touch screen, audio input and audio output.

[0069] Network interface 119 may be any suitable combination of hardware and software configured to communicate over a network. For example, network interface 119 may be implemented as a network interface driver and a network interface card (NIC). The network interface driver may be configured to receive instructions from other components of instrument 110 to perform operations with the NIC. The NIC provides a wired and / or wireless connection to the network. The NIC is configured to generate and receive signals for communication over network. In some embodiments, instrument 110 is distributed among a plurality of networked computing devices. Each computing device may have a network interface for communicating with other computing devices forming instrument 110.

[0070] In some embodiments, multiple instruments 110 are used together as part of system 100. Such systems may communicate via their respective network interfaces. In some embodiments, some components are shared among the instruments. For example, a single computer may be used to control all instruments. In one embodiment multiple areas on the test object are scanned using multiple sensors simultaneously or in an otherwise coordinated fashion to use multiple instruments and multiple sensor arrays with multiple integrated connectors to inspect the test object surface faster or more conveniently.

[0071] Actuator 101 may be used to position sensor cartridge 140 with respect to test object 130 and ensure that the liftoff of the sensor 120 is in a desired range relative to the test object 130. Actuator 101 may be an electric motor, pneumatic cylinder, hydraulic cylinder, or any other suitable type or combination of types of actuators for facilitating movement of sensor cartridge 140 with respect to test object 130. Actuators 101 may be controlled by motion controller 118. Motion controller 118 may control sensor cartridge 140 to move sensor 120 relative to test object 130.

[0072] Regardless of whether motion is controlled by motion controller 118 or directly by the operator, position encoder 103 and motion recorder 116 may be used to record the relative positions of sensor 120 and test object 130. This position information may be recorded with impedance measurements obtained by impedance analyzer 117 so that the impedance data may be spatially registered.

[0073] For some applications the performance of system 100 depends (among other things) on the proximity of sensor 120 to test object 130; that is to say the sensor liftoff may be critical to performance for such applications. For example, crack detection in an aerospace application may require cracks 0.5 mm (0.02 inches) in length be reliably detectable in test object 130 (e.g., a turbine disk slot). In order to achieve reliable detection of a small crack, sensor 120’s liftoff may need to be kept to under 0.25 mm (0.010 inches). Further, for such an application, sensor 120 may preferably be a sensor array, thus the liftoff of each element in the array may need to be kept to under 0.25 mm (0.010 inches). (It should be appreciated that these dimensions are illustrative and the specific requirements will be dictated by the details of the application.) Measurements may be complicated when test object 130 has a complex curved surface that may change along a measurement scan path.

[0074] To permit high-performance operation at higher excitation frequencies or longer distances between sensor 120 and instrument 110, use of current sensor 108 to estimate the current in drive winding 122 may not be sufficient. The inventors have recognized and appreciated that measurement performance may be improved by measuring the current carrying excitation signals 121 closer to drive winding 122 of sensor 120 than internal current sensor 108. Specifically, inline current sensor 125 may be located in cable 150 to more accurately measure the current in drive winding 122 of sensor 120. This is contrasted with measurement of the drive current much further from sense element 124 using current sensor 108 which is typically within instrument housing 107.

[0075] FIG. 4 shows embodiments of instrument 110 with a specific focus on data collection and analysis. It should be appreciated that other aspects of instrument 110 discussed in connection with FIG. 4 or elsewhere may also be part of such an embodiment.

[0076] Prior to using instrument 110 to collect and analyze sensor data as part of system 100, instrument 110 may be configured for a specific measurement application. An instrument control module 230 may be used to configure instrument 110 for a specific measurement application. Instrument control module 230 may utilize a session file 210 to store an instrument configuration 211, a measurement sequence instructions 212, and an interpolation configuration 213.

[0077] Instrument configuration 211 may store information identifying the type of sensor to be used, the excitation frequencies and their respective amplitudes, specific grids within precomputed database 203 for impedance data interpolation, the type of calibration to be used, the modules that are used as part of the measurement such as the specific signatures within signature library 205 for data analysis, and other information for configuring instrument 110 for a measurement application. The calibration typically uses an air calibration or an air with a one point reference measurement calibration. The term “air calibration”, as used herein, is calibration away from any conducting or magnetic materials (e.g., in a gas, air, vacuum, or in the presence of non-conducting, non-magnetic materials). This requires that conducting or magnetic materials are far enough away from the sensor so as to not impact the sensor response. For an air calibration itself, a measurement of the sensor response in air is used to adjust the measurement impedances to known and reproducible values. This approach does not require the use of reference standards for the instrument adjustment, but measurements on a reference part or material is recommended for verification of the calibration itself. To reduce channel -to-chann el variations in the sense element responses and improve consistency of the conductivity measurement, a second measurement point can be used as part of the calibration. This second measurement is usually for a reference material with known electrical properties. This provides consistency with other standard procedures for conductivity measurements. Note that one or more reference point measurements could be used but this tends to be less robust than including a measurement response in air since the reference part measurement for calibration requires knowledge of the conductivity of the reference material. The instrument configuration 211 typically also includes information about the data acquisition rate and the configuration of auxiliary information that could be associated with each measurement such as position encoder information, temperature, strain gages, etc.

[0078] Measurement sequence instructions 212 may define the sequence of actions that are to take place for a measurement. Instructions 212 may specify motor control, triggers, changes to the instrument configuration, and prompt user actions. For example, instructions 212 may indicate that after initializing a measurement, a first motor is to move at a certain speed during measurement collection and, after reaching an end point, measurement is to stop. As another example, after a first measurement is taken the instructions 212 may indicate the user is to be prompted to take an action (e.g., lay a non-conducting layer between the test object and the sensor to increase sensor liftoff) and then wait until a user initiated trigger is received. As yet another example, after taking first measurements the instructions may cause instrument 110 to be reconfigured to an alternate instrument configuration (e.g., having different excitation frequencies or other configuration properties).

[0079] Measurement sequence instructions 212 may also include definitions of the views to be presented to the end user. These views may be read by graphics generation module 270 to affect the graphical presentation to the user. Note that the graphics generation could also be in the form of data tables.

[0080] In some embodiments, an inverse interpolation module 220 is used to process impedance data 201 obtained from sensor 120 by immittance analyzer 117. Inverse interpolation module 220 utilizes a grid database 203 to estimate physical properties from impedance data 201. Physical properties estimated may include properties such as layer and gap thicknesses, electrical conductivity as a function of spatial position, and magnetic permeability as a function of spatial position. For example, the physical properties estimated by inverse interpolation module 220 for a sensor scanning a coated substrate material may include (i) liftoff, (ii) coating thickness, (iii) coating electrical conductivity, and (iv) substrate electrical conductivity. Secondary properties may also be estimated using the output of the inverse interpolation module, such as layer thicknesses, gaps between layers, the size of a chamfer, and further to estimate defect sizes or to identify types of anomalies.

[0081] Interpolation configuration 213 of session file 210 may be used to specify aspects of the inverse interpolation. For example, in some embodiments a hierarchical approach can be used to increase numerical stability and accuracy of the multiple unknown inversion. Property effects can be systematically separated from one another by using specific excitation frequencies and / or segmented fields to estimate the properties they are most sensitive to. For example, a coating conductivity property may be estimated using only a high frequency excitation measurement, and then both the high and a low frequency used to determine coating thickness and substrate conductivity (with the coating conductivity in this second step assigned the value determined from the high frequency alone). This may be useful for example for inspection through a bushing. In one embodiment of this invention, the use of multiple frequencies and the inverse interpolation module along with the ability to scan the internal surface of the busing in a hole, is used to detect cracks in the stackup / layers / skins through a bushing. This can utilize other aspects of this invention, after accounting for the thickness and properties of the busing to estimate the conductivity or magnetic permeability of the “substrate” which in this case is the properties of the structural layers, aircraft skin, material that is inspected through the busing.

[0082] Further discussion of the operation of inverse interpolation module 220 may be found in the ’057 patent.

[0083] In some embodiments, instrument 110 is also equipped with a forward model module 240 for precomputing grids for grid database 203 using a sensor-material model. The model may be a physics-based model, an empirical model based on prior measurements, or any other suitable type of model for creating measurement grids. In some embodiments, forward model module 240 is not made a part of instrument 110 and only grids are stored in grid database 203 of instrument 110. For example, forward model module 240 may be a software application run on a computer to produce grids which are then stored in grid database 203.

[0084] In some embodiments, instrument 110 includes a signature definition module 250 for defining characteristic responses (“signatures”) of a feature to be enhanced or suppressed in measurement data. In some embodiments signatures and their use may be similar to those described in the ’317 patent and the ’007 publication. Signature definition module 250 may allow a user to identify signatures and store them in a signature library; alternatively or additionally, signatures may be identified in an automated or semi -automated way. For example, a crack defect signature may appear in the electrical conductivity response measured by a sensor scanning over the crack. In the case of a sensor array, the response may be observed on a single or multiple adjacent channels. A signature may be identified as a single channel response or a multi-channel response. Signature definition module 250 may standardize signatures prior to storing them in library 205. For example, signatures may be standardized to a specific number of points or a specific amplitude range. Signatures may also include metadata that provide additional information about the signature such as the size of the defect the signature was obtained from.

[0085] Detection and sizing module 260 may be used to detect and size defects in measurement data from a test object using signatures from signature library 205. Module 260 may evaluate the correlation between a measurement and a signature. If the correlation exceeds a threshold a detection may be flagged. The threshold may be set based on the detection and false alarm requirements of the application. Signature library 205 may contain multiple signatures that may be tested against measurement data. The signature having the greatest similarity with the measurement may also be used to size a detected defect. For example, the defect size may be estimated to be the same as the size of the defect the signature. Module 260 may also be used to suppress features that are not of interest such as fasteners or through holes. For example, a through hole in a plate typically has a significant effect on the estimated electrical conductivity of the substrate material if a planar model is used to estimate conductivity. The shape of the conductivity response with respect to position as the sensor is scanned over the hole depends upon the actual electrical conductivity of the substrate material, the excitation frequency, and the geometry (e.g., sense element size and spatial wavelength) of the sensor. However, for a given sensor array, because the conductivity response of the through hole is consistent, it may be removed from the conductivity estimate. For example, module 260 may identify a highly correlated through hole signature with the conductivity response from measurement. The conductivity response may then be updated to remove the signature. This will flatten the conductivity response and may also allow for the hole location to be accurately estimated from the measurement data. While this example discussed suppressing the response for processed data such as the estimated conductivity of the material this approach can also be used for unprocessed data such as the sensor impedance or transinductance.

[0086] Graphics generation module 270 may provide a graphical representation to the user to assist the user in the data collection and / or analysis process. Module 270 may present such a graphical presentation on a video display integral to and / or separate from instrument 110. Information may be presented as tables, A-scans, B-scans, C-scans, or any suitable way. In some embodiments, module 270 configures the graphical environment based on instructions 212. In this way a consistent presentation of information can be provided to the user.

[0087] Report Generation Module 280 may be included to facilitate review of measurement results outside of the graphical environment of instrument 110. For example, report generation module 280 may produce a report of measurement data in pdf, docx, rtf, xlsx, or other suitable format. Session file 210 may specify the report format which may be used by module 280 to generate reports for measurement data.

[0088] In some embodiments, the output includes a decision with regards to the future disposition of the test object. Modules 270 and / or 280 may present such a decision. Examples include pass / fail decisions on the quality of a component, or the presence of flaws. As another example, it may be determined whether the test object may be returned to service, repaired, replaced, scheduled for more or less frequent inspection, and the like. If it is determined that the application was not determinative, instrument 110 may re-perform the procedure(if automated), or advise the user to re-perform the procedure. A procedure may need to be re-performed, for example, if all requirements of the procedure were not met. For example, the procedure may require the liftoff of the sensor to be below a threshold amount over the inspection surface and require re-performance if the liftoff requirement is not met.

[0089] Software implementations are focused on increasing data analysis, speed and large file handling. In one such embodiment, software is upgraded from 32 bit to 64 bit to improve the speed of data analysis and rendering of multiple images for viewing analyzed data. In some embodiments, multithreading, vector processing, or other methods for implementing rapid data analysis for multivariate inverse methods, intelligent filtering, or AI / ML implementations are utilized to improve the speed for data analysis and viewing. Inspection speed may also be affected by the scan speed of motors and the data acquisition rate. The scan speed of motors and data acquisition rate are set to provide a minimum number of data points on a prescribed defect size (e.g., 50x50 mil comer cracks, or 50x25 mil midwall cracks) where the minimum number of data points required is determined from empirical data taken at two or more scan speeds / data rate combinations. Scan speeds and data rate should also take into account the type of data analysis to be implemented (e.g., MIM, intelligent filtering, AI / ML). Intelligent filtering is the use of signature libraries and shape filtering as described, for example, in Dunford I.

[0090] In some embodiments the measurement results are used to control a process. For example, a property measurement may be fed back into a control circuit that controls a process.

[0091] FIG. 5 shows a system 300 according to some embodiments. System 300 includes immittance instrument 110, cable 150, and sensor 120, each of which may be similar to those discussed in connection with system 100 (FIG. 3). FIG. 5 provides additional details found in some embodiments such as a coupling interface 310 between instrument 110 and cable 150, and coupling interface 320 between cable 150 and sensor 120. Coupling interfaces 310 and 320 may be integral couplings or detachable couplings. For example, coupling interface 310 may include an instrument-side connector similar to instrument side connector 105 discussed in connection with FIG. 1 and a mating cable connector. Similarly, coupling interface 320 may include a sensor connector and a mating cable connector. In embodiments that utilize connectors, any suitable connectors may be used. The mating cable connectors may be the same or different in terms of both sex and style at each end of cable 150.

[0092] In some embodiments, cable 150 is operably connected to the immittance instrument through a first coupling interface 310, which includes an instrument-side connector and a first cable-side connector. Similarly, cable 150 may be operably connected to sensor 120 via a second coupling interface 320 which includes a sensor-side connector and a second cable-side connector. The instrument-side connector is mated with the first cable-side connector, and the sensor-side connector is mated with the second cable-side connector. The instrument itself includes the instrument-side connector, the sensor itself includes the sensor-side connector, and the cable may have the first and second cable-side connectors on respective ends. Each connector may have suitable electrical contacts to form the electrical connections as well as mechanical support to secure the connection and to provide strain relief.

[0093] Another aspect involves a cable that is either integral with or connectable to the sensor. This cable includes a drive lead that is integral with or connectable to the drive conductor of the sensor, a sense lead integral with or connectable to the sense element, and a current sensor containing a current sense element.

[0094] Cable 150 may include (i) an inline current sensor 125, (ii) a drive lead 156 to connect instrument 110’s signal generator 112 to drive winding 122, (iii) one or more sense leads 154 to connect instrument 110’s sense channel hardware 114 to sensor 120’s sense elements 124, and a current-sense lead 153 to connect inline current sensor 125 to sense hardware 114.

[0095] In some embodiments, inline current sensor 125 includes a drive winding 151 and a sense winding 152. Drive winding 151 may be connected inline with drive lead 156 between instrument 110 and drive winding 122 of sensor 120. Sense winding 152 may be connected to sense hardware 114 of instrument 110 via current-sense lead 153. Sense elements 124 may similarly be connected to sense hardware 114 via respective sense leads 154.

[0096] It is noted that sensor 120 appears as a simplified linear drive winding eddy current array, this choice is illustrative and any suitable sensor 120 may be used.

[0097] In some embodiments sensor 120 is an inductive sensor comprising one or more drive segments and one or more sensing elements. The sensing elements may have any suitable number of turns such as five or more turns (e.g., 5, 6, 7, 8, 9, 10, 15, 20, 40, 50, 100, 200, 500, 1,000). Providing sense elements with multiple turns increases the sense voltage response to a material or test object condition. Increasing the number of turns increases the response, but also can increase the response from noise or error sources, so the number of turns is selected to provide the highest reliability for sensing performance. Such multi-turn sensing elements may be incorporated into a relatively large footprint sensor where at least one dimension is greater than 4 inches and may be on a flexible substrate to enable conformity to different test object shapes. For such an embodiment it can be challenging to incorporate a remote current sensor within the sensing footprint, thus locating the remote current sensor at the end a cable, but proximate to the sensor offers a better solution. In some embodiments cable 150 is fabricated as a separate component from sensor 120.

[0098] In one embodiment, sensor 120 is integrated with a scanner, and the sensor moves across a test object to produce an image of damage, condition, temperature or stress. In another embodiment the sensor is installed in a fixed position on a test object such as a pipe, vessel, connector, riser, or structure, and the cable is connected either permanently or intermittently to receive the response of the sensing elements, and in some embodiments, to provide the drive current.

[0099] In some embodiments, sense elements 124 are magnetoresistive, or other sensors for detecting magnetic field or flux density. In some embodiments, the remote current sensor may use a magnetoresistive element or other sensor for detecting magnetic field or flux density.

[0100] FIG. 6A shows an inline current sensor 600 according to some embodiments. FIG. 6B shows an exploded view of inline current sensor 600. Current sensor 600 represents some embodiments of inline current sensor 125. Current sensor 600 includes a bobbin 604 and cap 601, a sense coil 602 and a drive coil 603. In some embodiments a magnetically permeable core is used. For example the permeability of the core may be exactly, greater than or equal to, greater than, less than or equal to, or less than 2, 5, 10, 15, 20 40, 50, 100, 200, 500, 1,000 times the magnetic permeability of free space, go. In some embodiments, bobbin 604 and 601 are manufactured using a ferrite to increase the magnetic flux density and thus magnetic coupling between the drive coil 603 and sense coil 602. Though any suitable material may be used. By concentrating magnetic fields within current sensor 600, the effect of other environmental factors are reduced so that the response measured from current sensor 600 is substantially independent from the surrounding environment which may be changing during operation. Advantageously, reducing fields produced by current sensor 600 outside of its enclosure also reduces interference on other systems. In this context, “substantially independent” means that the use of current sensor 600 provides an improvement over using internal current sensor 108 alone.

[0101] In some embodiments the transimpedance of current sensor 600 is assumed to be constant to permit estimation of the current in drive winding 122.

[0102] Sense coil 602 and drive coil 603 are wrapped around bobbin 604. Sense coil 602 and drive coil 603 are illustrated as simple hollow cylinders, but it should be appreciated that the illustration represents coils with one or more turns. In some embodiments, sense coil 602 and drive coil 603 are made using insulated wire. Sense coil 602 and drive coil 603 also have leads that may be used to connect current sensor 600 to leads within cable 150 as illustrated in FIG. 5. Current sensor 600 may have notches in cap 601 to permit such electrical connections to be made. The final assembly may be potted to prevent changes in geometry or damage to current sensor 600.

[0103] The selection of the number of turns in each of sense coil 602 and drive coil 603 may be determined in any suitable way. In some embodiments the number of turns in sense coil 602 and / or drive coil 603 may be exactly, greater than or equal to, greater than, less than or equal to, or less than 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 200, 500, 1,000, or 10,000 (excluding the case of “less than 1 tum(s)”). Though, sense coil 602 and drive coil 603 may have any suitable number of turns. Sense coil 602 and drive coil 603 need not have the same number of turns, though in some embodiments sense coil 602 and drive coil 603 do have the same number of turns.

[0104] In some embodiments, inline current sensor 600 is designed to have a transimpedance that matches the transimpedance of a sense element of the sensor in a known environment (e.g., in “air”). For a given excitation of the drive (alternating current of a certain frequency and amplitude), the design goal may be to have the sense element produce the same voltage magnitude as the remote current sensor. (As both the inline current sensor and the sense element are excited by the same drive current an equal voltage response is equivalent to equal transimpedance.) If the sensor has multiple sensing elements (e.g., a sensor array), the current sensor design may seek to match the transimpedance of a representative sense element in the array, an average transimpedance of the sense elements of the sensor, or another target that defines the target transimpedance for the inline current sensor. The design of inline current sensor 600 may be customized to match the target transimpedance in any suitable way. For example, the number of turns in sense coil 602, the number of turns in drive coil 603, the radius of bobbin 604, and the choice of material used for bobbin 604 may each be a design variable that can be used to achieve the target transimpedance. In some embodiments, final adjustments to the number of turns inline in sense coil 602 or drive coil 603 may be made after partially assembling current sensor 600 and measuring its transimpedance. For example, a turn or turns may be added or removed to increase or decrease the measured transimpedance until no further improvement can be made. Then the final assembly steps (e.g., potting) may be performed to complete assembly. Those of skill in the art will recognize that inline current sensor 600 by itself is a type of transformer and that the performance of of a particular design can often be reasonably well predicted using electromagnetic theory via hand calculation or electromagnetic simulation. The design of the inline current sensor in FIG. 6A-6B is illustrative and many other embodiments are possible.

[0105] In some embodiments, sense coil 602 and / or drive coil 603 are made using Litz wire. Litz wire may comprise multiple, individually insulated wires that may be twisted or woven together along the length of the coil.

[0106] It should be appreciated that although current sensor 600 was discussed as employing a ferrite bobbin with concentric drive and sense windings, other geometries and constructions may be used while maintaining the general configuration in which current in a first winding induces a measurable voltage in a second winding. For example, a toroidal transformer geometry may be employed, in which the primary winding carrying the current to be measured and the secondary winding providing the induced voltage are both disposed on a closed-loop core. Other suitable magnetic structures include pot cores, RM, EP, ETD, PQ, planar, E-I, E-E, U-I, C-core, and double-C cores formed from ferrite, nanocrystalline, amorphous, laminated, or powdered materials. The windings may be realized as discrete round wire, Litz wire, foil, ribbon, or printed circuit board conductors, and may be arranged concentrically, orthogonally, bifilarly, interleaved, or as figure-eight or gradiometric pairs to improve noise rejection. In certain embodiments, the current sensor may be implemented as a split-core or clamp-on structure to allow placement around an existing conductor. In other embodiments, the windings may be embedded in or on a substrate, overmolded or potted with the core, or integrated into a connector or cable assembly. Regardless of the specific geometry, current sensor 600 maintains the essential function of coupling magnetic flux from a primary winding carrying the measured current into a secondary winding in which a voltage is induced, thereby allowing the current to be determined from the known transimpedance and measured voltage.

[0107] In some embodiments, cable 150 consists of a set of drive conductors and multiple sets of sense conductors. In one embodiment, the drive conductors consisted of 6 smaller conductors twisted around a non-conductive core. Three of the conductors are connected in parallel for each leg of the drive. There is a braided shield over the 6 wires. The conductors for the sense element consist of a shielded twister pair (two wires twisted together with a common braided shield). The drive and sense conductors are bundled together inside of a nylon braid. A braided shield may or may not be included beneath the nylon braid. The remote current sensor is placed inside of the nylon braid near the sensor-end of the cable, but not so close to the sensor that it’s affected by the magnetic field produced by the sensor. An example would be to place the inline current sensor at a distance from the sensor’s drive winding at twice the spatial wavelength of the sensor.

[0108] Attention is now turned to FIG. 7 which shows a flow diagram of method 700 according to some embodiments.

[0109] At step 701, a system is provided having an instrument, cable with inline current sensor and a sensor having at least one sensing element.

[0110] At step 703, method 700 measures in a known environment a first response of the remote current sensor and a first response of the sensing element. The known environment may be in air, or any other suitable environment such that the transimpedances of the remote current sensor and the sensing element may be known. The measurements may be taken simultaneously. By taking the measurements simultaneously the impedance of the leads to the inline current sensor and sensing element will be similar for both elements.

[0111] At step 705, method 700 determines a calibration factor from the first responses. The calibration factor may be determined in ways similar to those used in the ‘218 patent for analogous measurements. In some embodiments the calibration factor is a complex number.

[0112] A step 707, method 700 measures second responses of the sensing element placed proximal to a test object and of the inline current sensor. The second response of the inline current sensor may be measured in the same known environment used at step 703. Though a different environment for the inline current sensor may be used in some embodiments.

[0113] At step 709, method 700 divides the second response of the sensing element by the second response of the remote current sensor to produce a dividend. The dividend may be a complex number in some embodiments.

[0114] At step 711, method 700 calibrates the dividend with the calibration factor. In some embodiments, the calibration occurs by multiplying the dividend by the calibration factor.

[0115] Method 700 may end after step 711. The calibrated result produced by method 700 may be used in subsequent processes such as in a multivariate inverse method to estimate material properties of the test object. Such calibrated results and / or material properties may be used to control a process or determine whether the test object should be approved, scraped, reworked, or otherwise treated. Though the sensor, system and method described here may be used as a measurement tool and thus the use of the calibrated result may vary greatly from embodiment to embodiment and application to application.

[0116] In some embodiments, after step 711 method 700 continues via path 713 and returns to step 707 and repeats steps 707, 709, and 711 one or more additional times. This may be the case, for example, in a scanning application where data is taken repeatedly as a sensor is scanned across the test object. By continuing to measure second responses during a scanning operation the sequential measurements from the sensor can be each calibrated by a corresponding measurement from the inline current sensor.

[0117] Method 711 may also continue after step 711, via path 715, to step 703 and continue from that point. For example, in a sequential layer additive manufacturing application the sensor may perform a scan after fabrication of a layer and then return to the known environment while a subsequent layer is built. For example, the known environment may be “air” away from the build area or a metal surface with known properties. Prior to scanning the subsequent layer, step 703 may be performed in the known environment so that a calibration factor can be captured for use in calibration for data collected on the subsequent layer.

[0118] Paths 713 and 715 may each be taken multiple times before method 700 ends.

[0119] Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art.

[0120] Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.

[0121] All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference. To the extent publications and patents or patent applications incorporated by reference contradict the disclosure contained in the specification, the specification is intended to supersede and / or take precedence over any such contradictory material.

[0122] As used herein, references to specific immittance quantities (e.g., “impedance,” “admittance,” “transimpedance,” “transadmittance,” or related parameters) are provided by way of example only. Unless expressly stated otherwise, such references are intended to be interchangeable and to support embodiments employing any equivalent immittance representation. Thus, for instance, a disclosure describing an “impedance measurement” is likewise deemed to support embodiments in which the corresponding immittance is expressed or measured in terms of admittance, transimpedance, transadmittance, or other immittance forms that characterize the voltage-current relationship of interest. The above-described embodiments of the present invention can be implemented in any of numerous ways. For example, the embodiments may be implemented using hardware, software or a combination thereof. When implemented in software, the software code can be executed on any suitable processor or collection of processors, whether provided in a single computer or distributed among multiple computers.

[0123] Further, it should be appreciated that a computer may be embodied in any of a number of forms, such as a rack-mounted computer, a desktop computer, a laptop computer, or a tablet computer. Additionally, a computer may be embedded in a device not generally regarded as a computer but with suitable processing capabilities, including a Personal Digital Assistant (PDA), a smartphone or any other suitable portable or fixed electronic device.

[0124] Also, a computer may have one or more input and output devices. These devices can be used, among other things, to present a user interface. Examples of output devices that can be used to provide a user interface include printers or display screens for visual presentation of output and speakers or other sound generating devices for audible presentation of output. Examples of input devices that can be used for a user interface include keyboards, and pointing devices, such as mice, touch pads, and digitizing tablets. As another example, a computer may receive input information through speech recognition or in other audible format.

[0125] Such computers may be interconnected by one or more networks in any suitable form, including as a local area network or a wide area network, such as an enterprise network or the Internet. Such networks may be based on any suitable technology and may operate according to any suitable protocol and may include wireless networks, wired networks or fiber optic networks.

[0126] Also, the various methods or processes outlined herein may be coded as software that is executable on one or more processors that employ any one of a variety of operating systems or platforms. Additionally, such software may be written using any of a number of suitable programming languages and / or programming or scripting tools, and also may be compiled as executable machine language code or intermediate code that is executed on a framework or virtual machine.

[0127] In this respect, the invention may be embodied as a computer readable medium (or multiple computer readable media) (e.g., a computer memory, one or more floppy discs, compact discs, optical discs, magnetic tapes, flash memories, circuit configurations in Field Programmable Gate Arrays or other semiconductor devices, or other tangible computer storage medium) encoded with one or more programs that, when executed on one or more computers or other processors, perform methods that implement the various embodiments of the invention discussed above. The computer readable medium or media can be transportable, such that the program or programs stored thereon can be loaded onto one or more different computers or other processors to implement various aspects of the present invention as discussed above.

[0128] In this respect, it should be appreciated that one implementation of the above-described embodiments comprises at least one computer-readable medium encoded with a computer program (e.g., a plurality of instructions), which, when executed on a processor, performs some or all of the above-discussed functions of these embodiments. As used herein, the term “computer-readable medium” encompasses only a computer-readable medium that can be considered to be a machine or a manufacture (i.e., article of manufacture). A computer-readable medium may be, for example, a tangible medium on which computer-readable information may be encoded or stored, a storage medium on which computer-readable information may be encoded or stored, and / or a non-transitory medium on which computer-readable information may be encoded or stored. Other non-exhaustive examples of computer-readable media include a computer memory (e.g., a ROM, a RAM, a flash memory, or other type of computer memory), a magnetic disc or tape, an optical disc, and / or other types of computer-readable media that can be considered to be a machine or a manufacture.

[0129] The terms “program” or “software” are used herein in a generic sense to refer to any type of computer code or set of computer-executable instructions that can be employed to program a computer or other processor to implement various aspects of the present invention as discussed above. Additionally, it should be appreciated that according to one aspect of this embodiment, one or more computer programs that when executed perform methods of the present invention need not reside on a single computer or processor, but may be distributed in a modular fashion amongst a number of different computers or processors to implement various aspects of the present invention.

[0130] Computer-executable instructions may be in many forms, such as program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Typically the functionality of the program modules may be combined or distributed as desired in various embodiments.

[0131] Also, data structures may be stored in computer-readable media in any suitable form. For simplicity of illustration, data structures may be shown to have fields that are related through location in the data structure. Such relationships may likewise be achieved by assigning storage for the fields with locations in a computer-readable medium that conveys relationship between the fields. However, any suitable mechanism may be used to establish a relationship between information in fields of a data structure, including through the use of pointers, tags or other mechanisms that establish relationship between data elements.

[0132] Various aspects of the present invention may be used alone, in combination, or in a variety of arrangements not specifically discussed in the embodiments described in the foregoing and is therefore not limited in its application to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments.

[0133] Also, the invention may be embodied as a method, of which an example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.

[0134] Where this specification discloses a range of numerical values, it is to be understood that the disclosure of that range includes each integer value and each sub-range falling within the broader range, unless the context clearly dictates otherwise. For example, a disclosure of “1 to 10,000” expressly supports values such as 5, 500, 5,000, and 9,999, as well as sub-ranges such as 100-1,000 or 4,000-6,000. Likewise, where a specific value is disclosed (e.g., 100, 1,000, or 5,000), it should be understood to disclose “about” that value (e.g., within ±10%, ±5%, or ±1%) and to support nearby intermediate values. Recitation of representative values (e.g., 10, 50, 100, 500, 1,000, 2,500, 5,000, 10,000) is intended to provide explicit written description for those values and for other values reasonably encompassed by the disclosed ranges and examples.

[0135] As used herein, the terms “about,” “approximately,” “close to,” and “substantially” are intended to allow for reasonable variation from the exact value or condition stated. Unless otherwise specified or dictated by context, for non-zero numerical values these terms encompass variations within ±10% of the stated value, and in certain embodiments within ±5% or ±1%. For zero values, the terms “close to zero” or “substantially zero” are intended to mean values that are negligible in the relevant context, such as less than 0.01, less than I O3, or below a measurement threshold that would materially affect system performance. For non-numerical attributes, such as “substantially parallel” or “substantially free of defects,” the terms are intended to mean that the attribute is present to a degree that achieves the intended technical effect despite minor deviations. These definitions are illustrative rather than limiting, and other tolerances may be appropriate in view of the precision of available measurement tools or the requirements of a particular embodiment.

[0136] Use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

[0137] Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or “having,” “containing,” “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

Claims

CLAIMS1. A system comprising: an immittance instrument having first and second measurement channels; a sensor having a drive conductor and a sense element; and a cable operably connecting the drive conductor and the sense element of the sensor to the immittance instrument, and having a current sense element, wherein the first and second measurement channels are operably connected to measure responses of the current sense element and the sense element, respectively.

2. The system of claim 1, wherein the sensor is an inductive sensor and the sense element is a coil comprising five or more turns.

3. The system of claim 1, wherein the cable is operably connected to the immittance instrument via a first coupling interface comprising an instrument-side connector and a first cable-side connector, the cable is operably connected to the sensor via a second coupling interface comprising a sensor-side connector and a second cable-side connector, the instrument-side connector is mated with the first cable-side connector, the sensor-side connector is mated with the second cable-side connector, the instrument further includes the instrument-side connector, the sensor further includes the sensor-side connector, and the cable comprises the first and second cable-side connectors.

4. The system of claim 1, wherein the cable comprises an immittance-instrument end that is operably connected to the immittance instrument and a sensor end that is operably connected to the sensor, and the current sense element is closer to the sensor end than the immittance-instrument end.

5. The system of claim 4, wherein the current sense element is located within a length portion of the cable that is closest to the sensor end and is less than 25% of an entire length of the cable.

6. The system of claim 1, wherein the current sense element is part of a current sensor, the current sensor further comprising a drive element that is operably connected in series with adrive lead of the cable that connects the drive conductor of the sensor to the immittance instrument.

7. The system of claim 6, wherein the current sense element comprises a sense coil, the drive element comprises a drive coil, and the drive coil and sense coil are wrapped around a core having a magnetic permeability greater than 2 go.

8. The system of claim 1, wherein the current sense element is a magnetoresistive sensor.

9. The system of claim 1, wherein the sensor is permanently installed on a test object.

10. The system of claim 1, further comprising a scanner, wherein the sensor is integrated into the scanner for scanning measurements.

11. The system of claim 1, wherein the sense element is among a plurality of sense elements forming a sensor array, the second measurement channel is among a plurality of second measurement channels, and the cable operably connects each of the plurality of sense elements to a respective member of the plurality of second measurement channels.

12. A system comprising: a sensor having a drive conductor and a sense element; and a cable integral with or connectable to the sensor, the cable comprising a drive lead integral with or connectable to the drive conductor; a sense lead integral with or connectable to the sense element; and a current sensor comprising a current sense element.

13. The system of claim 12, wherein the current sensor further comprises a drive element that is inserted in series with the drive lead of the cable.

14. The system of claim 13, wherein the current sense element comprises a sense coil, the drive element comprises a drive coil, and the drive coil and sense coil are wrapped around a core having a magnetic permeability greater than 2 go.

15. The system of claim 12, wherein the current sense element is a magnetoresistive sensor.

16. The system of claim 12, wherein the sensor is an inductive sensor and the sense element is a coil comprising five or more turns.

17. The system of claim 12 further comprising an immittance instrument having first and second measurement channels, wherein the first and second measurement channels are operably connected to the sensor via the cable to measure responses of the current sense element and the sense element, respectively.

18. The system of claim 12 further comprising an immittance instrument having a measurement channel, the immitance instrument operably connected to the sensor via the cable to measure responses of the current sense element and the sense element, respectively.

19. The system of claim 18, wherein the instrument comprises a multiplexor to switch the measurement channel between the sense element and the current sense element.

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