Abstract: A method of inspecting a preselected area of an electrically conductive component to determine whether flaws are present. The method includes the steps of permanently mounting an eddy current element on the component over the preselected area and energizing the element to generate alternating magnetic fields proximate the component. An electrical signal generated by a secondary magnetic field formed proximate the component is detected using the element and the detected electrical signal is compared to a reference signal to determine whether the detected signal is different than the reference signal. Differences indicate the presence of a flaw in the component. Inspection apparatus for performing this method is also disclosed.

Abstract: A sensor head with multiple sensors for ACFM based crack detection and sizing. An alternating current electromagnetic yoke is used to induce a uniform magnetic field on the surface of the test piece. A reference coil in the sensor head detects the background field strength of the magnetic field. Multiple sensors, the axis of each of which is in an angled relationship to the reference coil, detect variations in the magnetic field. The sensor coil axes can be chosen to detect and size both angled and straight cracks.

Abstract: A method is disclosed for processing, optimization, calibration, and display of measured dielectrometry signals. A property estimator is coupled by way of instrumentation to an electrode structure and translates sensed electromagnetic responses into estimates of one or more preselected properties or dimensions of the material, such as dielectric permittivity and ohmic conductivity, layer thickness, or other physical properties that affect dielectric properties, or presence of other lossy dielectric or metallic objects. A dielectrometry sensor is disclosed which can be connected in various ways to have different effective penetration depths of electric fields but with all configurations having the same air-gap, fluid gap, or shim lift-off height, thereby greatly improving the performance of the property estimators by decreasing the number of unknowns.

Abstract: A method and a measuring device for determining the spatial distribution of a magnetic field vector. At least a pair of sensor elements is provided. Each sensor element measures a component of the magnetic field vector. The sensor elements are aligned in a parallel, spaced-apart relationship along an axis parallel to the measured components.

Abstract: A method is provided for determining magnetic characteristics of an electrically controlled solenoid. The method includes providing an electronically controlled solenoid having an armature, a stator and a coil operatively associated with the stator. The armature, stator and coil define a magnetic circuit. The armature is spaced from the stator to define an air gap between the armature and the stator. Current to the coil is ramped in a generally linear manner over a period of time to define a known current curve. A resulting rate of change of flux in the magnetic circuit is observed and recorded at certain points along the current curve. In accordance with another aspect of the invention, flux in the magnetic circuit is ramped in a generally linear manner over a period of time to define a known flux curve. A resulting current in the coil is observed and recorded at certain points along the flux curve.

Abstract: A device for inspecting a part by eddy currents, the device comprising at least one measurement bridge having an active coil which is connected between a first terminal and a second terminal, and a reference circuit which is connected between said second terminal and a third terminal, said first and third terminals being for connection to an AC voltage generator so that an alternating magnetic field is generated by the active coil in the part to be inspected in order to enable any variation in the impedance of the active coil on passing over a defect in a part under inspection to be detected by analyzing an output voltage of the device, wherein the reference circuit is a reference coil identical to the active coil, wherein the first terminal and the third terminal are for receiving voltages applied by the AC voltage generator which are equal in value and of opposite signs relative to a neutral phase of said generator, the output voltage being the voltage read between said second terminal and said neutral phas

Abstract: The probe for inspecting electrically conducting parts (1) of the invention comprises a row of transmitter and receiver coils (27), (28) that form an array of energized coils. The receiver coils (28) are influenced by different magnetic fields created by several neighboring transmitter coils (27) at the same time, making them sensitive to different types of flaws. The array of energized coils is displaced along the row. The probes are usually used for inspecting steam generator tubes of nuclear power plants.

Abstract: An eddy current inspection probe for inspecting a preselected surface at least partially defining an opening in a component. The eddy current inspection probe includes a core moveable between a retracted position and an expanded position in which the probe is sized and shaped for at least partially filling the opening and contacting the preselected surface for inspecting the surface. The probe includes a compliant covering positioned over the exterior surface of the core and an eddy current array positioned over the outer face of the covering. Further, the probe includes an element positioned between an exterior surface of the core and an inner face of the covering having a coefficient of friction selected to permit the inner face of the covering to move tangentially with respect to the exterior surface of the core as the core is moved from the retracted position to the expanded position to ensure intimate contact between probe and the preselected surface of the component being inspected.

Abstract: A method for evaluation of an eddy current testing signal is provided. The method includes the steps of generating a feature amount based on a sample eddy current testing signal obtained by measuring a standard specimen, the feature amount including a feature highly correlated to a secondary factor which is other than a depth of the flaw and which affects the waveform of the signal; generating an evaluation parameter by using the feature amount, the evaluation parameter being a parameter for outputting a value with a sufficiently small error relative to correct answer data on the sample eddy current testing signal; and estimating the depth of a flaw, expressed by an actual measurement eddy current testing signal, by use of the evaluation parameter.

Abstract: A method and apparatus for detection of rare earth metal oxide inclusions in non-magnetic metal. The method utilizes a D.C. magnetic search field coupled with a magnetic field sensor for detecting the response of a rare earth metal oxide casting fragment inclusion through the bending and amplification of the ambient magnetic field at the defect location.

Abstract: A test device and process for inspecting the integrity of prestressed construction elements. The device comprises a testing head having a magnetization device for generating a magnetic field around the construction element. The testing head is connected to a controller device for controlling the magnetization process and for processing signals corresponding to the magnetic field. The testing head magnetizes the construction element over a predetermined measurement section. The controller switches the magnetization device after the magnetization process is completed and then stores and processes the signals recorded.

Abstract: The present invention relates to a device for continuously monitoring the junction of a conveyor belt which is made of rubber or a rubber-type plastic material and which comprises supports inserted therein for reinforcing the same. In an advantageous embodiment, the device essentially comprises the following constituent members for the junction area: mainly four reference marks, two addresses as well as four detection heads, the heads being located above the carrier surface of the conveyor belt. This invention further relates to other advantageous embodiments of this device.

Abstract: The present invention provides a method for the direct measurement and quantification of the material volume loss on the surface of a substrate and thus provides an accurate depiction of the surface profile of the surface. The method of the invention comprises inducing eddy currents in a test substrate, measuring the magnitude of the eddy current produced within the substrate at a plurality of locations on the surface of the substrate, and converting the measured eddy current magnitudes at the locations to corresponding volume losses on the test surface using the eddy current magnitude measurements of a reference substrate having defects of predetermined volume loss. Typically, the measurements of the eddy current magnitude on the test surface are converted to actual volume losses by multiplying the measured eddy current magnitude for a sector of the test substrate by the area of the sector and a calibration factor (Cf) representing the volume per unit area eddy current magnitude.

Abstract: In a non-destructive inspection device of the present invention which detects in a non-destructive manner a defect of a member to be inspected, based on a change in magnetic fluxes due to eddy currents that are generated by an inspection probe having a coil, a driving section which adjusts a position of the inspection probe, and measuring device for, based on a detection signal of the inspection probe, measuring a lift-off between the inspection probe and the member to be inspected are disposed. The driving section is controlled in accordance with a result of measurement of the measuring device, whereby a control of making the lift-off constant is performed.

Abstract: An eddy current probe is configured with one axis of the electrical coil elongated to span a much larger distance than that of conventional coils. Thus, a single pass of the elongated coil can inspect a path of up to 100 times wider than the conventional coil. The parts of the eddy current probe include a pair of elongated ferrite cores disposed end-to-end in a housing block. A pair of receive coils are disposed in the housing block respectively surrounding the elongated ferrite cores. A transmit coil is wound around the receive coils in the housing block, and a pair of ferrite shields are disposed in the housing block sandwiching the transmit coil, the pair of receive coils, and the pair of elongated ferrite cores.

Abstract: A method of analyzing defects in a magnetic thin film is provided. A magnetic field is applied to the magnetic thin film. The magnetization of the magnetic thin film is measured over a range of different field strengths. A value representative of a magnetic hardness coefficient is calculated for the magnetic thin film from the magnetizations measured. The calculated value is compared with a reference value. Defect information is determined in dependence upon the comparison made.

Abstract: Flexible eddy current probes that allow an inspector to interrogate the blade roots or disk slots of different types of blades and disks while using a limited number of probes. The probe includes a rectangular-shaped block assembly, a rectangular-shaped loading platform having a slot therein, and stabilizing slide rods that couple the loading platform to the block assembly. The slide rods are adapted to slide through the block assembly as the block assembly is urged towards the loading platform. The probe further includes a flexible coil within a flexible membrane that produces a magnetic field during the inspection. The flexible coil extends from the block assembly and remains within the device, that is, between the loading platform and the block assembly, when not deployed. When deployed, the flexible coil passes through the slot in the loading platform to allow contact with the surface being inspected. Outriggers within the probe guide the flexible coil onto the surface during deployment.

Abstract: An apparatus and method for detecting defects in electrically conductive materials. A detection method and apparatus are provided for using applied magnetic fields to induce magnetic fields in the material under test, and then directly detecting changes in the induced magnetic field attributable to corrosion, cracks, flaws, or anomalies in the material under test. The invention features the use of one or more giant magnetoresistance sensors to detect directly the changes in the induced magnetic field, which changes provoke a response in the giant magnetoresistance sensors in the form of a change in resistance signal. The apparatus may be configured in various ways, including absolute field detection and differential field detection configurations, with either passive or active field compensation, and single sensor or multiple sensor arrays. A plurality of giant magnetoresistance sensors may be disposed upon a single substrate, or on multiple substrates.

Abstract: A computer implemented information extraction process that locates and identifies eddy current signal features in digital point-ordered signals, signals representing data from inspection of test materials, by enhancing the signal features relative to signal noise, detecting features of the signals, verifying the location of the signal features that can be known in advance, and outputting information about the identity and location of all detected signal features.

Abstract: The apparatus enables eddy current inspection of a metal tube having a thin layer on its outside face with magnetic or electrical characteristics that are different from those of the metal in-depth. The apparatus comprises a measurement head having a measurement coil (14) for surrounding the tube and means for powering the coil with voltage at high frequency, greater than 100 kHz, and for analyzing the impedance of the coil. The head contains a magnet (22) surrounding the coil and magnetic flux guides (24) on either side of the coil in the axial direction and co-operating with the magnet to constitute a magnetic circuit that creates a magnetic field whose maximum intensity lies inside the coil and close thereto.

Abstract: An openable ring assembly is externally centered around and moved parallel to the centerline of a stationary pipe. As a low-frequency EM source signal is applied to the ring assembly, the time and/or frequency shifts of a detected EM signal from the source signal can be correlated to pipe wall thickness without removal of external pipe insulation and metal cladding, if present. The ring assembly may be opened or expandably segmented to allow pipe thickness detection around obstructions or larger diameter pipe. Centering is preferably accomplished by using rollers circumferentially attached to the ring assembly.

Abstract: The eddy current probe for non-destructive testing of a conductive elongated member includes an oscillating magnetic field generator for producing a magnetic field directed towards a cross-sectional peripheral surface of the elongated member. The magnetic field generator includes a pair of coils arranged to be spaced apart along the elongated member to produce an enhanced combined magnetic field component perpendicular to the cross-sectional peripheral surface in a space between the coils and a reduced magnetic field component lengthwise along the elongated member. A ferromagnetic member is movably mounted for altering the magnetic field at points along the cross-sectional peripheral surface provided between the coils. A detecting and analyzing system measures an impedance of the coils as the generator is moved along the elongated member and as the field altering member is moved over the peripheral surface. An enhanced signal is obtained.

Abstract: An apparatus to detect anomalies in a member, such as a conveyor belt, having reinforcing cables therein made of a magnetically permeable material. There is coil means arranged to create a magnetic field as two longitudinally spaced first and second field components at longitudinally spaced locations. There are Hall effect sensors arranged to respond to modifications in each of the first and second field components.

Abstract: A probe, such as an eddy current probe, which can be moved by hand to a surface to be tested. A toroidal-shaped first resilient member contacts the bottom face of a support member. An elastic membrane extends over the bore of the first resilient member, contacts the bottom lateral surface of the first resilient member, and is unattached to the radially-inward-facing surface of the first resilient member. A more elastic, second resilient member is placed in the bore, is unattached to the first resilient member, and contacts the bottom surface of the elastic membrane. A flexible, surface-conformable, eddy current sensing coil overlies a portion of the bottom side of the second resilient member.

Abstract: An eddy current probe which can be moved by hand to a surface to be tested. A toroidal-shaped first resilient member contacts the bottom face of a support member. An elastic membrane extends over the bore of the first resilient member, contacts the bottom lateral surface of the first resilient member, and is unattached to the radially-inward-facing surface of the first resilient member. A more elastic, second resilient member is placed in the bore, is unattached to the first resilient member, and contacts the bottom surface of the elastic membrane. A flexible, surface-conformable, eddy current sensing coil overlies a portion of the bottom side of the second resilient member.

Abstract: An eddy current testing apparatus for nondestructive examination of pipe. The apparatus includes an eddy current coil adapted to removably circumferentially surround the pipe, the coil including a cable having a plurality of conductors adapted to form a continuous conductor coil when the cable is circumferentially wrapped around the pipe. A guide system extends along the length and adjacent to the surface of the pipe and a coil form is adapted to removably circumferentially surround the pipe and engage the guide system to provide for travel of the coil along the pipe.

Abstract: The present invention uses a magnet in relative motion to a conductive material, and a coil that is stationary with respect to the magnet to measure perturbation or variation in the magnetic field in the presence of an inclusion. The magnet and coil sensor may be on the same side of the conductive material.

Abstract: To test coiled tubing, at least one test is performed on a coiled tubing that has been used, such as in an oil or gas well. Performing such test includes obtaining a specific output data event (e.g., a nondestructive evaluation test readout) for the used coiled tubing. The specific output data event is compared with a predetermined sequence of output data events (e.g., a collection of data defining a "lifeline" for the coiled tubing) for determining where the sequence and the specific output data event correspond. A coiled tubing status indication is generated in response to where the specific output data event corresponds with the sequence as a measure of a point in the useful life of the used coiled tubing.

Abstract: A portable measuring device for measuring electromagnetic radiation reflection. The device has a holder, a transceiver, and a display. The transceiver is movably mounted to the holder. The holder can be moved to several locations on a member being tested. The transceiver is moved up and down on the holder through the peaks and valleys of the reflected electromagnetic wave, in and out of phase, passing through and detecting the maximum reflected energy point. A system can be provided that uses the measurement at a predetermined frequency in comparing the measured property to a characteristic curve of the property for the material of the member being tested. The system can be used to plot a three-dimensional graph of surface reflection of the electromagnetic energy.

Abstract: Both a system and method are provided for mapping the magnitude of residual compressive stresses over the surface of a ferromagnetic machine component, such as a valve ring of the type used in refrigeration compressors. The system includes an eddy current probe having a detection coil for emanating a fluctuating electromagnetic field that shallowly penetrates the surface of the valve ring or other ferromagnetic component, a probe circuit connected to the coil for both conducting a high frequency alternating electric current through the coil and detecting changes in the impedance in the coil, and a scanning mechanism having a turntable for supporting and rotating the component. A support arm positions the coil of the eddy current over a central portion of the valve ring while the ring is rotated by the turntable and changes in coil impedance are detected by the probe circuit.

Abstract: A method and apparatus for electro-magnetically testing surface regions of elongated test objects for irregularities, such as flaws, and which is particularly suitable for testing test objects with non-circular or elliptical cross sections. Testing is performed by at least one coil, particularly an eddy current coil, through which a test object passes. The test coil has a coil plane passage of predetermined cross-section, and a modification of the passage cross-section of the test coil can be obtained by tilting the test coil. The test coil can optionally be rotated about an axis defined by the travel direction of the test object, and may also be moved in directions perpendicular to the travel direction. A disclosed apparatus for performing the method has several tiltable and rotatable and/or slidable test coils which are successfully arranged in the travel direction in the form of a coil group.

Abstract: The process relates to the aptitude for detectability of defects using eddy-currents on metal tubes cold laminated using a pilger mill and relates more particularly to the possibility of reducing the background noise and increasing the ratio between a standard signal and this background noise.The process consists of carrying out, after reduction in section by at least 30% in a cold pilger mill, a hollow drawing pass with a reduction in the external diameter of approximately 0.1% to 5%. The signal/background noise ratio can in this way be multiplied by a factor of between 2 and 3.7, in the case of a series of tubes made of INCO 690 alloy, as shown in the single figure.The invention also relates to tubes produced using this process.Application in production of steam generating tubes for nuclear power stations.

Abstract: An array of sensors is provided at or near the surface of a material arranged to detect magnetic flux leakage occurring when a magnetic field is induced in the material. The sensors in the array are coupled in respective pairs (differential pairs) such that when one partner of a respective pair overlies a discontinuity, a differential output signal is produced dependent on the difference between the output signals from the sensors of the respective differential pair. Because of the nature of the change of the flux leakage field produced by a discontinuity, respective partners of each pair of sensors are spaced relative to each other according to the invention. In one embodiment, partners of each sensor pair are spaced relative to one another both in the direction of travel of the apparatus and also in a direction transverse thereto.

Abstract: A novel test method enabling residual stress in non-ferromagnetic metal objects to be reliably measured which requires particular circuit elements in the alternating current bridge circuit being employed for measurement to be environmentally controlled. In doing so, the selected circuit resistor elements are thermally isolated in a manner enabling lift-off impedance values to non-destructively measure near-surface residual stress in the metal object being tested.

Abstract: Eddy current testing is performed at known locations on a metal object having recurring features to provide a data string that is applied to a signal processor that determines a template for one feature and conducts a correlation operation with the template and the data string to create a second string with peaks that periodically appear between two locations. The average width between those two locations is determined. The average value for each location in the second data string along the average distance between peaks is computed. The actual value of the second string at each location is combined with the average computed value to produce a deviation value that shows faults without a superimposed average geometry value. The location of the fault is indicated in response to the deviation signal.

Abstract: An ultrasonic scan assembly for use in inspecting downhole gas pipes comprises a sensor section which rotates in relation to an end section that remains essentially level forming a rotating interface. The sensor section includes at least one ultrasonic transducer for transmitting interrogating pulses into a pipe wall and for receiving return pulses that are analyzed for determining the maintenance and repair needs of the gas pipe. Provided in the scan assembly is a rotary transformer for magnetically coupling signals, such as return pulse data or power, across the rotating interface of the scan assembly. The rotary transformer includes a primary winding on one section of the scan assembly and a secondary winding on another section of the scan assembly. The primary windings and secondary windings associated with respective sections of the scan assembly can be placed in parallel or concentric relationship.

Abstract: An a.c. field measurement testing system for detecting and sizing defects in a conductor includes a probe head having field coils located on a yoke so as to induce an a.c. field in the conductor and sensor coils arranged such that central longitudinal axes of the sensor coils are orthogonal one to another. The coils are wound on a former at the same location on the former and one of the sensor coils is oriented so that a longitudinal axis thereof is parallel to the induced a.c. field.

Abstract: In order to control the direction of a magnetic field induced by a current sheet in a sheet conductor, relative to anomalies in a test sample, the current sheet is either rotated relative to the sheet conductor, by using either electrical or mechanical commutation of the current sheet, or the phases of plural independent current sheets in the sheet conductor are shifted relative to each other.

Abstract: An apparatus to detect anomalies in a member, such as a conveyor belt, having reinforcing cables therein made of a magnetically permeable material. There is coil means arranged to create a magnetic field as two longitudinally spaced first and second field components at longitudinally spaced locations. There are Hall effect sensors arranged to respond to modifications in each of the first and second field components. In a first embodiment, there is one set of sensors positioned between the first and second field components. In a second embodiment, there are two sets of sensors spaced at said first and second field components.

Abstract: A method and apparatus for testing an elongate product for faults and defects, which comprises a rotatable testing head which permits the elongate product to be passed coaxially therethrough and which mounts a pair of testing probes so as to permit adjustment of their operating diameter. In order to automatically adjust the positions of the probes to accommodate elongate products of different sizes, there is provided an external adjustment unit, which stops the testing head in a predetermined angular position. The adjustment unit contains an external adjustment drive and when the rotation of the testing head has stopped, the external adjustment drive is advanced into operative engagement with the adjustable mounting of the testing probes.

Abstract: A magnetic field generator positioned externally of a non-ferrous metallic tructure being examined, is rotated at a relatively low speed to produce a rotating magnetic field penetrating the metallic structure to a selected depth as a function of spacing between magnetic poles of the generator parallel to a planar surface of the metallic structure. Traction between the metallic structure and the magnetic field accompanying its rotation is measured. Corrosion of the metallic structure at subsurface depths is detected and quantified from such traction measurements.

Abstract: A sensor arrangement and a method of acquiring properties of the surface layer (3) of a metallic target (2), which allow a nondestructive and substantially distance-independent measurement to be performed, with the requirements to be met by the sensor positioning being minimal. The sensor arrangement (1) comprises a combination of at least one eddy-current sensor (5) with at least one displacement measuring sensor (6), the depth of penetration of the eddy currents generated by the eddy-current sensor (5) corresponding to at least twice the thickness of the surface layer (3), and the displacement measuring sensor (6) serving to determine the distance of the sensor arrangement (1) from the target surface (4).

Abstract: A test head through which passes a test object has at least one test probe guided in a circular orbital path around the test object. The shape of the circular orbital path of the probe, when considered in the travel direction of the object, diverges in a predetermined manner from a circular shape. A rotor guides the probe on a circular path, and the rotational axis of the rotor can be tilted with respect to the travel direction of the test object. The rotor is driven by a driving unit positioned laterally to the travel direction on a base plate by a belt drive which runs in a transmission element carrying the test head and linking it with a drive unit.

Abstract: Defects such as corrosion located on the exterior of a component such as a metal pipe, tank, vessel or support structure which is insulated by a coating or cover, are detected by a low frequency eddy current (LOFEC) system. A magnetizing yoke in the shape of an inverted U is placed on the cover insulating a metal component. An excitation coil is wrapped around the magnetizing yoke for carrying an altering current in order to produce an alternating magnetic field by the magnetized yoke. The alternating magnetic field produced by the magnetized yoke induces an eddy current which runs through the metal component between the legs of the yoke. A pair of magnetic flux sensors are used in differential connection beneath one or more excitation coils which can be articulated to conform to varying pipe diameter. In addition, an absolute signal response can be obtained from one of the receiver coils.

Abstract: A system and method of automatic, in-line electrical quality control of a carbon anode including detecting internal flaws in the carbon anode by measuring an eddy-current loss of the carbon anode and determining intrinsic resistivity of the carbon anode by measuring resistivity of the carbon anode and determining the electrical quality of the carbon anode according to the measured eddy-current loss and the measured resistivity.

Abstract: A system for monitoring ferromagnetic materials in proximity to a sensing region, which is particularly applicable to traffic monitoring and controlling. A magnetic probe generates a signal in response to magnetic flux changes caused by a vehicle moving through a sensing area. A processor analyzes the signal to determine the duration of the signal and correlates that duration to a vehicle velocity. A checking system periodically sends a checking signal to the magnetic probe and monitors the return signal to verify that the probe is operative and also analyzes the return signal to determine whether a stationary vehicles is in the sensing area.

Abstract: The detection of an internal damage in an FRP member constituted by reinforcing fibers, a matrix resin and magnetic members having a magneto-mechanical property is conducted by disposing the magnetic members in the FRP member, and measuring a change in the magnetic properties of the magnetic members by a non-destructive inspection method.

Abstract: A device for detecting longitudinal cracks on slabs, in particular on steel slabs, issuing from a continuous casting, by way of eddy current measuring probes fed with an alternating voltage, and device for detecting variations in the voltage indicating the presence of a crack. The device for detecting longitudinal cracks includes on each side of upper and lower faces of the slab, a crack detection unit each including a measuring probe which undergoes a transverse reciprocating motion relative to the direction of travel of the slab, and a device for maintaining the measuring probe of each detection unit at a constant distance relative to the corresponding main face of the slab.

Abstract: A method of magneto-optic eddy current imaging for detecting defects in a ferrous metal, non-ferrous metal, or non-metallic structure test object uses a sensor, magnetic field system, optical system, a video camera and a display. The method includes canceling undesired background of a two-dimensional magneto-optically generated image of a defect in the test object by dithering the image and processing signals from the video camera in compatibility with the dithering. The image is dithered once per frame of the camera, or at a sub-multiple of the frame of the camera, and the dithering may be accomplished manually or mechanically.

Abstract: In order to improve product quality control through quantitative determination of a defect and quantitative judgement of the quality of a product, an alternating current is applied to a standard product coil into which is inserted a standard object, and to a test object coil into which is inserted a test object, and eddy currents are measured by means of a bridge circuit. If the test object coil is at a location removed from a flaw, the bridge circuit output voltage is zero, while if the test object coil is at the location of the flaw, a predetermined voltage is output. A determination of torsional breakage torque of the shaft inspection is carried out by correcting the output voltage for dependence on the cross sectional area ratio of the test object relating to the cross sectional area of the coil and for the influence of flaw size depending on the location.