Abstract: A measuring circuit obtains desired characteristic values of a device under test by accurately measuring a voltage and a current. Errors are eliminated that originate from the transmission characteristics of cables used in measurements at high frequencies and measurements using long cables. The errors are eliminated by connecting resistors that are equal in resistance to the characteristic impedance of cables, to the inputs of the cables which connect the device under test to a measuring device.

Abstract: An eddy current surface inspection array probe and method for detecting cracks and flaws in aircraft skin metal immediately surrounding rivets, without requiring rivet removal or manual scanning. The array probe includes a circular array of small sense coils positioned beneath a much larger drive coil encased in ferrite. The sense coils are differentially connected in pairs such that the signals from two sense coils located on opposite sides of the rivet (180.degree. apart) subtract to produce a resultant output signal. During operation, the probe is positioned concentrically over the rivet and data acquired from all sense coil pairs. If no cracks or other defects are present, all sense coil pairs produce a null (zero) signal. If a crack exists, some sense coil pairs (the exact number depending on the crack length, number of sense coils, and sense coil spacing) produce a non-zero signal.

Abstract: The present invention provides an eddy current sensing device capable of in-situ operation within a high temperature and high vibration environment of a combustion turbine engine. The eddy current sensing device is preferably utilized in an eddy current sensing system for monitoring crack formation and displacement of rotating members of the combustion turbine engine. The method according to the present invention provides inducing eddy currents in the rotating member, detecting the eddy currents, providing a signal indicative of the detected eddy currents, filtering the signal based on the condition to be monitored and evaluating the filtered signal to determine whether the condition, such as the formation of a crack in the surface of the rotating member exists, and if so, determining whether the condition is critical or routine.

Abstract: Device to detect surface faults in a hot metallic bar or wire rod (11) travelling at speeds up to 130 meters per second, the device comprising upstream and/or downstream rough alignment lead-in means (38), in which device are included first coils (29) and at least one pair of second coils (13) coaxial with the first coils (29), the first coils (29) generating an alternating magnetic flow which causes on the surface of the bar (11) parasitic currents that generate in the second coils (13) a magnetic feedback flow, the first (29) and second (13) coils defining a measurement assembly (12), at least two measurement assemblies (12) being included and having their lengthwise axis able to move from an open position defining an intake hole (15), in which the various lengthwise axes coincide substantially with the nominal axis of the feed of the bar (11), to an inspection position defining a resulting inspection hole (15R), in which inspection position the lengthwise axes are substantially parallel to the nominal axis

Abstract: An improved eddy current probe array having means to compensate the entire array for varying different element liftoff, is described. An array consisting of a plurality of sense elements and means for compensating these sense elements is scanned across an inspection surface to produce respective scan responsive signals wherein the scan responsive signals of the sense elements are proportionately normalized or calibrated against the scan response of said compensating means during routine signal processing of the array signals in order to compensate for any lift off experienced by the sense elements. Array lift off compensation is attributable to sense element design cooperating with at least one lift off compensating sense element and a method of normalization/calibration performed during signal processing of the array signals.

Abstract: The present invention relates to a flaw detector for metal material for maintaining and managing pipelines using a remote field eddy current sensor. An AC signal having a constant level and shifted by predetermined phase angle is added to signals received in receiving coils of the remote field eddy current sensor to obtain accurate phase detection in a normal, nonflawed portion of the pipeline to be tested (e.g. uniform thickness, no holes, etc.). By preventing generation of abnormal flaw data, precise diagnosis of the pipeline can be performed. An AGC circuit may be used to maintain at a constant level of received signal. Two sets of spaced apart receiving coils are spaced from an exciting coil a distance greater than a predetermined distance (about two time the pipeline diameter). The set of receiving coils closest to the exciting coil has a greater number of coil turns than the other set.

Abstract: An instrument for non destructive evaluation (NDE) is called an electromagnetic microscope, formed by superconductive microprobes arrayed in parallel rows. When moved over a test piece, the array generates a scanned image of flaws, stress variations or changes in composition. Each microprobe has a drive coil a few mm in radius that encircles pickup loops forming a concentric, coplanar gradiometer 1 mm or less in diameter, coupled to a superconducting quantum interference device (SQUID). Drive coils transmit an oscillating magnetic field that induces eddy or magnetization currents in conductive or ferromagnetic materials, respectively. The gradiometer senses distortions in paths of induced currents. The sensitivity of SQUIDs increases sensitivity, penetration depth, and spatial resolution of flaws.

Abstract: The present invention relates to a flaw detector for metal material for maintaining and managing pipelines using a remote field eddy current sensor. An AC signal having a constant level and shifted by predetermined phase angle is added to signals received in receiving coils of the remote field eddy current sensor to obtain accurate phase detection in a normal, nonflawed portion of the pipeline to be tested (e.g. uniform thickness, no holes, etc.). By preventing generation of abnormal flaw data, precise diagnosis of the pipeline can be performed. An AGC circuit may be used to maintain at a constant level of received signal. Two sets of spaced apart receiving coils are spaced from an exciting coil a distance greater than a predetermined distance (about two times the pipeline diameter). The set of receiving coils closest to the exciting coil has a greater number of coil turns than the other set.

Abstract: A system for processing signals produced by magnetic flaw detection apparatus having facility for examining objects in the course of transport thereof at speeds varying from a prescribed slow speed to a prescribed high speed, with transport frequency thus being within a first frequency range. The system comprises first circuitry for detecting the speed of transport of an object under examination and generating output signals indicative of the detected speed and extending over a given characteristic range correspondingly with the first frequency range. Second circuitry is provided for receiving the first circuitry output signals and transforming the same into a second frequency range substantially expanded as compared to the first frequency range.

Abstract: On the basis of a finding that a magnetic hysteresis of a metal material, among magnetization characteristics changing with secular degradation of the metal material, shows a clear correspondence with the degree of degradation of the metal material, a change in such a magnetization characteristic is measured to estimate the degree of secular degradation of the metal material. In a typical embodiment, a superconducting quantum interference device is used to detect the magnetization characteristic of a measuring object. According to the present invention, the degree of embrittlement of a metal material used in an environment of high temperatures can be quickly detected in a non-destructive fashion so that the danger of brittle fracture of the metal material can be reliably prevented.

Abstract: Apparatus for detecting surface flaws in cylindrical articles having central longitudinal axes, including a guide assembly for guiding the cylindrical articles along a displacement path having a central longitudinal axis extending coaxially of the central longitudinal axes of the articles and a detection coil assembly positioned in annular relationship with the displacement path for producing a signal representative of the surface geometry of a cylindrical article which traverses the displacement path.

Abstract: Apparatus for measuring flux density within the surface of a ferromagnetic material (24) includes a probe (10) having an end for location on or adjacent the surface of the material (24), a first sensor at the said end of the probe (10) and capable of producing a first output signal representative of the strength of the magnetic field to which said first sensor is subjected, and a second sensor at the remote end of the probe (10) and capable of producing a second output representative of the strength of the magnetic field to which said second sensor is subjected. An electronic circuit produces a difference signal representing the difference between the first and second outputs, and an output device (14) displays and/or records said difference signal (16).

Abstract: On the basis of a finding that a magnetic hysteresis of a metal material, among magnetization characteristics changing with secular degradation of the metal material, shows a clear correspondence with the degree of degradation of the metal material, a change in such a magnetization characteristic is measured to estimate the degree of secular degradation of the metal material, In a typical embodiment, a superconducting quantum interference device is used to detect the magnetization characteristic of a measuring object. According to the present invention, the degree of embrittlement of a metal material used in an environment of high temperatures can be quickly detected in a non-destructive fashion so that the danger of brittle fracture of the metal material can be reliably prevented.

Abstract: Detection of both surface defects of a non-ferromagnetic test body as well s the presence of ferromagnetic particles in the test body by inducing eddy currents and D.C. fields in the body. The resulting signal voltages are filtered and separately examined.

Abstract: In eddy current testing of coated metal objects for corrosion, test values are arranged into fields corresponding to metal object and coating characteristics permitting direct readout of corrosion existence underneath coating without requiring coating removal.

Abstract: An electrical coil driven by an alternating current develops an alternating magnetic field. A segment of a wire-rope specimen is placed next to and on the axis of the coil, but perpendicular to the axis, so that the specimen lies in the field. Two sensor coils detect the field on the opposite side of the specimen from the field coil. The sensor coils are mutually conaxial, and paraxial with the specimen. The sensor coils are spaced apart very slightly, along the length of the specimen--one in each direction from the field-coil axis. Each sensor coil is asymmetric, in the shape of a "D," with its sensitive axis just within the "D" but nearer to the flat side; the specimen is placed just outside the "D" but also next to the flat side. Alternating current induced in the sensor coils are applied to the respective input terminals of a differential amplifier, producing an output signal in which the common signal components tend to cancel out.

Abstract: Method and apparatus for monitoring a rod mill and flexible wire drawn and annealed from a stiff coil of rod in the rod mill are disclosed. The fault signals provided by an eddy-current tester are counted on a per unit time basis in order to permit the detection of rod mill problems before serious deterioration of the mill occurs. This is accomplished by direct observation of an increasing rate of fault signal occurrence. A totalized fault signal count is also provided to aid in detecting low quality wire. This is accomplished by direct observation of uniformly high levels of fault signals. A control function is disclosed whereby the rod mill is shutdown in the presence of a high rate of increase in fault signal occurrences. A "change coil" message may be sent upon detecting uniformly high levels of faults. Fault signals are stored and identified for purposes of traceability.

Abstract: Method and apparatus for performing eddy current flaw inspection on workpiece material such as steel bar stock. A drive mechanism propels a workpiece longitudinally along a workpiece path. An array of electromagnetic transmitter coils is disposed about the workpiece path. An electromagnetic source energizes the transmitter coils under control of multiplexing circuitry. The multiplexing circuitry and source actuate respective transmitter coils in a predetermined iterative sequence. The sequential actuation induces eddy currents in the workpiece at a succession of locations extending iteratively about the workpiece circumference. Circuitry coupled to multiple, differentially wound sensing coils detects variations in eddy current produced in the workpiece and utilizes these detected variations to produce flaw indicating signals.

Abstract: A device for measuring or testing of an object, for example rolled wire, a tube, or a billet, to detect surface discontinuities employs a sensing transducer which is oscillated backwards and forwards over the surface of the test object by means of a motor, the oscillations taking place in the form of a curved path extending transversely of the longitudinal extent of the object.

Abstract: An apparatus for detecting magnetically sensible objects in an object stream longitudinally passing a predetermined location, for instance at the intake end of the conveyor of a field chopper, has according to the invention a support at the location extending transversely adjacent the object stream and having a pair of transverse ends and a center therebetween and a magnet assembly on the support having a north pole directed from between one of the ends and the center of the support transversely of the support and of the stream into the crop stream and a south pole directed parallel to the north pole from between the other end and the center of the support. The assembly forms between its poles a magnetic field having lines of force extending mainly transversely through the stream. Respective north and south sensing coils at least partially surround the respective poles so that a magnetically sensible object perturbing the field will generate respective currents in the coils.

Abstract: Eddy current distance measuring apparatus includes a multiplier connected to one secondary coil of a pair of secondary coils in an eddy current sensor. The secondary coil outputs are inputted to a differential amplifier, and the resulting difference is adjusted to be zero when an object the distance to which is to be measured is not present. Thereafter, the sensor is located within measuring distance of, e.g., a steel plate, and the output of the differential amplifier is combined by an amplifier circuit with an oscillator output supplying a current to the primary coil of the sensor. An eddy current distance signal output is thus obtained.

Abstract: Eddy current test apparatus of the type that generates eddy currents in an object and that senses flaws or defects by sensing changes in the induced eddy current. Two differential encircling coils surround a moving workpiece moving relative to said coils. One of the two test coils has an enclosed tubular pathway forming a loop adjacent to the coil. A steel ball is placed in the enclosed tubular pathway and is air driven through the pathway so that it continuously revolves in close proximity to the coil. The steel ball disrupts the magnetic field flux generated by the test coil in the workpiece. This disruption modifies the eddy current in the workpiece which in turn induces a well defined output signal in the test coil. In an alternate and preferred embodiment, two ferrite object are rotated near the two encircling coils to disrupt the eddy currents produced by both coils. The ferrite objects are radially offset so that they do not disrupt the magnetic field near a flaw at the same time.

Abstract: A magnetic device for nondestructively inspecting elongated objects such as wire cables and the like, for loss of metallic cross-section due to abrasion and corrosion and internal defects has magnets which induce a saturated magnetic field axially through a short section of the cable as the device and the cable move relative to one another. A sensing coil located in close proximity to the cable between the magnetic field poles detects small changes in leakage flux at the surface of the cable in the saturated condition. The sensed flux changes are applied to an integrator to measure the net variation in flux and correspondingly the total change in cross section. Multiple sense coils mounted on core pieces conforming to the external surface of the cable ensure complete continuity of the inspection process and allow the magnetic device to be installed and removed at intermediate stations along the cable.

Abstract: The distance between the tip of a probe and a high-temperature object of measurement is continuously and accurately measured by arranging the probe comprising a primary coil and a pair of secondary coils substantially vertically to the object of measurement; inducing an AC voltage (e.sub.1) and an AC voltage (e.sub.2) respectively in the pair of secondary coils by means of an AC magnetic field of the primary coil excited by an output voltage (e.sub.out) of a positive feedback amplifier; generating an eddy current in the object of measurement by means of the AC magnetic field of the primary coil to generate another AC magnetic field in the direction opposite to that of the AC magnetic field of the primary coil; impressing an equal DC voltage onto each of the pair of secondary coils to detect respectively a DC voltage (E.sub.1) and a DC voltage (E.sub.2) of the pair of secondary coils; calculating an error voltage (e.sub.

Abstract: Process and device for non-destructive testing or inspection by eddy currents with correction of the air gap effects. A differential measurement and an absolute measurement are performed and the result of the former is divided by that of the latter, which supplies a signal with respect to which the effects of the air gap separating the probe from the member to be inspected are corrected. Application to the inspection and testing of metal members.

Abstract: A reflection type probe for an eddy current testing instrument comprises a ferromagnetic core 2, 3 and a driver coil system 8 and a pick-up coil system 9 mounted on the core, the core having four limbs 4 to 7 each with a free end. One of the coil systems 9 is wound on the four limbs with its turn equally distributed between the four limbs and the other coil system 8 is wound on a core part remote from the turns of the coil system 9 and which interconnects the core limbs at least in pairs. Advantageously the coil system which is wound on the limbs 4 to 7 is the pick-up coil system. A detector coil section of the pick-up coil system can then have its turns equally distributed between one pair of limbs and a balancing coil section having its turns equally distributed between the other pair of limbs.

Abstract: A process and apparatus for controlling the level of a molten metal surface in a continuous casting mould uses a probe located either in the molten or above the surface of the molten metal. The probe is connected to a high-frequency transmitter which is arranged to induce voltages in each of two secondary receiver-coils, the receiver-coils being in coupling relationship with a compensating coil and a further coil connected to the probe. The receiver-coils are connected in opposition to one another so that a difference voltage of zero is arranged to be produced when the molten metal surface is at the required level but that the difference voltage is used, when departing from zero, for control purposes of the height of the molten metal surface.

Abstract: Casing inspection apparatus and method are disclosed for determining defects and other anomalies in ferromagnetic oil well casing. The inspection apparatus utilizes a pair of coaxial transmitter coils for generating an alternating magnetic field in the casing thereby inducing circumferential currents in the casing wall. These circumferential currents and the magnetic field associated with the currents are perturbed by corrosion, holes, and other anomalies both inside and outside the casing wall. Differential receiver coils are urged in proximity with the casing wall to generate a differential receiver signal in response to such perturbations in the magnetic field. The differential receivers are provided with three coils serially connected and having N, 2N and N winding turns respectively. The windings of the coils are disposed in adjacent relationship to one another and wound in a direction opposite to the adjacent winding.

Abstract: Magnetic flux is induced in the tape by applying a magnetic field to the tape. Where there is a perforation or a crack air gaps are created and magnetic flux radiates outwardly from the tape across these air gaps. The presence of the crack is detected by sensing the radiating flux at two distances from the tape. At one distance, close to the tape, the total flux is the sum of the flux from the crack and the perforation. At the other distance, further from the tape, the flux is solely that produced by the perforation. A coil is placed at each position to sense the flux. The tape is moved, which causes the flux to intersect the coils. The intersection produces an output signal from each coil. The signal produced by the coil further from the tape is subtracted from the signal produced by the coil closer to the tape; the difference being a signal caused by the additional flux produced by the crack. An alarm is sounded and in indicator lights when the signal is present.

Abstract: An automatic eddy current inspection system for discrimination of defects in elongated parts made of conducting materials comprises an alternating current generator connected in series to an amplitude selector via a differential encircling eddy-current transducer and a detector. The amplitude selector has two selection levels. The system also comprises a signal analyzer with a controllable switch and the following counters: a counter for determining the length of long cracks; a minor defects counter; a major defects counter; and a counter for determining the length of tested parts. The outputs of the counters are connected to the inputs of a sorter having its outputs connected to quality grade indicators. The controllable switch of the signal analyzer has its control input connected to the output of the amplitude selector which corresponds to a higher selection level.

Abstract: An electromagnetic flaw detection system and method having automatic dynamic error balancing is disclosed.The system includes means for producing an alternating electromagnetic field and for passing a metallic workpiece to be tested along a path through the field. A differential detection coil is disposed in the field near the workpiece path. The coil responds to nonuniformities in the field caused by workpiece flaws, such as voids, to produce flaw indications. Detection circuitry actuates alarm apparatus in response to the flaw indications to further indicate need for corrective action.Automatic balancing circuitry compensates for an error signal, which the differential coil generates due to minute undesired assymmetries in the coil's mechanical structure. The balancing circuitry includes means for generating a reference signal. The reference signal is continually adjusted, in response to characteristics of the error signal, to exactly counterbalance the error signal in phase and amplitude.

Abstract: A readily portable battery operated eddy current device is disclosed for detecting fissures, cracks or other defects in metal surfaces such as the walls of rivet holes in aircraft parts. Dual sensing transformer secondaries having a high-frequency energized common primary are embedded with pole faces peripherally exposed in a rotary detection probe insertable in a test hole. Differentially connected in a response circuit, these secondaries, constructed with slight mismatch between them, yield a composite response to the presence of a hole wall defect that when differentiated provides a uniquely definitive monopolar pulse of magnitude and relative phase position uniquely indicating on an oscilloscope screen the nature and the precise location of the defect.

Abstract: An eddy current flaw detection apparatus which is particularly adapted for inspecting articles at elevated temperatures. A plurality of detectors are supported about at least a portion of a workpiece path of travel to detect and locate flaws in workpieces. A non-magnetic, metallic shield is between the detectors and the workpiece path. A cooling medium is applied to the heat shield to protect the detectors from the heat of a hot workpiece. The cooling medium is also used to purge foreign matter from the assembly.In one embodiment an exciter and detector assembly is disclosed which is constructed as an integral unit encapsulated within moisture-impervious material. In this embodiment, the assembly is movable relative to the workpiece path.In another embodiment, the detectors and the exciter surround the workpiece path.Metallic powder is sprayed on a hot workpiece to mark the location of detected flaws. The heat of the article fuses the marking metal powder in place on the hot workpiece.

Abstract: A device for inspection by eddy current methods of materials exhibiting cumferential conductivity. This device finds application for the inspection of filament-wound carbon fiber reinforced composites which do not usually have sufficient conductivity in the axial direction to allow inspection by conventional surface probes while still providing the desired resolution. This device is also useful in inspecting thick-walled circumferentially conductive materials, including metal, where their thickness would require a surface probe of such diameter as to be impractical.