Abstract: In accordance with the present invention there is provided an eddy current probe for the detection of defects within a structure. The probe has a sensing end with a coil disposed therein. The coil is operative to generate an eddy current field within the structure when placed adjacent to the structure. Furthermore, the probe of the present invention includes a metallic shield disposed around the coil and operative to focus the eddy current field within the structure. In order to generate the eddy current field, the coil is in electrical communication with a frequency generator. The frequency generator is operative to generate a high and low frequency signal within the coil in order to enhance detection of defects within the structure.

Abstract: An eddy current sensor including an arrangement for generating a first magenetic flux, which is essentially directed vertically with respect to a moved body, a detector coil for detecting an eddy field in the moved body and a second arrangement which generates a further adjustable magnetic flux, which is superimposed on the first magnetic flux to form a resultant magnetic flux.

Abstract: A pipeline inspection vehicle which can be towed through a pipeline via a cable. The vehicle includes a power unit, a master processor module, and a coil which generates an eddy current field which passes along the pipe. The resultant field is detected by a master sensor ring and slave sensor ring. Information on an amplitude and phase of the detected field together with vehicle orientation information is sent to a base station which has a computer. A distance encoder also is provided to assist in locating the position of any detected faults.

Abstract: The present invention provides a leakage flux flaw detecting method in which a ferromagnetic substance such as a steel sheet or coil is magnetized by a plurality of magnetic fields with different intensity and magnetic flux leaking from the ferromagnetic substance having been magnetized is detected by a magnetic sensor, and output signals of the magnetic sensor after the detection of leakage flux are processed so that a signal caused by a flaw in the ferromagnetic substance is highlighted. Since this leakage flux flaw detecting method makes it possible to detect flaws with high accuracy, a scaled or descaled hot rolled steel sheet or coil in which the accurate flaw information such as location, density, size, and the like is known can be provided by applying this method to the manufacturing of hot rolled steel sheet or coil.

Abstract: An inductive sensor head for detecting ferrous or non-ferrous electrically conducting objects, in particular rebars in a surrounding medium like concrete or a brick wall, comprising at least one field coil with a small axial length compared to its diameter and at least one twin pair of sense coils with a small diameter compared to the diameter of the field coil. The number of turns of wire on the field coil is small relative to the number of turns of wire on the sense coils. The common axis of the sense coils is arranged perpendicular to the axis of the field coil so that there will be no component or a minimum component of maximum flux that is coaxial with the sense coils. A twin pair of coaxially arranged identical field coils is provided that are sequentially excited for giving not only positional but also depths information. In a center plane between the field coils an orthogonal arrangement of two twin pairs of sense coils is provided enabling for a three-dimensional hidden object positioning.

Abstract: A variable reluctance sensor is shown for determining the speed or position of a moveable target object. The sensor has a magnet which is coupled to a pole piece. A wire coil is located annularly around the pole piece. The magnet generates flux in the coil which is changed by the movement of the target object. A second bucking magnet is annularly located around the coil and generates a flux field to reinforce the flux in the coil and to prevent flux from leaking from the wire coil and pole piece. In this manner, the voltage output from the coil is increased due to the decrease in flux leakage. A processor unit is coupled to the wire coil. The processor unit measures the reluctance generated in the coil from the movement of the target object.

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 method is provided for creating a spectral EM frequency to calculate the thickness of a material with unknown permeability and conductivity using metallic transparencies. The method comprises the steps of testing empirically to approximate the conductivity, testing empirically to approximate the permeability, creating a first set of electromagnetic waves adjacent to the material to be measured of a relatively low frequency, impinging the first set of electromagnetic waves on the material for saturating the material, creating a second set of electromagnetic waves having specific constant amplitude of a higher frequency than the first set of electromagnetic waves, the second set of electromagnetic waves for engaging the material and generating a sensing signal having modified characteristics, and receiving the sensing signal through the saturated material such that the modified characteristics of the sensing signal are processed to determine the thickness of the material.

Abstract: A system for characterizing coatings and substrates of a material under test. A sensor is positioned against a coated sample which is to be measured to obtain phase and magnitude measurements. Penetration depth of the magnetic waves of the sensor is a function of frequency. Measurements are made at each of a plurality of signal frequencies. The measured phase and magnitude data is applied with respect to a frequency independent parameter, such as conductivity, using a grid method. The conductivities of the coating and the substrate are determined by the limits of conductivity with respect to frequency. With the assumed conductivities of the coating and substrate, the sensor is once again placed over the material, and coating thickness and lift-off are determined. By examining the coating thickness versus frequency the accuracy of the measurement can be determined, since actual coating thickness does not vary with frequency in the material.

Abstract: A method for measuring the thickness of an oxide layer formed on the cladding surface of nuclear fuel rods and underlying a crud layer containing ferromagnetic material using eddy current lift-off measurements by exciting a probe coil at a first frequency which penetrates only into the crud layer and by exciting a probe coil at a second frequency which penetrates the crud layer, the oxide layer and into the cladding of a nuclear fuel rod. By subtracting vectorally the complex impedance resulting from exciting the probe coil at the first frequency from the complex impedance resulting from exciting the probe coil at the second frequency, the thickness of the oxide layer formed on the cladding is measured.

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: A magnetic stripe card provides a quantitative tool for the measurement of magnetic sensitivity for fine-grained iron, iron oxide or other ferro-magnetic powders, that may be used for magnetic particle inspection and other purposes. The magnetic stripe card is encoded to establish distinct areas on the magnetic stripe. Each distinct area has a specific magnetic gradient. Ferro-magnetic powders are attracted to the gradient in proportion to the value of the gradient. A higher gradient more strongly attracts the powder. A determination of the sensitivity of the powder can be ascertained by observing the gradient with the lowest value to which the powder is attracted.

Abstract: A surface profile detecting device comprises a plurality of bar-like cores disposed in a line with predetermined intervals in a predetermined disposing direction. Each core has tip ends that are arranged on a single plane and which face a surface of an object to be measured having recesses and protrusions in a magnetic field such that they are relatively movable in a direction orthogonal to said disposing direction. The detecting device also includes detecting arrangement provided in each of the bar-like cores for detecting changes in magnetic flux generated due to the uneven profile of the object to be measured. An A/D converting device is provided for A/D converting the output of the detecting arrangement with a predetermined timing. A memory is also provided for storing the output from the AND converting device. The uneven profile of the object to be measured in a predetermined range is detected from the data stored in the memory.

Abstract: A flatness measuring apparatus is adapted to measure the flatness of the surface of a plate-shaped object such as a disk in a non-contact fashion. A disk is removably held by a measuring table, with the projection of the measuring table engagedly received in a central through hole of the disk. A plurality of eddy current undulation sensors are arranged in a sensor head that is arranged so as to be able to linearly move back and forth along the measuring table. Said eddy current undulation sensors generate an eddy current in said disk and detect any undulation on the surface of said disk. A flatness map is produced for the surface of the disk based on a signal representing the position of the sensor head and on signals from the eddy current undulation sensors, and then is output to a display and/or a printer.

Abstract: In accordance with the present invention, the initialization for orienting the magnetized directions of the free layers of GMR heads (mounted on the diagonally shaded surface of sliders 14) by an external magnetic field is again executed also for the opposite direction, thereby to increase the yield of the GMR heads. Further, it is determined whether the magnetized direction of the pinned layer of GMR heads can be once reversed to the opposite direction, thereby to select damaged GMR heads at an early stage. Then, by performing a reset while performing a quasi-static test for seeing the read back response of the GMR head after restoring the magnetized direction of the pinned layer to a positive rotation, a safe and efficient reset is executed. The reset can be executed not only by applying only a pulse, but also while providing an external magnetic field in the pinning direction, or only by giving a high magnetic field.

Abstract: Oscillatory signal build-up is increased in the polar coordinates sensor by integrating the rotating driving flux with the resonating flux resulting from the series resonant pick-up coil current. The imbalance flux linking the pick-up coil is more dependent on radii proximate the z-axis and is more suitable for detection of cracks radial to an aircraft rivet.

Abstract: An eddy current sensor assembly of a magnetic inspection device is for nondestructive detection of structural faults in an elongated magnetically permeable object, such as a pipe. The sensor assembly has an auxiliary magnet including first and second auxiliary magnetic poles oppositely polarized relative to each other and spaced from one another for positioning and movement longitudinally relative to an elongated magnetically permeable object to be tested. The auxiliary magnet is to be interposed between primary magnets of the magnetic inspection device. A ferromagnetic member couples the first and second auxiliary magnetic poles. Compliant pole pieces such as magnetically permeable brushes are coupled to the auxiliary poles and are to be interposed between the auxiliary poles and the object to be inspected.

Abstract: A metal detecting device for a crop conveyor has several closely spaced permanent magnets fixed within a hollow feed-roller in parallel with the shaft thereof. One pole of each magnet is directed radially outwardly such that its magnetic field penetrates through the hollow feed-roller and an adjoining crop-feed slot from inside to out, and wherein said magnetic field also passes axially through a respective sensor winding that is likewise arranged within the hollow feed-roller.

Abstract: The invention provides a system and method for normalizing and calibrating a sensor array. The sensor array can comprise differential element sensors, such as for example eddy current sensors, or absolute sensors. A single test specimen is used to normalize and calibrate the sensor array using one or more scans of the test specimen. Notably, only one alignment of the sensor array to the test specimen is required. The test specimen is preferably made of the same or similar type of material as the part to be tested and is of a similar geometric shape that can have a simple flat surface or a more complex surface. A linear feature and several notches are machined into the surface of the specimen by using, for example, electro-discharge machining methods, to provide the necessary signals when scanned by the sensor array. Signals from the linear feature on the test specimen are used to remove any bias and to normalize the dynamic ranges of all of the sensors in the array.

Abstract: The defect detection system of the present invention includes an encircling coil for providing a saturating DC magnetic fields to tubular goods. Also included is an encircling drive coil for applying a low level AC field using three-phase AC. Encircling pick up coils within the AC drive coils detect uniform, time varying magnetic fields to reveal defects within the tubular goods passing through the system.

Abstract: A method and a device for non-contacting measurement of the measures and position of objects of electrically conductive materials based on electromagnetic induction is provided. A measuring object, a transmitter coil and a receiver coil are placed in relation to each other such that a time-varying magnetic field generated by the transmitter coil at a measuring region of the measuring object is substantially parallel to the surface of the measuring region. The receiver coil is placed such that a conceived field line which touches the measuring region in its extension reaches the receiver coil. On the basis of the voltage induced in the receiver coil, the position and dimensions of the measuring region relative to a given reference point can be calculated.

Abstract: The process first applies a magnetostatic field to a target magnetic body to magnetize the target magnetic body. The process then cuts the magnetostatic field off and measures a transient variation in a differential magnetic flux density at a plurality of positions in the vicinity of the target magnetic body. The process subsequently determines a time constant of the transient variation in the differential magnetic flux density at the plurality of positions. The process then determines a specific characteristic value relating to the internal structure of the target magnetic body, based on a distribution of the time constant over the plurality of positions. This arrangement enables a variety of internal structures of the target magnetic body to be examined in a non-destructive manner.

Abstract: The passive torsional flux characteristics of polar sensors as related to the effective flux length coupling the pick-up coil are elucidated. A sine-cosine excited toroidal driving core comprising stacked magnetic materials having different permeabilities for enhanced helical induction coupling to the pick-up core. Also an active torsional flux means utilizing stacked driving toroids concentrically coupled to the polar sensor pick-up core. Also, integral sensor/driver embodiment utilizing at least two stacked toroids.

Abstract: A meandering winding magnetometer (MWM) includes a meandering primary winding and at least one sensing winding or coil on a membrane to be pressed against a test surface. The membrane may be supported on a flexible carrier which is translatable into a probe. Abutments in the probe press the carrier against the test surface but allow the carrier and membrane to conform to the test surface. One MWM circuit includes meandering primary and secondary windings. The return leads from the secondary winding return to connector pads in close alignment with the test array, while leads from the primary winding are spaced at least one wavelength from the array. In another MWM circuit, individual sensing loops are positioned within the meandering primary winding. The MWM circuit may be provided on an adhesive tape which may be cut to length.

Abstract: A device for non-contacting measurement of a measuring object is provided. The device includes at least one pair of associated coils, including a transmitter coil and a receiver coil. The transmitter coil generates a time varying magnetic field. In the receiver coil, a voltage is induced. The voltage is dependent on the location of the transmitter coil, the receiver coil and a measuring region of a measuring object. The device comprises a U-shaped structure with two branches. A retaining part is arranged between these branches. The transmitter and receiver coils are fixed to the branches of the U-shaped structure and the measuring object is intended to be arranged centrally in the opening of the U-shaped structure.

Abstract: A detecting coil device mounted on part of a cable to evaluate the degree of corrosion of the cable, which is used, for example, on suspension or skew bridges. The detecting coil device is provided with a detecting coil and Hall elements. A magnetizer having a magnetizing coil is mounted as to enclose the cable and the detecting coil device. When current flows through the magnetizing coil, it magnetizes the cable. The magnetic field strength is detected by the Hall element, and the amount of magnetic flux passing through the cable is detected using the detecting coil. The cross-sectional area of the cable is also calculated on the basis of the magnetic field strength and the amount of magnetic flux which are detected and the permeability of the cable. The degree at which the cross-sectional area of the cable is decreased (the corrosion degree) is evaluated by comparing the calculated cross-sectional area of the cable with the cross-sectional area of a reference cable.

Abstract: The invention relates to a device for determining the dissolution time of medication in pressed form, like tablets and capsules, (especially to DAB 10, 3rd Supplement 1994, or the European Pharmacopoeia or USP [USA]), consisting of a frame (1) with a central column (7) and a base plate (3, 10) having a plurality of holes (5, 5', 11) covered from below by a mesh (4). Test tubes (6, 6') are arranged upright in said holes inside the frame (1). A disk (8, 15) can be movably inserted into said test tubes to weight the individual pressed medication. An electric coil (12) is disposed around each hole (11) and on and/or in the base plate (10), wherein the electric coil forms part of an electrical oscillation circuit (17). A conductor loop (16) is disposed on and/or in the disk (15) for damping the electrical oscillation circuit (17) depending on distance.

Abstract: A method and an apparatus are provided for measuring the mechanical properties of ferromagnetic, elongated structures, such as cables, through the measurement of Barkhausen signals. The method comprises creating a magnetic field, that varies as a function of time or of position, and measuring the Barkhausen signals rate as a function of the magnetic field for each section of the structure to be tested. The mechanical properties are determined for each section from the Barkhausen signals relative to it. The apparatus comprises means for generating the variable magnetic field, a plurality of Barkhausen signal sensors distributed along the structure length, and means for comparing the signals relative to each section to be tested.

Abstract: Apparatus and method for measuring the Barkhausen signal of a moving magnetic film, ribbon or fiber wherein first and second stationary electromagnet coils are arranged and separated by a distance, d, along the path of movement of the film, ribbon or fiber. The first and second coils are energized in a manner to generate first and second opposing DC magnetic fields through which the moving film, ribbon or fiber passes along its path of movement. As the film, ribbon or fiber moves through the first and second opposing magnetic fields at a velocity, v, it experiences one complete cycle of magnetization in a period of time equal to d/v. A stationary third signal pick-up coil is disposed between the first and second coils to detect the Barkhausen signal from the moving film, ribbon or fiber. The pick-up coil typically is disposed midway between the first and second coils where the Barkhausen signal will be approximately maximum.

Abstract: A method for the operation and for the evaluation of signals of an eddy cent probe wherein a transmitting coil is supplied with alternating current with preferably three frequency components. The receiving coil signal corresponding to an a.c. voltage is broken down into corresponding frequency components and by phase-control rectification projection signals are formed corresponding to a real part or an imaginary part of the coil signal. From at least two, optionally individually amplified projection signals of the same type (real or imaginary signal) differential signals are formed. Finally, by the combination of at least two differential signals a combination signal is formed and evaluated. In particular, quotients and amount or value sums of differential signals are formed. The method offers decisive advantages in seeking mines in connection with the suppression of disturbing ground or soil signals and in the identification and classification of mines on the basis of signals from an eddy current probe.

Abstract: An electromagnetic-field-focusing remote-field eddy-current probe for inspecting anomalies in a conducting plate. The probe is designed to have the electromagnetic energy released from an excitation coil penetrate through the plate twice, so that the signals received by one or more receiver units (pickup coils, magneto-resistors or SQUIDs) have passed twice through the plate wall; from one side of the plate at the excitation coil to the other side, then back to the original side at the receiver units. The probe detects flaws, with good and substantially equal sensitivity, irrespective of their depth in the plate. It can detect, from one side of a plate, flaws located on the other side of the plate, which is useful for inspecting the bottom plate of a huge tank which is sitting on the ground. The thickness of inspected plates can go up to one inch for aluminum plates and to 3/8" for ferromagnetic plates. The probe generates a periodic magnetic field.

Abstract: A metal detector (10) which uses a metallic test sphere (5) to pass with the product through the detector head (2) at periodic intervals. The frequency generator (21) which generates the signal sent to the oscillator coil (11) is capable of operating on numerous frequencies in the 50 kHz to 2 MHz range. The product is passed through the detector head (2), with and without the sphere (5) present, for each of the operating frequencies. The detected signal from the product and the product with metal is characterized for each of the operating frequencies. In this manner the frequency which produces the highest ratio of product with metal present signal to product signal without metal present can be identified. A second version of the metal detector (40) uses a frequency synthesizer (43) which may be rapidly scanned through a range of frequencies while the product is passing through the detector head (41).

Abstract: Apparatus and methods are disclosed which provide increased sensitivity, selectivity and dynamic range for non-contact measurement of actual physical and/or kinematic properties of conducting and magnetic materials. The apparatus and methods are based upon various methods for increasing sensitivity, selectivity and dynamic range through proper construction of a magnetometer sensor and for proper selection of operating point parameters for the application. A measurement apparatus for measuring one or more MUT properties includes an electromagnetic winding structure which, when driven by an electric signal, imposes a magnetic field in the MUT and senses an electromagnetic response. An analyzer is provided for applying the electric signal to the winding structure. A property estimator is coupled to the winding structure and translates sensed electromagnetic responses into estimates of one or more preselected properties of the material.

Abstract: An object sensing system (10) employs a resonant sensor (20) that receives drive energy coupled from an oscillator (12) operating at a frequency equal or close to the resonant frequency of the resonant sensor. The resonant sensor preferably includes an planar winding (60) that maximizes its distributed inductive and capacitive components, which are sensitive to a proximal conductive, nonconductive, magnetic, or nonmagnetic object (22). The resonant sensor is electrically connected in one leg of a voltage divider that produces a changing output signal voltage in response to resonant frequency changes caused by the object in proximity to the resonant sensor. The signal voltage is amplified, filtered, and processed to extract relevant data indicative of the presence, distance, movement, or proximity of the object.

Abstract: A metal detector has multiple transmit and receive coils for producing multiple detection fields. In one embodiment, a transmit coil is combined with two receive coils in a configuration that enables the detector to generate two detection fields, one being substantially narrower than the other. The transmit coil is inductively balanced with the receive coils such that the transmit coil induces minimum signals in each of the two receive coils. A metal target lying within a detection field changes the coupling between transit and receive coils and produces signals in the receive coils. The received signals are utilized to identify the target's presence within one or both of the detection fields. The use of two detection fields, substantially different in size, enables the metal detector to search over a broad area for object detection and then narrow the search to more precisely locate the detected object.

Abstract: A spectrogram of secondary magnetic field strength as a function of frequency and spatial relationship is used to identify hidden objects. A time-varying multi-frequency primary electromagnetic field is generated, preferably over the range 100 Hz to 300 kHz, which induces a time-varying multi-frequency secondary electromagnetic field about the hidden object. The strength of the secondary field, typically inphase and quadrature, is plotted as a spectrogram over a low frequency broadband spectrum as a function of frequency and spatial relationship between the hidden object and the secondary field strength detector. From this spectrogram, indications may be had of the hidden object's characteristics such as location, size and shape, and material composition. Preferably, the measured spectrogram is compared against a library of reference spectrograms by a computer to identify the hidden object.

Abstract: Poly-phase induction motor-stator rotating magnetic fields are utilized as driving cores coupled to polar coordinate sensors for higher driving flux utilization and size reduction. External internal and combinational driving core structures are disclosed. An unsegmented stator having an extended longitudinal coupling portion is also disclosed.

Abstract: A device and process for determining the uniformity of a superconducting film's critical current density and transition temperature over a large area uses an array of ac coils placed in close proximity to a superconducting film. A variable ac current is passed through each coil which induces a proportional current in the superconducting film. A lock-in amplifier set to the third harmonic of the ac current is put in parallel with the ac current source. When the current in the film exceeds the critical density of the film then the third harmonic is picked up by the lock-in amplifier. In this way one can measure the critical current density of the film at each of the coils. The above coils are mounted within a flat plate (the film side of the substrate is placed against the plate). The entire assembly is cooled within a cryostat so that the temperature can be precisely controlled.

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: For the nondestructive testing of an electrically conductive part (T), an eddy current sensor (22a) is proposed having two transmitter windings (26) and one receiver winding (28). These three windings are arranged symmetrically with respect to a reference plane (P1) oriented perpendicular to the surface of the part (T). The receiver winding (28) is placed between the active portions (26a) of the emitter windings (26) and perpendicular to the plane (P1), whereas the transmitter windings (26) are substantially parallel to said plane. The coils and connections of the transmitter windings are such that the receiver winding is not traversed by any current in the absence of a fault. A tool for testing a tube (T), such as a steam generator tube, has two sensors oriented at right angles to one another.

Abstract: A combination of three factors for increasing the spatial resolution of a polar coordinates sensor. (1) a coefficient of coupling factor including a gap in the magnetic circuit path between the driving core and the pick-up core. (2) a tuned "tank-circuit" factor including a capacitor connected in shunt with the pick-up coil. (3) a driving frequency spectrum factor for modulating the frequency of the sine-cosine excitation to the driving core.

Abstract: A sensor arrangement (1) comprising at least one measuring coil (2), at least one voltage source (3) for the measuring coil (2), and an evaluation unit (4) with means for detecting, processing, and evaluating measured signals. This sensor arrangement (1) is used to measure distances and thicknesses substantially independently of the material involved, without the user having to know the physicomathematical relations between the influencing quantities and the measured values. In order to evaluate the measured signals, the evaluation unit (4) of the sensor arrangement comprises a neural network (5) with an input layer, at least one hidden layer, an output layer, and connection weights for the individual layers. The connection weights are determined and stored in a learning phase by measurements taken on a plurality of different suitable learning objects with known actual values.

Abstract: A device for measuring residual stress in ferromagnetic and non-ferromagnetic metal objects. The device having four electrically identical induction coils which form a four terminal alternating current bridge circuit. There is a fine wire shield formed of fingers for shielding the coils from stray capacitance. The bridge having four coil terminals. Two diagonally opposite coil terminals are connected to a variable frequency constant voltage generator. The other two diagonally opposite coil terminals are connected to a low noise broad band preamplifier. The preamplifier amplifies any unbalance in the bridge. There is a double pole double throw switch connected to two coil terminals which are diagonally opposite each other. Connected to the preamplifier is an amplifier. The amplifier is connected to a phase detector which is connected to a computer. The phase detector detects in phase and quadrature component signals.

Abstract: A method and apparatus for determining the thickness of at least one layer superimposed on a substrate, at least one of the layers or the substrate being a conductor of electricity. The method includes the steps of generating an electromagnetic alternating field in the vicinity of the outer most layer with a coil in order to cause any currents to be generated in the conductor which act upon the alternating field. The frequency of the alternating field is adjusted to at least two different frequencies and is measured at these frequencies. The thickness of the layers is then determined based on the measurements and the electromagnetic properties of the substrate and the layers.

Abstract: A dual-mode coating thickness measuring probe for determining the thickness of a coating on ferrous and non-ferrous substrates. The probe has a first winding assembly including an induction winding and two search or pick-up windings and a second winding assembly including a search winding disposed on a non-magnetic and non-conductive former. A magnetic cylindrical pin of a material with a high resistance to impact and abrasive wear passes through the first and second windings. A conductive non-magnetic coaxial screen through which the pin extends separates the first winding from the second winding. The position of the screen is such that it has a minimal effect on the second winding while shielding its field from the first winding. The first and second windings are connected to signal conditioning circuitry which produces outputs representing the coating thickness measured.

Abstract: In a method and a measuring device for metal detection with the use of a coil arrangement the spatially offset transmitting coils are controlled with pulse sequences of different pulse patterns. The receiving coils associated with the transmitting coils are scanned with respect to the received measuring signals with a scan pattern corresponding to the respective associated pulse pattern. It is therefore possible to control simultaneously all transmitting coils and to provide a spatial determination of a metal object located in a throughgoing region of a gate frame.

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: Apparatus for performing nondestructive magnetically testing and inspection of elongate objects. The apparatus concentrically surrounds the elongate object to be tested and includes means for inducing a magnetic field in the elongate object and a partial ferrous return path for the magnetic flux emanating from a pair of magnet arrays. The partial ferrous return path is engaged with a sensor for detecting variations or flaws in the elongate object.

Abstract: A process for characterization of magnetic materials for validating documents carrying marks which include magnetic materials is based on an analysis of signals supplied by an oscillator generating a low frequency signal supplying emitter windings and receiver windings that have different conformations. The receiver windings (A) and (B) are joined to an amplifier that has two outputs (S1) and (S2), output (S2) yielding, upon conformation, a signal (X) that is used as a time reference, and output (S1) yielding, after various transformations, two signals (Y) and (Z), each of which is entered into a microprocessor which, together with valid magnetic marker data, generate signals accepting or rejecting the document.

Abstract: Devices and analytical techniques are disclosed for measuring spatial profiles of complex permeability and conductivity of a material by multiple wavenumber interrogations. Coil array structures are disclosed which define a number of different fundamental wavelengths (or wavenumbers). Spatially periodic interrogation signals (of temporal frequency ".omega.") from the coil array structures are attenuated by varying degrees in the material undergoing analysis, depending on the wavenumber ("k"), thereby permitting the derivation of composite complex permeability/conductivity profile.