Abstract: An improved flexible coil array for nondestructive reflective-mode eddy-current testing of conductive members is disclosed. The assembly comprises a flexible substrate having a first array of coils formed on one side thereof. The first array of coils are connected in series in parallel columns. One end of each of the rows is connected to a common ground connection, while the other ends of each row are successively connected to a source of excitation energy. A second array of series-connected rows of coils, orthogonal to the columns, is formed on the opposite side of the substrate. Again, one end of each of the rows is connected to a common point while the other end of each of the rows is successively connected to means for detecting a voltage induced on the coils of the row. The voltage will vary if one of the coils is disposed in juxtaposition to a discontinuity of the member to be inspected.

Abstract: An apparatus for producing a uniform magnetic field in a test sample having an angled end during a magnetic particle test procedure, includes a conductive, angled fixture having a contact surface and an overall shape corresponding to that of the angled end of the test sample, so that when a pulsed current is passed through the blade, the resulting uniform magnetic field permits detection of defect indications in the angled end.

Abstract: A magnetic and electric force sensing method uses a force responsive transducer made of a micromachined, solid state magnetic sensor consisting of a central silicon platform surrounded and supported by a thin silicon membrane. The silicon substrate is placed over an aluminum pad recessed into a well on a supporting glass substrate. The magnetic sensor responds to a static method of measuring force whereby the Earth's magnetic field or magnetic field or other origin acts as an attractive or repulsive force towards the magnetic material placed onto the silicon platform. The magnetic force mechanically displaces the silicon platform and diaphragm membrane which is transduced to an electrical signal where a change in capacitance is measured. Geometry of the silicon platform, diaphragm membrane and glass well depth are used to affect the linearity, sensitivity and range of measurements of the magnetic sensor.

Abstract: A magnetic heading sensor alignment device for an acoustic towed line array s described. It includes a generally cylindrical non-magnetic piece having a longitudinal opening along its central axis to accommodate the heading sensor. A plurality of longitudinal non-magnetic strips or springs are provided around the cylindrical piece by securing them at the ends of the cylindrical piece to form a cage. This provides a spring-like action when the alignment device including the heading sensor is inserted inside the hose of the towed line array and thus keep the heading sensor aligned during the deployment of the acoustic towed array.

Abstract: An apparatus is provided for verifying the presence or, conversely, determining that one or more ferromagnetic components is missing from an inspected assembly. The apparatus includes a scanning head that creates a magnetic field. An assembly having one or more ferromagnetic components is located in a predetermined position relative to the magnetic field. A load cell subassembly of the scanning head produces an output signal representative of its movement, which movement is proportional to the number and location of ferromagnetic components in the assembly. The apparatus further includes a processing network that processes the output signal in order to provide an indication as to whether or not one or more ferromagnetic components is missing from the assembly. In conjunction with such processing, previously obtained reference values are compared with the determined magnitude obtained by processing the output signal from the load cell subassembly.

Abstract: An array of nested sets of electromagnetic coils. Each set of two coils is useable both as Helmholtz coils and as deGaussing coils. In each set, the two coils are wound in the same direction and the two coils are on a common axis. The common axes of the three sets are mutually orthogonal. For each set of two coils, the outer two ends of the two coils are connected to two single terminals, while the inner two ends of the two coils are connected to one common terminal. By connecting one side of a DC power supply to one single terminal, and by connecting the other side of the DC power supply to the other single terminal, each set of two coils will operate as Helmholtz coils. By connecting one side of a DC power supply to parallel variable resistors, each resistor in turn being connected to a single terminal, and by connecting the other side of the DC power supply to the common terminal, each set of two coils will operate as deGaussing coils.

Abstract: A detector of ferromagnetic materials having a permanent magnet floating in a contaier and restrained under the influence of a soft ferrite mass spaced below it to rotatable movement about a vertical axis centrally of the container. The magnet has a normal at rest position from which it is rotatable when a ferromagnetic material moves through its magnetic field. The magnet carries a curved mirror onto the concaved face of which a light beam is focused, and which beam in an at rest normal position of the magnet is reflected by the mirror onto a zero point of an observer's readout scale. When the magnet is caused to rotate from its at rest position by a ferromagnetic material moving through its magnetic field, the light beam is caused to move away from the zero point; and when the ferromagnetic material has moved out of the magnetic field, the magnet and light beam return to their normal positions but with some oscillation before doing so.

Abstract: A device for discriminating metal in an object is provided including a sense coil and related circuitry, with variations in the self inductance of the sense coil being measured as the object is passed substantially through the center of the coil.

Abstract: An eddy current sensor probe which includes first and second rigid end portions coupled together with a central portion comprising a flexible membrane. The flexible membrane includes indentations comprising sensor supporting regions. A differential pressure is applied across the membrane to position the sensors in a favorable location for collecting data related to the condition of the wall portion of hollow tubes.

Abstract: A rotating head mechanism of a rotary type AC magnetic flux leakage flaw detector comprises a rotating disc which has an opening for passing a test piece for flaw detection, mounting frames which are disposed in the rotating disc so as to oppose to each other with the opening located therebetween, shafts which are rotatably disposed across the mounting frames and each of which has external threads of senses opposite to each other at a position on one side of the opening and a position on the other side thereof, a first nut which engages the external thread of one sense in the external threads of each shaft, a second nut which engages the external thread of the other sense in the external threads of each shaft, a first cradle which is coupled to the first nuts, a second cradle which is coupled to the second nuts, a first exciting magnetic poles/detecting probes-assembly which is mounted on the first cradle, a second exciting magnetic poles/detecting probes-assembly which is mounted on the second cradle, and ro

Abstract: A proximity sensor has a metal case with a sensing coil at one end and a coaxial cable extending out the other end for placement in proximity to rotating machinery to sense imbalances by position change of, for example, a shaft. The sensor includes a cylinder integrally molded with a plastic bobbin which carries the coil on its end. This unitary assembly then has inserted in it the coaxial cable and the typically wire braided outer conductor is soldered onto the cylinder to provide a permanent interlock resistance against axial and torsional forces. A plastic insulating cap is placed over the entire assembly including the sensing coil and epoxied thereto. A sleeve over the junction between the cable and cylinder prevents unwanted epoxy from filling the coaxial cable. Finally, this permanent affixing of the cap allows the metal casing normally having a nut and thread to be crimped onto a notch in the cap. Moisture proofing is also provided by injection of silicone rubber in the cavity of the bobbin.

Abstract: An eddy current testing system consists of a multi-sensor probe, a computer and a special expansion card and software for data collection and analysis. The probe incorporates an excitation coil, and sensor coils; at least one sensor coil is a lateral current-normal coil and at least one is a current perturbation coil.

Abstract: Method, according to the eddy current method, for checking damage on the surface of round, e.g., ball-shaped, metal objects, whereby a similar object is supported and made to rotate around at least one axis while an electronic contact-free scanner or sensor is aimed at the surface of the object, characterized by the fact that the round object is placed on a fixed support and a gaseous medium, e.g., air is blown against the object in such manner that between the support and the object a gas or air layer is formed which carries the object, and the object is made to rotate by the gas or air flow.

Abstract: In a system for determining the relative position of a first object with respect to a second object, electrical detection of registration is achieved. This registration can be used during the manufacture of printed circuit boards or discrete wiring boards to determine the registration between layers of wiring, or between wiring layers and printed circuit layers. The system introduces an a.c. current at a suitable frequency into at least one first conductive pattern wired or etched or otherwise provided near the perimeter of a printed or wired first layer of a circuit board panel. The panel having the first pattern is moved relative to similarly wired second conductive patterns on a second layer or base plate, mounting table, etc., to which detection circuits are connected. Voltage induced in the second patterns is detected and indicates the positional relationship between the first and second conductive patterns and, hence, objects associated with such patterns.

Abstract: A linear guide includes a linear guide member provided over a guide range, a movable member being displaceable along the linear guide member and a ball bearing assembly provided on the movable member in a portion which comes in sliding contact with the linear guide member. A position detection device for the linear guide comprises the ball bearing assembly and a coil assembly and the ball bearing assembly has a casing and a succession of plural metallic balls disposed within the casing to form an endless ball array with each adjacent one of the balls being in close contact with another whereby the balls are linearly displaceable in accordance with displacement of the movable member. The coil assembly is provided on a part of the casing and includes a coil member which is excited by an ac signal. A magnetic path is formed through the ball located at the part of the casing and a reluctance change is produced in the magnetic path in accordance with displacement of the balls.

Abstract: An improved sensor assembly for providing an electrical signal representative of the velocity of a movable body. The assembly includes a sensor for sensing the velocity of the body and providing the signal and a mounting block disposed close to the body for locating the sensor in a predetermined position with respect to the body. The mounting block has a passageway extending through the block for receiving the sensor and for restricting the movement of the sensor along a direction co-existent with respect to the longitudinal axis of the sensor. The sensor itself includes an elongated barrel portion having a sensing tip in one end. The elongated barrel portion includes a shoulder stop located along the elongated barrel portion at a predetermined position from the end of the elongated barrel portion having the sensing tip.

Abstract: A rotation angle detection circuit for a step motor providing an up/down control signal for determining positive and negative rotation of the step motor and a mask control signal for determining rotation angle of 15.degree. and 30.degree.. The circuit can correctly detect the rotation angle of the step motor by counting the pulse signals from the up/down control signal and mask control signal. It is thereby useful for application in a system which electrically measures the rotation of the step motor.

Abstract: A magnetoelectronic transducer includes a housing; a circuit board (21) provided within the housing and having a processing circuit (51); an element holder (22) provided within the housing and extending perpendicular to and beyond the circuit board; a magnetoelectronic transducer element (24) provided on a front end of the element holder; a power circuit (50) provided on a basic section (22b) of the element holder; and a cable (28) connected to the power circuit.

Abstract: Apparatus and methods for monitoring a magnetic field and/or detecting ferromagnetic materials. Two transducers are disposed adjacent one another and arranged to provide signals directly related to magnetic field components in parallel but opposite sensing directions. Signal processing apparatus provides an output related to the difference between these two signals. The transducers may be oriented so that the sensing directions are transverse to the magnetic field and the output signal is substantially zero when the magnetic field is in a rest condition. When the magnetic field is disturbed, as by a ferromagnetic body, the output signal changes.

Abstract: A method employing torque magnetometry for measuring magnetic properties of a workpiece, for example, measuring the anisotropy of a magnetic thin film. The present method utilizes a novel alternative to known methods of torque magnetometry, namely, employing a viscometer, as modified in accordance with the present invention. The present method preserves all the virtues of torque magnetometry, yet realizes method objectives of efficiency, low cost, and accurate measurement.

Abstract: A system for photoinductive imaging for flaw detection of materials and for calibrating eddy-current probes includes positioning an eddy-current probe adjacent to a specimen to be analyzed or to be used as a calibration fixture. A source of thermal energy is modulated and focused to a localized area on the specimen. Thermal energy is then scanned across at least a portion of the detection area of the eddy-probe. The resulting signal from the eddy-current probe is recorded and can depict either thermal-influenced components of the specimen or the response pattern of the eddy-current probe. The record can therefore be used to image flaws or physical holes or shapes of the specimen or calibrate the eddy-current probe.

Abstract: A rotating eddy current roller head for inspecting tubing. A main body portion has a set of whisker wheels rotatably attached thereto which center the main body portion in the tube. A roller housing slidably mounted on the main body portion for radial movement relative thereto is caused to track the surface of the tube by opposing magnets mounted in the main body portion and roller housing. An eddy current coil is mounted in a coil holder which is pivotally mounted in an offset manner at the exterior end of the roller housing. A spring mounted in the roller housing biases the trailing edge of the coil holder against the surface of the tube to maintain the eddy current coil at a constant distance from the surface of the tube during inspection procedures.

Abstract: A cantilever beam is employed to place a magnet in proximity to a sample while the sample is maintained at a superconducting temperature. The magnet causes the sample, assuming it is superconductive, to itself generate a magnetic field which interacts with the magnet. Means are provided for measuring the movement of the cantilever beam, such movement being a measure of the interaction of the sample's magnetic field with the magnet. Several types of cantilever beams are disclosed, one of which is adapted to move in a direction orthogonal to the surface of the sample and another of which is adapted to move parallel to the surface of the sample. This enables the obtaining of quantitative measurements of the bulk properties of high temperature superconducting materials.

Abstract: A ferrous metal inspection device particularly for elongated parts provides high intensity DC magnetic fields in each of two modes contemporaneously. One mode is generated by passing a DC current axially through the part to be inspected and the other is generated by a separate DC current passing through a pair of electromagnet coils positioned one at each axial end of a part to be inspected. Magnetic field lines are thereby generated in a pair of mutually orthogonal planes. Control and polarity of the two direct currents is effected by controlling the phase of conduction of separate corresponding silicon controlled rectifiers. The part to be inspected is drenched with a mixture of fine ferrous particles in a liquid vehicle. Solenoid wound coils connected in series or parallel are placed, one at each end of the part and a third coil surrounds the part circumferentially, thereby producing two substantially orthogonal magnetic fields.

Abstract: A magneto-optic Kerr effect hysteresis loop measuring apparatus is provided which employs a pair of pole-pieces of the same magnetic polarity providing a high and uniform magnetic field strength in the gap between the oppositely disposed faces of the pole-pieces. The spot on the product which is to be nondestructively tested is placed in the gap between the pole-pieces in a region of uniform saturating magnetic field. A laser beam having a high polarization ratio is directed along an incident path with a spot on the surface of the product to be nondestructively tested, and a reflected beam is processed in a Kerr effect detector to provide hysteresis loop data. This data is capable of providing information sufficient to determine the squareness of the hysteresis loop and the coercivity of high coercivity material being nondestructively tested.

Abstract: In the embodiments described in the specification, a device having gear teeth to provide magnetic asymmetries rotates adjacent to a permanent magnet which is part of a mechanical mounting for a piezoelectric transducer. Relative motion between the gear teeth and the magnet subjects the transducer to a varying mechanical stress so that it generates a pulsed output voltage signal having an amplitude which is independent of surrounding influences.

Abstract: The invention consists of a toothed wheel which in conjunction with a fixed sensor measures the revolutions or the angular velocity of a rotating component. The toothed wheel is constructed as a coil spring mounted on a circular ring-shaped mounting device and moved around a pivot with the rotation motion to be measured. The coil spring consists of an infinite helix the windings of which are of ferromagnetic material. Since the coil spring is moved past the fixed sensor, the change of the magnetic field in the coil of the sensor causes the generation of an alternating voltage the frequency of which is substantially proportional to the angular velocity of the toothed wheel.

Abstract: An adjustable mounting shoe 10 for sensing coils 31 of a pipe inspection apparatus. The mounting shoe 10 comprises a base member 12 with a recess 14 in a surface thereof in which the magnetic sensing coils 31 are mounted. A thin shim 40 of magnetically transparent material is removably supported on the base member 12 in covering relationship to the sensing coils 31 whereby the coils are protected from abrasive contact with the exterior surface of a pipe to be inspected. A pair of adjustable contact members 51 are mounted on opposite sides of the recess 14 and provided with contact surfaces 51b positioned to engage the exterior surface of a pipe while supporting the magnetic sensing coils protected by the shim in an optimum sensing range from the surface of the pipe.

Abstract: A transducer measures the angular relationship between a drive and a driven member throughout a range of relative angular positions therebetween. The transducer provides a signal indicative of that angular relationship, and the signal can be transmitted to a controller that regulates the torque applied by the drive shaft. The transducer can be used in a web spooling apparatus where the position of the driven member relative to the drive shaft during web winding operation is a function of tension transients in the web. The transducer enables the system to adjust the torque of the drive shaft as a function of the angular relationship of the driven member and drive shaft so that the system can reduce tension transients in the web being wound onto the spool.

Abstract: An apparatus for measuring the thickness of a coating of, for example, paint or other electrically non-conductive material on a metallic base comprises a sensor head housing an electrical measuring coil and supported above the coating on a cushion of air. The air is supplied at a constant predetermined pressure to nozzles carried by the sensor head, and a constant force urging the sensor head towards the surface of the material is yieldably applied to the sensor head through a spring.

Abstract: A magnetic tile sensor has a permanent magnet having a surface coated with a magnetic fluid and housed in a hollow portion of a nonmagnetic case, and a magnetic sensing element arranged outside the bottom portion of the case. When the case is tilted or is abruptly moved, the permanent magnet in the case is relatively displaced. The magnetic sensing element detects this displacement. Since the nonmagnetic case is sealed by a cold welding method, workability and reliability can be increased. In addition, a cap having a predetermined weight covers the permanent magnet so that a response characteristic is improved.

Abstract: The invention provides an arrangement for determining the speed and rotor position of an electric machine, which arrangement consists of a tachometer generator having a permanent-magnet-excited rotor and a coaxially arranged rotor position transmitter which has a rotor body equipped with permanent magnets. Around the circumference of the rotor body magnetic-field sensitive sensor elements are arranged. A compact assembly of the tachometer generator and rotor position transmitter without detrimental mutual interference is possible by the provision that first permanent magnets magnetized in the tangential direction are arranged centered to the pole gaps of the tachometer generator rotor at the rotor body in such a manner that the sides of two adjacent permanent magnets facing each other have the same polarity as the magnet pole extending between the respective pole gaps of the tachometer generator rotor.

Abstract: For enabling a resolver to have absolute position sensing over a wide displacement range while still obtaining the resolution, accuracy and precision obtainable by operation in an incremental mode, the resolver is provided with a number of terminals for providing offset pitch phase indications as a function of position. A microcomputer is programmed to execute a decoding procedure for reading the offset pitch phase indications and from them computing the absolute position. This method is applicable to linear as well as rotary position sensing. By using multiplexing, digital signal processing and large-scale circuit integration for interfacing the resolver to the microcomputer, the method can achieve absolute position sensing with high reliability and low cost. The offset pitch phase indications are readily provided by inductive coupling between a multiplicity of windings, including a set of offset pitch windings connected to the terminals.

Abstract: An apparatus for locating the geometrical center of symmetrically shaped bore (3) in a material (2) includes a detector (4) distinguishably responsive to a property of the material (2), bore traversing means (6, 9, 10, 11) for moving the detector (4) adjacent the material (2) and along a predetermined raster scan path, and control means (15, 16, 17) responsive to changes in electrical signal outputs of the detector (4) as the traversing means (6, 9, 10 11) is scanned across the bore (3) in two mutually orthogonal directions. The control means is operative to monitor the coordinates of the interceptions of each of two mutually perpendicular chords across the bore (3) with an edge of the material (2), and to calculate the coordinates of the center of the bore (3) from these. Preferably the apparatus includes an eddy current detector (4) for determining the position of a bore (3) and an ultrasonic detector (5) for inspecting the material (2) around the bore ( 3) for flaws.

Abstract: A sensing head for a metal detector including means for magnetic transmission and detection of a retransmitted signal from a target by means of at least one coil, the head being characterized in that at least some of the conductor material forming the coil and providing for passage of current through the coil is such as to provide for such passage wherein the arrangement is such or the selection of conductor material is such as to restrict the magnitude of eddy currents in the conducting material. Coils wound from wires in parallel, and in particular, Litz wires, are disclosed.

Abstract: There is proposed a tilt sensor in which a first permanent magnet having a magnetic fluid adhered to its surface is housed in a nonmagnetic case, a magnetic sensing element is arranged outside a bottom portion of the case, and a second permanent magnet is arranged so as to surround the magnetic sensing element and have polarity directions opposite to those of the first permanent magnet. When the case is tilted at an angle larger than a predetermined angle, the first permanent magnet is instantaneously moved, and the magnet sensing element detects changes in magnetism, thereby detecting a tilt of the case.

Abstract: There is proposed a tilt sensor in which a permanent magnet having a surface coated with a magnetic field is housed in a hollow portion of a nonmagnetic case, and a magnetic sensing element is disposed outside a bottom portion of the case. When the case is tilted at an angle exceeding a predetermined angle, the permanent magnet is greatly moved and the magnetic sensing element detects the movement of the magnet. Furthermore, adverse influences due to magnetic attraction between the permanent magnet and the magnetic sensing element or a surface tension of the magnetic fluid are compensated.

Abstract: An apparatus for the inspection of a stack of cylindrical objects such as roller bearings, uses an eddy current probe. The probe is positioned at an angle with respect to the surfaces of the objects in order to achieve an acceptable signal and then the objects are rotated while the probe is advanced along them to fully scan the surfaces.

Abstract: Apparatus is disclosed for locating and measuring wear in nuclear reactor control rods. Circumferential and radial eddy current test probes produce outputs corresponding respectively to volume and thickness of the control rod. A method is disclosed to determine cladding wear when the volume and thickness varies beyond preselected limits.

Abstract: A proximity detector includes a magnet having steel or iron pole piece plates mounted at front and rear pole ends of the magnet, and a silicon integrated circuit mounted to the outer surface of the front pole piece centered about at the magnet pole axis. The integrated circuit includes two essentially identical Hall elements having outputs connected series opposing, i.e. differentially rather than aiding, so that distortion of the magnet field ambient to the integrated circuit caused by a ferromagnetic article passing by results in a gradient field between the Hall elements producing a differential output signal. The dual Hall element integrated circuit leads to a low differential composite offset voltage while the front pole piece renders the magnetic flux density much more uniform further reducing this dual-Hall-element composite offset voltage.

Abstract: An apparatus by which a sensor holder of a surface testing apparatus can be moved along a preselected path of movement over the surface to be examined. The apparatus has a guide rail establishing the path of movement, which can emulate the contour of the surface and on which the sensor holder is supported.

Abstract: An improved eddy current probe system and method for simultaneously detecting different types of flaws at different depths within a metallic wall, such as a section of Inconel tubing, is disclosed herein. The system comprises a current generator for generating alternating currents of substantially different frequencies, a probe head including first, second and third concentrically arranged coils in separate communication with the current generator, shielding material disposed between the coils for preventing cross talk between each coil and the pulsating magnetic field of the coils adjacent to it, and a detector circuit which may include an inductive bridge for providing an electrical output representative of the impedance changes in the respective coils. In operation, each of the coils conduct currents having substantially different frequencies, the highest frequency being conducted by the smallest-diametered coil and the lowest frequency being conducted by the largest-diametered coil.

Abstract: A magnet assembly for measurement of displacement of a rod is formed as a ring encircling the rod. The rod is displaceable along its axis and perpendicular to a plane of the ring. The rod includes a collar for interaction with a magnetic field produced by the magnet assembly. The assembly includes a magnetic field sensor and a first permanent magnet disposed along an inner surface of the ring, which are diametrically opposed on opposite sides of the rod. Second and third permanent magnets of like polarity are also disposed along the inner surface of the ring, and symmetrically positioned relative to the first magnet.

Abstract: This invention involves resonance enhancement of signals obtained from magnetic specimen undergoing changes in magnetic state. This is accomplished by placing the sample, magnetized by a quasi-static magnetic field, in a high frequency resonant cavity. By adjusting the resonance frequency of the sample-containing cavity so that it is resonant at a d.c. field corresponding to domain wall motion or domain rotation, clear signals can be obtained from the sample.

Abstract: A method and apparatus for measuring casing wall thickness using an axial main coil for generating a flux field enveloping the casing wall, and sensing actual field distribution by means of plural radial sensing coils each disposed at a radial position within the casing thereby to derive data sufficient to model a reference calibration for good casing wall structure; and, sensing flux leakage from the casing wall to detect anomalies of wall structure relative to the established reference calibration for output indication versus position along the casing.

Abstract: A shaft monitoring system for sensing axial movement of a shaft, especially in a gas turbine engine, comprises a toothed wheel attached to and rotatable with the shaft, and a pair of inductive sensors disposed radially of the toothed wheel for sensing the passage of the teeth as the shaft rotates. In one embodiment, the toothed wheel has two axially-spaced sets of teeth, one set straight cut and the other set diagonal cut, so that the phase difference between the respective outputs of the sensors varies with axial movement of the shaft. In another embodiment, the sensors are positioned at opposite axial ends of the toothed wheel, so that axial movement of the shaft causes one sensor output to increase in amplitude while the other decreases.

Abstract: An angle sensor (1) with a rotatably arranged transmitter part (5) and a fixed transmitter part (9). The rotatable transmitter part (5) has a coil (10) which can be connected to a source of alternating current, is wound helically on a support and extends on both sides of an axis of rotation (53) with longitudinal axis extending transverse to it. The fixed receiver part (9) contains at least one sensor for electromagnetic fields which is arranged facing and spaced from the coil (10).

Abstract: An electromagnetic measuring probe has a pole-piece composed of a magnetic material of high magnetic permeability. The pole-piece has a front face. A recess is machined into the front face and extends into the pole-piece. A pin is positioned within said recess. The pin is composed of hard metal which has a low magnetic permeability in comparison to the material of the pole-piece. The pin has an external front face which comprises the crowned contact surface of the measuring probe.

Abstract: A method and an apparatus are provided for detecting magnetic discontinuities, for example corrosion pits, in a specimen of magnetizable material. A horseshoe shaped magnet (32) is supported with its poles just clear of a surface of the specimen (12) by a wheeled frame (20), and is moved over the surface. An array of sensors (48) between the poles detects the leakage flux near the surface. The signal from any one sensor at a particular location is corrected by subtracting from it the average of the signals from the same sensor at a plurality of other locations preceding and following that location. If the corrected signal exceeds a threshold value, this indicates abnormally large localized leakage flux, and so indicates metal loss from the specimen.

Abstract: In magnetic bearings and magnetic suspension devices, sensors (4), as they are used for bearing regulation of support and guide magnets in magnetic transportation technology, continuously measure the distance of a magnet (6) from a reaction rail (7), in order to obtain a signal with which the magnet (6) is controlled with regard to the energizing current in such a way that it remains suspended at the predetermined distance. In known devices, there is no accurate monitoring of the sensor signal, which can result in faulty regulation of the excitation if the sensor signal is faulty, which represents a significant safety risk.