Abstract: A method of calibrating a thickness measuring device having preferably two noncontacting or scanning displacement measuring sensors (2, 3), which allows to calibrate in a simple manner, at the location of measurement, thickness measuring devices operating by different measuring principles by means of a reference object (7).

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: A high frequency magnetic field exposure meter for use in an induction heat sealing operation for heat sealing metal foil elements in closures to containers to be closed by the closures. The meter has a magnetic field sensing coil, a rectifier to convert the a.c. output from the coil to a d.c. output, an integrating circuit to integrate the d.c. output over an exposure period to an h.f. magnetic field, and a display device to indicate the integrated exposure value generated by the integrating circuit. During operation, the meter generates a quantitative reading indicating exposure to the h.f. magnetic flux as an integral of the magnetic flux, which generates the induction heating currents, over the exposure period during the induction heat sealing operation, and the reading provides a useful measure of the induction heating generated in an induction heat sealable closure.

Abstract: A system is provided for measuring the thickness of a ferromagnetic layer formed over a conductive base layer. An eddy current probe is provided for measuring the thickness of the ferromagnetic layer. The eddy current probe can be placed in direct contact with the ferromagnetic layer, or it may be spaced above its surface by an unknown standoff distance. This spacing may be caused by the presence of an overlying nonferrous, nonconductive layer applied over the ferromagnetic layer, or it may be an air gap over the ferromagnetic layer. An analog detector connected to the probe provides output values in two dimensions corresponding to the modulation of the probe's magnetic field by the ferromagnetic and conductive layers. These values are utilized to determine a mapping between the detector output values and ferromagnetic layer thickness and standoff values. The output of the mapping function provides two values, a ferromagnetic layer thickness and a standoff distance, which corresponds to the detected values.

Abstract: A device for testing a proximity sensor and precisely measuring the rigging gap between the sensor and its metal target. The sensor is stimulated with a signal of a known frequency and sensor impedance or a component thereof, such as inductance, is measured. The measured value is converted into gap width using a lookup table. The gap width may be displayed to the operator or automatically compared to an optimal range of gap widths for a sensor of the type under test. An operator may also test the sensor using a precision tool that has a dielectric spacer of a known width attached to a metal target. While the operator holds the tool with the spacer in contact with the face of the sensor, the present invention measures impedance and converts it into a gap width. The gap width should equal the known width of the spacer if the sensor is functioning properly. If the difference between the known spacer width and the measured width is less than a predetermined tolerance, the difference may be stored as a gap error.

Abstract: A storm monitoring apparatus and method is described wherein two H-field antennas are oriented with respect to the heading axis of an aircraft or the like at an angle of 45.degree.. The signals developed by these two antennas are picked-up by small R-F transformers which serve the inherent function of integrating the signals and extracting the H-field current component. A printed circuit board structuring of the two antennas provides for consistency of fabrication and reliability as well as compactness. The monitoring apparatus exhibits broad band frequency response to evaluate lightning strike rate to determine storm range and intensity. A computer control test utilizing diagnostic coils at the antenna carries out periodic testing of the performance of the device and a component such as a gravity switch provides an indication to the control system as to the orientation of mounting of the antenna on an aircraft.

Abstract: Wear particle monitoring is carried out on samples of a lubricating oil extracted from lubricated equipment together with the naturally appearing burden of ferromagnetic particles. The extracted sample is collected in a bottle to a depth sufficient to exceed the flux field of a sensing coil to which the bottle is subsequently applied whereby the numerical value (PQ value) assigned to the particle burden is substantially insensitive of the volume of liquid in the bottle. From time dependent measurements information as to the size of the particles in the burden can be obtained.

Abstract: A metal detector system includes two transmitter-receiver antenna pairs supported by respective side panels of a portal. The relative positions of an adjacent transmitter antenna and receiver antenna within an antenna pair may be adjusted to calibrate the antennas, such as by crossing adjacent antennas or by increasing the distance between adjacent antennas.

Abstract: An eddy-current apparatus for measuring the conductivity of a conductive material and for reducing the influence of lift-off on conductivity measurements is provided. The apparatus includes a probe for inducing an eddy-current in a conductive material and a digital LCR meter for measuring the impedance of the probe when it is placed near the conductive material. A digital processor uses calibration impedance data obtained from a series of reference materials and an impedance measurement for a test material to produce a conductivity value independent of lift-off between the probe and the test material.

Abstract: The operational fitness of a magnetic sensor for detecting buried magnets can be tested from time to time by an electromagnet installed in proximity to the sensor. The electromagnet is a small coil of wire mounted near the sensor, such as a Hall effect device, which when energized, generates a test magnetic field. The analog output of the sensor is compared with preestablished values when the electromagnet is energized to verify the proper operation of the sensor; it is also compared with preestablished values when sensing buried magnets to confirm operation of the sensor, the strength of the buried magnet, and the alignment of the sensor with respect to the magnet. A threshold detector senses the output of the sensor to indicate when a magnetic field is detected, and the peak analog output of the sensor is stored and compared to a reference after the sensor passes the magnet.

Abstract: A metal casting control device is provided for use in conjunction with a semi-continuous metal casting system. The control device is an integral module containing a metal surface elevation sensing device, a valve actuator for positioning a metal distribution control valve, and electronic circuits associated with these mechanical components. The control device module is adapted to be connected to an overhead metal distribution launder by a single quick-coupling for convenient and simple removal and replacement. Calibration of the control device is performed after installation by mounting a calibration target on the metal casting system and vertically adjusting the metal surface elevation sensing device until an integral calibration indicator positioned on the control device indicates that the proper vertical position has been attained.

Abstract: In an improved electromagnetic induction-type conductivity meter utilizing primary and secondary transformer coils about a liquid sample passageway, a resistance circuit having a conductive lead line extending also through the coils and parallel with the sample passageway is provided. The resistance circuit can be selectively opened and closed, and has the capacity to contribute to the measurement voltage detected on the detector coil when the primary coil is excited. The value of this additional resistance voltage can be used for calibration and monitoring the condition of the conductivity meter.

Abstract: An angular position sensor for sensing the angular position of a pivotally mounted device includes a magnetically sensitive device, such as a Hall effect IC, and a plurality of flux concentrators, rigidly disposed relative to the Hall effect IC, forming an assembly. The assembly is disposed in a housing a fixed distance from a rotatably mounted standard magnet defining a fixed air gap therebetween. The magnet is disposed in rotatably mounted magnet holder which also acts as a drive arm that is adapted to be mechanically coupled to a pivotally mounted device. The configuration of the flux concentrators assembled to the magnetically sensitive device cause the output of the Hall effect IC to be generally linear. In order to avoid problems associated with electrically adjustable angular position sensors, the angular position sensor in accordance with the present invention is adjusted mechanically. In particular, a flux concentrator, preferably having a halo shape, is disposed adjacent the magnet.

Abstract: A nondestructive method for determining the thickness of a non-electrically conductive material is provided that comprises the steps of uniformly dispersing a quantity of a ferromagnetic particulate tagging substance in the material whose presence and distribution is detectable by a form of radiant energy, such as the high-frequency electromagnetic field emanated from an eddy current probe, and then calibrating the output of the eddy current probe with a sample material having a known thickness that has been tagged with the same tagging substance at the same density. The thickness of the material is then determined by comparing the amplitude of electromagnetic coupling with the material with that obtained with the sample. The method may advantageously be applied to determine the thickness of a granular material such as asphalt concrete over a roadbed, as well as the strain and wear patterns in gaskets formed from elastic materials.

Abstract: Field strength of an electromagnet is monitored at a threshold with a coupling coil positioned to monitor magnetic flux in a leg of an electromagnet. In the context of magnetic particle inspection for surface flaws (e.g. cracks) in ferromagnetic materials, sensing magnetic flux in a portion of a magnetic circuit including the material being inspected provides a continuous direct indication of whether or not the magnetic field strength produced is sufficient for reliable inspection to be performed. Since the magnetic flux in the electromagnet will be reduced with increases in reluctance of the magnetic circuit, the continuous monitoring of magnetic field strength also effectively monitors correct inspection technique by the magnetic particle inspection methodology.

Abstract: A system for detecting the presence of a magnetic field emanating from a video display terminal (VDT) in which a current induced through a sensing element is first amplified by a high gain amplifier stage having a very broad low band frequency response curve then rectified by a precision rectifier to convert the AC signal induced through the sensing element to DC current. The DC current is used as one input to a comparator, the other input being set by means of a potentiometer to provide flexibility in setting a threshold input voltage differential representative of a harmful magnetic field radiation level. The output of the threshold comparator triggers a driver which is connected to a battery powered solenoid. The solenoid actuates an indicator flag in the presence of a magnetic field which exceeds the threshold magnetic radiation level.

Abstract: A calibration fixture for an MWD logging tool consists of a plurality of concentric co-planar conductive calibration loops are mounted around the logging tool mandrel coaxially with the usual transmitter(s) and receivers that are mounted on the tool. The calibration loops are terminated with a multiple-tap impedance quantizing means for discretely varying the impedance of the calibration loops. When a transmitter is activated to emit an electromagnetic signal, the calibration loops are excited to reradiate a portion of that signal into the receivers with an intensity that is a function of the loop impedance thereby to simulate the effects of formations having known resistivities.

Abstract: An electronic compass (10) having at least two sense windings (11, 12) is mounted in a vehicle. The outputs (x(h), y(h)) of the windings are measured for a number of compass directions (headings). From this data an error difference angle (.phi.), from a nominal angle, which actually exists between the output windings is calculated. Preferably a look-up table (21, 39) is created relating actual compass heading (h) to measured sense winding outputs by utilizing the calculated error difference angle (.phi.). This table is then utilized for calculating actual compass heading based on actual measured sense winding outputs. The calculated error angle (.phi.) can also be used to calibrate the compass without creating a look-up table. The calibrated compass compensates for misalignment of the sense windings and provides a more accurate electronic compass without requiring creating a calibration table by orienting the compass in a very large number of exactly known directions.

Abstract: In a position detection probe having a magnetostrictive wire stretched between a head and a reflective foot end termination, and a magnet displaceable along the probe and using the sonic pulse propagation time from the magnet to the foot as a position detection parameter, compensation for thermal expansion and thermal change of propagation velocity is made based on the property of the total propagation time along the wire length being a unique function of temperature and calibrating the probe at different temperatures to yield either equations or look up tables of true positions as functions of the total propagation time and the position detection parameter. By mapping wire characteristics at a plurality of magnet positions and temperatures to construct look up tables, wire nonlinearities as well as thermal effects can be compensated for.

Abstract: A method utilized with an underground conductor detection system for calibrating a downhole transmitter to compensate for detuning of the transmitter antenna by geologic formations. The method comprises sending a synchronization signal to the transmitter antenna, measuring the current flow through the transmitter antenna and adjusting the current to a constant level, and measuring the phase difference between the transmitter antenna current and the synchronization signal. A receiver transmitter is calibrated by sending a synchronization signal to a radiating antenna in the receiver that in turn sends a calibration signal to the receiver antenna that is directed over the entire signal pathway back to surface located signal processing equipment. Another method of underground conductor detection sends a surface wave to the downhole receiver to cancel the effect of the surface wave modulation on a target wave being radiated by the underground detector.

Abstract: A storm monitoring apparatus and method is described wherein two H-field antennas are oriented with respect to the heading axis of an aircraft or the like at an angle of 45.degree.. The signals developed by these two antennas are picked-up by small R-F transformers which serve the inherent function of integrating the signals and extracting the H-field current component. A printed circuit board structuring of the two antennas provides for consistency of fabrication and reliability as well as compactness. The monitoring apparatus exhibits broad band frequency response to evaluate lightning strike rate to determine storm range and intensity. A computer control test utilizing diagnostic coils at the antenna carries out periodic testing of the performance of the device and a component such as a gravity switch provides an indication to the control system as to the orientation of mounting of the antenna on an aircraft.

Abstract: A DC superconducting quantum interference device has a superconductive ring and a feedback modulation coil for detecting a magnetic field. A variable bias current is applied to the superconductive ring and a modulating signal is applied to the feedback modulation coil. A signal change-over circuit is provided for superposing a false signal on the modulating signal, the false signal electrically simulating the effect of an applied magnetic field to enable adjustment of the variable bias current and the modulating signal under measurement conditions. A flux locked loop circuit of the DC superconducting quantum interference device has an external input terminal or a low-frequency oscillator for supplying a low-frequency signal to the signal change-over circuit which is superposed on the modulating signal applied to the feedback modulation coil.

Abstract: The invention concerns apparatus and a process for the non-destructive measurement of the ohmic resistance of thin layers according to the eddy-current principle. Here an inductor (2) is fed with a high frequency voltage (U.sub.osz) and the magnetic field of this inductor (2) is directed at the thin layer to be measured, whereby an eddy current flows in this layer the magnetic field of which weakens the magnetic field of the inductor (2). The inductor (2) is here part of an oscillating circuit (3) which is held always at resonance by means of a phase-correcting arrangement (14). Under these resonance conditions the reactive values of the oscillating circuit (3) may be neglected so that the current flowing into the oscillating circuit (3) depends solely on the ohmic resistance of this oscillating circuit (3), which in turn is determined by the ohmic resistance of the layer to be measured.

Abstract: Both a system and a method are provided which allows an eddy current probe to accurately determine both the proximity and dimensions of non-conductive structures which are normally invisible to such probes. The system includes a portable target medium that is movable into a known position with respect to the non-conductive structure, and that includes a conductive material that couples strongly with a fluctuating magnetic field, and a movable eddy current probe that emanates a fluctuating magnetic field and which generates a signal indicative of the magnitude of the interaction between the field and the portable target medium from which the distance between the two may be computed. The system may be used to determine the proximity of non-conductive structures such as plastic pipes that have been buried under ground, as well as the dimensions of such non conductive structures.

Abstract: A position detection method and apparatus is disclosed which utilizes an electromagnetic probe as the control element in a relaxation oscillator circuit. The probe is energized by a pulse voltage waveform and the decay time of the induced transient probe voltage is utilized to modulate the frequency of the pulse generator. The probe transient voltage decay time is influenced by the proximity of an electrically conductive or magnetic object. Therefore, a frequency output is generated which indicates the position of the conductive or magnetic object.

Abstract: Apparatus for testing metal detecting apparatus employs a test piece of representative metal which is passed through a section of the electromagnetic field of the metal detecting apparatus to record a response signal as if metal has been detected. The testing apparatus comprises the test piece and a housing for the test piece which extends through said section of the electromagnetic field and acts to guide the test piece along its path, said movement of the test piece causing distortion of the electromagnetic field and actuation of the detecting mechanism to give the required signal. Metal detecting apparatus may have the testing apparatus attached thereto or moulded integrally therewith.

Abstract: An alignment process is applied to each sensor of an array of three axis magnetic sensors to electronically align the three axes of each sensor after the array has been deployed. The alignment process compensates for each sensor not being aligned perfectly with the earth's N-S, E-W and vertical magnetic field components. A field registration process is applied to each sensor of the array that uses a dipole moment detection and localization process and the alignment process combined with a known calibrated dipole source to define the shape of the array. The present invention improves the performance of the array of sensors in detecting magnetic anomalies by digitally compensating for sensor-to-sensor nonalignment and magnetic interferers within interfering range. The alignment process electronically aligns the three axes of each of the sensors to gain maximum performance from the sensor array.

Abstract: A non-contact eddy current inspection system provides for compensation for variations in the distance between the eddy current probe and the workpiece surface. Probe height from the surface is first determined for a scan using a vector analysis of the signals through inductive coils. Height compensated data signals are then compared against a threshold value to determine the presence of flaws in a workpiece surface.

Abstract: The distance between substantially parallel metal tubes forming a flat sheet and the thicknesses of oxide layers covering the tubes are simultaneously measured. The tubes may particularly be sheaths of a nuclear fuel assembly.

Abstract: The operation of a biomagnetometer is verified using a tool containing a dipole source of known strength having a fixed, known position. The tool includes a hollow nonconducting and nonmagnetic sphere filled with an electrically conducting fluid, and at least one well-characterized dipole source within the fluid. The position of the dipole source relative to fixed locations on the surface of the sphere is established by X-ray measurement, and the the fixed surface locations and strength of the dipole source are measured with the biomagnetometer. The position and strength of the dipole source determined in this manner are compared with the known position and strength of the dipole source, to verify the operation of the biomagnetometer.

Abstract: The invention makes it possible to detect and measure the movement of a moving member (50) through an amagnetic or low permeability metal wall. The installation requires ferromagnetic material targets placed at regular intervals over the moving member. The transducer is positioned facing the moving member by its detection face (16). It comprises two ferromagnetic cores (2, 8) surrounded both by an exciting coil (4) and a measuring coil (10), at whose terminals the measuring signal is taken. The latter is proportional to the variable reluctance of the magnetic circuit, which varies as a function of the position of the ferromagnetic targets (48). The transducer is completed by a balancing core (34). Application to the measurement of the displacement of control rods in the vessel of a pressurized water reactor.

Abstract: The area of a loop made of superconducting material is decreased to incre the magnetic field on the surface of a test piece adjacent the loop for determining the critical field, H.sub.c, of the test piece. A loop with a gap having a temporary plug placed therein in which a persistent current is established has a nozzle forming the gap thereon for receiving a test piece. The test piece then completes the circuit permitting removal of the temporary plug. The area of the loop is then decreased resulting in an increase in magnetic field at the surface of the test piece. When the critical field of the test piece is reached, magnetic flux will leak from the internal area of the loop, thereby determining the critical field of the test piece. A continuous length of superconducting material can be tested for discontinuities or spots of low critical field, H.sub.c.

Abstract: A device for simulating a moving test object sensing transducer uses a plurality of individual transducers which are stationary relative to each other (for example eddy-current based surface transducers), and a selector unit. The individual transducers are, for example, mounted in a plane parallel to the surface of the test object to be sensed and scan the test object with respect to a characteristic, for example a crack. The resultant simulated transducer signal is signal processed by means of, for example, automatic compensation and vector transformation techniques.

Abstract: A magnetic rotation sensor is disclosed, in which by raising the precision of the size between a first hole for positioning a magnetic rotation drum and second holes for positioning pin guides and at the same time by keeping the outer diameter of the pin guides at a high precision, the gap between the drum described above and a sensor supported by the pin guides can be kept precisely almost without any adjustment.

Abstract: Methods are provided for assembling a magnetic encoder wherein fluctuation of a magnetic gap arising from a change in temperature is minimized. The magnetic encoder comprises a magnetic scale having thereon a magnetic pattern which can be detected by a magnetic sensor, a sensor retainer for securely retaining the magnetic sensor with a magnetic gap left between the magnetic scale and the magnetic sensor, and a supporting member to which the sensor retainer is secured.According to the invention, a jig is affixed to a surface of the sensor retainer, and the jig is moved until the gap between the magnetic scale and the magnetic sensor reaches a predetermined width. The sensor retainer may be secured to a supporting member by first and second securing agents, the second securing agent being the harder and applied closer to the magnetic sensor than the first securing agent.

Abstract: A non-contact level measurement system for monitoring distances with very high accuracy between a sensor coil and a metallic object such as a molten liquid level over either very narrow or extended distances. Controllers coupler with heaters, thermocouples, coolant air are provided for maintaining the sensor coil at a operating temperatures within the range of 400.degree. F. and 1200.degree. F. to eliminate variations to the operation of the sensor coil. The system incorporates an L-C resonant circuit connected between the output of an oscillator and the input of an operational amplifier. A variable inductor parallel with the capacitor of the L-C resonant circuit is used to obtain a precise offset operating frequency of the resonant circuit from the frequency of the oscillator.

Abstract: A tool dullness indicator and method comprising the measurement of eddy currents at a known, controlled frequency directly in the tool by measuring the phase angle shift in a coil when a sample is put into or next to the coil. The phase angle change caused by presence of a workpiece is measured when the tool is sharp to provide a reference reading taking into account the surface hardness and other bulk properties of the workpiece, and arriving at a parameter that is dependent on eddy current changes, such as phase angle shift or other measurable changes related to eddy currents in the part, and then analyzing the workpiece, either while working, or at a set programmed check time to determine when the tool is dull as a function of the change in eddy current characteristics caused by work hardening.

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: A field strength indicator for a magnetic particle inspection process is used to determine field strength and direction sufficient to identify real flaws in a test piece. The field strength indicator is a substantially flat shim having at least one series of artificial flaws formed therein by electric discharge machining. The artificial flaws have a geometry which render them compatible with real flaws and thus enable the magnetic field strength and direction to be properly set for conducting a magnetic particle inspection procedure. The surface containing the artifical flaws must be covered with a thin inert and non-magnetic coating for proper operation.

Abstract: An electromagnetic field sensing apparatus used for locating and determining the distance to buried conductive conduits including at least two receptor means, each adapted to receive a signal from the conduit and produce an output voltage proportional to the signal received, and also including a calibrating coil, with known relative coupling to the receptor means, and capable of inducing calibrating signals therein. Computing means are employed to calculate the relative sensitivities of each said receptor means using the voltage signals induced therein by the calibrating coil, and said known relative coupling relationships. The computing means further uses the output voltages from said receptor means, induced therein by the signal radiating from the conductive conduit, and said relative sensitivities to calculate the distance to and location of the conduit. Display means are provided to indicate this distance and location.

Abstract: This is a coin sorting and counting apparatus for providing very accurate high throughput processing of heterogeneous coin mixtures. A rotating drum having parallel annular channels, each of which has equally spaced counterbores located around it is rotated within a vacuum plenum. A novel sensor coil constructed as a balanced transformer of four coils having rectangular geometries is used, in conjunction with a dual frequency excitation signal, to detect at least three electronic signatures for each coin, the signatures are detected by separating the frequency components in the output of the sensor coil and obtaining a peak value for the excursion of the high frequency response caused by passage of the coin, and width values corresponding to the time the excursion of the signal was above a predetermined threshold for both the high and low frequency responsive channels.

Abstract: An apparatus for testing the operativeness of a Hall effect device (HED), such as in an automotive application, without requiring removal of the HED for testing. The apparatus includes a connector for connection to the HED, a connector for connection to a voltage supply, and an indicator. A permanent magnet is physically positioned with respect to the HED so that a properly functioning HED would produce a Hall effect current within a predetermined range. A ferrous metal strip is provided, shiftable between an interference position between the permanent magnet and the HED and a clear position not between the permanent magnet and the HED. The indicator is connected so as to be lit when the HED is producing a current within the predetermined range, and not lit when the HED is not producing a current within the predetermined range. Also disclosed is a method for testing the operativeness of a HED. The method includes supplying a testing apparatus as described above.

Abstract: An electronic motor control system is taught herein which utilizes a speedometer testing circuit. The (electronic) speedometer/odometer of a vehicle is tested, with the testing device being interconnected with the (input) terminals of the speedometer, exclusive of whether the speedometer is installed or removed from the vehicle. The testing device is utilized without vehicle input to the speedometer in order to determine whether the speedometer can produce an expected signal upon testing thus determining whether the speedometer is functional or not. The testing circuit has a self-contained power supply, is compact in size, and lightweight, thereby insuring complete mobility of the testing unit and dual application of the circuit to both installed and disengaged speedometer and odometer mechanisms.

Abstract: A transducer arrangement comprising a magnetoresistive transducer including a magnetoresistive element responsive to magnetic flux passing therethrough in a predetermined direction to change its electrical resistance as a function of the intensity of the magnetic flux in the predetermined direction and a magnet to provide said magnetic flux. The transducer can include a permanent magnet having a planar surface with a magnetoresistive element offset from the axis of the magnet and optionally at an angle to the planar surface. The transducer can also include a concave surfaced magnet with the magnetoresistive element at an acute angle to the parallel flux lines emanating from the concave surface. As a further embodiment, the magnetoresistive element can be tilted on the magnet surface in two directions to provide a bias field and calibration.

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: 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: An eddy current sensor having a coil set with a reference coil and a measng coil, and a sine generator whose output signal is applied to the reference coil and the measuring coil. The output signals of these coils are subtracted from one another by a first subtracter, whose ouput signal is applied to a first modulator and to a second demodulator through a 90 degree phase shifter. The output signal of the sine generator is provided to the first and second demodulators as an additional signal via a phase shifter having an adjustable phase angle. A phase angle is selected such that the interference signals have a specified direction in the formed signal plane. The output signal from the first demodulator is applied through an amplifier having an adjustable amplifying factor (a) to an input of a second subtracter. Similarly, the output signal of the second demodulator is provided through an amplifier having an adjustable amplifying factor (b) to the second subtracter.

Abstract: A phase and amplitude calibration system for an electromagnetic propagation based earth formation evaluation tool is presented. In accordance with the present invention, improved phase and amplitude logs of a borehole section are provided by an automatic calibration system which compensates for errors caused by temperature and pressure variations in the borehole. This improvement is accomplished by applying in-phase, equal-amplitude reference signals to both measurement channels of a two channel system to thereby characterize system errors for correction of data used for logging. The reference signals are applied by tightly coupling a calibration signal to each receiving antenna. In a first embodiment, this is accomplished by adding a second antenna (a calibration antenna) to each of the two spaced receiving antennas.

Abstract: In a method for calibrating multi-channel SQUID systems having gradiometers of an arbitrary order, calibration coils, each having the same number of ampere turns are symmetrically arranged at identical distances between the parallel coil planes with respect to every gradiometer coil, so that every gradiometer coil is penetrated by a common, oppositely directed magnetic field generated by the calibration coils. The field that the calibration coils produce at the locations of the gradiometer coils are numerically calculated to obtain a net gradient field value which is divided by the measured voltage at the output of the allocated SQUID electronics in order to calculate the calibration factor.

Abstract: The present invention provides a method for determining biaxial stresses in a steel component by first generating a calibration datum from an experimental test piece having metallurgical properties similar to steel component and then applying values representative of measured Barkhausen noise levels obtained from the steel component to the calibration datum. The practice of the present invention yields values of strain in the first and second principal directions at the selected location on the steel component under examination.