Abstract: A method for compensating mechanical stresses in measuring the magnetic field strength by Hall sensors is disclosed. It is proceeded in a manner that the electric resistance and/or a measuring quantity proportional to the electric resistance of the Hall sensor is determined in at least two different directions, that the mean value of the determined resistances and/or measuring quantities proportional thereto is calculated, and that the current conducted through the Hall sensor is chosen to be proportional to the mean value calculated.

Abstract: A magnetic field probe includes a substrate and a conductive layer provided on the substrate. The conductive layer has a coil, lead wires, and pads. The coil has at least one turn and outputs a signal indicative of a magnetic field from a device under test in a vicinity of the magnetic field probe. The lead wires extend from the coil to the pads, the signal from the coil being transmitted to the pads through the lead wires. An isolating layer of a dielectric material is provided on the lead wires to protect the lead wires between the coil and the pads in the conductive layer. A shielding layer of a conductive material is provided on the isolating layer to protect the isolating layer. The shielding layer prevents distortion of the magnetic field at the lead wires in conjunction with the isolating layer.

Abstract: A method for operating an eddy current sensor (10) with a measuring coil (2) and an evaluation circuit (4) for determining material or geometric parameters of a test object (5), in which the test object (5) is arranged at a distance (d) from the measuring coil (2). The impedance of the measuring coil (2) is evaluated, while the measuring coil (2) is being supplied with an alternating voltage of a predetermined frequency, and the evaluation circuit (4) determines the material and geometric parameters of the test object (5) based on the impedance of the measuring coil (2). The impedance of the measuring coil (2) is determined at an alternating voltage of a first frequency, and the impedance of the measuring coil (2) is determined at an alternating voltage of a second frequency, and the evaluation circuit (4) computes the material and geometric parameters of the test object (5) on the basis of the impedances of the measuring coil (2) at the first and the second frequencies.

Abstract: A magnetic flux detector comprises a core member 12 and an armature member 11, and the core member 12 generates a magnetic flux by an exciting coil 13 when the exciting coil receives an excitation current controlled by an excitation current controller 30. The magnetic flux detector further comprises a search coil 14, which is provided in a magnetic path for the magnetic flux, and a magnetic flux calculator 40, which determines the magnitude of the magnetic flux by measuring an electromotive force induced in the search coil 14 by a change in the magnetic flux. The magnetic flux calculator 40 has a potential setup resistor 43, whose resistance B is sufficiently larger than the internal resistance A of the search coil 14 (approximately A=B/3˜B/30).

Abstract: A head testing apparatus is provided for testing a magnetic data recording head. The apparatus includes a test volume adapted to receive the magnetic data recording head and a magnetic field source positioned to generate a magnetic field within the test volume. A Hall sensor is positioned relative to the test volume and has bias current input terminals, voltage output terminals, an operating temperature and an impedance between the bias current input terminals, which varies with the operating temperature. A bias current source is electrically coupled to the bias current input terminals and is adapted to provide a bias current, which is modulated based on the impedance of the Hall sensor.

Abstract: A system and method for sensing magnetic anomalies uses a gradiometer having at least one pair of triaxial magnetometer-accelerometer (TMA) sensors. Each TMA sensor has X, Y, Z magnetic sensing axes and X, Y, Z acceleration sensing axes that are parallel to one another and to the X, Y, Z magnetic sensing and acceleration axes of all other TMA sensors. Each TMA sensor outputs components (Bx, By, Bz) of local magnetic fields and components (Ax, Ay, Az) of local gravitational acceleration fields. The components (Bx, By, Bz) and (Ax, Ay, Az) output from each TMA sensor are processed to generate motion-compensated components (Bcx, Bcy, Bcz) of local magnetic fields. A difference is generated between the motion-compensated components (Bcx, Bcy, Bcz) for each pair of TMA sensors thereby generating differential vector field components (&Dgr;Bx, &Dgr;By,&Dgr;Bz).

Abstract: A magnetic field measuring apparatus for precise cancellation of environmental noise includes a plurality of first SQUID gradiometers to detect noise and biomagnetic fields, a plurality of second SQUID gradiometers to detect noise, a driving circuit to drive these gradiometers, and a computer to execute signal processing after collecting the signals detected by these gradiometers. First and second SQUID gradiometers are provided which include first-order gradient pickup coils with the baselines formed by the coils of second gradiometers being shorter than those of first gradiometers. The apparatus cancels noise, from detected biomagnetic signal waveforms, caused by variant noise cancellation rates of the coils of first gradiometers, different baselines of the coils of second gradiometers, and the frequency property of a magnetically shielded room in which the apparatus is installed.

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: The sheet resistance meter has: a coil which produces a magnetic field; a sensor head provided to enable the magnetic field to induce eddy currents in a thin film formed on a substrate so that the lines of a magnetic force exerted by the magnetic field extend on one side of the substrate; a control device for detecting the sheet resistance of the thin film according to a variation of the magnetic field caused by the eddy currents; a capacitor for achieving resonance with the coil; and a groove section, a primary air port, an auxiliary air port, and a side air port, provided in the sensor head, for controlling the temperature of the coil. The arrangement stabilizes results of the measurement of a sheet resistance by a sheet resistance meter of a one-sided eddy current detection type when it is used continuously.

Abstract: A magnetic sensor with a signal processing circuit includes a magnetic sensor section 4 composed of a compound semiconductor thin film or a magnetic thin film, and a signal processing circuit 5 for amplifying a magnetic signal the magnetic sensor section detects as an electrical output. The signal processing circuit 5 includes an operational amplifier 51 and a constant current circuit 52 for carrying out feedback. The constant current circuit 52 in the signal processing circuit 5 includes a plurality of resistors with two or more different temperature coefficients, and the current output from the constant current circuit has a temperature coefficient inversely proportional to the temperature coefficient of the combined resistance of the plurality of the resistors.

Abstract: The invention relates to measurement technology and can find application for nondestructive testing electrically conducting and/or ferromagnetic materials and products. The differential eddy-current transducer comprises a primary detector (1) which incorporates two similar search coils (2, 3) and an additional coil (4) having its leads connected in series aiding to respective first leads of the search coils (2, 3) to second leads of which voltage is applied in antiphase. The transducer further comprises an electronic unit (5) which is electrically connected to the primary detector (1) and incorporates a potentiometer (6), a capacitive element (7), and an operational amplifier (8). Two leads of the potentiometer (6) are connected to common connection points of the leads of the search coils (2, 3), and its midpoint lead is connected to the capacitive element (7) which in turn is connected to the inverting input of the operational amplifier (8) whose noninverting input is grounded.

Abstract: Disclosed is a method of obtaining information in-situ regarding a film of a sample using an eddy probe during a process for removing the film. The eddy probe has at least one sensing coil. An AC voltage is applied to the sensing coil(s) of the eddy probe. One or more first signals are measured in the sensing coil(s) of the eddy probe when the sensing coil(s) are positioned proximate the film of the sample. One or more second signals are measured in the sensing coil(s) of the eddy probe when the sensing coil(s) are positioned proximate to a reference material having a fixed composition and/or distance from the sensing coil. The first signals are calibrated based on the second signals so that undesired gain and/or phase changes within the first signals are corrected. A property value of the film is determined based on the calibrated first signals. An apparatus for performing the above described method is also disclosed.

Abstract: A differential spiral magnetic field sensing device is constructed such that two soft magnetic film cores are arranged parallel to each other, each soft magnetic film core is divided into several parts in a detection axial direction to reduce anti-magnetic field components, the differential excitation coil, the magnetic flux variation detecting coil and the zero magnetic field detecting coil are laminated and wound turn by turn around the soft magnetic film cores, and there is no induced voltage waveform to the magnetic flux variation detecting coil without external magnetic field. Also, in order to minimize the leaked magnetic field components of the soft magnetic film cores, the soft magnetic film cores are sandwiched to form closed magnetic paths, and the differential excitation coil, the magnetic flux variation detecting coil and the zero magnetic field detecting coil are spirally laminated around the sandwiched soft magnetic film cores.

Abstract: A sensor module (1) is constructed as a solid state integrated circuit (IC) and has a sensor (2) as well as at least one measuring amplifier (3), wherein the sensor module has external connections at least for the power supply and for the output measurement signal. In the sensor module an evaluation circuit (6) is provided that is connected to at least one internal measurement point of the circuit. The evaluation circuit (6) is connected to a modulator (10) for modulation of the supply current and/or the supply voltage and/or the output measurement signal, in order to output a diagnostic signal, which is formed from an internal circuit measurement value, via the available external connections of the sensor module.

Abstract: An improved method of measuring vehicle speed based on the output signal of a variable reluctance speed sensor responsive to the teeth of a transmission output gear adjusts the sensitivity of a signal processing circuit in dependence on the mode of operation of the vehicle so as to reduce sensitivity to output signals produced by gear tooth vibration. The signal processing circuit only passes portions of the sensor output signal that have an amplitude greater than a predefined threshold and a frequency less than a predefined frequency, except when an electronic controller identifies a condition of potentially erroneous speed sensing characterized by substantially stationary vehicle operation with the engine decoupled from the output gear and an engine speed in excess of a calibrated threshold.

Abstract: Through differentiation of input signal Vw from a sensor the angular frequency &ohgr; becomes included in the amplitude component. Through a plurality of differential operations the amplitude including the angular frequency &ohgr; varies, but the time-dependent term becomes equal. Since the amplitude of the signal Vw outputted from the revolution speed sensor 10 is approximately constant, the angular frequency &ohgr; proportional to the revolution speed can be extracted by determining a ratio thereof.

Abstract: An apparatus for reducing rotation of an article such as a bird for holding a superconducting quantum interference device for use in airborne transient electromagnetic mineral prospecting. The apparatus includes a support sphere having an inner shell and an outer shell. Liquid is contained between the inner and outer shells and a sphere has openings through which support strings project for locking to an internal point within the sphere. The strings have one end connected to an internal point within the support sphere and another end connected to a spring. The spring includes a damper for damping movement of the spring. Baffles are arranged in the cavity between the inner and outer shells in which the liquid is contained for damping movement of the liquid.

Abstract: In a method for determining a thickness of a layer of electromagnetically conductive material, the measurement errors resulting from different quality of the basic material are eliminated. For each basic material, one dimensionless characteristic value (K) is ascertained. With the aid of a characteristic calibration curve, each characteristic value (K) can be assigned a correction factor (F), with which the measured value of the layer thickness (DM) can be converted into a real value of the layer thickness (D). Different electrical and magnetic properties, dictated by the different quality of the basic material, can thus be largely eliminated.

Abstract: A Hall sensor has a Hall plate having terminals for supplying a supply current and for tapping a Hall voltage. A Hall circuit connects the terminals. A device for orthogonally switching the supply current and the Hall voltage between a first set of the terminals and a second set of the terminals, arranged orthogonally to the first set of terminals, is provided wherein a geometry of the Hall plate is identical for the first and second sets of the terminals. A summation device is configured to receive measured Hall voltage values from the first and second sets of the terminals and to determine an offset-compensated Hall voltage value. The summation device is configured to receive and/or process the Hall voltage values of the first and second set of the terminals such that, for stress measurement, a portion of the Hall voltage values resulting from the magnetic field acting on the Hall sensor are compensated and only the portion of the Hall voltage values resulting from the offset are measured.

Abstract: A cancellation circuit removes interfering signals from desired signals in electrical systems having antennas or other electromagnetic pickup systems. The cancellation circuit provides amplitude adjustment and phase adjustment to electrical signals induced in an electrical system by received electromagnetic signals. The cancellation circuit may be adapted to process received electromagnetic waves having multiple frequencies. Phase adjustment compensates for electrical path-length differences between signals resulting from propagation delays, circuit delays, and multipath. The amplitude-adjusted and phase-adjusted signals are combined to cancel the effects of electromagnetic interference. In an electromagnetic receiver, a plurality of receiver elements provide the cancellation circuit with different complex proportions of desired and interfering signals to enable removal of the interfering signals.

Abstract: A circuit for sensing a magnetic field has at least one saturable coil (L1). The circuit includes switches (S1, S2) controlled by a comparator (12) to drive the coil (L1) to saturation by alternating polarities of current. In the absence of an external magnetic field the currents are balanced. An applied external magnetic field causes an unbalance in the coil (L1) in reaching saturation. An unbalance current is applied through a sensing resistor (R2) to an integrator (20) to develop an output voltage (Vo) as a measure of the applied magnetic field. The switches (S1, S2) are implemented by transistor switches. Dual (FIG. 1) and single (FIG. 2) supply rail circuits are disclosed. The circuit finds particular application in torque transducers using magnetoelastic elements.

Abstract: A method for the detection and the characterization of corrosion in multi-layer metallic structures using a pulsed eddy current technique. For this technique, a coil (or coils) is used both as field source (driven by a square wave voltage-controlled excitation), and/or as field sensor (measuring a transient response). The field sensor allows the capture of information about the condition of the area of the structure under inspection. The ability of this technique to detect corrosion hinges on the use of a transient response feature (i.e., Lift-off Point of Intersection) to infer the presence of material loss. With the help of a calibration standard, the Lift-off Point of Intersection provides the ability to quantify material loss in multi-layered structures. The results obtained with this method are independent of lift-off variations inherent to field inspections (i.e., changes in distance between the transducer and test object).

Abstract: Systems and methods for detecting the magnetic field created by a magnetic target. An arrangement of multiple magnetic field sensing elements and circuit elements configured to select and/or interpolate between the sensing elements to give enhanced performance and to compensate for external mechanical factors. The circuit arrangement is integrated on a single silicon chip to form an integrated circuit sensing device in one embodiment.

Abstract: An electronic circuit for automatically compensating for errors in the output signal of a displacement sensor. The electronic circuitry includes an analog to digital converter for converting an analog output signal from a linear displacement type sensor. The digital output signal from the sensor is processed by a microcontroller which automatically compensates for errors in the output signal. Ideal values, stored in an electronic memory, are used for compensation.

Abstract: A gradiometer for measuring properties of a magnetic field and in particular, for measuring magnetic field gradient components, comprising at least two magnetic sensors wherein at least two of the magnetic sensors are arranged to sense the magnetic field component in substantially the same direction. The magnetic sensors may be super conducting quantum interference device (SQUID) magnetometers, Hall probes, flux gates or magneto-resistive magnetometers. The gradiometer also includes a computer processor loaded with an adaptive signal-processing algorithm, for performing adaptive signal balancing of the magnetometer outputs. In a preferred embodiment the gradiometer may comprise at least eight magnetometers in a three-dimensional arrangement, and a set of three orthogonal global feedback coils, one for each direction x, y, z, such that the five independent magnetic field gradient components may be measured. The gradiometer may also be used to measure second or higher order magnetic field gradient components.

Abstract: A method for operating an eddy current sensor (10) with a measuring coil (2) and an evaluation circuit (4) for determining material or geometric parameters of a test object (5), in which the test object (5) is arranged at a distance (d) from the measuring coil (2). The impedance of the measuring coil (2) is evaluated, while the measuring coil (2) is being supplied with an alternating voltage of a predetermined frequency, and the evaluation circuit (4) determines the material and geometric parameters of the test object (5) based on the impedance of the measuring coil (2). The impedance of the measuring coil (2) is determined at an alternating voltage of a first frequency, and the impedance of the measuring coil (2) is determined at an alternating voltage of a second frequency, and the evaluation circuit (4) computes the material and geometric parameters of the test object (5) on the basis of the impedances of the measuring coil (2) at the first and the second frequencies.

Abstract: A sensor for measuring a parameter includes at least one transducer adapted to provide an analog transducer signal, and at least one converter adapted to convert the analog transducer signal into a digitized transducer signal, and a memory device associated with the converter capable of receiving the digitized transducer signal directly from the converter. The memory device is configured to provide a digitized output value from a memory location, the memory location being associated with or corresponding to the digitized transducer signal received by the memory device.

Abstract: A method of compensating periodic error signals in sensor output is provided. The method comprises obtaining a sum signal from sensing outputs of M sensor elements (where M is a positive integer), obtaining the amplitude and phase of N frequency components included in the sum signal, and calculating a sensing output gain adjustment coefficient for each sensor output. To ensure that a sum signal level obtained by summing a pre-adjustment output of each sensor element multiplied by the gain adjustment coefficient equals a sum signal level obtained by summing the unmodified outputs of the sensors, a gain adjustment coefficient is obtained for each sensor output by using a calculated scaling coefficient to perform pre-adjustment scaling of each gain adjustment coefficient. The adjustment gains thus obtained are used to adjust the gain of each sensor output.

Abstract: It is an object of the invention to provide a magnetic sensor apparatus and a current sensor apparatus each of which incorporates a fluxgate element for reducing an offset voltage and reducing variations in offset voltage. A drive section for exciting a sensor coil (2) includes a self-excited oscillation circuit having a resonant circuit part of which is made up of the sensor coil (2). The self-excited oscillation circuit includes an npn transistor (21) and a pnp transistor (31) that are amplifier elements used for continuing oscillation. The npn transistor (21) operates when an oscillation wave is on the positive side. The pnp transistor (31) operates when an oscillation wave is on the negative side. In the self-excited oscillation circuit, clamping of oscillation waves similarly occurs on both positive and negative sides. Therefore, the oscillation waveform has symmetrical positive and negative portions or has minor asymmetry if any.

Abstract: This invention prevents the failure of detection for horizontal and oblique lift-offs in a probe for an eddy current flaw detection test. A plurality of probes are provided, and each probe includes four detection coils. Two adjacent eddy current flaw detecting probes commonly own (share) one of the four coils. The detection coils are connected to a bridge circuit for picking up a flaw signal. The detection coils are adjusted so that interlinkage magnetic fluxes generated inside the detection coils by the eddy current become equal. An excitation coil for inducing the eddy current in a test piece by AC driving can be disposed over the detection coils. The center of the excitation coil is positioned on the center axes of the detection coils. An oscillator for applying an AC current to this excitation coil is connected to the coil.

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

Abstract: An eddy current sensor (1) has at least one measuring coil (2) that can be supplied with an alternating current, and an evaluation circuit (3). The eddy current sensor allows the temperature influences on the impedance of the measuring coil to be reliably compensated with a simple design and an evaluation circuit. For this purpose, the eddy current sensor has a compensating coil (4) which can also be supplied with an alternating current and which is arranged closely to the measuring coil, i.e. in thermal contact therewith, in such a way that the electric fields of compensating coil (4) and measuring coil (2) are orthogonal to each other. More particularly, the measuring coil (2) is in an annular form and the compensating coil (4) is wound around the measuring coil in the form of a torus.

Abstract: A cancellation circuit removes interfering signals from desired signals in electrical systems having antennas or other electromagnetic pickup systems. The cancellation circuit provides amplitude adjustment and phase adjustment to electrical signals induced in an electrical system by received electromagnetic signals. The amplitude-adjusted and phase-adjusted signals are combined to cancel the effects of electromagnetic interference. In an electromagnetic receiver, a plurality of receiver elements provide the cancellation circuit with different proportions of desired and interfering signals to enable removal of the interfering signals. An electromagnetic-wave transmitter having multiple transmitter elements is provided with a cancellation circuit for canceling electromagnetic signals in at least one predetermined region of space.

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

Abstract: Arrangements, specific apparatus and associated methods for skin depth compensation in underground boring applications are described. Compensation for skin depth error is accomplished by measuring a locating signal transmitted from a boring tool such that measurements of the locating signal include skin depth error introduced as a result of the electrical conductivity characteristic of the earth. Thereafter, the measurements are used in a way which determines a skin depth corrected position of the boring tool. In one aspect, a multi-frequency approach is provided which utilizes measured intensities of the locating field at two or more frequencies to extrapolate a zero frequency value of intensity. The zero frequency value of intensity is then used in position determination.

Abstract: A device for detecting random objects that are being carried inside a container includes an excitation coil and a sensing coil with a gap therebetween. When the construction of the container includes a conducting loop, the container is positioned on a path between the two coils, with the plane of the loop substantially perpendicular to the path. The excitation coil is then activated to generate a magnetic field that is directed along the path. This magnetic field has both a sinusoidal component and a cosinusoidal component. Importantly, the cosinusoidal component is adjusted to match a characteristic dimension of the loop, to thereby cause zero mutual inductance with the loop in the magnetic field. On the other hand, conducting objects inside the loop will cause inductance perturbations in the magnetic field which can be detected to establish the presence of the objects in the container.

Abstract: An improved Hall effect sensor includes a four-terminal Hall plate with orthogonally paired terminals that produce voltage signals in response to changes in an ambient magnetic field created by the proximity of a ferrous gear tooth to the sensor. Voltage signals from orthogonally paired terminals of the Hall plate are controlled by switches that are coupled to a clock signal generator. In response to the clock signal, the switches allow current to flow in a first direction corresponding to a first phase of the clock and to flow in a second direction corresponding to a second phase of the clock. A plurality of pass gate transistors in the sensor circuitry are connected to a timing generator synchronized with the clock signal generator. The timing generator outputs are received by the gate transistors and the gate transistors control the sequence in which a plurality of capacitors are charged. This plurality of capacitors store the voltage output from the Hall plate.

Abstract: A magnetic detector to detect a magnetic object's rotation and movement using a magnetoresistive element having hysteresis. The magnetoresistive element is set so as to tilt from the magnetizing direction of a magnet up to a predetermined angle &thgr; between the rotational magnetic object to be detected and the magnet. The magnetic detector provides a high accuracy signal that corresponds to the distance between the rotational magnetic object to be detected and the magnetoresistive element. The signal obtained is independent of the rotational direction or rotational speed of the magnetic object to be detected or the atmospheric temperature of an apparatus. Moreover, the temperature dependency of the output signal (amplitude) of the magnetoresistive element is decreased.

Abstract: A circuit configuration compensates for disturbance variables in a measurement pickup which has a measured-variable dependent resistance that is added from a fundamental resistance, which is independent of measured variables, and a measuring resistance, which is dependent on measured variables. The fundamental resistance and the measuring resistance are disturbance variable-dependent in opposite directions. A bridge circuit has two measurement pickups using difference evaluation to eliminate the disturbance variable dependency of the fundamental resistance. A bridge voltage controller sets the bridge diagonal voltage in the opposite direction to the disturbance variable dependency of the measuring resistance, and thus compensates for the disturbance variable-dependency of the measuring resistance.

Abstract: A method and apparatus for controlling temperature stability of an inductor by using a magnetically coupled metallic object is disclosed in which a metallic object is magnetically coupled to the inductor by a magnetic field emanating therefrom. In one embodiment, the apparatus is tailored for use in a proximity probe of a machine monitoring system and includes the metallic object magnetically coupled to a sensing coil for controlling a resistance versus temperature profile including compensating for a proximity effect resistance of the coil.

Abstract: A nondestructive method for inspecting steel pipelines for plastically deformed regions caused by mechanical damage to the pipeline. The invention is a method and system that uses nonlinear harmonic detection methods to detect mechanical damage in pipelines. The invention uses a time-varying magnetic field to sense magnetic properties of the pipeline. The odd-numbered harmonic frequencies are detected and their amplitudes are related to the magnetic condition of the material under test to determine areas of mechanical damage. This technique can be used for rapidly surveying stress states in pipelines where nonlinear harmonic sensing devices are attached to a pigging device moving through a pipeline at a relatively high rate of speed.

Abstract: A magneto-impedance element comprises an alloy composed of at least one of Fe, Co and Ni. The alloy has a mixed texture of an amorphous phase and a fine crystalline phase having an average crystal grain size of 50 nm or less. The magneto-impedance element shows a change in impedance in response to an external magnetic field by applying an alternating current. The magneto-impedance element is applied to an azimuth sensor, an autocanceler, or a magnetic head.

Abstract: The method for measuring magnetic properties of sheet material is able to deliver reliable signals at both low and high magnetic particle density in the sheet material. First a measuring head converts the magnetic properties of the sheet material into electric signals. The electric signals produced by the measuring head are amplified in a certain signal range such that the lower-amplitude electric signals produced by the areas with low magnetic particle density of the sheet material are amplified to a greater extent than the electric higher-amplitude signals produced by the areas with high magnetic particle density of the sheet material. For this purpose the signal range is divided into at least three ranges which are each amplified constantly. The amplification in the two outer ranges is selected equal, and the amplification in the middle range greater than the amplification in the outer ranges.

Abstract: A flux gate inductor responsive to an external magnetic field produced by a rotating magnetoelastic sleeve and oscillating voltage applied to the flux gate inductor induces a field in the flux gate inductor, for inducing current flow through the flux gate inductor, which flows through a shunting resistor, creating a voltage which is triangular as a result of the inductance of the flux gate. The sum of the induced and external fields exceeds the saturation flux density of the flux gate, causing the flux gate inductance to zero. This results in a rise in the current through the flux gate inductor and a voltage spike across the shunt resistor. The spike is detected for causing a change in an inverter for producing the oscillation voltage. Meanwhile, the external magnetic field causes an asymmetry between positive, negative currents required to saturate the flux gate inductor. This asymmetry results in a departure of the oscillation voltage from a 50% duty cycle.

Abstract: A cancellation circuit removes interfering signals from desired signals in electrical systems having antennas or other electromagnetic pickup systems. The cancellation circuit provides amplitude adjustment and phase adjustment to electrical signals induced in an electrical system by received electromagnetic signals. The amplitude-adjusted and phase-adjusted signals are combined to cancel the effects of electromagnetic interference. In an electromagnetic receiver, a plurality of receiver elements provide the cancellation circuit with different proportions of desired and interfering signals to enable removal of the interfering signals. An electromagnetic-wave transmitter having multiple transmitter elements is provided with a cancellation circuit for canceling electromagnetic signals in at least one predetermined region of space.

Abstract: A cancellation circuit provides active electromagnetic shielding for canceling inductive noise in electrical circuits caused by electromagnetic flux. The cancellation circuit includes amplitude-adjustment and phase-adjustment circuits for adjusting the amplitude and phase of electrical signals, and a combining circuit for combining electrical signals such that the effects of electromagnetic induction cancel. An electromagnetic pickup is provided with a cancellation circuit for canceling its response to electromagnetic flux. An electromagnetic drive coil is provided with a cancellation circuit for canceling electromagnetic flux in a predetermined region of space, and a compensation circuit compensates for frequency-dependent phase and amplitude variations in electrical pickup signals and transmitted electromagnetic flux. The cancellation and compensation circuits may be combined to provide a device that can simultaneously transmit and receive electromagnetic radiation.

Abstract: A closed loop Hall effect current transformer in which the Hall effect device has an input resistance which varies with its operating temperature. The Hall effect device is driven by a fixed voltage passing through a current limiting a resistor with variations in voltage across the resistor being indicative of the operating temperature of the device. Further, variations in the input resistance of the device caused by variations in its operating temperature is corrected for by mixing a correcting signal with the outputted signal from the device, said correcting signal being derived from a voltage signal taken across the resistor at the driving input of the device.

Abstract: A detector for a magnetic field having a low frequency compared to background EMF and having a magnitude approximately 1,000 times less than the EMF, the detector comprising: a pickup coil for capturing the magnetic field and the background EMF; an integrator coupled for receiving a signal having respective components representative of the magnetic field and the background EMF, the integrator having a time constant such that successive positive and negative polarity portions of the component representative of the background EMF cancel out one another in the integrator, but the component representative of the magnetic field results in a net output signal from the integrator, the net output signal being indicative of the magnitude of the magnetic field; and, a magnetic field strength output indicator responsive to the net output signal from the integrator, whereby the magnetic field can be detected with great sensitivity notwithstanding the background EMF.

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

Abstract: An electronic circuit for automatically compensating for errors in the output signal of a displacement sensor. The electronic circuitry includes an analog to digital converter for converting an analog output signal from a linear displacement type sensor. The digital output signal from the sensor is processed by a microcontroller which automatically compensates for errors in the output signal. Ideal values, stored in an electronic memory, are used for compensation.