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

Abstract: The content of even harmonics is used in both a method and apparatus for the detection of the disturbing static and quasi-static magnetic fields effects in measurement systems using force and torque transducers operating with magnetoelastic effect. The even harmonic content corresponds to the degree of static and/or quasi-static magnetization and is an input signal to a regulator the aid of the direct current in, for example, a separate winding, reduces the static and/or quasi-static magnetization to zero.

Abstract: In a scanning head position sensing method and apparatus, a plurality of distinct electromagnetic signals are transmitted from a corresponding plurality of transmitter sites surrounding a central position on one side of a web of material. The signals are transmitted through the web and are received by an electromagnetic energy sensor on the opposite side of the web of material. The electromagnetic energy sensor is positioned to receive approximately equal signal energies from all the transmitters when the energy sensor is positioned substantially opposite to the central position across the web. The transmitters and the sensor are fixedly positioned relative to the first and second sensor heads such that the relative positioning of the heads is determined by combining the signals with one another.

Abstract: Eddy current probes for detecting defects in a ferromagnetic tube are disclosed. The probe uses partial magnetic saturation and includes two or more eddy current measuring coil assemblies in a probe housing. The coil assemblies are spaced apart from each other and located at positions of different magnetic saturation.

Abstract: An apparatus is provided for measuring a very weak magnetic field generated by a human body, etc. External magnetic noise components coming from other magnetic sources and existing around an object whose magnetic field is to be measured are detected by compensation coils of the apparatus. The compensation coils are oriented in multiple dimensional directions. The detected noise components are weighted and added to each other to correctly find the noise components. Thereafter, the noise components mixed in the objective very weak magnetic field are removed, thereby correctly measuring the very weak magnetic field.

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: An electromagnetic position and orientation detector. A determination is made by a calculator of the position and the orientation of a mobile sensor as a function of the coupling coefficients measured between each of the coils of the sensor and each of the coils of a transmitter. These measurements are tainted with errors due to the imperfections in gain of the various elements of the transmission and reception channels. To eliminate these errors, a stationary sensor is used whose coupling coefficients with the coils of the transmitter are measured to serve as a reference to correct the coupling coefficients between the coils of the transmitter and of the mobile sensor.

Abstract: An apparatus for measuring a carburized portion occurring in inside of a tubular article, the apparatus comprising a first detecting unit having opposite magnetic poles of a first magnet arranged in parallel to an inspecting face of a case made of nonmagnetic material and a magnetism detector disposed at an intermediate portion between the poles, a second detecting unit having opposite magnetic poles of a second magnet arranged perpendicular to the inspecting face of the case and a magnetism detector provided for one of the poles of the second unit, and a data processing circuit for processing the output signals from the first and second detecting units to produce a difference signal.

Abstract: Permeameter suited for measuring permeability of a small, non-magnetic (i.e., the permeability value is close to 1) object. The probe of the permeameter is of the differential transformer type with an exciting coil and two detecting coils placed at both ends of the exciting coil. The difference in the outputs of the detecting coils is analyzed and the effect of the eddy current is effectively eliminated, whereby the signal representing the permeability of the object is extracted from the difference signal by the phase shift analysis. By reducing the distance between the two detecting coils, the influence of the disturbance of the eddy current at the boundary of the object sample is minimized and the permeameter can measure a small object sample without sacrificing accuracy and sensitivity.

Abstract: A circuit configuration for contactless detection of the rpm of a rotating gear wheel includes two identical firmly mounted and magnetically prestressed Hall sensors being mutually spaced apart by a center distance equal to one-half the tooth pitch of a gear wheel whose rpm is to be detected. Each of the Hall sensors includes at least one pair of identical Hall generators having signal paths and being driven with an impressed control current or impressed control voltage. Voltage/current converters are each coupled to the signal path of a respective one of the Hall generators and each have an output. An evaluation circuit links together the outputs of the voltage/current converters connected to one of the Hall sensors and the outputs of the voltage/current converters connected to the other of the Hall sensors in phase opposition.

Abstract: A transformer and method for sensing displacement, A linear variable displacement transformer (LVDT) 50, 100, 150, 200, and 250) is disclosed with respect to several embodiment,s each including a core (52, 102, 152, 202, and 252) having a primary leg (56, 104, 154, 204, and 254), and two secondary legs (58 and 60, 106 and 108, 158 and 160, 206 and 208, and 258 and 260). A primary coil (54, 110, 156, 210, and 264) is disposed on the primary leg, and secondary coils (62 and 64, 112 and 114, 162 and 164, 212 and 214, and 266 and 268) are disposed on the secondary legs. Pole pieces (70 and 72, 120 and 122, 170 and 172, 222 and 224, and 274 and 276) are disposed in gaps between the primary leg and each secondary leg, so that they control the reluctance to a magnetic flux produced by an electric current flowing thorugh the primary coil.

Abstract: A position detecting apparatus detects the position of an object and includes a sensor device which outputs first and second AC detection signals which have a predetermined phase relationship and which correspond to a detected position of the object. An instantaneous value detecting unit detects and outputs instantaneous values of the first and second AC detection signals. A DC component detecting unit processes the instantaneous values to obtain first and second DC components of the first and second AC detection signals, respectively. A position calculating section calculates the position of the object based on a difference between the first DC component and the first AC detection signal, and a difference between the second DC component and the second AC detection signal.

Abstract: A resistor formed in the same epitaxial layer of semiconductor material in which a Hall element is formed is used to provide a temperature dependent voltage source which is inversely proportional to the resistance of a temperature sensitive load resistor on the Hall element output. A current mirror circuit is used to apply a current proportional to the current through the epitaxial layer resistor to the load resistor so that the voltage across through the load resistor varies in a direct relationship with the sensitivity of the Hall element.

Abstract: A toroid turns counter for a toroid with at least one winding with turns to be counted by electric counting device connected to said winding having a test winding with an opening for receiving the toroid, a movable contact arm for electrically closing the opening after the toroid has been received in the opening, an activating arrangement which is coupled to the contact arm, and controls coupled to the activating arrangement for controlling the closure of the contact arm.

Abstract: Eddy current probes for detecting internal defects in a ferromagnetic tube are disclosed. The probe uses a plurality of eddy current measuring means, each being operated at a different operating point on the impedance diagram. By operating more than one such eddy current measuring means simutaneously, noises by, for example, permeability variation of a ferromagnetic material and internal magnetic deposit, can be made less influential.

Abstract: A foreign matter detector includes an oscillator for generating an oscillating signal, a phase shifter connected to the oscillator and adapted to provide a phase shifted oscillating signal, and an electromagnetic transducer. The transducer includes an excitation coil connected to the oscillator and two interconnected detection coils magnetically coupled to the excitation coil and adapted to produce a differential signal therebetween when an object is passed through the transducer. The detector also includes a first detector adapted to produce a first detected analog signal corresponding to the component of the differential signal in phase with the oscillating signal and a second detector adapted to produce a second detected analog signal corresponding to the component of the differential signal in phase with the phase shifted oscillating signal.

Abstract: The damping of a coil (L1) can be influenced by an object (1) so that the high-frequency voltage at the coil (L1) depends on the distance (a) of the object (1) from the coil (L1). A constant dc current is superimposed on the high-frequency current through the coil, the dc voltage drop at the coil (L1) which corresponds to the dc resistance of the coil (L1), damping the coil (L1), being influenced by the temperature. The high-frequency excitation (5, 6) of the coil (L1) is controlled by the dc voltage drop in order to compensate for the influence of the temperature on the high-frequency voltage so that the high-frequency voltage depends solely on the distance (a). The high-frequency voltage, having a nonlinear correlation to the distance (a), is linearized in a nonlinear member (15) with a semiconductor element with respect to the distance (a). In this connection, the effect of the temperature on the linearization is compensated for by means of a second semiconductor element.

Abstract: For measuring the rotational speed of a wheel is an antilocking protected vehicle brake system a rotational speed sensor is provided in which in accordance with the rotational speed of the wheel signals are electromagnetically induced which have an amplitude and frequency which increase regularly with the rotational speed. When due to error sources the amplitude of the induced signal does not increase with the frequency of the signal a rotational speed measured value is determined by means of the measured amplitude, i.e. not on the basis of the measured frequency. To avoid erroneous measuring signals it may likewise be provided that when the amplitude of the signal does not increase with its frequency the last measured value of the frequency of the induced signal at which the amplitude still increased with the frequency is used to determine the speed of rotation.

Abstract: The detector of metalliferous objects comprising an electrically coupled to an alternating voltage generator driving loop, rigidly fitted to two pairs of receiving loops, positioned at opposite sides of the driving loop, coaxial and parallel to one another. The receiving loops are connected to connected in series balancers, differential amplifiers, electric signal compensators with the control inputs thereof connected to the generator, selective amplifiers, data processors, logic OR gate, and signalling unit.

Abstract: A foreign matter detector includes an oscillator for generating an oscillating signal, a phase shifter connected to the oscillator and adapted to provide a phase shifted oscillating signal, and an electromagnetic transducer. The transducer includes an excitation coil connected to the oscillator and two interconnected detection coils magnetically coupled to the excitation coil and adapted to produce a differential signal therebetween when an object is passed through the transducer. The detector also includes a first detector adapted to produce a first detected analog signal corresponding to the component of the differential signal in phase with the oscillating signal and a second detector adapted to produce a second detected analog signal corresponding to the component of the differential signal in phase with the phase shifted oscillating signal.

Abstract: A biomagnetometer measures the magnetic field produced by the brain as a result of a visual stimulus delivered by a display device such as a cathode ray tube (CRT). The output signal of the biomagnetometer is filtered to remove noise introduced by the operation of the display device itself, such as the repetitive scan signal of the CRT, and the CRT monitor is otherwise operated from DC power to minimize periodic variations that can interfere with the detection of brain signals. The filtering is preferably accomplished using a comb-notch filter. Cancellation coils and shielding are also preferably used to remove a portion of the noise introduced by the display device.

Abstract: Circuit arrangement for a gradiometer with super conducting quantum interferometer (SQUID) for measuring low-intensity biomagnetic fields. In the circuit arrangement a modulated output voltage that is proportional to a measured magnetic field is supplied to an analog-to-digital converter for digitization and quantization, a modulated output signal of the analog-to-digital converter serving as a digital measured signal.

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 circuit for processing a high frequency output signal from a variable reluctance transducer, this signal including an unwanted low frequency component, comprises a comparator having a first input receiving the transducer signal and a second input receiving the same transducer signal but via a low pass filter. The comparator therefore provides an output representing the high frequency variations in the transducer signal and substantially unaffected by the low frequency component. Alternatively, the transducer signal may be applied to a circuit providing a first output signal varying as the low frequency component and also providing a second output signal varying as the high frequency variations in the received transducer signal, the first output signal being used as a feedback control which tends to render the second output signal free of low frequency variations.

Abstract: A microprocessor-controlled electronic coin chute is designed for use in a coin telephone station and adapted to operate over an extended temperature range while making coin acceptance/rejection decisions that are both rapid and accurate. Within the coin chute are a pair of coin quality sensors designed to measure a different property of a coin such as composition and size. Each coin quality sensor comprises a series-connected pair of coils placed on opposite sides of the coin path. These coils are part of an oscillator circuit having a maximum frequency when the coin is positioned between them, and an idle frequency otherwise. Idle frequency measurements are made each time an associated telephone switchhook is operated. The measured idle frequency serves as a temperature indication which, together with a stored program, is used by the microprocessor to establish acceptability limits for each coin in an allowed set.

Abstract: The present invention is an inspection instrument of the type which reacts to induced eddy currents in a workpiece to be inspected and includes a probe having at least a first probe coil. The instrument further includes a bridge circuit having the first probe coil connected in a first bridge arm. The bridge circuit also has input and output terminals. Connecting cable connects the instrument to a remote signal interpretation unit, and individual buffers connected between each of the output terminals and the cable isolate the capacitive of the cable from the bridge circuit.

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: 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: Apparatus for measuring the number of turns on a toroidal coil includes a conductive member adapted to receive the coil to be tested; circuitry for energizing the coil to be tested including an oscillator and coupler circuitry connected in circuit between the oscillator and the coil energizing terminals; and circuitry connected to the conductive member including a comparator having first and second inputs and an output. Circuitry responsive to the connection of the conductor member in circuit applies a reference voltage signal to a first input of the comparator; circuitry responsive to the voltage induced in the conductive member by the energized toroidal coil to be tested applies a signal proportional to the induced voltage to the second input of the comparator; and circuitry responsive to the output of the comparator stabilizes the voltage applied from the oscillator to the toroidal coil when the input signals to the comparator are equal.

Abstract: A highly accurate, predictable and stable magnetic voltage and/or current reference that is substantially impervious to potentially hazardous radiation including neutrons, single or multiple particles, ionizing doses, particle beams and the like. The magnetic reference includes a stable permanent magnet which functions as a primary magnetic reference and generates a magnetic field. A magnetic field detector, comprising a second harmonic null detector (or fluxgate), senses the magnetic field generated by the magnet. A fed back current applied to control windings of the magnetic field detector cancels the magnetic field generated by the magnet and, in so doing, produces an AC error signal. This AC error signal is processed by an electronic control amplifier which provides the current that is fed back to the magnetic field detector.

Abstract: A magnetic speed sensor air gap fault-detection arrangement having a two-input AND gate for each of the two-axle trucks of a railway vehicle for conditioning a gap process circuit common to each axle. Each of the gap process circuits of each axle is activated to provide a logical "1" output to an associated two-input AND gate. The associated two-input AND gates each outputs a logical "1" to a respective gap counter circuit when the axle rate reaches a predetermined value. The respective gap counter circuits count the logical "1's" and activate an associated gap fault check circuit to reset the respective gap counter circuit and to display an error code and to output a logical "1" signal to the dynamic diagnostic apparatus.

Abstract: An arrangement which eliminates or reduces the negative influence of small variations in the charge-carrier concentration of a semiconductor material upon the longterm stability of a magnetic field sensor such as a Hall element is disclosed. In an illustrative embodiment, the arrangement comprises a magnetic field sensor, a voltage/current converter which provides a supply current to the magnetic field sensor, an amplifier connected sequentially downstream of the voltage/frequency converter, and an analog/digital or voltage/frequency converter connected sequentially downstream of the amplifier. The amplifier provides a transmission ratio which is proportional to (1+.delta.n/n) or (1-.delta.n/n) where n is the carge-carrier concentration of the semiconductor material in which the magnetic field sensor is formed and .delta.n is a variation in time of the charge-carrier concentration n.

Abstract: A pair of permanent magnets adjoining each other and magnetized with opposite polarities are coupled with a movable object through a connecting shaft so that the pair of permanent magnets are aligned in a direction of displacement of the movable object. A first and a second Hall element is disposed stationary at a position opposing to the pair of permanent magnets and aligned also in the direction of displacement of the movable object with a predetermined space interval between the first and second Hall elements. When the movable object is displaced in one direction, and hence the pair of magnets are moved from a neutral position at which the boundary of the pair of magnets corresponds to the center of the interval of the first and second Hall elements, output voltages of different phases are respectively generated by the first and second Hall elements.

Abstract: An eddy current testing device for inspecting test objects, for example billets, with respect to surface defects, for example surface cracks, comprises at least one transducer/sensor, for example a surface transducer or surface transducer arrangement, which is made to scan the surface of the test object. The device is characterized in that the effect of harmless surface blemishes on the testing device is suppressed, at least partially, by compensating for the sensitivity characteristic, in the scan direction of the transducer/sensor, with respect to the surface defect.

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. Means are provided for compensating for temperature and other non-linear effects including other inductive fields, environmental changes and the like. The system incorporates an L-C resonant circuit connected between the output of an oscillator and the input of an operational amplifier.

Abstract: In a system for detecting stray metal in an article, the article passes through an alternating magnetic field generated from a coil. The magnetic field is detected by coils which generate induced voltages and the difference between the induced voltages is applied to a tuning and phase-shift circuit. An output signal having a phase, generated from the tuning and phase-shift circuit, is detected by a detector and the peak level of the detected output signal is held in a peak hold and comparing circuit. A plurality of the peak levels are stored in a memory circuit and are processed by a CPU to determine the preferred phase of the output signal. The tuning and phase-shift circuit is so switched as to apply the preferred phase to the output signal.

Abstract: A magnetic field compensating apparatus having a plurality of compensating units comprising a plurality of serial coils each of which is disposed concentrically along the main magnetic field and symmetrically with regard to a plane perpendicular to the main magnetic field and a plurality of power sources which separately supply currents to these compensating units, and made in such a manner that a plurality of error magnetic field components are generated by each of the compensating units, a compensating magnetic field is obtained by the whole of a plurality of the compensating units, and each of the currents supplied to the compensating units is decided in accordance with a constitution of a corresponding compensating unit.

Abstract: A device for detecting irregularities in the surface of an object comprises at least one transducer which is movable relative to the surface of the object and an associated signal-processing unit which receives and processes output signals generated by the transducer. The signal-processing unit includes two electrical circuits, the first circuit providing a signal A which is derived from the output signal from the transducer and the second circuit including an analog shift register to provide a signal B which is derived from the output signal from the transducer and which is time delayed relative to signal A. The signal-processing unit also includes means for combining signals A and B to provide a measuring signal C.

Abstract: A device for accurately detecting and monitoring the position of an object inside biological tissue, particularly an endotracheal tube inside a patient's throat, comprising a circuit which generates an electromagnetic field of limited width and depth, and which is disturbed by the presence of material having a high magnetic permeability such as a metal band on the distal end of such an endotracheal tube, but which is otherwise stable and not affected by temperature or other such factors. Included in the invention is a probe for generating the electromagnetic field, which probe is insensitive to temperature changes.

Abstract: An improved non-contact type pattern sensor includes a magnetic resistor element arranged facing a pattern track on a recoridng medium having a magnetized pattern in the pattern track. A clearance sensor is arranged to face the pattern track on the recording medium and generates a detection signal as a function of the distance between the clearance sensor and the pattern track. The control unit connected to the clearance sensor generates an output signal which varies as a function of the detection signal. A magnetic field generator connected to the control unit is arranged near the magnetic sensor element and generates a bias magnetic field whose intensity varies as a function of the output signal.

Abstract: A magnetic circuit is coupled with a primary conductor in which flows the current to be sensed. The magnetic circuit has an air gap with a magnetic field detector and is coupled with a measuring coil producing a magnetic flux for compensation the flux generated by the primary current. The necessary current in the measuring coil to achieve such flux compensation is a measure for the primary current. A yoke part of high magnetic permeability is arranged in the vicinity of the air gap inside the measuring coil so as to form a magnetic shunt between the two magnetic circuit portions forming the air gap.

Abstract: A railroad track segment simulator for assessing track signal susceptibility to electric power line interference including a circuit including a series dc resistor, a series inductor, and an inductive network representing characteristic impedance of an electrical R-L transmission line, resistor, inductor, and network being serially connected as a series circuit, a first ballast resistance connected between one end of series circuit and a ground potential, and a second ballast resistance connected between another end of series circuit and a ground potential. The impedance of the segment is expressed as: ##EQU1## where: f=frequency (hz),r.sub.o =effective radius of rail at power line ac frequencies=0.09 m for 132 lb/yd rail,R.sub.dc =dc resistance per kft of track,j=imaginary number,Ln=impedance per track segment.A plurality of segments can be serially connected to simulate any length of line.

Abstract: A transient electromagnetic method for detecting irregularities on container walls by measuring wall thickness. The method utilizes a transmitting antenna and a separate receiving antenna arranged in a loop-loop configuration. The transmitting antenna induces current into the container wall and the receiving antenna and the receiver detect the decay of the induced current, which is then analyzed to detect wall thickness. A receiving antenna array of many receiving antennas is used to increase the spatial resolution. Simultaneous measurement of the induced current by the receiving antennas reduces noise that is coherent across the array. Use of a noise antenna located so as to be unaffected by the transmitting antenna further reduces noise. The received signal from the receiving antenna array is displayed on a two-dimensional display in a spatial arrangement that corresponds to the spatial arrangement of the receiving antennas.

Abstract: A wire loop of almost negligible inductance is coupled with the excitation and receiver coils of metal object detection apparatus which is opened and closed to produce signals in phase with noise signals produced by poorly conductive soils. Enhanced suppression of noise signals is achieved.

Abstract: A compensation winding for improving the linearity of a displacement transducer. The displacement transducer is the type having an electrically conducting non-ferromagnetic wall which moves in telescoping relation with the coil and is excited by a signal at a sufficiently high frequency that skin effect on the wall permits displacement of the wall to vary the reluctance of the coil flux path and thereby vary its inductance proportionally to displacement of the wall. The compensation winding is wound in telescoped, coaxial relationship to the coil in a fixed position. The compensation winding has a pitch which is a decreasing function of the distance from the end of the coil which is nearest the wall when the wall and the coil are in their least overlapping relationship.

Abstract: This invention relates to a method for nondestructive inspection (NDI) of mposite materials comprising conductive fibers. The depth of broken fiber damage in nonmetal matrix composites such as graphite/epoxy and carbon/carbon materials may be ascertained and eddy current inspection is extended to include thick metal sections by this method. Inspection is possible with access limited to a single surface.

Abstract: This invention relates to a method and device for measuring the resistivity f materials. In particular, the methods measure resistivity in carbon fiber reinforced composites as well as any materials with a relative magnetic permeability of 1. The measurement may be made with access restricted to a single side of the material under test.

Abstract: A plurality of speed-sliding compensation amount functions are stored in a sliding compensation amount data memory and one of these functions is selected in response to input of a selection signal. In the selected function, sliding compensation amount data corresponding to the speed of the object of positioning is read out. At least one of current position data and positioning target position data of the object is corrected by the read out sliding compensation amount data. A brake signal is generated on the basis of comparison of the current position data and target position data which have been subjected to this correction and a positioning control of the object is performed by this brake signal. On the other hand, a sliding amount detection circuit is provided for detecting sliding amount of the object from generation of the brake signal until actual stop of the object.

Abstract: A dual speed sensor pickup assembly (140) for sensing the rotational velocity of two independently rotatable, closely axially spaced exciter rotors (116 and 118) is provided. The pickup assembly includes two speed sensor assemblies (136 and 138) each including a pole piece (152,160) having a longitudianl axis (152a,160a) with the longitudinal axes skewed relative to one another but radial relative to the common axes of rotation (24) of the exciter rotors. Each speed sensor includes a permanent magnet (154,162) disposed between an end of the pole piece (152,160) and having a face divided into first and second surface (154a,154b and 162a,162b) by a slot (154c,162c) therein. In one embodiment a primary coil (156,164) and a secondary or anti-cross talk coil (158,166) surrounds the pole piece of each sensor (136,138), and each secondary coil is conductively connected to the primary coil of the other sensor.

Abstract: An apparatus and method for measuring physical characteristics of an electrically conductive material by the use of eddy-current techniques and compensating measurement errors caused by changes in temperature includes a switching arrangement connected between primary and reference coils of an eddy-current probe which allows the probe to be selectively connected between an eddy current output oscilloscope and a digital ohm-meter for measuring the resistances of the primary and reference coils substantially at the time of eddy current measurement. In this way, changes in resistance due to temperature effects can be completely taken into account in determining the true error in the eddy current measurement. The true error can consequently be converted into an equivalent eddy current measurement correction.