Abstract: A device to detect the presence of particles, principally metallic particles, in fluid lines. The fluid to be sampled flows through a former on which is wound a coil assembly comprising a sensor coil flanked upstream and downstream by two field coils. The former is constructed with a double wall and air gap such that pressure fluctuations in the fluid are not transmitted to the coil assembly to adversely affect the positions and readings of the coils. The field coils are driven by a high frequency signal derived from a crystal oscillator and the upstream and downstream sections are wound in opposite directions such that the magnetic field from each section is cancelled out in the plane of the sense coil.

Abstract: In order to improve product quality control through quantitative determination of a defect and quantitative judgement of the quality of a product, an alternating current is applied to a standard product coil into which is inserted a standard object, and to a test object coil into which is inserted a test object, and eddy currents are measured by means of a bridge circuit. If the test object coil is at a location removed from a flaw, the bridge circuit output voltage is zero, while if the test object coil is at the location of the flaw, a predetermined voltage is output. A determination of torsional breakage torque of the shaft inspection is carried out by correcting the output voltage for dependence on the cross sectional area ratio of the test object relating to the cross sectional area of the coil and for the influence of flaw size depending on the location.

Abstract: A linear Hall circuit that utilizes a single-ended output Hall current to sense a magnetic field so as to measure the magnetic field strength. A first operational amplifier configured as a transresistance amplifier converts the output Hall current of a Hall device to an output voltage. To avoid inducing a bias-based nonlinearity in the output Hall current, a second operational amplifier, having two resistors connected to both bias electrodes of the Hall device, respectively, is used to inject feedback Hall currents in them. The average value of the bias currents is then kept from varying with the output Hall current of the Hall device.

Abstract: An object detecting device for detecting an object at least partly having a magnetic substance or magnetic-flux permeable material is formed of a detection coil arrangement including a primary coil for generating magnetic flux and a secondary coil disposed separately from the primary coil at a predetermined interval for receiving the magnetic flux from the primary coil; and a detection circuit for detecting an increase of the magnetic flux transmitted to the secondary coil due to presence of the object within a space between the primary and secondary coils. The detection circuit produces signal indicating the presence of the object upon detection of the presence.

Abstract: A detection and processing circuitry of a magnetostriction type torque sensor is disclosed. An alternating current voltage signal Vo is generated and output from an oscillator. A shift circuit shifts a phase of the AC voltage waveform of the oscillator by 1/4 period and outputs the phase shifted voltage to a detector. The detector modulates the inverted voltage signal Va on the basis of the phase shifted voltage signal and an integrator integrates the detector output voltage in a time range from (.alpha.-.pi./2) to (.alpha.-3.pi./2). Thus, the output voltage signal Vd from the integrator indicates a resistance value of an imaginary part, i.e., inductance of the impedance of the detection coil of a magnetostrictive shaft of the torque sensor which is not dependent on the change in a temperature.

Abstract: A system and method is provided for aligning a scanning surface of an inspection probe relative to a workpiece surface under inspection. The probe preferably includes at least three alignment eddy current elements, each producing a respective spacing indication electrical signal in accordance with a spacing between each alignment eddy current element and the workpiece. The system further comprises processing means which receives each spacing-indication electrical signal so as to generate data indicative of the relative alignment between the scanning surface of the probe and the workpiece surface. A controller is responsive to the alignment data for aligning the probe such that in operation the scanning surface thereof is substantially parallel relative to the workpiece surface. The probe can include inspection eddy current elements, in which case the alignment and the inspection eddy current elements can be fabricated to form an integral eddy current inspection probe.

Abstract: Device to detect surface faults in a hot metallic bar or wire rod (11) travelling at speeds up to 130 meters per second, the device comprising upstream and/or downstream rough alignment lead-in means (38), in which device are included first coils (29) and at least one pair of second coils (13) coaxial with the first coils (29), the first coils (29) generating an alternating magnetic flow which causes on the surface of the bar (11) parasitic currents that generate in the second coils (13) a magnetic feedback flow, the first (29) and second (13) coils defining a measurement assembly (12), at least two measurement assemblies (12) being included and having their lengthwise axis able to move from an open position defining an intake hole (15), in which the various lengthwise axes coincide substantially with the nominal axis of the feed of the bar (11), to an inspection position defining a resulting inspection hole (15R), in which inspection position the lengthwise axes are substantially parallel to the nominal axis

Abstract: For improved offset compensation, a Hall sensor is provided with a device for orthogonally switching the Hall detector supply current and the Hall-voltage taps. A summing device determines an offset-compensated Hall-voltage value from first and second predetermined Hall-voltage values. The Hall-voltage values are formed by means of a Hall detector containing at least first and second Hall cells for offset-voltage precompensation. The first and second Hall cells are identical and are orthogonally switchable. The geometrical orientation of the first and second Hall cells includes an angle other than 0.degree. and 180.degree..

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: A method and apparatus for nondestructively detecting a flaw such as a hairline crack or defect within a conductive object to be inspected. Surface flaws can be distinguished from deep flaws. The pulse duration of the pulse voltage induced in the secondary coil of a sensor is measured at two separate time instances. At one time instance, the pulse duration is affected by variations in the distance between the sensor and the object but is not affected by the flaw. At the other time instance the pulse duration is affected by said variations and also by the flaw. The effect of said variations is cancelled, using these two measured pulse durations. Only a signal correctly indicating the flaw is extracted to detect the presence of the flaw.

Abstract: A speed or torque probe comprises a permanent magnet havings its north-south axis extending radially of a bladed rotor, so that the tips of the blades pass in close proximity to one pole of the magnet, and a T-shaped pole piece. A first portion of the pole piece, corresponding to the upright portion of its T-shape, extends tangentially of the rotor, with its free end in contact with the other pole of the magnet, while the other portion of the pole piece, corresponding to the cross-piece of its T-shape, again extends radially of the rotor. As a result, the magnet, the first portion of the pole piece and the half of the other portion nearer to the rotor form a variable magnetic circuit, such that the passing rotor blades induce eddy currents in a first coil wound upon the half of the other portion of the pole piece nearer to the rotor.

Abstract: Disclosed are methods for processing and interpreting data acquired from an eddy current probe array inspection system, based on a background subtraction technique. Test and reference waveform data sets are acquired, and subsequently combined. However, the data sets are first normalized and registered to the same position, registering on characteristic signals produced when scanning over edges. Specific techniques are disclosed for normalizing, correcting for spatial offsets, determining the actual locations of edge signals by peak detection and correlation, and adjusting for variations in the number of points in the test and reference data sets.

Abstract: An improved eddy current probe array having means to compensate the entire array for varying different element liftoff, is described. An array consisting of a plurality of sense elements and means for compensating these sense elements is scanned across an inspection surface to produce respective scan responsive signals wherein the scan responsive signals of the sense elements are proportionately normalized or calibrated against the scan response of said compensating means during routine signal processing of the array signals in order to compensate for any lift off experienced by the sense elements. Array lift off compensation is attributable to sense element design cooperating with at least one lift off compensating sense element and a method of normalization/calibration performed during signal processing of the array signals.

Abstract: An interface circuit for connecting a signal source [10], such as a variable reluctance sensor, to a digital circuit [20] such as a microprocessor. A comparator [40] generates a logic signal [at 49] indicating whether the signal from the source is greater than or less than the signal's average value. The inputs to the comparator are connected across a pair of back-to-back diodes [44,46] which are serially connected with a current limiting resistor [42] between the source and the output of an operational amplifier [35] which generates an average value voltage. The operational amplifier's output is directly connected to its negative input so that it exhibits unit gain, and the operational amplifier's input is connected to the sensor voltage by a low-pass filter [32,34] so that amplifier responds only to the DC content of the sensor's output signal.

Abstract: In a magnetic inspection method and apparatus, a magnetizer (4) is provided such that a pair of magnetic poles (4a, 4b) face an object (10) to be inspected. A magnetic field is generated by the magnetizer (4) in the object (10). A magnetic sensor (7a) is situated at a substantially middle point of a line connecting the magnetic poles (4a, 4b) or a line parallel to this connecting line. Shield bodies (22a, 22b, 23a, 23b) with a low coercive force are arranged on those sides of the magnetic sensor (10) which face the magnetic poles. The magnetic sensor (7a) detects a leakage magnetic flux due to an internal or surface defect of the object (10). In addition, the distance (2A) between the shield bodies (22a, 22b) is 2.2 times or more, and 2.8 times or less, the distance (L) between the magnetic sensor (7a) and the object (10).

Abstract: A switched-magnetization closed-loop magnetometer having a magnetoresistive bridge for sensing external magnetic fields. The output signal from the bridge to an amplifier, is magnetically nulled by a feedback coil. Each of the bridge elements have a magnetic easy axis that is periodically and magnetically flipped by a reset coil. The output of the amplifier goes to an analog switch and an integrator in one or the other order. The output of the analog switch or the integrator may go on to a sample and hold circuit, or other sampling device, that alternately samples the output to it in synchronism with the reset coil. The output is processed by a low pass amplifier. A clock provides signals to the reset coil, the analog switch and the sample and hold switch.

Abstract: A magnetic sensor for the collection and measurement of ferrous particles through the use of an electronic tuned circuit is disclosed. The sensor contains an electrical inductance coil along with an integral magnet to attract ferrous particles suspended in the fluid. The ferrous particles collecting on the magnetic surface of the sensor causes a change in the inductance of the integral coil which is measured by an electronic circuit. The electronic circuit operating in conjunction with the sensor utilizes a series resonant circuit. A measurement of the voltage across the series resonant circuit is responsive to changes in temperature of the inductance coil. A microprocessor is used to determine the change in period of the resonant oscillation with change in inductance of the coil. The microprocessor uses the data on temperature variation to correct the observed change in oscillator period for the effects of temperature.

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: In a method and with a circuit for compensating for the temperature of inductive sensors having at least one coil from the inductance of which an output variable is formed as measure for a physical variable to be measured, a variable which is dependent on the resistance of the coil is measured and used for correction upon the forming of the output variable.

Abstract: A device for evaluating periodic signals from inductive pick-ups compensates for the lag of the pick-up signal. This lag increases with increasing frequency as a consequence of the inductance of the pick-up, with respect to the position of a movable part that is to be scanned by the said pick-up. The relative time shift in the evaluation edge of the pick-up signal, which is phase-compensated via the frequency, is compensated for via changes in the amplitude of the pick-up signal.

Abstract: An eddy current imaging system includes an eddy current sensing coil positioned proximate a workpiece for scanning the workpiece to produce a signal indicative of the integrity of the workpiece for regions in an x,y array of data. Such a signal may be a complex impedance signal representative of the amplitude and/or the phase of the signal. Two data processing techniques are disclosed for enhancing the display of a flay in the workpiece. The first includes the step of calculating a spatial derivative of the amplitude and/or phase indicative signal from the coil and providing an image of the spatial derivative to produce a C scan of the spatial derivative. The second includes the steps of determining the regions of maximum ascent and/or descent of the signal for regions in the scan and calculating an impedance plane trajectory from the data array of path points for displaying a reconstructed optimum signal independent of path pattern.

Abstract: A SQUID measurement apparatus for detecting weak magnetic field signals that change over time such as from a biomagnetic field source includes at least one measurement channel, a SQUID, and a superconductive flux transformer disposed in front of the SQUID that includes at least one detection loop for receiving the weak magnetic field signals. The apparatus also includes at least one connection conductor coupled to the detection loop and electromagnetically shielding for at least the at least one connection conductor of the flux transformer. The shielding includes at least one superconductive shielding element that extends in a direction substantially parallel to the at least one connection conductor and substantially equidistant from the at least one detection loop. The shielding element has a discontinuity at a separation point in a region of the detection loop.

Abstract: A method and system includes digitally linearizing a digital output signal originating from a magnetoresistive sensor by detecting the digital output signal originating from the magnetoresistive sensor. A linearization factor is then correlated to the digital output signal. Then, the digital output signal is modified the linearization factor to linearize the digital output signal.

Abstract: A coin detection apparatus is disclosed which is particularly suitable for low power applications. The coin detection apparatus utilizes a detector coil as part of a resonant circuit. The resonant circuit with no coin present in the detector coil has a damped impulse response. When a coin is present within the detector coil, the damping of the impulse response of the resonant circuit is increased. Periodic generation of an impulse input to the resonant circuit and measurement of the resulting impulse response enables the presence of a coin within the detector coil to be ascertained.

Abstract: Edge position determination of metallic materials by means of evaluation of the voltages which are induced in coils located at the edges of the material below the material and partially covered by the material as well as coils located inside of the first-mentioned coils in the transverse direction of the material, which latter coils are completely covered by the material in connection with a decaying magnetic field which is generated by the same coils.

Abstract: A thin film magnetometer includes first and second thin film magnetoresistive elements and first and second thin film laminated flux collectors. The first magnetoresistive element is located in a gap formed by the flux collectors, and the second magnetoresistive element is subtantially magnetically shielded by the flux collectors, and acts as a thermistor. The magnetoresistive elements are connected in a bridge circuit whereby any signal component due to thermal effects on the magnetoresistive elements is removed from the signal produced by the first magnetoresistive element.

Abstract: In a non-destructive method for the detection of surface cracks in metals, an eddy current is induced in the surface region of a workpiece under test, at a frequency sufficiently high to generate an alternating magnetic field solely in the skin region of the workpiece. That alternating surface magnetic field is interrogated by means of a relatively small electro-magnetic induction sensor, having regard to the overall area of the induced magnetic field. The sensor provides a voltage output which is analysed, preferably in real time, to yield an indication sensor. Also described is a probe for performing such a method.

Abstract: In a preferred embodiment, an inductor excited by a square-wave alternating current to produce a magnetic field in the inductor. A member movable in proximity to the inductor causes losses in the magnetic energy, which losses are directly related to the position of the member with respect to the coil. In another aspect of the invention, there is provided an inductor excited by an alternating current and a moving member which includes a ferromagnetic core having disposed thereon a thin sleeve of high resistivity material. In a further aspect of the invention, there is provided an inductor excited by an alternating current and a moving member, the excitation circuit including an oscillator having a positive temperature coefficient of frequency.

Abstract: A direct-current electromagnetic device for nondestructively detecting localized discontinuities in ferromagnetic objects is disclosed. The device comprises an adjustable dc excitor means, a magnetic flux injector means, an external magnetic field detector means, a plurality of position sensors, a signal processing means and a control means. It is particularly adapted for detecting flaws in soiled and distorted ferromagnetic objects such as water wall tubes in industrial boilers. An apparatus incorporating the device and a method of detecting discontinuities are also disclosed.

Abstract: The disclosure relates to devices for the measurement of signals in the field of wideband phenomena. More precisely, a device is disclosed for the processing of electrical signals coming from a derivative type of sensor designed to measure an electrical or magnetic field, currents, surface charges or other derivative variables, said processing including the computation of the primitive of the part of said signal having a spectral frequency higher than a low frequency f.sub.1, the device comprising:means for the electronic integration of said signal, from a frequency f.sub.2 higher than said low frequency f.sub.1 ;compensation means amplifying and integrating said signal between the frequencies f.sub.1 and f.sub.2. FIG. 2 .

Abstract: A system for processing signals produced by magnetic flaw detection apparatus having facility for examining objects in the course of transport thereof at speeds varying from a prescribed slow speed to a prescribed high speed, with transport frequency thus being within a first frequency range. The system comprises first circuitry for detecting the speed of transport of an object under examination and generating output signals indicative of the detected speed and extending over a given characteristic range correspondingly with the first frequency range. Second circuitry is provided for receiving the first circuitry output signals and transforming the same into a second frequency range substantially expanded as compared to the first frequency range.

Abstract: Method and apparatus for determining the nature or property of a non-metallic material in which the material is passed through a time varying magnetic field. The signals which are induced in the sensing coil for the magnetic field are processed for measurement. Although the material is non-metallic, it may have sufficient conductivity at the frequencies employed to cause the flow of eddy-currents to generate a measurable signal. The method of the invention also provides for measurement of permittivity or diamagnetic properties of the material which may also give rise to small measurable signals.

Abstract: A system and method for noiseless measurement of a biomagnetic field uses magnetic field magnitude and gradient measurement at a reference point together with mathematical extrapolation techniques to provide an effectively infinite order gradiometer response from a lower order physical gradiometer. Such a system has the advantages of potentially lower cost, higher accuracy, and easier adjustment and balancing.

Abstract: A rotary head for scanning the surface of elongated test materials (62) by eddy current transducers (60) is additionally provided with means for magnetization of the test material (62) over an intended test range making it now possible to achieve sensitive testing of non-bare ferromagnetic bars and wires, testing for "smeared cracks" where surface has closed above the material separation, and testing of welded austenitic pipes. For the magnetization, parts of the housing (10) as well as a rotating hollow shaft (40) are employed in the conduction of magnetic flux, and special measures are taken for the homogenization of the magnetic field in the test range.

Abstract: An eddy-current defect test instrument with a rotary head (30) and test probes (32, 34, 36, 38) offset-mounted along a circular track (66) with only one distance probe (40) to achieve compensation for variations in spacing between the probes and the workpiece which only requires one distance signal processing device (60) and only one rotary transmitter (100). This is accomplished by storing the control signals obtained from the distance probe during one revolution of the rotary head (30) and retrieving those control signals associated with the probe position and appropriately modifying a defect signal.

Abstract: Apparatus for measuring flaws in an object, such as a tube, having both an erratic motion, e.g. a back and forth oscillation, and a net axial motion has an idler wheel engaging the tube, and a digital rotary shaft encoder attached to the wheel. A POP circuit is coupled to the encoder. A pair of coils disposed around the object make up the active elements in an eddy current bridge. An ADC is coupled to both the bridge and POP circuit and corrects the signal from the bridge for motion complications. A method for doing same comprises sensing only the net motion of the object, detecting flaws in the object, providing an erratic motion complicated flaw signal, and correcting the flaw signal for the erratic motion.

Abstract: A high pressure proximity sensor for high pressure environments uses a balanced bridge variable inductance magnetic core structure to detect the presence of a external ferrous object by a change in inductance. The sensor magnetic flux path is defined by the sensor's specific geometry which includes core windings on the core and a sensor housing. The core includes a center post of a nonmagnetic material to transfer stress from a housing sensor face to the core's symmetric axis to cancel the effect of an external pressure induced stress on the sensor. The center post is encircled by an elastomer barrier between the housing sensor face and an adjacent end of the internal core to prevent migration of an internal potting compound between the core end and the sensor face. This structure provides satisfactory sensor operation in environments imposing shock and vibration on the sensor as well as high external pressures.

Abstract: An embodiment comprises a generator constituted by a quartz crystal oscillator and programmable frequency dividers; a power amplifier providing a periodic excitation signal, of squarewave form; two coils electromagnetically coupled to a metal part to be tested; and measuring means comprising two synchronous detectors for measuring the real part and the imaginary part of the difference between the complex impedances of the coils. The frequency stability of the generator effects an improvement in the accuracy of the impedance measurements, when these measurements are made at different frequencies. For application to non-destructive testing of metal parts by eddy currents, at different frequencies.

Abstract: Methods and validation apparatus for achieving improved acceptance and rejection for coins, bills and other currency items. One aspect includes modifying item acceptance criteria by creating and defining three-dimensional acceptance clusters, the data for which are stored in look-up tables in memory associated with a micorprocessor. A second aspect involves fraud prevention by temporarily tightening or readjusting item acceptance criteria when a potential fraud attempt is detected. A third aspect relates to minimizing the effects of couterfeit items such as slugs on the self-adjustment process for the item acceptance criteria. A final aspect relates to calculation of a relative value of the acceptance criteria in order to conserve memory space and minimize computation time.

Abstract: A coin validator includes improved compensation circuitry for compensating for ambient conditions such as temperature or the presence of metallic objects, includes a path (1) for passage for coins under test, sensor coils (2, 3, 4) which form an inductive coupling with coins under test during their passage along the path, detectors (DM1, ADC) responsive to the impedance presented by the coil in the absence of a coin, for producing an ambient condition signal which is a function of an ambient condition such as temperature of the presence of metallic objects a controller (MPU 17) responsive to the inductive coupling between a coin travelling along the path past the coil, for providing signal which is a function of a characteristic of the coin, and a microprocessor (MPU) for modifying operation of the controller in dependence upon the ambient condition signal.

Abstract: A meter (10) for measuring extremely-low-frequency radiation includes a coil circuit (22) whose output is filtered by a sharp-cut-off high-pass filter (24) to pass standard house-current frequencies but suppress the frequency components that would predominate as a result of movement of the meter with respect to the earth's magnetic field. An integrator (26) compensates for the frequency response of the coil circuit (22), an RMS circuit (35) converts the signal to its root-mean-square value, and a display circuit (28) provides a display determined by the resultant signal.

Abstract: An RF oscillator induces eddy currents to be measured in an object. An eddy current probe senses alterations, such as teeth on a disc, for example, in the object which are represented as eddy current signals sensed by an eddy current probe. The present invention separates alteration current signals from offset currents in the eddy current signal to aid in discriminating levels in the alteration current signals. The alteration currents are separated from the offset currents by AC coupling with a high pass filter or separated by a microprocessor as part of a data processing detection routine.

Abstract: Apparatus for measuring hysteretic properties of thin film recording disks is provided which comprises a magnetic field generator for magnetizing a spot on a piece of magnetic material to be tested. The magnetized spot is moved past a stationary Hall effect sensor which detects the magnetic flux being emitted from the magnetized spot. The process of magnetizing and detecting the flux emitted from the same spot is repeated at different magnetization levels to provide a set of automatic measurements that are recorded in a memory of a controller processor. An analysis of the recorded data permits the automatic computation of residual flux, remanent coercivity, switching field distribution as well as other hysteretic properties.

Abstract: A device is provided for measuring unwanted electric and magnetic field induced voltages in a test lead of a remote measurement sensor. A test lead is encased within a magnetic shielding conduit and is electrically connected to a remote sensor. Another electrical lead, identical to the test lead and also encased within the magnetic shielding conduit, is terminated by a short circuit in the vicinity of the sensor. This electrical lead travels through the same environment as the test lead on its way to the measuring equipment. Electro-magnetic field interference along the path of this electrical lead is an indication of the electro-magnetic field interference along the path of the test lead.

Abstract: A coin testing apparatus has a sensor outputting a detected signal corresponding to a deposited coin, a determinator for determining the value of the detecting signal, a discriminator for discriminating the authenticity and type of the coin by comparing the determined value with a coin acceptance range defined by maximum and minimum reference values, an initializor for initializing the coin acceptance range and memory for renewing the coin acceptance range by adding a predetermined value to or subtracting the predetermined value from the maximum and minimum reference values, respectively, when the practical determination range varies. Since the coin acceptance range is automatically corrected by the operation even if there is a variation in the range of the detected signal due to a drift of an electronic circuit or by variation in temperature, a correct and precise determination can be achieved.

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: A probe comprises a magnet and a Hall element which are provided in a magnetically impermeable case. The Hall element is disposed at the midportion between the two poles of the magnet in parallel with the lines of magnetic force. The presence of a carburized portion in the member to be inspected and the depth of carburization are detected by passing d.c. current across the Hall element and detecting the Hall effect electromotive force produced between the two ends of the element which are opposed in a direction perpendicular to the direction of flow of the current.

Abstract: A small diameter proximity coil for use in proximity sensors to sense imbalance in rotating machinery which has a coil of less than 0.3 inch diameter is constructed of a silver/palladium alloy of 89% silver and 11% palladium. This provides for, because of the inherent balancing out of AC and DC resistance changes, temperature errors of less than 10% over a wide temperature range of operation.

Abstract: A magnetometer having only a single coil winding for sensing the magnetic field along a single axis. Functionally, the invention comprises an oscillator, an integrator, and a voltage-controlled current source. The oscillator uses a saturating inductor which also serves as the magnetic-field-sensing element. The inductor is driven with a positive voltage and when the current through the inductor exceeds a value which indicates that the core is saturated, the driving voltage switches to an equal-magnitude negative value. This negative drive is maintained until the current again indicates the core to be saturated, at which point the driving voltages switches back to the positive value. With no externally applied field, the inductor current averages to a zero value. An externally applied field helps the core saturate in one direction and hinders it in the other, resulting in a change in average inductor current.