Abstract: A compact hand-held metal detector that detects small ferrous and non-ferrous metal objects, that has a detection pattern in three planes, and that includes a plurality of detection alarm indications including visual, audio, and tactile detection alarm indications is provided. The invention includes a single small detection coil combined with an electronic control circuit that permits the coil and associated electronic components to be mounted adjacent each other in a compact enclosure. The coil provides a spherical detection pattern that is active in all three planes which detects metal objects in any orientation with respect to the coil. Upon detection of a metal object, the detector provides a visual and audio or tactile alarm indication.

Abstract: An integrated circuit for measuring the distance houses an oscillator in a package. Further, a plane inductor is provided on the surface of the package housing the oscillator. The plane inductor is connected to the oscillator so as to specify a frequency of the oscillator. If conductive material approaches the surface of the package, the frequency of the oscillator is varied by means of the plane inductor. The approaching distance of the conductive material is detected by detecting the frequency of the oscillator. The conductive material is mostly metal, however, the integrated circuit for measuring the distance can measure the approaching distance of non-metal conductive material such as conductive liquid.

Abstract: The present invention relates to a digital oscillator comprising an oscillator (40), a counter (41), a memory (42), a digital-analog converter (43) and a low-pass filter (44). The memory is able to directly store a complex signal, rendering the use of a real time calculating unit unnecessary.

Abstract: A device and method is provided for sensing an object or vehicle in proximity to a sensing zone, wherein the device is exposed to an environment temperature. The object sensing device comprises a sensor, such as an inductive loop having a characteristic, such as the inductance of the inductive loop, responsive to the proximity of the object is to the sensor; a signal generator, such as an oscillator, coupled to the sensor for producing a first periodical signal cycling at a first frequency dependent on the sensor characteristic and the environment temperature.

Abstract: A proximity sensor includes a transducer and a circuit having a switch that changes state in response to a presence of an object in spaced relation to the transducer. The transducer includes a magnetic form defining a generally planar surface facing a sensing zone of the sensor. The magnetic form includes a side surface that extends away from the sensing zone and an internal cavity that opens outwardly toward the sensing zone. A sensing coil is positioned within the magnetic form cavity. The transducer additionally includes a sensor housing supporting the sensing coil and the magnetic form in relation to the sensing zone. A non-ferrous metal shield is positioned inside the sensor housing to surround at least a portion of the magnetic form and enhance a sensing range of the proximity sensor. The shield has an edge that faces the sensing zone located substantially co-incident with the generally planar surface of the magnetic form.

Abstract: A universal inductive proximity detector including an oscillator, whose oscillating circuit is powered by a current source. A fixed frequency master oscillator 16, which controls the current source 18, is coupled to the oscillator 10 so that the current source excites the oscillating circuit with a pulsed direct current.

Abstract: In a method for measuring a distance between a conducting reaction track and a functional surface moving relative to the reaction track a sensor with two signal transmitters is provided on the functional surface. An alternating field is generated in the sensor. The alternating field changes as a function of the distance between the conducting reaction track and the functional surface. Each of the two signal transmitters detects the changes of the alternating field as distance information. Each signal transmitter produces decoupled distance information values. These decoupled distance information values are processed in separate distance measuring channels to provide processed signals. The processed signals are constantly fed to and compared in a comparator. A distance information signal is emitted only when the processed signals of the separate distance measuring channels are identical within a predetermined tolerance range.

Abstract: A computer-based automated method to detect and identify features in digital point-ordered signals. The method is used for processing of non-destructive test signals, such as eddy current signals obtained from calibration standards. The signals are first automatically processed to remove noise and to determine a baseline. Next, features are detected in the signals using mathematical morphology filters. Finally, verification of the features is made using an expert system of pattern recognition methods and geometric criteria. The method has the advantage that standard features can be, located without prior knowledge of the number or sequence of the features. Further advantages are that standard features can be differentiated from irrelevant signal features such as noise, and detected features are automatically verified by parameters extracted from the signals. The method proceeds fully automatically without initial operator set-up and without subjective operator feature judgement.

Abstract: Apparatus is disclosed for detecting the presence of the type of debris in a fluid system. The apparatus detects the presence of debris, measures the accumulation and identifies the specific types of the debris. A plurality of sensors, connected in a bridge detecting circuit, are assembled in the apparatus in the fluid flow, each of said sensors are tuned to a specific preselected frequency which is characteristic of one material type of the debris. A variable frequency power supply is connected to the detecting bridge for exciting the bridge. Switching means are provided external to the detecting apparatus for selecting one of said sensors as the detecting leg of the bridge. When the sensor has been selected, the bridge is excited at the resonant frequency of the selected sensor for identifying a specific material type of the debris.

Abstract: A shaft position detection device for detecting a certain position on a shaft comprising: a movable shaft including a detection portion to be detected, a characteristic of which is different from the other portions; a position detection coil to which the movable shaft is freely inserted; an inductance detecting means for detecting changing of inductance between a case of the movable shaft being in the position detection coil and a case of the movable shaft being out of the position detection coil; in which a position of the detection portion in response to the changing of the inductance. The difference of the magnetic characteristic is defined by a cross section area of the shaft, winding a magnetic tape, forming a magnetic layer.

Abstract: A device and method for passively activating an inductive loop vehicle sensor. The sensor has an inductive loop in a roadway that produces an electro-magnetic field and utilizes the changes caused by the interaction of a detectable vehicle with the field to activate it. The device includes at least one metallic foil having sufficient area and thickness to cause changes sufficiently similar to changes caused by a detectable vehicle to activate the sensor when said foil is placed within the electro-magnetic field. The method includes providing such a device and deploying the device in a plane substantially parallel to the roadway and within the field of the loop.

Abstract: An improved sensor includes an inductor coil which is formed about a central axis. The inductor coil is configured to provide a magnetic field radially outwardly of the central axis. The monitor circuit monitors changes in the impedance of the coil, to in turn provide an indication of the amount of metal mass radially outwardly of the sensor. The monitor circuit is set to be triggered at a particular amount of metal mass, which would in turn be tailored to the particular application. In one desired application, the sensor is utilized to detect the presence of a nut in a metal plate. Metal plates as are typically utilized with vehicles will often include a number of holes which are to receive nuts. If the nuts are not received in the holes, then that particular metal plate should not be further assembled into the product. One widespread use of such a technique is with the assembly of vehicle bodies. The side sensor will detect the presence of a nut in the hole when positioned within the bore of the nut.

Abstract: The invention relates to an electric circuit for measuring the length of a shock absorber unit of a vehicle, comprising: a coil with windings which are fitted around the shock absorber unit, of which a casing of electrically conducting material connected to a part of the wheel suspension of the vehicle is axially movable relative to the coil when there is a change of length of the shock absorber unit as a result of a change in the force absorbed by the wheel suspension; an oscillator connected to the coil, for exciting the coil with an excitation signal of a predetermined frequency; and processing means which are connected to the coil and are designed for determining the value of a relation between the voltage across the coil and the current through the coil, which value is a measure of the length of the shock absorber unit.

Abstract: In one aspect of the present invention, an apparatus for detecting particles within a fluid is disclosed. A bobbin defines a debris collection chamber. Spaced apart first and second coils are wound about the bobbin in the proximity of the debris collection chamber, wherein the inductance of the coils are responsive to the particle accumulation within the collection chamber. An electromagnet is wound about the second coil to attract ferrous particles into the proximity of the second coil. A reference coil is wound about the bobbin to compensate for the changing temperature of the fluid. An oscillator is coupled to the first, second and reference coils for selectively producing an oscillating waveform at a frequency that induces eddy currents in the particles. The frequency of the oscillating waveform is indicative of the amount of accumulation of both the ferrous and non-ferrous particles.

Abstract: In one aspect of the present invention, an apparatus for detecting particles within a fluid is disclosed. A bobbin defines a debris collection chamber. A first coil is wound in a helix about the bobbin in the proximity of the debris collection chamber, wherein the induction of the first coil is responsive to the particle accumulation within the collection chamber. A reference coil is wound in a helix about the bobbin to compensate for changing fluid temperature. An oscillator is coupled to the first and reference coils for selectively energizing the coils with an oscillating waveform at a frequency that induces eddy currents in the particles. The frequency of the oscillating waveform is indicative of the amount of accumulation of both the ferrous and nonferrous particles.

Abstract: Electromagnetic actuators having a coil and an armature are used in a number of applications in which it is useful to have an indication of the position of the armature with respect to the coil without the use of external sensors. Accordingly, an actuator control system is provided for determining the position of the armature with respect to the coil in response to the current magnitude and frequency of current flowing in the coil.

Abstract: A test device for vehicles has a wheel rotation speed sensor which is sensitive to magnetic fields. The test device, having a wheel rotation simulation device, contains a sensor stimulating magnet coil, which can be positioned in the magnetic field region of the sensor such that a magnetic field coupling is provided. A control unit, drives this magnet coil with an AC voltage at a frequency which determines the wheel rotation speed. This allows the performance of functional tests of components which are sensitive to wheel rotation speed while keeping the wheels stationary. In addition, a compact roller unit, which is preferably transportable, is provided in order to carry out actual wheel rotations in order to make it possible to test further components, such as the brake system or electronic transmission control.

Abstract: A device for detecting a bending magnitude of a rotary shaft comprises a first pair of coils spaced from and facing the outer surface of a shaft and having an inductance value, and a second pair of coils spaced from and facing the outer surface of the shaft and connected in series to the first pair of coils at respective nodal points. The second pair of coils has an inductance value different from the inductance value of the first pair of coils. A pair of high frequency oscillators applies a high frequency voltage across the first and second pairs of coils to generate at each of the nodal points an output signal corresponding to a bending magnitude of the shaft, each output signal having a constant linearity characteristic resulting from the difference in inductance value between the first and second pairs of coils. An amplifier is connected to each of the nodal points for amplifying the output signals from the nodal points.

Abstract: In an inductive debris monitor (IDM) an inductive probe is disposed at a fluid flow passageway to be monitored, and an RF bridge containing a variable resistance network is used to detect changes in the impedance of the probe due to the passage of metallic debris. An indirectly heated thermistor is utilized in the resistance network for balancing the bridge. Thus the operating temperature range is significantly extended without compromising reliability or experiencing degradation.

Abstract: A counter is provided for measuring counting transitions of an oscillator having an inductor in a frequency determining circuit. The inductor is at least in part air-cored and has a port therein for admitting a sample diamond for testing. First, the oscillations are up counted over a precise time interval with no sample present, and then a sample diamond is placed into the pont to change the frequency of the circuit by an amount related to the quantity of ferromagnetic material in the sample diamond. Thereafter, a down count is performed for the oscillations with the sample diamond in place over a second time interval equal to the first interval. The difference in the up counts and the down counts is determined and displayed in a digital readout as a measure of the degree of likelihood of the sample being synthetic.

Abstract: A method and apparatus for performing conductance measurements on a sample using an eddy current probe, without the need for measurement or knowledge of the separation between probe and sample. The probe comprises sense and drive coils mounted in close proximity to each other (or a single coil which functions as both a sense and drive coil), circuitry for producing AC voltage in the drive coil, and a meter for measuring in-phase and quadrature components of induced voltage in the sense coil. Look-up table data can be generated for use in subsequent measurements on samples of unknown conductance by performing eddy current measurements on samples having different known conductances to generate reference lift-off curves, processing the reference lift-off curves to determine a conductance function relating each known conductance to a location along a selected curve, and storing conductance values determined by the conductance function for different points on the selected curve as the look-up table data.

Abstract: A method for quantifying the permeability or conductivity of a conducting material, comprises the steps of providing a circuit including an inductor with a coil and a capacitor connected in parallel to the inductor, the coil having an interior space adapted to enclose the sample material therein; inserting the sample material into the interior space of the coil to completely enclose the sample material therein; resonating the circuit with the capacitor with capacitance C' with the inserted sample material at a resonant frequency f.sub.0 and measuring the resulting impedance, Z' of the circuit; measuring the impedance of the loaded circuit at various frequencies above and below the resonant frequency f.sub.0, and plotting a first bell-shaped curve from the measured impedances against frequencies; resonating the circuit with the capacitor with capacitance C' at a resonant frequency f.sub.x with the sample material removed from the coil and measuring the resulting impedance, Z.sub.

Abstract: A debris detecting apparatus is provided which collects debris from a fluid system in a screen member and measures the accumulation of debris by measuring the change of inductance in a coil surrounding a portion of the screen member. A bridge detection means is used which includes the inductive coil as one leg of the bridge. A second sensor in the fluid connected as a second leg of the bridge provides temperature compensation for the bridge. The bridge is excited with a high frequency voltage at or near the resonant frequency of the sensing coil.

Abstract: An inductive proximity sensor has a resonant circuit including a sensing coil and driven by an oscillator at a predetermined frequency. To sense selectively ferrous and non-ferrous objects, the excitation frequency is a subcritical excitation frequency and discriminator logic is provided to process a phase-shift signal and a damping signal.

Abstract: A proximity sensor includes a coil for sensing metal objects which are part of an oscillatory circuit and an oscillator which drives the oscillatory circuit at a constant frequency. A tuning device is connected in parallel with the oscillatory circuit. The tuning device is a variable gain amplifier with feedback via an inductive or capacitive impedance.

Abstract: A reference value used in a vehicle detector is checked and adjusted. The vehicle detector determines the speed of a vehicle which it has detected and then makes a sample measurement after the vehicle has left the detection area of its inductive sensor. The timing of the measurement is based on the speed of the vehicle. The sample measurement is compared to the reference value, and adjustment of the reference value is made accordingly. In order to identify the cause of changes in the sensor drive oscillator signal frequency, the frequency of the oscillator signal is measured while connected to a dummy sensor not affected by vehicles. The reference value also is adjusted to reflect slow changes (drift) in sensor drive oscillator frequency. To identify changes in sensor drive oscillator frequency caused by mechanical difficulties which require maintenance activity to correct, a rate of frequency change of the sensor drive oscillator signal is determined over the plurality of measurement scanning segments.

Abstract: In order to improve a sensor for detecting an electrically conductive or netizable object with an oscillator comprising a resonant circuit including an inductance and a capacitance, the resonant circuit impedance depending on a damping distance between the inductance and the object and rising steeply in the range of small damping distances, further rising less steeply in the range of medium damping distances and substantially having a constant value in the range of large damping distances, and a closed adaptive loop stage supplying a loop current for the resonant circuit and generating a course of an amplitude value dependent on the damping distance, and an evaluation circuit detecting an oscillator voltage applied to the resonant circuit, such that the oscillator also oscillates in the range of small damping distances and has a characteristic curve, with which the oscillator voltage varies with the damping distance also in the range of small damping distances, it is suggested that the course of the amplitude

Abstract: An electrical conductivity tester accurately measures the time-varying electrical conductivity .sigma.(t) and steady-state electrical conductivity .sigma..sub.ss, of a test material. In a first embodiment, the transmission phase of a probe circuit is monitored to determine the conductivity of a test material. In the first embodiment, an oscillator circuit generates a reference oscillator signal. A probe circuit receives the reference oscillator signal, magnetically couples to the test material, and modifies the reference oscillator signal via electromagnetic induction to derive a modified transmission phase signal. Finally, a phase detector circuit derives a transmission phase signal by combining the reference oscillator signal and the modified transmission phase signal, the transmission phase signal being directly convertible to the conductivity. In a second embodiment, an amplifier is connected to the probe circuit to form an oscillator circuit.

Abstract: A proximity switch circuit including first and second transistors Q4, Q6 connected as a long tail pair with an inductive sensing circuit LC connected to one leg thereof and an emitter follower circuit Q7, Q8 connected between said one leg and the base of the transistor of the other leg, whereby an oscillator circuit can be provided which is non-critically damped to enable faster speed of operation of the proximity switch.

Abstract: A coin analyzer system includes a coin detecting sensor having a body defined by a magnetic core with spaced apart sides to define there-between an air gap that is large enough to position any size coin which may be deposited. A coil that is magnetically coupled to the core generates a uniform magnetic flux through the air gap from one side to the other so that the positioning of the coin in the air gap is not critical. A return path is provided in the core for returning the magnetic flux to the one side from the other side and thereby completing the magnetic circuit. The arms surrounding the coin sensing region define facing surfaces which converge outwardly from the bite portion in order to produce a uniform magnetic circuit reluctance for all portions of the facing surfaces. The core may be divided into two core portions separated by a secondary air gap in the return path with a pair of coils provided, one magnetically coupled with each of the core portions.

Abstract: To screen or test the electrical properties of HEMT-like wafers for their quality, the critical layer qualities of a wafer (16) are evaluated by measuring its conductivity (sigma or s) and mobility (mu or m) at upper and lower temperatures, which need only be sufficiently different as to remove uncertainties in the test data but, in practice, are room and liquid nitrogen temperatures. Novel equations show (1) that the crucial quality or merit factor (n.sub.s) the electron sheet density of two-dimensional electron gas (2DEG), can be determined by measuring the total layer conductivity (sigma or s) at the lower or liquid nitrogen temperature and mobility (mu or m) at the upper or room temperature and (2) by measuring overall layer effective mobility (mu or m) at both room and liquid nitrogen (the upper and lower) temperatures to provide a means to measure the value of the 2DEG density, n.sub.s which has better accuracy then where the temperature of mobility is only made at room temperature.

Abstract: An apparatus for sensing a target characteristic, such as relative distance between the apparatus and target, target thickness, target material, or lateral position between the apparatus and the target, includes a coil for directing an electro-magnetic field at the target. A voltage controlled oscillator energizes the coil at a resonant frequency which is functionally related to the target characteristic. The coil has an effective impedance value at resonance functionally related to the target characteristic. A frequency monitor measures the resonant frequency. An impedance monitor determines the impedance value when the drive frequency is at the resonant value. A PROM or controller determines the target characteristic in response to the measured resonant frequency and the determined impedance value. The PROM or controller provides a signal responsive to the determined target characteristic.

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: An inductive debris monitor for detecting chip-particles in tubing of a fluid wetted system. The inductive debris monitor includes a multi-turn detector and an electronic circuit having a resistor bridge configuration. The multi-turn probe detector wraps around the tubing of a fluid wetted system a plurality of times to detect the presence of the chip-particles while the electronic circuit analyzes and deciphers the detected chip-particle information.

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: A coin testing apparatus is provided in which two oscillating magnetic fields interact with a coin and these interactions are monitored to test for the acceptability and/or the presence of a coin. The fields are associated with respective inductive coils which have a common core so arranged that not more than a minor proportion of the field of one coil interacts with the other coil. In a preferred embodiment one of the two coils encircles the other, which provides a very compact two-field coin sensing arrangement. In some embodiments one coil encircles the other but they have respective core elements.

Abstract: A coin analyzer system includes a coin detecting sensor having a body defined by a magnetic core with spaced apart sides to define there-between an air gap that is large enough to position any size coin which may be deposited. A coil that is magnetically coupled to the core generates a uniform magnetic flux through the air gap from one side to the other so that the positioning of the coin in the air gap is not critical. A return path is provided in the core for returning the magnetic flux to the one side from the other side and thereby completing the magnetic circuit. The arms surrounding the coin sensing region define facing surfaces which converge outwardly from the bite portion in order to produce a uniform magnetic circuit reluctance for all portions of the facing surfaces. The core may be divided into two core portions separated by a secondary air gap in the return path with a pair of coils provided, one magnetically coupled with each of the core portions.

Abstract: An inductive type proximity switch (S) includes an open-ended loop (L3) adjacent to the inductor (L1, L2) of the parallel resonant circuit of its main (LC) oscillator. A high speed bistate switch (S1) is connected between the ends of the loop (L3). A pulsed input to the switch (S1) causes sequential making and breaking of a connection between the ends of the loop (L3) whereby the loop (L3) functions as a Faraday shield to inhibit mutual inductive linking of the inductor (L1, L2) with an inductor (L4) of a passive (LC) resonant circuit (L4, C4) of a target (T) when the target (T) is in proximity with the proximity switch (S) and the connection between the ends of the loop (L3) is made by the bistate switch (S1).

Abstract: A determination is made whether a minimum threshold period (or frequency) change has occurred in an oscillator signal indicating the initial presence of a vehicle over an inductive sensor. The change in period of the oscillator signal is measured over each of a plurality of frame segments. A magnitude of period change in the oscillator signal is recorded. If the number of frame segments that occur between detection of the threshold change in period and the magnitude change in period is less than a predetermined number, the detector does not make a speed measurement calculation. If the number of frame segments equals or exceeds the predetermined number, the time rate of change of the period of the oscillator signal is estimated. A vehicle detector calculates a sensor entry distance for a particular vehicle. A vehicle entry time is calculated by dividing the magnitude of period change by the rate of period change. Speed is then calculated by dividing the entry distance by the vehicle entry time.

Abstract: The invention relates to a temperature-stable transistorised tuned-circuit oscillator. Provided for the purpose of temperature stabilisation of the tuned-circuit voltage is a transistor T2, which is thermally coupled to the tuned-circuit coil L and controls a current source Q in the circuit of the oscillator L, C1, T1, in such a way that temperature-induced variations of the data of the tuned-circuit coil L are compensated.

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: Apparatus and method for noncontact, radio-frequency shielding current characterization of materials. Self- or mutual inductance changes in one or more inductive elements, respectively, occur when materials capable of supporting shielding currents are placed in proximity thereto, or undergo change in resistivity while in place. Such changes can be observed by incorporating the inductor(s) in a resonant circuit and determining the frequency of oscillation or by measuring the voltage induced on a coupled inductive element. The present invention is useful for determining the critical temperature and superconducting transition width for superconducting samples.

Abstract: An inductive proximity switch contains an oscillator that generates an alternating magnetic field and which, when a trigger penetrates the alternating field, changes its oscillating state. An evaluation circuit uses the change in state to generate a switching signal to control a load switch. To achieve a proximity switch response distance that is as large as possible regardless of the trigger material and the ambient temperature, two sensing coils are located in the alternating field to detect the difference between voltages induced in them. The sensing coils are designed so that the alternating voltage differential becomes zero at a desired response distance. When the alternating voltage differential is zero at an input of oscillator amplifier, the oscillator abruptly changes its oscillating state. The change in oscillation state is detected by the evaluation circuit and converted into a binary switching signal for the load switch.

Abstract: A temperature sensor has a body whose thermal expansion is evaluated in the event of a change in temperature, there being deposited on the body a layer which has a layer structure containing less than 8% by weight of phosphorus, preferably containing up to 3% by weight of phosphorus, up to 2% by weight of an element of main group IV or main group V, in particular antimony, and up to 5% by weight of a transition metal element, in particular cobalt. The percentages by weight resulting from the sum being increased up to 100% with nickel. The layer modifies the magnetic flux in a coil arrangement comprising at least one coil. This change in the magnetic flux in the coil arrangement is evaluated and the change in the magnetic flux being detected as a change in the inductance. The change in length of the body and the change in temperature are deduced therefrom.

Abstract: A method and apparatus for measuring the temperature and heating rate of a workpiece during the induction heating cycle by inducing and detecting a plurality of eddy current pulses at varying frequencies during a short power interruption to the induction coil and correlating the pulses to generate a workpiece profile which is compared to a reference profile to determine whether to reject the inductively heated workpiece.

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

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

Abstract: A vibration detector for sensing imbalance of a part in a balancing machine uses an eddy current proximity detector for sensing vibration movement of a portion of the machine. To prevent spurious signals due to magnetic fields varying at the part rotation frequency, a mu-metal can is secured to the vibrating portion of the machine, an electrically conductive coupon is attached inside the can for vibrating movement therewith, and the proximity detector is spaced from the coupon by a small gap for producing AC signals representing the vibration amplitude.

Abstract: Method and apparatus for non-destructively monitoring the thickness and uniformity of electrically conductive coatings (12) that have been deposited upon optical waveguide fibers (10). The monitoring may be performed while coated fiber (22) is at rest or while it is in motion. Physical contact with fiber (22) is not required. Monitoring is accomplished by feeding coated fibers (22) through an inductive coil (24) while simultaneously measuring an electrical value that is dependent upon the electrical resistance of conductive coating (10) then passing through inductive coil (24). The electrical value measured for a given section of coated fiber (22) becomes indicative of the coating thickness and uniformity of the coating about optical waveguide fiber (10) by correlating the electrical value measured with previously measured electrical values generated by coated fibers having coatings of known thicknesses and having no bald spots or other non-uniformities.

Abstract: A magnetic detection device including at least one oscillator circuit having a magnetoresistance element which converts a change of magnetism detected into a digital signal and a comparator for comparing the digitalized oscillating frequency of the oscillator circuit with another digitalized oscillating frequency generated from another oscillating circuit by taking a ratio thereof or by detecting a phase difference between the pulse signals. Utilizing the magnetic detection device, the amount of change of magnetism can be stably detected with a high accuracy within a wide range of ambient usage temperatures.Also, a physical quantity detection device including the magnetic detection device which can detect any physical quantity with a high accuracy.