Abstract: A magnet position detector, particularly for implantable medical devices, has a resiliently supported coil, a current source delivering a current to the coil and a detecting device for detecting the movement of the coil in a magnetic field when fed with an electric current from the current source. The coil has a core with a non-linear B-H curve and the current source is a pulse source delivering current pulses with at least one positive and one negative side. The detecting device detects the movements of the coil in opposite directions respectively excited by differentiated signals respectively corresponding to the leading and trailing edges and permits the magnitudes of the respective, oppositely directed movements to be compared to each other, thereby indicating the position of a source of the magnetic field, relative to the coil, to be determined.

Abstract: A plurality of magnetic field members are provided, each for selectively generating a time-varying magnetic field for combination into a o time-varying composite longitudinal magnetic field with magnetic flux lines which are substantially aligned with the central longitudinal axis of the cylindrical ferromagnetic member. Additionally, a traverse magnetic field member is provided which selectively generates a time-varying traverse magnetic field with magnetic flux lines which are substantially traversed to the central longitudinal axis of the cylindrical ferromagnetic member. The plurality of magnetic field members and the traverse magnetic field member are maintained out of contact with the cylindrical ferromagnetic member. Magnetic particles are placed on selected portions of the cylindrical ferromagnetic member. A time-varying composite longitudinal magnetic field and a time-varying traverse magnetic field are applied to the cylindrical magnetic member, while it is being rotated.

Abstract: The invention relates to method and apparatus for measuring and displaying the eccentricity or off-set position with respect to coaxiality of a metallic conductor within an insulating coating during an extrusion process. The measuring apparatus employs a combination of optical and electrically inductive techniques to determine respectively the position of the outer coating of the cable and that of the core within the cable. By relating these positional measurements it is possible to determine the position of the core relative to a desired location namely the coaxial position so that appropriate corrections can be made to the extrusion process to keep the core in that coaxial position.

Abstract: A magnetic field generator positioned externally of a non-ferrous metallic tructure being examined, is rotated at a relatively low speed to produce a rotating magnetic field penetrating the metallic structure to a selected depth as a function of spacing between magnetic poles of the generator parallel to a planar surface of the metallic structure. Traction between the metallic structure and the magnetic field accompanying its rotation is measured. Corrosion of the metallic structure at subsurface depths is detected and quantified from such traction measurements.

Abstract: A method and an apparatus for determining the size and shape of a slot, for measuring, e.g., the profile of the discharge opening (slice) of a paper machine. In the method, using at least two magnetometers attached to an edge of the slot, the magnetic field depending on the size and shape of the slot is measured. An alternating electrical current is applied to a current conductor attached to the edge of the slot to create an alternating magnetic field, measurement of the alternating magnetic field is phase-locked with the applied electrical circuit, and the size and shape of the slot are calculated from the measured values of the magnetic field.

Abstract: Conductivity distribution on the cross section of metal or alloy is measured by an eddy current type conductivity meter and conductivity distribution contour map is prepared. Based on the pattern of this conductivity distribution contour map, heat history of an ingot and segregation of added element are analyzed and melting and/or casting conditions of metal or alloy are re-established. This method allows to carry out the testing and analysis within short time and quickly provides assessment results for re-establishment of melting and/or casting conditions. Thereby, metal or alloy ingots which may create poor quality products during the following steps can be eliminated; in particular, applying this method to a manufacturing of copper precipitation hardening alloy and the like, more sound ingots can be obtained and suitability of ingots for the material which should be worked in the following step can be assessed.

Abstract: A sensor arrangement and a method of acquiring properties of the surface layer (3) of a metallic target (2), which allow a nondestructive and substantially distance-independent measurement to be performed, with the requirements to be met by the sensor positioning being minimal. The sensor arrangement (1) comprises a combination of at least one eddy-current sensor (5) with at least one displacement measuring sensor (6), the depth of penetration of the eddy currents generated by the eddy-current sensor (5) corresponding to at least twice the thickness of the surface layer (3), and the displacement measuring sensor (6) serving to determine the distance of the sensor arrangement (1) from the target surface (4).

Abstract: In one aspect of the present invention, an electromagnetic actuator is disclosed. The electromagnetic actuator includes a plunger adapted to move between first and second positions, a pull coil adapted to receive electrical energy and responsively produce a high electromagnetic force causing the plunger to move from the first position to the second position, and a hold coil adapted to receive electrical energy and responsively produce a low electromagnetic force for maintaining the plunger at the second position. A sensing device is included to detect the magnetic flux density produced by the coils and responsively produce a position signal having a magnitude responsive to the position of the plunger. Advantageously, signal conditioning circuitry receives the position signal, and de-energizes the pull coil in response to the position signal indicating that the plunger is at the second position.

Abstract: A system to determine the position of an electrically conductive element movably positioned in a housing, like a metal disc in a check valve, with greater accuracy and resolution than single magnet systems includes first and second A.C. electromagnets positioned in close proximity to the element on opposing sides of the housing. The magnets are excited with A.C. currents to generate magnetic fields which penetrate the housing and the element. The magnetic fields are sensed by a magnetic field sensor. A control portion of the system includes a microprocessor configured to allow an operator to adjustably select and set a common frequency, individual amplitudes and a phase difference between the two currents supplied to the two magnets so that the currents might be adjusted to cause the magnets to generate magnetic fields at least partially and preferably essentially cancelling one another at the sensor.

Abstract: A metal detector has three magnet/coil units positioned end-to-end. Each magnet/coil unit has a generally rectangular bobbin supporting a coil and a pair of bar magnets at opposite ends thereof. The three coils are connected electrically in a three-phase "Y" configuration. The voltages generated by all three coils are received by a microprocessor-based signal processing unit (SPU). The SPU generates a three difference signals V(x-y), V(y-z) and V(z-x) which represent the differences between the individual coil voltages. The SPU generates a sum signal representing a sum of the absolute values of all the difference signals and generates a trip signal if the sum signal is greater than a threshold. The SPU determines over which side of the coil assembly the piece of metal passes by comparing to a threshold the difference signal corresponding to a difference between the voltages from the coils at opposite ends of the coil assembly.

Abstract: The present invention is a method and system for accurately analyzing shaft encoder signals from rotating machines. The invention reduces noise and other interferences in the encoder signals by novel means that yield an unprecedented power for extracting useful information. Signal distortion due to variation in the rotation rate of the machinery and due to FFT leakage are eliminated by acquiring digital values of the encoder signals at a set of discrete times that are determined by the properly averaged rotation rate of the shaft and requiring a fixed integer number of these discrete times per rotation of the shaft. Amplitude modulation is eliminated by proper spectral combination of left and right sidebands of the main encoder signal. Additive noise is removed by multiplying sidebands and averaging the results over a number of data records.

Abstract: A sensor for measuring the density of a magnetic porous material such as foam. The sensor includes a load cell connected to a magnet. The magnet is spaced a predetermined distance away from the material. The load sensed by the pull of the magnet is translated into a perceivable density value.

Abstract: A system for scanning the interior of a cargo container includes a propagator device for producing a magnetic field at each of (I) positions adjacent a first side of a cargo container and a detector device for detecting magnetic field strength at each of (J) positions adjacent a second side. The (I) positions are spaced apart in a direction generally parallel to a Y axis of a Cartesian coordinate system and components are included for mapping information about magnetic field strength at each of the (J) positions for each of (K) positions of the cargo container as it passes between the propagator and detector devices in a direction generally parallel to an X axis. Spaced apart orthogonal propagator and detector elements may be disposed in vertical columns adjacent the cargo container, and computerized control components may be used to map and process the information and to produce and display an image.

Abstract: An adjustable scanning range is provided for vehicle-activated measuring equipment of the type which includes receiver coils positioned on opposite sides of a transmitter such that voltages induced in the received coils from the transmitter are altered as the vehicle passes, the measuring occurring through the application of the induced voltages to a comparison circuit. Altering the input(s) to the comparison circuit by a constant voltage value allows the scanning range to be adjusted.

Abstract: An apparatus, for non-destructively testing for flaws in materials, having a housing assembly with a rotor and a stator for passing over the testing material, an ultrasonic probe fixed to the stator, and an eddy current probe mounted on the rotor. In operation the rotor rotates the eddy current probe about the ultrasonic probe and an indexing coil on the ultrasonic probe monitors the relative position of the eddy current probe. The rotating eddy current probe generates eddy currents in the testing material such that internal flaws effect the normal feed back to the probe. Changes in this feed back are monitored to determine, in conjunction with the indexing coil, the existence and location of flaws in the testing material. In the preferred embodiment a rotary transformer electromagnetically bonds the rotating eddy current probe to the housing stator.

Abstract: A pipeline inspection pig includes a drive mechanism, a first field generator and first sensor section connected to the drive mechanism and is driven thereby helically through the pipeline in a clockwise rotational direction. A second field generator and second sensor section is also connected to the drive mechanism and is driven thereby helically through the pipeline in a counterclockwise direction. A data recorder is operatively connected to the first sensor section and to the second sensor section for recording field interruption data from which a plot of anomalies in the pipeline can be generated as a grid of intersecting helical sensor signal pathways of the first and second sensors.

Abstract: A disk drive includes an on-board digital sampling analyzer. The drive has a data storage disk spinning at a predetermined velocity, a data transducer head for reading information recorded on a storage surface of the storage disk, an electromechanical actuator mechanism for positioning the data transducer head relative to the disk, a digital actuator controller means for controlling the actuator mechanism within a closed loop head positioner servo and having internal registers at addressable locations, a memory for storing information read from the disk and for storing at least one trace record, and a memory controller for controlling addressing of the memory. A trace taking process and structure reads at least one of the internal digital registers of the actuator controller during a sampling interval and records a resultant trace value within the trace record of the memory. An on-board analyzer process retrieves and processes the trace record into a correction.

Abstract: The present invention provides an eddy current sensing device capable of in-situ operation within a high temperature and high vibration environment of a combustion turbine engine. The eddy current sensing device is preferably utilized in an eddy current sensing system for monitoring crack formation and displacement of rotating members of the combustion turbine engine. The method according to the present invention provides inducing eddy currents in the rotating member, detecting the eddy currents, providing a signal indicative of the detected eddy currents, filtering the signal based on the condition to be monitored and evaluating the filtered signal to determine whether the condition, such as the formation of a crack in the surface of the rotating member exists, and if so, determining whether the condition is critical or routine.

Abstract: A magnetoelastic magnetometer having a magnetoelastic member for placement in a magnetic field, An effect on the stiffness of the magnetoelastic member caused by the magnetic field is measured, and magnitude of the field is determined in response.

Abstract: A system is provided for matching a new hole in an overlying member with an existing hole in an underlying member. With a magnet placed in the existing hole, an indicator device having an internal cavity, an outer boundary, and a ferrous ball freely movable within the internal cavity is slid across the surface of the overlying member and in engagement therewith. When the ferrous ball overlies the magnet, a position on the overlying member aligned with the existing hole in the underlying member is thereby located. Thereafter, the indicator means is removed from the overlying member and replaced by a drill guide means. The drill guide means is used to locate a drill to cut a hole through the overlying member coincident with the existing hole in the underlying member.

Abstract: A microcomputer or PC based non-destructive coated-object testing system and method combines thermoelectrically measured surface coating thickness data with flaw/crack depth data determined from eddy current measurements of the surface of the object to locate and selectively identify faults or cracks which penetrate the surface coating. The microcomputer controls scanning of eddy-current and thermoelectric probes over the object surface and stores measured data along with surface coordinate information to provide a color-keyed graphics display of surface conditions for visual analysis.

Abstract: A detection system for detecting and/or verifying the magnetic properties of the magnetic ink layer on common printed or copied documents includes, in order of interaction with the magnetic ink of a Document, a saturation record head, a saturation read head, a non-saturation record head, and a non-saturation read head. The disclosed method of operation is equivalent to the normal testing of the magnetic layer of a Document, but eliminates the need for an erase magnet.

Abstract: Two geophones located above an underground pipeline are spaced from each other and adjacent to both sides of a benchmark location. As a pig travels through the pipeline sound waves are generated. As a pig approaches a benchmark location, sound waves are received first by the geophone which is closest to the source of the sound waves, that is, the upstream geophone and then by the downstream geophone. The geophones generate electrical signals that are fed to a comparator circuit which is connected to upstream and downstream indicators, one of which is activated when a pig passes the benchmark depending on whether the sound was first received by the upstream or downstream geophone. An alternate embodiment adds a magnetometer at the benchmark location capable of sensing changes in the ambient magnetic field caused by the passage of a pig.

Abstract: A robotic sampling device (32) for cutting part of a tube wall (12) for sampling, containing a cutting head (36), a retrieval assembly (38) and a drive mechanism (40), is used to cut a window or hole (60) in the tube wall (12) and retrieve the tube wall sample (56), where the sample can be mounted onto a separate tube for testing the physical properties of the cut wall portion, and where a video probe (62) and the like can be passed through the window (60) to monitor conditions near the support plates (14) and tube sheets (16).

Abstract: The surface or internal structure of diamagnetic and paramagnetic materials is imaged by measuring, preferably with a superconducting quantum interference device (SQUID) magnetometer, perturbations to an applied magnetic field resulting from variations in magnetic susceptibility at an array of locations across the object. The array of perturbation measurements is processed to generate a map of local susceptiblities. For implementation of susceptibility tomography, multiple arrays of perturbation signals for a plurality of relative orientations between the object, the field, and the measurement locations are processed to generate values for local susceptibility at selected sites within the object, such as along a selected sectional plane.

Abstract: Apparatus for 360.degree. azimuthal imaging of steel casing employs a transducer that is rotated around the inside wall of the casing for inducing and measuring variations in induced flux density within the casing as an indication of changes in casing thickness.

Abstract: A multiparameter magnetic imaging system and method to be used in the localized measurement of the magnetic properties of a material and the display of those properties in the form of a false color image indicating the occurrence of those properties across the surface of a sample specimen. The system includes an inspection probe to measure certain magnetic parameters across the surface of the specimen and means to determine a multiplicity of magnetic property values based on the measured data. The system also includes a visual display system which selectively displays the data relating to the determined magnetic properties in the form of a false color image indicating the presence and variation of these magnetic properties across the specimen surface.

Abstract: A dielectric probe, of the type in which an electromagnetic wave is reflected from a dielectric/magnetic structure and spectrum analyzed, further includes a coil for applying a magnetic field to the structure as the wave is being reflected. Information about the intrinsic electromagnetic properties, integrity and structure of the material is obtained by comparing the reflected spectra for both the magnetic field on and off conditions.

Abstract: The present invention provides a method and system for analyzing signals generated by rotating components that slip in a rotating machine and for detecting faults in those components. Pulses from a shaft encoder serve as an external clock in digitizing the signal data. A fixed number of data samples are thereby acquired for each complete rotation of the rotating shaft of the machine. Complex spectra are provided for data records of a fixed length with the first sample of each data record always beginning at the same point relative to the shaft angular orientation. Signal-processing means multiply pairs of signal spectral components so that the complex products produced by the data for the component of interest has a fixed phase relative to the shaft orientation.

Abstract: A scan head includes an eddy current probe and a thermal print head. A sheet of thermal paper is mounted to the top of a laminated part being inspected and the scan head is moved across the surface of the part. A map of defect markings will appear on the thermal paper in a 1-to-1 relationship with the actual sub-surface defects. This greatly expedites the inspection process since the mapped defects are in spatial correspondence with the actual part.

Abstract: An apparatus for checking the surface condition of rollers for bearings, in particular barrel rollers, in which the pieces are conveyed and lined up in a row towards a checking station. In order to ensure the correct positioning of each piece during the checking operations, a compression force is applied to a section of the row, and in particular a thrust and a resisting action are applied at the ends of the section, urging the pieces of the section against one another in the course of their translation along a feed direction. Checking operations, for example through eddy current rotating heads, are carried out on pieces of the section.

Abstract: Remote control device for controlling apparatuses to be carried on the body, in particular hearing aids, and being provided with a circuit responsive to control signals. In order to give the remote control device a particularly simple and reliable design, it is provided that the remote control device comprises a permanent magnet (3) which is separate from the device (2, 8) to be controlled, and that the apparatus (2, 8) comprises at least one sensor (3; 10A, 10B) sensitive to a magnetic field and acting on a control circuit (20) via a signal converter circuit (6, 7, 12, 14; 13, 15) if so required.

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 non-contact thickness measuring sensor is disclosed which determines the thickness of an overlying material on a substrate. The sensor includes two non-contact separation distance measuring devices which may be utilized to measure the distance from the first device to a portion of the interface between the substrate and the overlying material, while the second device determines the distance from the second device to a portion of the surface of the overlying layer. The difference in the measured distances is related to the thickness of the overlying material. In one embodiment, two lasers are used to measure the separation distances. In another embodiment, the two measured distances are coincident. Because of the coincident geometry of these two measurements, the thickness measuring sensor of this embodiment is substantially insensitive to misalignment of the sensor from the normal to the surface of the overlying layer being measured.

Abstract: A measuring apparatus which accurately locates reinforcing bars in underwater concrete structures such as piers, retaining walls, easements and the like and measures the amount of concrete covering each reinforcing bar. The measuring apparus comprises a probe which generates a magnetic field and which is moved over the surface of the underwater concrete structure under test. When the poles of the magnetic field are in parallel alignment with and directly over a reinforcing bar within the structure a disturbance occurs in the magnetic field with the magnitude of the disturbance being indicative of the depth of concrete covering the reinforcing bar. An electronics module electrically coupled to the probe provides an analog output signal which is indicative of the distance between a reinforcing bar within the concrete structure under test and the probe.

Abstract: A method for monitoring the environment of a vessel provides a liquid (18) which may contain particles (20) in a vessel having containment walls (12), where a hollow member (26) such as a thin tube is inserted into the liquid near the containment walls, and the hollow member contains in it a robotic device (34), which can travel within the hollow member and which can emit and receive ultrasonic waves and electromagnetic fields, where both of the ultrasonic waves and electric fields can pass through the hollow member (26) to the containment walls (12), where the device: emits and receives low frequency ultrasonic waves to and from the containment walls (12) and high frequency ultrasonic waves to and from any particles (20), and emits electromagnetic fields to the containment walls (12) or their combination, where absorptions and reflections from the hollow member walls and the containment walls, and any particles present are measured and any current generated in the hollow member walls and the containment wall

Abstract: The duplex tube (1) comprises a tubular core (2) and a cladding or covering layer (3) made from an alloy, the base metal of which is identical to the base metal of the alloy constituting the tubular core (2).

Abstract: An eddy current probe for detecting material flaws by inducing and measuring eddy currents in the surface of a material. The probe is held at a constant lift-off distance from the surface by a probe carriage that slides across the surface in a straight scan line. The carriage moves relative to a motorized bracket that slides the carriage across the surface. This relative movement allows the carriage to move across an uneven surface without deflecting the probe from a straight scan line. The probe has a split core so that an adjacent pair of coils project and detect electromagnetic fields on the surface being measured. Both coils have opposing flat sides that allow the coils to be closely packed together within the probe body.

Abstract: A magnetic field controller for laboratory devices and in particular to dc operated magnetic field controllers for mass spectrometers, comprising a dc power supply in combination with improvements to a hall probe subsystem, display subsystem, preamplifier, field control subsystem, and an output stage.

Abstract: This probe comprises a cable (4) and a probe head (6) fixed to one end of the cable and having an inspection head (18) provided with transmission-reception means (22, 24) for inspection signals from a tube (2), a support (20) on which the inspection head is mounted in rotary manner, a motor (66) for rotating the inspection head, an encoder associated with the motor for determining the circumferential extent of faults which the tube may have, and a rotary collector (10) between the motor and the support in order to ensure a mechanical connection between the motor and the inspection head and the transmission of control signals for the said means (22, 24) and signals supplied by the latter. Articulated mechanical connections (14, 16) are provided between the motor and the collector and between the collector and the inspection head.

Abstract: In a known magnetic field detector, an electrical coil (8) is secured to a motion-sensitive, for example piezoelectric sensor (3); this electrical coil is charged with an electrical current for detecting the magnetic field with the sensor (3) and an evaluation means (14) which follows thereupon. In order to also be able to employ the magnetic field detector given arrangement thereof in an implantable medical device as activity sensor for the physical activity of a patient, the current charging of the coil (8) can be switched on and off with a control signal (21), whereby the control signal (21) is utilized for characterizing the sensor signal as an activity signal corresponding to the physical activity or as a detection signal that detects a magnetic field.

Abstract: A detector for detecting joints (5) in a cast iron gas main for instance comprises a sonde (1) having a central transmitting coil (2) and the two receiving coils (3, 4) spaced one on either side of the transmitting coil. At a joint, the gap (6) between the sections of pipe causes differential magnetic coupling between the pipe and the two receiving coils (3, 4). After a pulse of drive current from a control unit is applied to the transmitting coil, comparison by subtraction of voltages induced in the receiving coils and measurement of an appreciable voltage indicates that the sonde (1) is at a joint. In a second embodiment, the sonde (101) is provided with a sealing compound supply pipe (115) and nozzles (120) from which sealing compound can be sprayed into the joint on detection thereof.

Abstract: An arrangement for measuring a thickness of a sheet article during a sheet article transportation, especially for measuring the thickness of an X-ray sheet film in an X-ray cassette loading and unloading device, has a magnet carrier arranged in a spring-biased manner on a sheet article transportation path perpendicularly to one side of the transportation path, a permanent magnet arranged on the magnet carrier near the first side of the magnet transportation path, at least one roller body arranged on the magnet carrier rotatably in a transportation direction of the sheet aarticle, a probe carrier fixedly arranged parallel to a second side of the transportation path opposite to the matnet carrier, a Hall probe arranged on the probe carrier opposite to the permanent magnet, at least one roller body arranged on the probe carrier. The probe carrier has a number of the roller bodies which corresponds to a number of the roller bodies on the magnet carrier.

Abstract: A bale opener for removing fiber tufts from top surfaces of fiber bales assembled in a series includes a carriage for travelling back-and-forth along a generally horizontal, first path of travel along the fiber bale series; a tower mounted on the carriage for travel therewith; a fiber tuft detaching device extending from the tower and movable relative to the tower along a generally vertical, second path of travel; and an incremental rotary displacement signalling device including a shaft; a toothed rotary element mounted on the shaft; a counter element meshing with the rotary element which is movable relative to the counter element; and a signal generator coupled to the toothed element for generating signals as a function of rotary displacements of the toothed element.

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: An array for non-destructive material testing of cylindrical workpieces such as pipes or ends thereof by means of leakage-flux measurement and if necessary electrodynamic ultrasonic excitation is proposed. A leakage-flux measuring head (56) used for leakage-flux measurement comprises at least two Hall probes (80) disposed along a line parallel and/or vertical to the magnetic field generated by a magnet (10) and forming at least one Hall probe line. In addition, the leakage-flux measuring head has at least two sliding blocks (94, 96, 98, 100) spaced apart and supportable on the workpiece, between which the Hall probes are disposed. The leakage-flux measuring head is also provided with a protective plate covering the faces of the Hall probes on the workpiece side.

Abstract: A powder capsule loading system and apparatus for preparing and loading a gelatin capsule with a powder product for testing of the product in a magnetometer. The system includes a gelatin capsule which is readily available, such as those used in the pharmaceutical industry, and a sample tool including a handle section and a cup section which includes an aperture sized to receive part of a capsule portion and holds the capsule portion therein by friction fit. Initially, a top portion of the capsule and a bottom portion of the capsule are each received and held on different sample tools. The capsule portions received within the sample tools are dipped into a sample container of powder product to fill the respective portions with the powder product, followed by assembly of the capsule. The assembled capsule containing a substantially predetermined amount of powder therein is then weighed.

Abstract: A method and system for accurately inspecting an electroconductive film using an eddy current and a process and apparatus for production of an optical fiber which measures on-line the electrical resistance, which shows the state of formation of the electroconductive hermetic coating of the optical fiber by the electroconductive film inspection method and reflects back the measurement results to the hermetic coating forming conditions are disclosed. Optical fiber is made up of a core, cladding, amorphous carbon film or other electroconductive hermetic coating formed on the outer surface of the cladding, and a protective coating. The electrical resistance of the hermetic coating generates an eddy current at the coating, the eddy current generated is detected, and the phase angle of the complex impedance is detected to enable calculation.

Abstract: A plug released into an oil or gas well carries one or more metallic strips that affect the inductance of a resistive-inductive bridge circuit mounted adjacent a conduit through which the plug and fluids are pumped into the well. This unbalances the bridge circuit to produce a signal preferably uniquely identified with the plug so that an indicator can be activated to confirm proper release of the plug into the well. When an amorphous metal is used in the metallic strips, the unbalancing of the bridge produces a signal having an identifiable harmonic of a fundamental frequency of an oscillator signal driving the bridge circuit, which harmonic is not present in other signals resulting from the bridge circuit being unbalanced by other materials flowing in the conduit.

Abstract: A magnetic characteristics measuring apparatus attains high sensitivity measurement of magnetic characteristics of a specimen. A magnetic field is applied for a predetermined time to the specimen, which is suspended from a beam at one side of a balance, by a solenoid electromagnet, thereby imparting a magnetic force on the specimen. The free oscillating amplitude of the balance following removal of the magnetic force is detected by a laser micro-range finder. Magnetic characteristics of the specimen are measured based on a relationship between the oscillating amplitude and the intensity of the applied magnetic field. The influence of magnetic noise or of magnetic characteristics of the measuring apparatus itself is eliminated, and a very high sensitivity on the order of less than 10.sup.-12 emu is realized in finding magnetic susceptibility with a simple structure.