Abstract: A tool for measuring a gap between two plates for processing semiconductor wafers is provided. The tool has a solenoid for placement upon a first of the two plates. In the hollow cylinder of the solenoid a slug containing a magnet is mounted so that the slug can slide along the axis of the solenoid. The solenoid is connected to an electric circuit to drive an electrical current therethrough to displace the slug toward and into contact with the second plate. An ammeter measures the current through the solenoid. The measured current corresponds to the slug displacement and yields a measurement of the gap between said two plates.

Abstract: An apparatus for measuring change of position of a rotor in a drive system having a drive rotor and a driven rotor generally concentrically mounted with respect to the drive rotor, the drive and driven rotors being magnetically coupled together. The apparatus includes a conduction device stationarily mounted between the rotors and a device for measuring the EMF (Electro Motive Force) produced in the conduction device as the rotors rotate. The apparatus also includes a device for determining, from the measurement, the relative position of the two rotors and/or the position of one of the rotors.

Abstract: A transport control apparatus for a plurality of automated guided vehicles traveling a transport path having a confluence junction, a turnout or a crossing is comprised of a conductor of a loop-shaped configuration formed to surround the confluence junction, the turnout or the crossing, a magnetic field generating device provided on each of the plurality of automated guided vehicles and generating a magnetic field having a cycle peculiar to each of the automated guided vehicles, a magnetic field detecting device provided on each of the plurality of automated guided vehicles and detecting a magnetic field, wherein when the magnetic field detecting device of a rear automated guided vehicle detects a magnetic field from the loop-shaped conductor induced by the magnetic field generating device of a front automated guided vehicle, the rear automated guided vehicle is halted.

Abstract: A mobile sewer cleaning apparatus having a rotating drum and a flexible hose wound thereon. Preferably mounted on the sewer cleaning apparatus is a device for measuring the length of hose paid out from the drum. The measuring device may be used, among other things, for measuring the speed of the hose as it is wound or unwound from the drum, and for controlling a safety device intended to stop the flow of water through the hose as the hose is being wound.

Abstract: An apparatus for rotating a spherical object, which includes suspension means for supporting a spherical object in a fixed position relative to its center. The suspension means holds the sphere by simultaneously contacting its surface with contacting elements at at least four points spatially independent of each other on the surface. Each of the contact elements is of regular shapes, such as, spheres, cylinders, cones or other shapes having symmetry about an axis of rotation. At least one of the contact elements is rotationally driven by a rotating drive means. The rotating drive means is rotated at a fixed or time-varying speed to impart controlled movement to the sphere about an axis through its center. The speeds or time-varying functions thereof cause the resultant controlled rotational motion of the sphere by manipulating an axis of rotation through its center.

Abstract: The invention relates to an apparatus for implementing the automatic measurement of a spinning saw blade's lateral deformation or deflection otherwise known as "flutter." The apparatus comprises a mounting means for rotating the saw blade and a detector means for measuring the flutter of the saw blade and generating an electrical signal in response. A second means measures the spin of the rotating saw blade in order to provide a visual output signal indicating flutter as a function of rotational speed.

Abstract: An apparatus and method to facilitate the in situ detection of small leaks in fluid-filled, capacitive type pressure transducers by remotely and non-intrusively inducing a brief time varying transient signal, and then analyzing the frequency response of the transducer to such excitation in order to detect the presence and effects of a fluid leak. The adverse effect of this induced transient signal on the process control circuitry is insignificant, while providing for an accurate and sensitive method for detecting the extent of fluid loss in the transducer when evaluated according to the present invention. As a consequence of such transducer evaluation techniques, frequency responsive characteristics of such devices may be recorded and self-correlated over long periods of time.

Abstract: A magnetic signal pickup mechanism is presented. The mechanism comprises a moving magnetic element mass fixedly coupled to a moving element mass such as a nutator. A movable magnetic element wire is physically non rigidly coupled magnetically to the moving magnetic element mass and further coupled mechanically to quasi restrictive longitudinal pivot points wherein the pivot points restrain longitudinal movement in relation to the moving magnetic element mass, the pivot points being offset sufficiently distant from each other to prevent contact between the wire and any structure other than the pivot points, wherein the wire is non straight.

Abstract: The invention concerns a method whereby not only the relative speed of the body and axle but also a dashpot's farthest-in and farthest-out positions can be measured without using complicated and expensive sensors. Relative speed is detected with a known combination of sensor coil and permanent magnet. The induced voltage at the midsection of the coil is proportional to relative speed. The voltage induced as the end of the coil is traveled by is exploited as a signal representing the dashpot's farthest-in and farthest-out positions.

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: An eddy current analyzer is employed to locate and map a substrate edge hidden from view by a cover plate. A probe has an axial bore in which rests a spring-biased marker. The analyzer scope traces locate hidden points along the edge and the marker maps these along the cover plate. A line drawn between the points locates the edge thereby enabling holes to be drilled at equal distances from the hidden edge.

Abstract: The radiator and the sensor each comprise three pairs of Helmholtz coils which are disposed along three orthogonal axes respectively. The coils are wound in pairs of grooves which have different depths and are recessed in a cubic support. The radiator and sensor are particularly useful for helmet-type viewfinders.

Abstract: At each of a plurality of points of embedment in a conveyor belt, a set of at least two detectable elements is embedded, and a control unit is arranged (a) to receive and process signals from an externally installed sensor, the signals having a varied intensity corresponding to the number of detectable elements in a given embedment point, (b) to average the intensities of a plurality of the signals for the given embedment point, and (c) to judge, on the basis of the average obtained in (b), the presence or absence of a breakage of detectable element or elements at the given embedment point. The abovementioned arrangement is able to judge whether one of the two detectable elements is broken, and the judgment is not affected by variation of the distance between detectable elements and the sensor. If breakage of a single detectable element of any set is identified, the affected element may be repaired during an outage of the conveyor.

Abstract: An apparatus for detecting defects in discrete articles, such as fasteners having an indexable article carrier with a plurality of article holders on the article carrier for supporting articles in a holding position so that each article in the holding position moves in a prescribed path as the article carrier is operated; structure for incrementally indexing the article carrier to position each article holder alternatively in (a) a first position in which an article can be inserted therein from a supply, and (b) a second position spaced from said first position; structure for shifting an article in a holder in the second position out of the holding position therefor into an inspecting position and for rotating an article in a holder in an inspecting position so that the complete periphery of an article to be inspected is exposed for examination is included; and eddy current scanning structure for examining the exposed part of an article while being rotated in the inspection position therefor.

Abstract: Electronic measuring and control of countersinking depth and/or failure of a drilling tool. Eddy current proximity detecting means is utilized for stopping and retracting the countersink drilling process after a pre-selected depth is achieved wherein a visual indication of the countersink depth is provided by way of sequentially lit LED segments through structure for detecting a surface up and away from the working end of the tool thereby avoiding contamination problems. Further, detection of vibration or chatter in the workpiece is shown as a means for detecting tool defects.

Abstract: A method and device are shown for locating the longitudinal axis of a subterranean branch pipe from a main pipe. A magnetic field emitter is mounted in the branch pipe so that it radiates magnetic lines of force along the branch pipe and into the main pipe. The axis of the branch pipe is located by detecting the primary line of the magnetic flux emitted from the emitter using a location device which is moveable within the main pipe. By locating the axis of the branch pipe, a hole registering with the branch can be cut in a lining within the main pipe from which the branch pipe leads.

Abstract: A non-destructive measurement system for producing whole wafer maps of sheet Hall concentration and Hall mobility in a GaAs wafer. The wafer need only have van der Pauw patterns available for the wafer measurements to be made. The measurement system includes an automatic test prober apparatus modified to incorporate a powerful permanent magnet providing a magnetic field to produce a Hall effect in the GaAs wafer. A parametric measurement system coupled through test probes to the van der Pauw patterns is programmed to measure sheet resistivity, Hall voltage and magnetic field strength, from which are derived values of sheet Hall concentration and mobility that are stored and mapped.

Abstract: A stud finder includes a magnetic subassembly for detecting the presence of a ferrous metal object, such as the head of a nail or screw, in a wall, with the magnetic subassembly being mounted at one end of a base member. A level vial is mounted at the other end of the base member, and a slot is formed in the base member between the magnetic subassembly and the level vial. When the base member is placed against a wall and the presence of a stud is detected by the magnetic subassembly, the base member is moved to a position in which the level vial indicates level. The slot has its longitudinal axis oriented perpendicular to the longitudinal axis of the level vial, so that the user can place a vertical mark on the wall through the slot. The slot is oriented so as to be in vertical alignment with the nail or screw head, when the base member is moved such that the magnetic subassembly is directly over the nail or screw head.

Abstract: A device is disclosed herein for measuring the pressure that a magnetic object exerts which includes a housing having a movable diaphragm held in a taut condition across an internal cavity. A central area of the diaphragm mounts a metallic or magnetic sensitive element operable in response to the presence of a magnetic field to move into and out of the internal cavity to create a detectable and readable pressure level. An analog or digital meter displays the pressure reading. The problem of determining the force exerted by a magnetic field is solved directly.

Abstract: An eddy current flaw detecting endoscope apparatus has an endoscope having an elongate insertable part and an objective optical system provided on the tip side of the insertable part. A flaw detecting device is provided on the tip side of the endoscope. A signal processing device processes a signal for the flaw detecting device. An eddy current flaw detecting apparatus detects a flaw in an object to be inspected and generates a flaw detecting signal. A controlling device generates a control signal controlling a controlled device with a flaw detecting signal of the eddy current flaw detecting apparatus.

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: On the basis of a finding that a magnetic hysteresis of a metal material, among magnetization characteristics changing with secular degradation of the metal material, shows a clear correspondence with the degree of degradation of the metal material, a change in such a magnetization characteristic is measured to estimate the degree of secular degradation of the metal material. In a typical embodiment, a superconducting quantum interference device is used to detect the magnetization characteristic of a measuring object. According to the present invention, the degree of embrittlement of a metal material used in an environment of high temperatures can be quickly detected in a non-destructive fashion so that the danger of brittle fracture of the metal material can be reliably prevented.

Abstract: The present invention relates to a method and apparatus for remotely detecting impedance. It is specifically adapted for use on a polishing machine wherein the end point of polishing for removing a surface layer during the processing of semiconductor substrates is detected. A first, or stationary coil having a high permeability core is wound having an air gap and an AC voltage is applied to the stationary coil to provide a magnetic flux in the air gap. A second coil is mounted for rotation on the polishing table, in a position to periodically pass through the air gap of the stationary coil as the table rotates. The second coil is connected at its opposite ends to contacts which are embedded in the surface of the polishing wheel. The contacts are positioned to engage the surface of the substrate which is being polished and provide a load on the second or rotating coil.

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: An improved NDE method utilizes a laser source with modulator and scanning mirror, a pancake shape eddy current detecting coil, a lock-in amplifier, a system controller, and an impedance gain/phase analyzer. The laser is directed by the scanning mirror to a specimen to be analyzed. A very localized or small area of the specimen is impacted directly by the laser beam creating a thermal and stress wave in the specimen. An impedance gain/phase analyzer is connected to the eddy current detecting coil and to a lock-in amplifier through the system controller. The lock-in amplifier is also synchronized to the laser modulator. The system controller is used to control the lock-in amplifier, scanning mirror, and to process data from the analyzer. Raster scanning of the laser beam across the speciment allows the detection by the coil of the laser generated thermal and elastic strains induced in the specimen by the laser. The rastering of the laser beam is controlled by the controller by positioning the mirror.

Abstract: A method and apparatus for testing steel components for temperature embrittlement uses magneto-acoustic emission to nondestructively evaluate the component. Acoustic emission signals occur more frequently at higher levels in embrittled components. A pair of electromagnets are used to create magnetic induction in the test component. Magneto-acoustic emission signals may be generated by applying an AC current to the electromagnets. The acoustic emission signals are analyzed to provide a comparison between a component known to be umembrittled and a test component. Magnetic remanence is determined by applying a DC current to the electromagnets, then turning the magnets off and observing the residual magnetic induction.

Abstract: Characteristics of a superconductor such as a repulsive displacement of a superconductor against a magnet or a rotational resistance of the superconductor due to flux-pinning in the superconductor are measured by supporting the superconductor in a non-contact mode; disposing a magnet at a position opposite to the superconductor; and moving the superconductor toward the magnet relatively or increasing the magnetic force of the magnet. The measurement may be carried out while the superconductor is applied with a load or is rotating.

Abstract: A method and apparatus for testing steel components for temper embrittlement uses magneto-acoustic emission to nondestructively evaluate the component. Acoustic emission signals occur more frequently at higher levels in embrittled components. A pair of electromagnets are used to create magnetic induction in the test component. Magneto-acoustic emission signals may be generated by applying an AC current to the electromagnets. The acoustic emission signals are analyzed to provide a comparison between a component known to be umembrittled and a test component. Magnetic remanence is determined by applying a DC current to the electromagnets, then turning the magnets off and observing the residual magnetic induction.

Abstract: A hot flaw detector is equipped with a sensor holding member that has a circular opening through which the material to be inspected will pass and that holds a flaw detecting sensor. Provision is made of an annular cooling liquid injection port that is open at an end of the sensor holding member adjacent to the inner peripheral wall of the circular opening, and provision is further made of an annular cooling liquid introduction port that is open at the other end of the sensor holding member adjacent to the inner peripheral wall of the circular opening. The cooling liquid is injected from the annular cooling liquid injection port, and forms a liquid film along the inner peripheral wall of the circular opening, and is recovered through the annular cooling liquid introduction port. The inner peripheral wall of the sensor holding member is effectively cooled by the liquid film which drips little onto the material to be inspected.

Abstract: A tunneling tip piezo is incorporated into various devices for measuring effect of changes in environmental conditions (i.e., temperature, pressure, magnetic and electrical fields, etc) upon a material by sensing minute changes in the dimensions of the surface. The devices may be used to detect changes in environmental conditions or to determine physical properties of a material.

Abstract: A control device for piston and cylinder units comprises a sensor adapted to be operated by a moving member and arranged on a guide device which has at least one electrical track conductor. Via a contacting device the sensor is connected with the electrical track conductors so as to make possible the transmission of sensor signals without leads.

Abstract: A system for automatically detecting the presence of staples within a set of original document sheets loaded into a document handling tray and automatically inhibiting the operation of the document feeder to prevent damage to the document feeder or the original sheets in response to detecting a staple, particularly a staple in a preselected area of the document tray in which it is most likely that a staple would be present as documents are normally loaded into the document tray by the operator, including preventing inadvertent actuation or output of the staple detector by metal objects other than a staple, such as an operator's ring temporarily present in the document tray during initial loading the documents, preferably by coordinated confirmation of the completion of document loading into the document tray.

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, includes an A.C. electromagnet positioned in close proximity to the valve casing and the disc. The magnet is excited with an A.C. voltage to generate a magnetic field which penetrates the casing and the disc. The magnetic field is detected by a sensor. A.C. current and voltage signals from the electromagnet and a magnetic field signal from the sensor are presented to a processor portion of the system. The processor portion digitizes, amplitude and phase modulates each of the three signals and generates four traces: A.C. current amplitude, magnetic field amplitude, A.C. current phase and magnetic field phase. The latter two traces are derived with respect to an A.C. voltage phase signal. Comparable baseline signals previously gathered for the valve are stored.

Abstract: A sheet thickness measuring apparatus comprises a metallic back-up surface for supporting the sheet, a magnetic field utilizing sensor disposed above the metallic back-up surface and the sheet for outputting a measured value representative of a distance up to the metallic back-up surface, an optical sensor and a computing unit.

Abstract: A displacement sensor which is battery operated and suitable for use as a respiratory monitor to detect the onset of apnoea in infants or post operative patients is disclosed. The sensing device is easily attached to the patient by an elasticated belt, together with associated monitoring electronics in which the sensor signal is compared with a floating reference level in a level detector which is connected through a NAND gate 3 to prevent a timer 4 timing out while respiration signals are present. Cessation of respiratory movement for greater than 10 or 20 seconds is indicated by both audible and visual alarms 14 and 15. In another embodiment the sensor can be used to detect eye movements in a patient. Medical monitoring apparatus is also provided, said apparatus including a heart rate monitoring means and/or respiration monitoring means.

Abstract: A ferrous metal detector is used in conjunction with a ferrous metal mandrel of a pilger tooling set in a cold-pilgering machine to sense when the mandrel breaks during operation of the machine. The ferrous metal detector includes a transformer located adjacent to an end of the mandrel. The transformer has a primary winding and a secondary winding positioned along the path of tubing movement through the machine and sufficiently close to one another to be magnetically coupled together by a piece of the ferrous mandrel when located therebetween. The primary winding is excited by a suitable source with a constant predetermined signal which is transparent to non-ferrous metal of the tubing. Such signal couples a constant voltage in the secondary winding.

Abstract: A tool dullness indicator and method comprising the measurement of eddy currents at a known, controlled frequency directly in the tool by measuring the phase angle shift in a coil when a sample is put into or next to the coil. The phase angle change caused by presence of a workpiece is measured when the tool is sharp to provide a reference reading taking into account the surface hardness and other bulk properties of the workpiece, and arriving at a parameter that is dependent on eddy current changes, such as phase angle shift or other measurable changes related to eddy currents in the part, and then analyzing the workpiece, either while working, or at a set programmed check time to determine when the tool is dull as a function of the change in eddy current characteristics caused by work hardening.

Abstract: A detachable, articulated rotating eddy current inspection tool includes a body member having a connector at one end for mechanically and electrically attaching the body member to a rotating drive member while at the other an eddy current probe is supported for radial movement with respect to the axis of rotation of the body member. A motor located within the body moves a slide on which the probe is mounted while at the same time a counterbalancing slide is moved radially in the opposite direction to maintain said tool in dynamic balance. An encoder housed within said body member senses the location of said eddy current probe with respect to the axis of rotation of said body member. A rotary transformer is used to transfer signals which control the position of the probe and to receive information from the eddy current probe and the encoder. The encoder output signals are modulated by the eddy current probe exciter signal to enable probe position information to be sent through a rotary transformer.

Abstract: On the basis of a finding that a magnetic hysteresis of a metal material, among magnetization characteristics changing with secular degradation of the metal material, shows a clear correspondence with the degree of degradation of the metal material, a change in such a magnetization characteristic is measured to estimate the degree of secular degradation of the metal material, In a typical embodiment, a superconducting quantum interference device is used to detect the magnetization characteristic of a measuring object. According to the present invention, the degree of embrittlement of a metal material used in an environment of high temperatures can be quickly detected in a non-destructive fashion so that the danger of brittle fracture of the metal material can be reliably prevented.

Abstract: A measuring device for contactless control of a design of structural elements composed of an electrically conductive material comprises at least one coil through which an alternating current flows and whose measuring voltage is influenced by a structural element, and electronic evaluating unit arranged to compare the measuring voltage of the coil influenced by the structural element with a nominal value, the coil being formed as a cylindrical coil.

Abstract: A measuring device for contactless determination of condition of screw shaped structural elements comprises two oppositely located coils supplied with an alternating current spaced from one another so that an electrically conductive structural element passes therebetween, and transporting elements formed so that the structural element is guided on an edge so that a distance between the structural element and at least one of the coils remains constant during a measuring process.

Abstract: A surface testing device comprising a vibratory system for the reciprocating movement of a sensor carrier (3) arranged above the surface to be tested and comprising an exciter arrangement for operating the system at or in the vicinity of its resonance frequency wherein the vibratory system contains spring elements in the form of pneumatic springs (5, 6) acting on the sensor carrier (3) in opposite directions, which pneumatic springs (5, 6) are pretensioned in the rest state of the system by a magnitude corresponding to at least half of the displacement path of the sensor carrier (3) FIG. 1.

Abstract: An apparatus for dynamic measurement of viscoelasticity of a sample through oscillating displacement thereof. A detector detects oscillating displacement of a sample and produces a corresponding displacement signal having top and bottom peaks and containing an amplitude component due to the oscillating displacement and an offset component due to long-term deformation of the sample. A driver shifts the detector relative to the sample. A measurement circuit measures values of the top and bottom peaks of the displacement signal. A CPU calculates the amount of the offset component according to the measured value of the top and bottom peaks and outputs a compensative signal based on the calculated amount of the offset component to the driver so that the driver shifts the detector relative to the sample according to the compensative signal to cancel the deformation of the sample to thereby remove the offset component from the displacement signal.

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

Abstract: A method and apparatus for determining the extent of defects in tubular elements for use in an oil or gas well is disclosed. The apparatus includes an electromagnetic or other suitable inspection device, cooperating with longitudinal and circumferential position detectors for determining the position and configuration of all defects within a tubular member. Signal generating means are provided for producing signals corresponding to the configuration, longitudinal position, and circumferential position of the defects located within the wall of the tubular member. The signals are processed, preferably by a computer, so that the presence, nature, and precise location of each defect is determined and visually displayed at a suitable display means. Display means are provided for generating a two-dimensional visual display wherein the circumferential and longitudinal positions of the defects are selectably displayed.

Abstract: An arrangement for detecting metallic particles carried by a fluid includes a metallic probe member which surrounds an elongated passage through which the fluid flows and which is constituted by a split tube having two marginal portions delimiting a gap which extends along said passage and completely separates the marginal portions from one another. Capacitors are arranged at the gap and alternating electric current is caused to flow in the probe member around the passage so that the probe member and the capacitors form a tank circuit having resonance characteristics that are influenced by any inclusion then present in the passage in a manner dependent on the electromagnetic properties of the inclusion. The character of any metallic particle then present in the passage is determined from variations in the alternating electric current that reflect the influence of such metallic particle on the resonance characteristics.

Abstract: A Speed Sensor for a rotating member utilizes a magneto optic switch and a magnet mounted in the vicinity of the rotating member. Under normal conditions the magnetic field is at right angles to the axis of sensitivity of the switch thereby blocking light transmission through the switch. When a ferrous tooth on the rotating member passes the sensor, the magnetic field is distorted due to the change in reluctance caused by passage of the tooth thereby generating a magnetic field component along the switch axis of sensitivity turning the switch on and producing an output speed signal.

Abstract: An apparatus is provided for verifying the presence or, conversely, determining that one or more ferromagnetic components is missing from an inspected assembly. The apparatus includes a scanning head that creates a magnetic field. An assembly having one or more ferromagnetic components is located in a predetermined position relative to the magnetic field. A load cell subassembly of the scanning head produces an output signal representative of its movement, which movement is proportional to the number and location of ferromagnetic components in the assembly. The apparatus further includes a processing network that processes the output signal in order to provide an indication as to whether or not one or more ferromagnetic components is missing from the assembly. In conjunction with such processing, previously obtained reference values are compared with the determined magnitude obtained by processing the output signal from the load cell subassembly.

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

Abstract: A method and apparatus for determining the extent of defects in tubular elements for use in an oil or gas well is disclosed. The apparatus includes an electromagnetic or other suitable inspection device, cooperating with longitudinal and circumferential position detectors for determining the position and configuration of all defects within a tubular member. Signal generating means are provided for producing signals corresponding to the configuration, longitudinal position, and circumferential position of the defects located within the wall of the tubular member. The signals are processed, preferably by a computer, so that the presence, nature, and precise location of each defect is determined and visually displayed at a suitable display means. Display means are provided for generating a two-dimensional visual display wherein the circumferential and longitudinal positions of the defects are selectably displayed.