Abstract: Embodiments are disclosed for a low-frequency detection and ranging. In an embodiment, an apparatus comprises: an open electrode; an alternating current (AC) voltage source configured to supply an excitation voltage to the open electrode at an excitation frequency; a resonant circuit coupled to the open electrode, the resonant circuit configured to oscillate when an object is within a detection distance of the open electrode; one or more processors configured to: obtain time domain samples of an output voltage of the resonant circuit when the resonant circuit is oscillating; convert the time domain samples into frequency domain samples; for each frequency domain sample, determine an amplitude difference and a phase difference as compared to an amplitude and phase of the excitation voltage; and determine a material class of the object based on the amplitude difference and the phase difference.

Abstract: A system for detecting disposal of metallic objects into an opening of a medical waste container, including: an indicator for indicating passage of metallic objects through the opening, a pair of receive coils and a transmit coil spaced therebetween shaped for receiving waste therethrough adjacent to the opening, and a controller in electrical communication with the coils. The controller generates and communicates a transmit signal to the transmit coil, which generates a magnetic field that induces voltage in each of the receive coils, which each generate a receive signal. The controller generates a waveform based on the receive signals with a baseline corresponding to absence of metallic objects, and analyzes the waveform with respect to opposite first and second thresholds. The controller activates the indicator in response to metallic objects passing through the coils when the waveform first exceeds the first threshold and then subsequently exceeds the second threshold.

Abstract: A method for managing operation of a circuit includes activating a trigger engine, receiving signals from a target circuit, and detecting a hardware trojan based on the signals. The trigger engine may generate a stimulus to activate the hardware trojan, and the target circuit may generate the received signals when the stimulus is generated. The trigger engine may be a scan chain which performs a circular scan by shifting bit values through a series of flip-flops including a feedback path. The target circuit may be various types of circuits, including but not limited to a high-speed input/output interface. The hardware trojan may be detected based on bit-error rate information corresponding to the signals output from the target circuit.

Abstract: A method is disclosed for determining a mechanical-technological characteristic variable of ferromagnetic metals, preferably ferromagnetic steels, and in particular fine-grained steels, which are used in pipelines. A magnetization apparatus, which has at least one permanent magnet or solenoid, magnetizes the metal which is to be determined, and a sensor apparatus comprising a transmission coil generates a magnetic field which interacts with the magnetic field which is generated by the magnetization apparatus in the metal, and which generates an eddy current. The eddy current is generated in the magnetically at least substantially saturated metal, and the eddy current is measured by an eddy current sensor of the sensor apparatus.

Abstract: A method for improving a performance of a metal detector, including: determining positions of a sensor head of the metal detector with respect to a coordinate system as the sensor head is moved on top of a ground; processing a receive signal received by the sensor head to produce a substantially ground balanced signal that is substantially insensitive to signals due to the ground; and actively controlling the step of processing based on one or more of the determined positions as the metal detector is moved on top of the ground; wherein, during a continuous use of the metal detector, the determined positions are processed to control, without any instruction or indication from an operator of the metal detector to do so, the step of processing the receive signal to produce the substantially ground balanced signal.

Abstract: A method includes receiving, from a plurality of magnetic field receivers including magnetic sensors, data characterizing samples obtained by the plurality of magnetic field receivers, the samples of a combination of a first magnetic field and a second magnetic field resulting from interaction of the first magnetic field and an object; determining, using the received data, a polarizability index of the object, the polarizability index characterizing a magnetic polarizability property of the object; classifying, using the determined polarizability index, the object as threat or non-threat; and providing the classification. Related apparatus, systems, techniques, and articles are also described.

Abstract: A method for electromagnetic and real-time measurement of a percentage of austenite contained in a steel strip in continuous motion during in-line manufacture or transformation thereof, by a device including the steel strip and a measuring device including at least: an alternating-current generator; a first coil supplied by the alternating-current generator, called a transmitting coil, and a second coil, called a receiving coil, the first and second coils being arranged parallel to each other or coaxial and on both sides of the steel strip, a distance between the coils being fixed and between 10 and 200 mm; a core of ferromagnetic material being a center of each coil, respectively; and at least one voltage-measuring device connected to terminals of the receiving coil, being a multimeter or an electronic acquisition system having an analog-digital converter coupled to a computer, to obtain the percentage of austenite contained in the steel strip.

Abstract: According to one embodiment, a measurement apparatus includes a magnetic field generation section that applies a predetermined magnetic field to a device under test. A current source supplies a current of a rectangular wave to the device under test in a direction of crossing the magnetic field. A voltage measurement section measures a voltage difference generated in the device under test. A restoration section demodulates the voltage difference using a demodulated signal having the same frequency as a frequency of the rectangular wave and synchronized with the rectangular wave, removes harmonic components from the demodulated voltage difference, and restores an electromotive voltage generated in the device under test. A computing section measures the device under test using low frequency components of the electromotive voltage.

Abstract: A multi-frequency platform for metal detection is disclosed. The transmission frequencies may be selected by the user or in an autonomous fashion. Further, the weighting of the frequencies may also be selected, either by the user or in an autonomous fashion. The ability to select transmission frequencies and weighting of the frequencies provides expanded detection capability, both in terms of the types of targets being sought and the types of ground conditions being experienced.

Abstract: In some preferred embodiments, an inverted U-shaped detector is provided that includes a) novel and convenient support structure to support lower ends of side panels and b) novel and convenient wheel structure to install wheels to a lower end of the side panels to facilitate manipulation, assembly, portability and/or transport. In some preferred implementations, the support structure can be attached to the lower ends of the side panels, then wheels can be attached to a lower end of one of the side panels, and then the device can be tilted and rolled for portability and transport. In some preferred embodiments, the structure is configured to enable a single individual to install the support structure and the wheel structure, and also to move, relocate or transport (e.g., roll) the detector device.

Abstract: A magnetic sensor device includes three magnetic sensors for detecting components of an external magnetic field that are in three directions, a magnetic field generation section, and a correction processor. The magnetic field generation section generates additional magnetic field components in three directions used for measurements of main- and cross-axis sensitivities of the three magnetic sensors. The correction processor corrects respective detection signals of the three magnetic sensors on the basis of the measurement results of the main- and cross-axis sensitivities of the magnetic sensors.

Abstract: The invention relates to a method for observing a magnetic field of a material volume, in particular for determining properties of a workpiece under, in particular, magnetic, mechanical, thermal, and/or electrical excitation of a material volume of the workpiece, wherein the magnetic field of the material volume is sensed as a function of time and of frequency with high frequency resolution.

Abstract: The transmission unit includes a digital signal source and a pulse generation circuit. The digital signal source generates a rectangular wave signal. The pulse generation circuit includes a short stub and an open stub, and generates a pulse signal corresponding to the rectangular wave signal. The receiving unit receives the pulse signal from the transmission unit via a lossy transmission path. A comparison circuit having a hysteresis function converts the received pulse signal into a rectangular wave signal.

Abstract: An apparatus to control a position of a camera module includes a magnetic member, a coil, a driver, a signal extractor, and a position detector. The magnetic member is disposed on a lens barrel of the camera module. The coil is disposed opposite to the magnetic member. The driver is configured to provide a position confirmation signal to the coil. The signal extractor is configured to extract a specific frequency component from a signal of the coil including the position confirmation signal and output a detection signal. The position detector is configured to provide a position signal corresponding to a position of the magnetic member based on the detection signal.

Abstract: According to an embodiment, a receiving circuit includes an envelope signal generating unit configured to output an envelope signal of a received RF signal, an amplitude signal generating unit configured to binarize the envelope signal which is captured in synchronization with a reference clock signal and output the binarized envelope signal as an amplitude signal, and a phase signal generating unit configured to binarize a phase component of the RF signal and output the binarized phase component as a phase signal, in which a digital RF signal is generated based on the amplitude signal and the phase signal.

Abstract: Disclosed herein are a method for analyzing heavy metal removal efficiency using phase difference analysis and an apparatus using the method. The method for analyzing heavy metal removal efficiency using phase difference analysis includes applying a magnetic field to a magnetite onto which a heavy metal is adsorbed, based on a first solenoid coil and a second solenoid coil that have an identical winding direction, applying a high-frequency signal to the magnetite, based on a third solenoid coil having a winding direction that differs from that of the first solenoid coil and the second solenoid coil, detecting a high-frequency signal transformed by the magnetite, and calculating a phase difference between a previously detected default high-frequency signal and the transformed high-frequency signal, and analyzing an efficiency of heavy metal removal by the magnetite by measuring a concentration of the heavy metal based on the phase difference.

Abstract: A method for monitoring local defects in a rotating engine component such as a gear uses one or more eddy current sensor(s) arranged to interact with the engine component as it is rotating during service. The eddy current sensor(s) may be carried by one or more teeth of a monitoring gear. A device is arranged to measure an output signal from the eddy current sensor(s) resulting from interaction with the rotating engine component. The output signal is processed so as to detect a change in shape of the output signal indicative of a local defect.

Abstract: The present disclosure provides a current monitoring circuit for monitoring current in a geophysical survey system. The circuit may be utilized in dipole-dipole systems including one or more electrode stations or in loop systems. The circuit includes a transmitter configured to generate an output current. One or more current monitors are positioned to detect current at or near the electrode stations or at positions along the one or more loops. Measured current data is transmitted back to the transmitter, which may be shut down if necessary. Methods for monitoring current in a geophysical survey system are also provided.

Abstract: A method for the non-destructive testing of a test component made of an electrically conductive material is described. The method employs movably mounted permanent magnets, which provides a means for generating a variable DC magnetic field within the test component, and eddy current probes to provide a means for performing a partial saturation eddy current test upon the test component. The eddy current probe preferably comprises an integrated magnetic field sensor which increases the accuracy and flexibility of the modes of operation of the described methods. The described methods are particularly suited for the inspection of tubular components that are often remotely located within the oil and gas exploration and production industries.

Abstract: A system for detecting the depth of an antenna embedded in the card body of a smart card includes a milling device for forming a cavity in the card body, a test device disposed in close proximity to the card body, a vector network analyzer (VNA) for measuring a linear characteristic of the test device, and a control device for regulating operation of the milling device in view of data collected by the VNA. In use, the VNA generates a test signal and measures the degree of signal reflection from the test device. Under normal conditions, the VNA observes a spike in forward return loss at the natural resonant frequency of the open antenna circuit. However, at the instant that the milling device contacts the antenna, a notable variance in the degree of signal reflection is observed which indicates that the proper antenna depth has been reached.

Abstract: This invention concerns a device and a method for inspecting aluminum cables with a steel core (ASCRs), installed in energized electrical energy lines, which use the ECT (Eddy Current Testing) technique for evaluating the remaining thickness of the zinc layer which covers the steel wires of the cables inspected, where the readings of the tension of the detection solenoid and the current of the excitation solenoid are taken as the current of the conductor reaches zero, the electrical parameters of the conductor are corrected for the average temperature during the inspection and the signal from the detection solenoid is filtered through a hybrid circuit which is designed to increase the sensitivity of the measurement.

Abstract: There are systems and methods for performing a geophysical survey using a hybrid aircraft which includes an apparatus configured to perform the geophysical survey. The system including: three mutually orthogonal transmitters configured to transmit electromagnetic (EM) waveforms towards the ground which creates a secondary magnetic field, wherein the three mutually orthogonal transmitters are attached to the hybrid aircraft; three mutually orthogonal null-coupled receivers configured to obtain measurements associated with the secondary magnetic field, wherein the three mutually orthogonal null-coupled receivers are attached to the hybrid aircraft; and three mutually orthogonal gradient receivers configured to obtain measurements, wherein the three mutually orthogonal gradient receivers are attached to the hybrid aircraft.

Abstract: Provided are a magnetic sensor and a method of manufacturing the same capable of arranging a magnetic converging plate on a substrate on which Hall elements and a circuit are formed, with a small variation in position while suppressing an increase in number of work processes, the magnetic converging plate having high magnetic permeability and low coercive force. In the magnetic sensor and the method of manufacturing the same, in forming Hall elements and a circuit on a silicon substrate, a magnetic converging plate holder having a pattern recessed to have the same shape and size as those of a magnetic converging plate is formed, and, into the magnetic converging plate holder, the magnetic converging plate manufactured through processes different from those of the silicon substrate on which the Hall elements and the circuit are formed is inserted.

Abstract: In conventional non-destructive inspection devices using magnetism, the subject of inspection was limited to the surface layer of the test object as a result of the skin effect, and it was not possible to perform flaw detection inspection at the interior or reverse surface of thick-structured test objects. The effect of the surface effect was eliminated by imparting an external signal canceling the detection output of the test object surface layer from the detection output of a magnetic field resulting from eddy currents induced in the test object. As a result, it has become possible to extract the detection output of the test object interior that had been masked by the detection output of the test object surface layer, and it has become possible to perform thickness inspection and flaw detection of the reverse surface and interior or a test object.

Abstract: A device and associated method for detecting metallic contaminants in a product using a signal received from a coil-based metal detector. A calibration module is configured to determine a product-specific, bowtie-shaped detection envelope based on calibration phase metal detector signals. A detection module is configured to compare, in a coordinate system for resistive and reactive components of a metal detector signal, a vector representation of the signal to the product-specific, bowtie-shaped detection envelope, and to indicate a presence of a metallic contaminant in the product when the vector representation of the signal extends to an area outside the bowtie-shaped detection envelope.

Abstract: Disclosed is a method and an apparatus for removing circling drifts on the display of the measured eddy current or other continuous waves. The circling dot which is supposed to be a static dot can obscure information required by the operator to judge if a small defect is present. Embodiments of presently disclosed harmonic rejection filters are tunable and employed to effectively abate or eliminate signals with frequencies that are multiples of operating frequencies, resulting in the removal of the circling effects on the display.

Abstract: A wafer test system includes an input device configured to transmit a test signal, a wafer including an optical port, an input port configured to receive the test signal, and an output port configured to output a result signal based on the test signal, a measuring device configured to measure the result signal, and an alignment device configured to align an optical fiber port of an optical probe with an alignment port based on the result signal and then align the optical fiber port with the optical port. The alignment port is the input port or the output port. The optical probe is configured to be the input device when the input port is the alignment port and the optical probe is configured to be the measuring device when the output port is the alignment port.

Abstract: A directional capacitive proximity sensor circuit capable of providing directional capacitive proximity sensing includes one or more guard electrodes, a first sensor, and a second sensor. The directional capacitive proximity sensor is installed in a device such that the first sensor is positioned near a first component of the device, and the second sensor is positioned near a second component of the device. The first and second sensors measure a capacitance to detect proximity of a user relative to the respective sensor, wherein the detected proximity is interpreted to determine a direction in which the user proximity is detected relative to the directional capacitive proximity sensor circuit. The guard electrode is provided to mitigate stray capacitance to reduce error in the capacitance measurements obtained by the first and second sensors.

Abstract: The apparatus and methods allow for correcting data from a sensor due to changes in relative speed of that sensor. The methods and apparatus described use a determined entropy from data associated with across a direction of travel of the sensor together with a determined entropy from data associated with in a direction of travel of the sensor. The determined entropies allow for providing for correcting the data for changes in the relative speed of the sensor. Also, described are methods and apparatus for correcting data from at least first and second sensors of a measurement device, whereby features are correlated from datasets taken from both sensors to determine one or more corresponding signatures. These signatures can then be used to correct the data from first and second sensors.

Abstract: A water-chamber working apparatus 1 according to the present invention includes a movable body that can move along a tube plate 12 of a steam generator 10, an extendable member 21 that extends and retracts in a direction in which a first coupling portion 21d approach each other and a direction in which these portions move away from each other, where the first coupling portion 21d is attached to a maintenance hatch 15 via a first joint 23a including two rotation axes intersecting with each other, and the second coupling portion 21e is attached to the movable body via a second joint 23b including two rotation axes intersecting with each other, which are different from the rotation axes of the first joint 23a.

Abstract: A magnetometer which includes an elongate reactor in which a sample can be secured in a sample support zone and which is located within a magnetic field space of a magnetic field generator and one or more signal pickup coils. Movement generating means is provided for generating relative movement in a generally linear direction between the reactor and at least one of the magnetic field and pickup coil, preferably by moving the reactor in its length. The magnetometer is characterised in that the reactor is a metal tube having a length which permits its ends to remain external of the signal pickup device during the relative movement.

Abstract: A facility for generating a detection signal upon the presence of metallic-conductive parts in a conveyed flow that is at least largely non-conductive, in which, for example, an alternating electromagnetic field is established in a section of the conveyed flow to be monitored by means of an alternating current generator and a transmitter coil system, whereby a variation of the signal of said field that is triggered by passage of a part is detected by a receiver coil system and converted into a detection signal by an analytical circuit. The individual components of the system are distributed over separate circuit modules which in turn act in concert by means of a bus system.

Abstract: A magnetic flux position sensor includes a primary coil, a secondary coil, and a magnetic flux conductor. The primary coil generates a magnetic flux and the secondary coil senses magnetic flux. The primary and secondary coils are substantially concentric and spaced apart by an annular passage. The annular passage has first and second ends, and the magnetic flux conductor is slidable from the first end to the second end of the annular passage. The magnetic flux transferred from the primary coil to the secondary coil varies as a function of position of the magnetic flux conductor.

Abstract: An eddy current sensor that includes: a probe and a computing unit. The probe has an exciting portion and a detecting portion. The exciting portion includes a first excitation coil that is wound around a non-magnetic bobbin so that a center axis direction is oriented in an x-axis direction and a second excitation coil that is wound around the non-magnetic bobbin to intersect with the first excitation coil so that a center axis direction is oriented in a y-axis direction. The detecting portion includes a detection coil that is arranged at the lower one of two intersecting portions of the first excitation coil and the second excitation coil. An eddy current measurement method for determining the thickness of a hardened layer.

Abstract: An energy converter includes a magnetism generation mechanism unit that generates a magnetic field when connected to an AC electrical power source, and a rotating mechanism unit having a single turn coil array member in which a plurality of single turn coils is disposed at a predetermined interval and a soft magnetic metal plate disposed on a side of the single turn coil array member opposite to the magnetism generation mechanism unit. The rotating mechanism unit is structured such that the single turn coil array member faces the magnetism generation mechanism unit across a predetermined magnetic gap and rotary driven by the magnetic field. Here, a drive signal period of the electrical power source is a period that maximizes an eddy current generated in the soft magnetic metal plate.

Abstract: An apparatus for testing of electrical or physical properties of a material include a single coil sensor mounted adjacent to a sample of the material. Sheet conductance of a wide variety of materials may be measured using the single coil to determine if the material conforms to generally accepted standards for the use to which the material will be put. In some examples, the material is a semiconductor wafer or flat panel. In other examples, the material is the body tissue of a patient. A non-invasive technique using the apparatus is also disclosed for monitoring the health of patient tissue such as musculature, and/or to determine whether healthy circulation is present, by measuring the conductance of the patient tissue in response to a magnetic field applied by the single coil. The single coil may be hand held, or it may be movable using an automated positioning system under computer control.

Abstract: A linearly polarized eddy current sensor including a source antenna and a parasitic antenna coupled to the source antenna, serves as a high sensitivity tool for the measurement of the surface impedance of sheet goods without requiring contact with the sample. Sheet goods can have an anisotropic, frequency-dependent surface impedance that is sensitive to minor changes in configuration of the sample. Because the electric field induced by the sensor is linearly polarized, measurement of directionally dependent sheet impedance can be achieved. The measurement is performed with the resonant device operating in resonance mode whereby the immediate proximity of the material to be measured causes damping and shifting of the coupled loop resonance. The resonant frequency of the sensor can be tuned by making changes to its geometry.

Abstract: A pipeline inspection tool includes two pole magnets oriented at an oblique angle relative to the central longitudinal axis of the tool body. An array of sensor coil sets is located between opposing edges of the two pole magnets and oriented perpendicular to the central longitudinal axis. Each sensor coil set includes a transmitter coil and two opposing pairs of receiver coils that are gated to receive reflections from the wall of a tubular member. Because the line of sensor coils is rotated relative to the magnetic bias field, the receiver coils are in-line with, and have the same angular orientation as, the transmitter coil. The tool provides improved sensitivity to small defects, substantial decrease in RF pulser power requirements, full circumferential coverage, self-calibration of the transmitted signals, and less interference between transmitter coils caused by acoustic ring around.

Abstract: A method for monitoring the operation of a metal detection system that comprises a balanced coil system with a transmitter coil that is connected to a transmitter unit, which provides transmitter signals having a fixed or variable transmitter frequency, and with a first and a second receiver coil that provide output signals to a receiver unit. A system adapted to operate according to an exemplary method is also provided. According to one embodiment, a carrier signal having the transmitter frequency and a monitoring signal having a monitoring frequency are provided to a modulation unit that suppresses the carrier signal and provides a modulated monitoring signal, which is supplied to a monitoring coil that is inductively coupled with at least one of the receiver coils, whose output signals are demodulated in a demodulation unit that provides a demodulated monitoring signal, which is compared in phase and/or in amplitude with a reference.

Abstract: A process for differentiating conductive and/or ferromagnetic objects (O) in a material stream (2) comprises generating an electromagnetic alternating field by exciting a coil (S) with a sinusoidal voltage (ue(t)) of a constant frequency (fM), detecting an impedance change in the coil, which has been caused by an object (O), by determining at least one pair of values from a peak value (ÎM) and a phase shift (?m) of the coil current (iM(t)) toward the excitation potential (ue(t)) of the coil, and determining the material by comparing the peak values (ÎM) and phase shifts (?m) with reference values, wherein the peak values (ÎM) of the coil current (iM(t)) are calculated at at least one measuring phase angle (?m) with the aid of a window comparator having a constant window width (?i), wherein the time (?tM) between the window inlet point (p4) and the window outlet point (p6) of the coil current (iM(t)) is measured and the gradient of the current profile (iM(t)) is calculated from the window width (?i) and the me

Abstract: An automated, non-destructive anhysteretic magnetization characterization method for studying and modeling soft magnetic materials. This measurement method employs a “reading-waveform” that allows multiple points of reference to be established in tracing out the B waveform. In using the reference values from this waveform, the components of B that cannot be measured directly may be calculated with precision. In turn, the initial magnitude of the B waveform is identified as the unknown component of the anhysteretic state. The processes can be repeated for different values of static fields as well as a function of temperature to produce a family of anhysteretic magnetization curves. The core characterization was performed without physically altering the core, so that the true anhysteretic magnetization curve, and the true B-H loop under applied bias H, is measured.

Abstract: A metal detector used for identifying contaminants in packages on a conveyor. The detector includes coils a search head and an analog to digital converter generating a reactive signal and a resistive signal in response to the presence of a contaminant. During a learning mode a sample product passes through the metal detector providing a representative product effect signal which is stored by the reactive learn memory and the resistive learn memory. The learn memory values provide a reference value subtracted from each product signal during a normal production cycle, canceling the product effect caused by contaminants in individual packages. The product effect is monitored during successive cycles composed of a series of packages undergoing normal inspection by the metal detector. A tracking processor averages the product effect signal produced by the individual packages and continuously updates a product effect trend signal that is subtracted from each product signal.

Abstract: An eddy current testing device which confirms that a change in characteristics of a target object is detected regardless of the magnitude of the change and specifying the position of a portion from which the change is detected. The device uses an eddy current probe to inspect a bent portion of a metal body, and has an inspection controller and a display unit. The inspection controller calculates a phase angle of a signal detected by the eddy current probe and generates flaw identification image data that indicates an area (or an area of the signal detected and determined to correspond to a flaw signal, based on the phase angle of the detected signal) of a flaw signal in coordinates in which the position of the portion of the target object is plotted along a coordinate axis. The display unit displays the flaw identification image data.

Abstract: A balancing circuit for a metal detector. The metal detector includes an oscillating power source, a transmit coil connected to the oscillating power source, first and second receive coils inductively coupled to the transmit coil, a first amplitude balancing circuit connected to the first receive coil, and a first phase balancing circuit connected to the first receive coil. The first phase balancing circuit includes a capacitor and a variable resistor.

Abstract: A radio receiver includes an in-phase channel and a quadrature channel, the channels being provided in parallel at a respective input with quadrature modulated radio frequency signals; and an error correction loop for detecting and correcting an imbalance in gain between at least part of the in-phase channel and a corresponding part of the quadrature channel, wherein the error correction loop comprises: a detector adapted to calculate Error_detnew=|I?|?|Q?|, where I? and Q? are the in-phase and quadrature channels respectively; a loop filter arranged to receive Error_detnew from the detector and calculate loop_filter_outnew+=Ki * Error_detnew, where Ki is the loop filter constant and loop_filter_outnew has an initial value of 1; and a multiplier arranged to receive loop_filter_outnew from the loop filter and adjust the signal of the quadrature channel by multiplying the signal by loop_filter_outnew.

Abstract: Variations in the lift-off separation between a probe and the surface of a structure to be tested often mask the detection of defects in the structure. A method and apparatus for automatically classifying and compensating for variations in the lift-off is described. A reference signal at a known lift-off may be weighted by a corresponding calculated ratio parameter and subtracted from a test signal to compensate for lift-off. A number of reference signals are preferably obtained and the largest magnitude gradient for each reference signal is preferably determined. The largest magnitude gradient for subsequent test signals is also obtained and the corresponding reference signal with the closest largest magnitude gradient to the test signal is identified and the corresponding reference signal is selected in the related compensation procedure. Such a method has been found to restore the signal such that lift-off is removed and defects are easily identified.

Abstract: A metal detector for detecting the presence of a ferrite object in the proximity of inductively coupled sensor having overlapping D shaped transmitter and receiver coils. The metal detector has a phase shift circuit to phase shifting a sensor output signal by a known amount and a switch operating in synchronization with an excitation signal of the sensor for sampling the amplitude of the phase shifted output signal.

Abstract: A metal detector (40) used for identifying contaminants in packages (49, 50, 51) introduced into the metal detector by a conveyor. The detector (40) includes coils (1), a search head (2) and an analog to digital converter (3) that generates a reactive signal (13) and a resistive signal (14) in response to the presence of a contaminant in the region of the coils. A high pass filter (4) receives the reactive and resistive signals (13, 14). During a learning mode a sample product is introduced into the metal detector (40) to provide a representative product effect signal which is stored by the reactive learn memory (19) and the resistive learn memory (28). The learn memory values (29, 32) are forwarded to reference processors (20, 35) to provide a reference value which is subtracted from each product signal during a normal production cycle, thereby canceling the product effect caused by each individual package as it passes through the metal detector.

Abstract: A balancing circuit for a metal detector. The metal detector includes an oscillating power source, a transmit coil connected to the oscillating power source, first and second receive coils inductively coupled to the transmit coil, a first amplitude balancing circuit connected to the first receive coil, and a first phase balancing circuit connected to the first receive coil. The first phase balancing circuit includes a capacitor and a variable resistor.

Abstract: Method and apparatus for monitoring the rotational speed of a shaft, in particular a shaft having a number of spaced features on or rotating with the shaft. Preferred embodiments of the invention are concerned with methods and apparatuses for processing signals in order to calculate, with high accuracy and a fast response time, the rotational speed of a gas turbine shaft. The invention recognizes that it is possible to accurately measure speed between two eddy current sensors (5, 6) by determining the time take for a turbine blade to pass therebetween provided that appropriate compensation is made for the effect of apparent changes in the magnetic distance between the sensors.