Abstract: A display terminal, an apparatus for cover opening detection, and a method of arranging a Hall sensor in a display terminal are provided. A display terminal includes a first body, and a Hall sensor disposed in the first body, the Hall sensor including a magnetic field sensing surface configured to sense a magnetic field, in which the magnetic field sensing surface is disposed at a slope with respect to an front surface of the first body.

Abstract: A system includes a capacitor, a plurality of notification devices connected in parallel with the capacitor, and a controller. The controller is capable of determining capacitance of the capacitor during charge-up of the capacitor, and the controller is capable of determining the wiring impedance of the emergency notification circuit during discharge of the capacitor.

Abstract: Provided is a coercive-force specifying apparatus capable of creating a demagnetization curve for each divisional area of a coercive-force distributed magnet without breaking the coercive-force distributed magnet and of specifying an average coercive force for each divisional area precisely. A coercive force specifying apparatus of the present invention includes: a yoke including an insertion space into which a coercive-force distributed magnet is to be inserted; a magnetizing coil; a search coil that detects a magnetization change when the magnetic field is applied to the coercive-force distributed magnet; and a tracer that creates a demagnetization curve on a basis of a voltage value generated due to the magnetization change. The end face is provided with two or more loop-shaped thread grooves bored therein, the search coil being provided in each thread groove.

Abstract: Disclosed is a proximity switch provided with an actuator unit and a sensor unit. The sensor unit is provided with an antenna coil, a transmitting circuit which transmits electromagnetic waves at a constant frequency to the antenna coil, a receiving circuit which detects external signals received by means of the antenna coil, and control circuits. The actuator unit is provided with an antenna coil, a power supply circuit which rectifies an electromotive force generated in the antenna coil, and a signal processing circuit which receives power supply from the power supply circuit, performs frequency-dividing to the signals received by means of the antenna coil, and transmits the signals from the antenna coil after the frequency-dividing. The control circuit of the sensor unit has memory for registering the frequency of the signals transmitted from the actuator unit.

Abstract: A welded portion quality determining system includes a first plate and a second plate, a welded portion defined at a point where the first plate and the second plate are welded to each other. Magnetic field generators generate a magnetic field to be supplied to the welded portion, and magnetic pickup devices receive the magnetic field generated by the magnetized welded portion to sense the received magnetic field. Therefore, a magnetic field may be generated by the welded portion through the magnetic field generators, and the magnetic field generated by the magnetized welded portion is sensed by the magnetic pickup devices so that quality of the welded portion may be rapidly and correctly verified.

Abstract: The invention relates generally to tracer particles for product identification and/or authentication. When incorporated into a manufactured item, that item can be subsequently authenticated by either detecting, or failing to detect, the tracer particle. The tracer particles of the invention are magnetically attractable, with micromarkings, and in some embodiments, are manufactured with food grade materials and of a particle size suitable for ingestion by humans. The particles can be analyzed qualitatively or quantitatively. In other aspects, the invention provides methods for the manufacture of the tracer particles, and in other aspects, provides methods for using the particles. Examples of products that can be tagged using the tracer particles of the invention include pharmaceuticals, animal feeds or feed supplements, and baby formula. Other applications include forensics, such as in explosive materials.

Abstract: There is provided a coercivity performance determination device for a coercivity distribution magnet that is capable of determining, in a short period of time, with precision, and at as low a testing cost as possible, whether or not each part of one coercivity distribution magnet has a coercivity that is equal to or greater than the required coercivity. A coercivity determining device of the present invention comprises: a substantially C-shaped magnetic body; excitation means that generates a magnetic flow in the magnetic body; and a flux meter that measures the residual magnetic flux of the coercivity distribution magnet. Protrusions are provided at corresponding positions on two opposing end faces of the magnetic body, and the coercivity distribution magnet is held between the two protrusions to form an annular magnetic circuit. An external magnetic field generation means is formed by magnetic regions caused by the protrusions and non-magnetic regions comprising the air in the periphery thereof.

Abstract: A solenoid current monitoring circuit of a solenoid actuator includes a solenoid drive board configured to receive a control signal, a sensing resistor configured to detect a current signal of a solenoid coil of the actuator resulting from the control signal, and a differentiator configured to differentiate the current signal. The solenoid current monitoring circuit detects the movement of the solenoid actuator based on a change in the differentiated current signal caused by a change in inductance of the solenoid coil.

Abstract: A sensor system comprises a sensor element adapted to sense at least one physical quantity, wherein the sensor element is adapted to generate a sensor signal in response to the at least one physical quantity, an evaluation circuit adapted to detect a manipulation of the sensor system based on the sensor signal and stored reference values and to output an indication signal in response to a detected manipulation and a package, the package housing at least the sensor element and the evaluation circuit.

Abstract: According to the present invention, a method for determining coercivity of a coercivity distribution magnet, whereby coercivity of each portion in the coercivity distribution magnet can be determined with good accuracy without, for example, cutting the coercivity distribution magnet into pieces and thus quality assurance can be achieved with good accuracy, is provided.

Abstract: A system for integrating radiolucent tracking sensors in a medical table, table mat, or surgical drape of a surgical navigation system, allowing the surgical navigation system to be less obtrusive in a surgery environment. A plurality of radiolucent magnetoresistance sensors are integrated into a table, table mat, or surgical draping of a surgical navigation system for improving surgical navigation workflow and eliminating image artifacts from intraoperative images. The plurality of radiolucent magnetoresistance sensors may be located within a table or adjacent to a table surface.

Abstract: A current sensor includes: a first magnetic sensor and a second magnetic sensor; a first analog-to-digital converter which is connected to the first magnetic sensor and converts an output signal of the first magnetic sensor from an analog signal to a digital signal so as to be output; a second analog-to-digital converter which is connected to the second magnetic sensor and converts an output signal of the second magnetic sensor from an analog signal to a digital signal so as to be output; and an operation device which is connected to the first analog-to-digital converter and the second analog-to-digital converter, and outputs an operation value by subjecting the output signal of the first analog-to-digital converter and the output signal of the second analog-to-digital converter to differential operation.

Abstract: A current sensor includes: a conductive member through which a current to be measured flows; first and second magnetic sensors which output output signals having reversed phases to each other due to an induction magnetic field from the current to be measured; and a control unit which performs differential operation on the output signal of the first magnetic sensor and the output signal of the second magnetic sensor, wherein sensing axis directions of the first magnetic sensor and the second magnetic sensor are fixed in the same direction, form a predetermined angle with respect to an application direction of the induction magnetic field from the current to be measured applied to the first magnetic sensor and the second magnetic sensor, and are fixed so that the induction magnetic fields are applied to the first magnetic sensor and the second magnetic sensor in reverse directions to each other.

Abstract: Magnetic tracking systems and methods for determining the position and orientation of a remote object. A magnetic tracking system includes a stationary transmitter for establishing a reference coordinate system, and at least one receiver. The remote object is attached to, mounted on, or otherwise coupled to the receiver. The transmitter can include a set of three mutually perpendicular coils having a common center point, or a set of three coplanar coils with separate centers. The receiver can include a set of three orthogonal coils. The position and orientation of the receiver and the remote object coupled thereto is determined by measuring the nine mutual inductances between the three transmitter coils and the three receiver coils. The magnetic tracking system provides reduced power consumption, increased efficiency, digital compensation for component variation, automatic self-calibration, automatic synchronization with no connections between transmitter and receiver, and rapid low-cost implementation.

Abstract: A method for estimating the value of the weight of the contents of the oscillating assembly of an electronically controlled household appliance is provided. The oscillating assembly is connected to a frame by a suspension system having a damper. The damper includes at least two mechanical elements adapted to move reciprocally, a magnetic element which detects reciprocal motion, depending upon the distance between the two elements, the magnetic sensor generates an electrical signal. A reading of an initial value of an electric parameter, is taken when the oscillating assembly is empty. A mathematical function is identified on the basis of the initial value and of a plurality of predetermined parameters, which relate the electrical parameter to the weight of the contents. A second reading is taken when contents have been loaded in, and the value of the weight of the contents is estimated by using the mathematical function and electric parameters.

Abstract: A transmit pad inspection device includes a magnetic coupling device, which includes an inductive circuit that is configured to magnetically couple to a primary circuit of a charging device in a transmit pad through an alternating current (AC) magnetic field. The inductive circuit functions as a secondary circuit for a set of magnetically coupled coils. The magnetic coupling device further includes a rectification circuit, and includes a controllable load bank or is configured to be connected to an external controllable load back. The transmit pad inspection device is configured to determine the efficiency of power transfer under various coupling conditions. In addition, the transmit pad inspection device can be configured to measure residual magnetic field and the frequency of the input current, and to determine whether the charging device has been installed properly.

Abstract: Apparatus and methods to enable the complete detection and assessment of electric currents flowing in a conductive medium not only parallel, but also perpendicular to the boundary separating the conducting medium from a non-conducting medium by means of a magnetometer located outside of the conducting medium itself.

Abstract: A magnetic sensor for an elevating motor, and more particularly to a magnetic sensor whose magnetic induction elements are sealed within a magnetically non-permeable minor sleeve. Meanwhile, a signal transmission line is extended therefrom. In addition, the minor sleeve and the magnetic induction elements are disposed within a gear box of the elevating motor. Since the magnetic sensor in accordance with the invention is designed in a built-in type, it is not easily affected and damaged by the external environment. As a result, the service life may be prolonged. Moreover, it is modularized for a compact structure and a practical installation. In addition, it approaches more to the rotational and magnetic pole, thereby enhancing the measuring accuracy.

Abstract: The invention relates to a method and arrangement for the contactless determination of conductivity-influencing properties and their spatial distribution over the entire cross section of an electrically conductive substance moving in a primary magnetic field (B). The substance may be a liquid or a solid. A simultaneous measurement of a number of mechanical state parameters of the magnetic system is performed (three-dimensional components of the force and the torque), said parameters being variable by the effect of a secondary field on the magnetic system, the secondary field being produced on the basis of eddy currents induced in the substance by the primary field (B). To determine the spatial distribution of the property that is sought, the primary field is changed in intensity or form a number of times and a measurement of the state parameters is carried out for each change.

Abstract: A biosensor is described. The biosensor includes a fixed multilayer stack providing a magnetization oscillation, a voltage source electrically coupled to the fixed multilayer stack, and a binding molecule covalently bonded to the biosensor. The voltage source provides a direct current through the fixed multilayer stack to generate the magnetization oscillation and a target molecule including a magnetic nanoparticle forms a complex with the binding molecule and alters the magnetization oscillation.

Abstract: Magnetically encoded shafts for use in detecting forces exerted on the shaft during operation. Magnetically encoded regions arranged in tracks or bands, encircle the shaft and are formed within or affixed to the shaft. The magnetically encoded regions define force-sensitive regions therebetween. Magnetic fields surround the force-sensitive regions and are altered by force vectors passing through the force sensitive region. These magnetic fields are sensed by magnetic field sensors to determine various shaft parameters including, for example: shaft rotational speed, shaft rotational position, and forces exerted on the shaft, e.g., torque, bending forces, stress forces and strain forces. To provide continuous detection of shaft operational parameters and forces, dead zones between magnetically encoded regions are aligned with force sensitive regions associated with magnetically encoded regions in other bands.

Abstract: Disclosed is a body panel inspection device that may be used to determine if a vehicle was in an accident. The inspection device uses a magnet with a particular magnetic strength and other characteristics in order to more accurately determine if a vehicle body panel has been damaged and subsequently repaired through use of non-ferrous filler materials. Also disclosed is a vehicle inspection kit carrying the disclosed magnetic inspection device and further including a method of vehicle inspection by use of the disclosed kit.

Abstract: A method for estimating the value of the weight of the contents of the oscillating assembly of an electronically controlled household appliance is provided. The oscillating assembly is connected to a frame by a suspension system having a damper. The damper includes at least two mechanical elements adapted to move reciprocally, a magnetic element which detects reciprocal motion, depending upon the distance between the two elements, the magnetic sensor generates an electrical signal. A reading of an initial value of an electric parameter, is taken when the oscillating assembly is empty. A mathematical function is identified on the basis of the initial value and of a plurality of predetermined parameters, which relate the electrical parameter to the weight of the contents. A second reading is taken when contents have been loaded in, and the value of the weight of the contents is estimated by using the mathematical function and electric parameters.

Abstract: An electromagnetic actuator having an annular pole piece and an annular armature with surfaces formed thereon through which a magnetic flux passes. The armature is axially movable relative to the pole piece between a first position and a second position. Magnetic flux is efficiently transmitted between the pole piece and the armature and the pole piece can be employed to guide the armature for movement thereon.

Abstract: An apparatus is provided for determination of at least one interface of a slag layer on top of a molten metal. The apparatus has a carrier tube and a measuring head arranged on one end of the carrier tube with a body fixed within the carrier tube and an end face facing away from the carrier tube. The apparatus further includes an oscillator arranged within the measuring head and an induction coil connected with the oscillator and arranged outside of the body and in front of its end face.

Abstract: A method used for determining a profile depth or wear on a tread of a tire of a vehicle, and/or a tire characteristic, a magnetic field being detected by a magnetic field sensor disposed in the interior of the tire, particularly in the area of the tread on the tire interior, or at a distance from the tire, particularly in the area of a wheel housing or a wheel well of the vehicle, the magnetic field being transmitted or changed by at least one indicator element disposed in the tread on the tire exterior. The current wear state of the tread and/or the tire characteristic, particularly a tire type and/or permissible top speed, is determined based on output signals of the magnetic field sensor. The invention further relates to tires.

Abstract: A method and apparatus are provided for measuring the thickness of a test object. The apparatus includes an eddy current sensor having first and second sensor heads. The sensor heads are positioned to have a predetermined gap therebetween for passage by at least a portion of the test object through the gap. The sensor heads make measurements at given sampling locations on the test object as the test object is moved through the gap. The apparatus also includes a position sensing mechanism to determine positions of the sampling locations on the test object. The apparatus also includes an evaluation circuit in communication with the eddy current sensor and to the position sensing mechanism for determining the thickness of the test object at the sampling locations.

Abstract: An electromagnetic actuator having an annular pole piece and an annular armature with surfaces formed thereon through which a magnetic flux passes. The armature is axially movable relative to the pole piece between a first position and a second position. Magnetic flux is efficiently transmitted between the pole piece and the armature and the pole piece can be employed to guide the armature for movement thereon.

Abstract: A system for integrating radiolucent tracking sensors in a medical table, table mat, or surgical drape of a surgical navigation system, allowing the surgical navigation system to be less obtrusive in a surgery environment. A plurality of radiolucent magnetoresistance sensors are integrated into a table, table mat, or surgical draping of a surgical navigation system for improving surgical navigation workflow and eliminating image artifacts from intraoperative images. The plurality of radiolucent magnetoresistance sensors may be located within a table or adjacent to a table surface.

Abstract: A method of detecting a characteristic (such as thickness) of first and second films formed on a substrate includes supplying a sensor coil with a first alternating current having a first frequency when detecting the first film, and a second alternating current having a second frequency when detecting the second film. An eddy current is thereby generated in the first film or the second film. An impedance across the sensor coil is measured, and the characteristic of any one of the first film and the second film is detected based on the impedance.

Abstract: A biosensor is described. The biosensor includes a fixed multilayer stack providing a magnetization oscillation, a voltage source electrically coupled to the fixed multilayer stack, and a binding molecule covalently bonded to the biosensor. The voltage source provides a direct current through the fixed multilayer stack to generate the magnetization oscillation and a target molecule including a magnetic nanoparticle forms a complex with the binding molecule and alters the magnetization oscillation.

Abstract: An element for generating a magnetic field, having an annular frame for receiving an annular magnet which rotates with a turboshaft. The magnet is mounted in the frame such that the frame stabilizes and guides the magnet mechanically. In order to specify an element for generating a magnetic field which reliably fixes and guides the magnet, the magnet is connected to the frame by at least one spot weld.

Abstract: An input shaft rotating speed detector detects an input shaft rotating speed Nin of an automatic transmission based on output signals from a resolver within a predetermined time period ?t1. An output shaft rotating speed detector calculates the number of pulse signals output from an electromagnetic pickup sensor within the predetermined time period ?t1, to detect an output shaft rotating speed Nout of the automatic transmission based on the time length of pulse intervals in the calculated number of pulse signals. With this configuration, the number of pulse signals used for calculating the output shaft rotating speed Nout can be changed, to thereby make a detection period of the output signals from the resolver used for calculating the input shaft rotating speed Nin be consistent with that of the pulse signals used for calculating the output shaft rotating speed Nout.

Abstract: Determination of at least one of physical, chemical and biological properties and parameters within an area of examination of an object of examination by introducing magnetic particles in at least a portion of the area of examination, generating a magnetic field with a spatial distribution of the magnetic field strength such that the area of examination includes a first sub-area with lower magnetic field strength and a second sub-area with a higher magnetic field strength, changing the spatial location of both sub-areas in the area of examination so that the magnetization of the particles changes locally, acquiring signals that depend on the magnetization in the area of examination influenced by the changing of the spatial location of both sub-areas, and evaluating the signals to obtain information about the anisotropy of the magnetic particles in the area of examination.

Abstract: An electromagnetic actuator assembly that includes an annular frame, a coil assembly, an annular armature, a plunger and a sensor. The coil assembly is coupled to the frame and includes an annular core and an annular coil. The annular armature is received in the frame and abutted against the plunger. A sensor target can be coupled to the armature or the plunger and includes a radially outwardly extending sensor target. The sensor is coupled to the frame and configured to sense a position of the sensor target. A method for operating an electromagnetic actuator is also provided.

Abstract: The present invention comprises methods and systems that use acoustic radiation pressure.

Abstract: In a coercive force distribution analysis device, a magnetic field is applied in substantially vertical direction to a sample having a magnetic thin film capable of recording vertical magnetism. A magnetic flux detection signal is generated in accordance with the leaking magnetic flux generated from a magnetic domain of the sample surface while the sample is horizontally moved. A first and a second external magnetic field corresponding to a first and a second threshold value selected from hysteresis characteristic corresponding to the sample average magnetization are applied to the sample so as to generate image data on a first and a second magnetic domain. The first and the second image data are subjected to digitization processing by the first and the second threshold value and the difference between them is generated as a first coercive force distribution pattern.

Abstract: A magnetic pressure sensing device for rotatably moving parts, of the type including at least one magnetic field source element associated to said rotatably moving part and a magnetic field sensing element associated to a fixed part to measure parameters of a magnetic field determined by said magnetic field source element, said parameters of the magnetic field being a function of the pressure applied to said rotatably moving part. The magnetic field source element includes means for rotating around at least one axis the direction of said magnetic field as a function of the pressure applied to said rotatably moving part.

Abstract: A portable electronic device includes a body, a flippable unit, a pivoting shaft, a first magnetizable element, a second magnetizable element, a magnetic induction sensor IC, and a magnet. The pivot shaft connects the body and the flippable unit. A display is disposed in the flippable unit for showing an image. The magnetic induction sensor IC is disposed in the body. The magnet is disposed at and rotatable with the pivoting shaft. The first and the second magnetizable elements are disposed between the magnet and the magnetic induction sensor IC to enlarge the magnetic field of the magnet such that the magnetic induction sensor IC is capable of detecting change of the magnetic field of the magnet when the flippable unit together with the magnet is pivoted relative to the body.

Abstract: A remote-controlled motion apparatus is controlled by a remote control apparatus. The remote control apparatus transmits a target motion signal by radio. The remote-controlled motion apparatus includes a communication module, a terrestrial magnetism sensing module, a processing module and a driving module. The communication module receives the target motion signal from the remote control apparatus. The terrestrial magnetism sensing module senses a terrestrial magnetism of the remote-controlled motion apparatus to output a terrestrial magnetism sensing signal. The processing module is coupled with the terrestrial magnetism sensing module and the communication module, and processes the terrestrial magnetism sensing signal and the target motion signal to output a driving control signal. The driving module is coupled with the processing module to receive the driving control signal, and adjusts the driving of the remote-controlled motion apparatus according to the driving control signal.

Abstract: An ultrasound system for inspecting an object is provided. The ultrasound system includes an electromagnetic acoustic transducer (EMAT) and a pulser-receiver system. The EMAT is configured to generate acoustic signals representative of the area being inspected and comprises a flux concentrating non-conductive pole piece separating a radio frequency (RF) coil and a magnet. The pulser-receiver system is coupled to the EMAT and configured to receive the acoustic signals and convert the acoustic signal to electrical signals.

Abstract: Systems and methods for magnetic field exposure indication. Exemplary embodiments include a magnetic field exposure indication system, including a main carrier body, a magnetic storage medium disposed on the main carrier body, an magnetochromic material indicator associated with the magnetic storage medium to indicate that the medium has been exposed to an a magnetic disruption, wherein the magnetochromic indicator is positioned on the main carrier body adjacent the magnetic storage medium where magnetic field disruption can be oriented to the magnetic storage medium and a comparison area disposed on the main carrier body, the comparison area including sample color regions illustrating the beginning color of an unexposed material and a color of the magnetochromic material indicator having been exposed to a magnetic disruption sufficient to damage the magnetic storage medium. Alternate exemplary embodiments include a magnetic disruption source to erase data stored on the magnetic storage medium.

Abstract: A method of detecting a contact between a player and a ball in a ball game, comprising a step of generating a magnetic field which may be associated with the player, the magnetic field being generated with a code sequence or a frequency which differ from a code sequence or a frequency which may be associated with the other player of the ball game, a step of detecting the magnetic field which may be associated with the player, and a step of determining the code sequence or the frequency with which the magnetic field was sent so as to obtain, on the basis of the code sequence or frequency, ball-contact information indicating whether the player had contact with the ball.

Abstract: A method and apparatus are provided for measuring the thickness of a test object. The apparatus includes an eddy current sensor having first and second sensor heads. The sensor heads are positioned to have a predetermined gap therebetween for passage by at least a portion of the test object through the gap. The sensor heads make measurements at given sampling locations on the test object as the test object is moved through the gap. The apparatus also includes a position sensing mechanism to determine positions of the sampling locations on the test object. The apparatus also includes an evaluation circuit in communication with the eddy current sensor and to the position sensing mechanism for determining the thickness of the test object at the sampling locations.

Abstract: Quasistatic sensor responses may be converted into multiple model parameters to characterize hidden properties of a material. Methods of conversion use databases of responses and, in some cases, databases that include derivatives of the responses, to estimate at least three unknown model parameters, such as the electrical conductivity, magnetic permeability, dielectric permittivity, thermal conductivity, and/or layer thickness. These parameter responses are then used to obtain a quantitative estimate of a property of a hidden feature, such as corrosion loss layer thicknesses, inclusion size and depth, or stress variation. The sensors can be single element sensors or sensor arrays and impose an interrogation electric, magnetic, or thermal field.

Abstract: A device for measuring the height of lift of poppet valves, in particular for poppet valves installed in internal combustion engines, with the help of inductive pickups, including a coil in a stationary mount and a metal sleeve which is in flush alignment in the valve shaft and is axially movable in the coil, and the sleeve is secured with axial play within the groove.

Abstract: A method and apparatus are provided for measuring the thickness of a test object. The apparatus includes an eddy current sensor having first and second sensor heads. The sensor heads are positioned to have a predetermined gap therebetween for passage by at least a portion of the test object through the gap. The sensor heads make measurements at given sampling locations on the test object as the test object is moved through the gap. The apparatus also includes a position sensing mechanism to determine positions of the sampling locations on the test object. The apparatus also includes an evaluation circuit in communication with the eddy current sensor and to the position sensing mechanism for determining the thickness of the test object at the sampling locations.

Abstract: Fabrication of samples having material conditions or damage representative of actual components inspected by nondestructive testing involves sensors placed near or mounted on the material surface, such as flexible eddy current sensors or sensor arrays, to monitor the material condition while the sample is being processed. These sample typically have real cracks in or around holes, on curved surfaces, in and under coatings, and on shot peened or otherwise preconditioned surfaces. Processing, such as mechanical or thermal loading to introduce fatigue damage, is stopped once the material condition reaches a predetermined level.

Abstract: A frequency measuring device capable of accurately detecting an end point of polishing a semiconductor wafer by obtaining a frequency measurement result highly accurately in a short period of time. A device FC, which measures the frequency of a measured signal comprises a counting section including a plurality of n-nary counters, a time reference circuit which outputs a time reference signal for every predetermined time interval, and a plurality of gate circuits whose outputs are connected to the inputs of the n-nary counters. The gate circuits receive the measured signal at a first input and receive the time reference signal at the predetermined time intervals at a second input. With this structure, the counting section supplies the frequency measured result of the measured signal every predetermined time interval.

Abstract: A method and apparatus for detecting a high flying condition of a transducer head in a computer disk drive is provided. The method and apparatus allow the detection of high fly write events that occur over one or a small number of data sectors. In addition, the present invention provides a method and apparatus for detecting high fly write events with a great deal of sensitivity. The method and apparatus of the present invention provide quick response and high sensitivity by monitoring the strength of a signal derived from data written to the disk, and signaling a high fly write event if the monitored signal strength in connection with a particular piece of data is less than a stored high fly write number corresponding to that piece of data by a predetermined amount.