Abstract: The method for non-destructive flaw detection of aluminium reduction cell anodes is claimed, including the building of a computed model of an anode or the use of a specified model with the known data on the geometry and specific resistance of the anode, the geometry and coordinates of internal defects, wherein several cyclic calculations are carried out; the results of calculations are represented in the form of a 3D-matrix of amplitudes and directions of vectors of calculated intensities or inductions of the electromagnetic field at the discretization points near the outer surface of the anode; at least a pair of electrically conductive contacts that supply the specified amount of electrical current through the anode are placed on the outer surfaces of the inspected anode; at least one sensor is placed near the outer surface of the inspected anode, and the amplitude and direction of the magnetic field intensity or induction vectors are measured and represented as a 3D-matrix of measured magnetic field intens

Abstract: The invention relates to a measuring arrangement and to a method for the inductive analysis of metal objects, comprising a coil arrangement having an excitation coil (1.1) that can be excited by means of an excitation current, and at least one receiver coil (1.2), said two coils being inductively coupled to one another. By means of an evaluation unit, an output signal (5.4) of the measuring arrangement is evaluated. Means for generating a ramp-shaped voltage signal of the excitation voltage (2.5) as a specification for a ramp-shaped current through the excitation coil are provided. A control device regulates the current at the base point of the excitation coil (1.1) such that a ramp-shaped excitation current is produced, which is modulated by the metal object (1.6), and which affects the change in the excitation voltage.

Abstract: Method and apparatus for surveying the downhole environment in a steam stimulated well such as a Steam Assisted Gravity Draining well are described. One method comprises interrogating an optic fibre (104) arranged along the path of a well shaft (202, 204) within a steam stimulated well with optical radiation. At least one downhole steam pulse is generated and data gathered from the fibre (104) in response to the steam pulse is gathered and processed to provide an indication of the acoustic signals detected by at least one longitudinal sensing portion of the fibre (104). In some examples, the processed data can be used to determine at least one characteristic of the steam chamber (210).

Abstract: A method for detecting an electrically conductive target in soil using a metal detector including the steps of: generating a transmit magnetic field for transmission into the soil based on the transmit signal; receiving a receive magnetic field; providing a receive signal induced by the receive magnetic field; determining a noise in the receive signal or a signal to noise ratio of the receive signal; and estimating, based on either the noise in the receive signal, or the signal to noise ratio of the received signal, or both, at least one effective detection depth of one or more types of electrically conductive targets in the soil.

Abstract: An electromagnetic geophysical exploration system includes transmitter-receiver pairs configured to transmit waveforms and sense signals in different frequency bands. A controller directs the transmitters of the transmitter-receiver pairs to transmit the waveforms at different moments while the electromagnetic geophysical exploration system is flown over a subsurface formation. The signals sensed by the receivers enable geophysical exploration of the subsurface formation.

Abstract: Methods and apparatus for surveillance of a downhole environment: the response of least one optical fiber to an acoustic impulse is sampled and processed to provide an indication of the acoustic signals detected by at least one longitudinal sensing portion of the fiber(s). The data comprises data indicative of at least one characteristic of the acoustic impulse and data indicative of the downhole environment. The data indicative of at least one characteristic of the acoustic impulse is used to interpret the data indicative of the downhole environment to provide an indication of at least one characteristic of the downhole environment. For example, the data indicative of at least one characteristic of the acoustic impulse may provide a ‘signature’ of the impulse, which may be used to deconvolve the data indicative of the downhole environment to provide an indication of at least one characteristic of the downhole environment.

Abstract: A method and system for active cancellation of transient signals and dynamic loop configuration for geophysical exploration is disclosed. The method includes controlling a transmitter to transmit a waveform in a frequency spectrum during an on-time. The transmitter includes a plurality of turns of wire. The method also includes controlling a plurality of switches to direct an electrical signal through the plurality of turns of wire. The plurality of switches electrically coupled to the plurality of turns of wire. The method further includes controlling a switch of the plurality of switches to direct a first portion of a transient current in an opposite direction from a direction of a second portion of the transient current during an off-time.

Abstract: A method for estimating a property of an earth formation in a zone of investigation, the earth formation having the zone of investigation and another zone, the method including: applying a compound pulse of electromagnetic energy to the earth formation, the compound pulse having a shape to induce a predominately greater amount of current in the zone of investigation than in the another zone, wherein the compound pulse includes a first pulse and a second pulse, the first pulse having an amplitude different from the amplitude of the second pulse; receiving a response of electromagnetic energy from the current induced by the compound pulse; and estimating the property from the response of electromagnetic energy.

Abstract: Apparatus and methods are implemented to determine characteristics of geological formations in a well. One or more transmitters and receivers electrically imitate a moving antenna. The moving antenna produces a distribution of frequencies by utilizing the Doppler effect. Each anomaly in the well produces reflections with different frequency, amplitude and phase information. Location and characteristics of multiple anomalies can be identified simultaneously in a well.

Abstract: A system and method to compress transient signals are described. The system includes a transmitter disposed in a borehole to change a transmitted current and induce a current in an earth formation, and a receiver disposed in the borehole to receive the transient signals resulting from the transmitted current. The system also includes a processor to compress the transient signals, the processor compressing the transient signals based on a spline approximation method or an Eigen value method for each transient signal based on whether the spline approximation method or the Eigen value method results in a fewer number of parameters representing the transient signal.

Abstract: A towable transient electromagnetic survey device for connection to a land, water based or an airborne towing vehicle is provided. The towable transient electromagnetic survey device includes a central body structure and a number of booms extending therefrom to interconnect the central body structure to the towing vehicle and suspend a transmitter loop for generating a primary electromagnetic field. Receiving loop(s) and transmitter loop(s) may also be housed in the central body structure. The central body structure may also be configured for switching in and out of connection of various transmitter and receiver loop configurations. In particularly preferred arrangements, the location of a transmitter loop or a pair of transmitter loops relative to a receiver loop is effective for substantially nulling mutual inductance between the transmitter loop(s) and the receiver loop.

Abstract: Downhole tools and techniques acquire information regarding nearby conductors such as pipes, well casing, and conductive formations. At least some method embodiments provide a current flow along a drill string in a borehole. The current flow disperses into the surrounding formation and causes a secondary current flow in the nearby conductor. The magnetic field from the secondary current flow can be detected using one or more azimuthally-sensitive antennas. Direction and distance estimates may be obtainable from the azimuthally-sensitive measurements, and can be used as the basis for steering the drillstring relative to the distant conductor. Possible techniques for providing current flow in the drillstring include imposing a voltage across an insulated gap or using a toroid around the drillstring to induce the current flow.

Abstract: A pneumatic vibration isolating suspension is disclosed for supporting a payload on a moving carrier while suppressing the transmission of vibrations in the 1 to 50 Hz band between the carrier and the payload. The disclosed invention can be deployed in the air in a towed carrier or sonde, and operated from aircraft power, making it a suitable platform for airborne geophysical instrumentation. It also has particular application to airborne electromagnetic surveying operating in the same frequency band because the sensor vibrations that result in noise created by the modulation of the sensor coupling with the earth's magnetic field are suppressed. Furthermore, the invention can be constructed from resistive composite materials and non-magnetic metals, so it can be operated without producing significant modification to the ambient electromagnetic field being measured.

Abstract: A method for noise signal analysis and communication with an underground transmitter. The method comprises the steps of measuring a noise floor when no signal is transmitted from a transmitter, detecting a signal when the transmitter is transmitting, and estimating the noise free component of the signal by removing the noise floor measurement. The measurement of the noise floor and detecting the signal from the transmitter may be done using a root mean square technique. The noise floor measurement can be removed from the measured signal by subtracting the noise floor measurement from the measured signal or alternatively by calculating the square root of the difference between the square of the measured signal and the square of the noise floor measurement. The noise estimation technique may be used in connection with a differential phased shift keying communication scheme or other modulation techniques.

Abstract: A method and apparatus is provided for collecting reservoir data. The method includes providing one or more electromagnetic sources for generating an electromagnetic field in a reservoir and providing one or more electromagnetic sensors equipped with capacitive electrodes. The electromagnetic source is located separately from the electromagnetic sensor. The electromagnetic sensor may either be located within a well or at the surface, is capable of measuring the electromagnetic field in three dimensions, and may be isolated from the well fluids. The data collected by the electromagnetic sensors can be used to create a model of the oil reservoir, including the water saturation.

Abstract: A method of determining anisotropy in a borehole is disclosed. An array of measurements along the borehole is obtained and a first depth in the borehole is selected. An arbitrary plane oriented with respect to the borehole at the first depth is designated and an anisotropy for the first depth with respect to the arbitrary plane is determined. The arbitrary plane is repositioned at the first depth and an anisotropy for different positions of the arbitrary plane at the first depth is determined. A minimum anisotropy coefficient with respect to the arbitrary plane at the first depth is identified based on anisotropy for different positions of the arbitrary plane. An anisotropy tensor for the first depth is then identified.

Abstract: Various embodiments include apparatus and methods to detect and locate conductive bodies and/or provide steam-assisted gravity drainage (SAGD) steering operation. Tools can be configured with receiving sensors (310) arranged to cancel substantially a primary signal associated with a probe signal without rotating the receiving sensors to cancel the primary signal and to capture a secondary signal generated from a conductive body (301) below the earth's surface. Additional apparatus, systems, and methods are disclosed.

Abstract: A stabilized field sensor apparatus collects field data, in particular magnetic field data, with reduced motion noise. The apparatus includes a tear drop shaped housing, a tow frame in the housing, a plurality of vibration isolating dampers spaced around the frame, a base assembly mounted to the dampers, a support pedestal having a bottom end fixed to the base assembly and an upper free end, a single spherical air bearing connected to the upper free end of the pedestal, an instrument platform with a lower hollow funnel having an upper inside apex supported on the air bearing for a one point support, principal and secondary gyro stabilizers for maintaining pivotal and rotational stability, and at least one field sensor mounted to the instrument platform for collecting the field data while being stabilized against motion noise including vibration, pivoting and rotation from the base assembly, from the tow frame and from the housing.

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: The invention provides a method and apparatus for the analysis of rocks and rock fragments. A method for the analysis of a rock fragment including: feeding the rock fragment to a microwave irradiation zone of microwave energy generated by a microwave source; gauging energy absorbed by the rock fragment; and correlating rate of change of the gauged energy absorbed by the rock fragment with compositional characteristics of the rock fragment.

Abstract: A transmitter antenna assembly for transient electromagnetic well logging instrument comprises an antenna coil coupled with a current source and a magnetic core having residual magnetization. Switching current in the antenna coil results in magnetization reversal in the magnetic core and change in magnetic dipole moment of the antenna. After the magnetization reversal is complete the current is removed and the new vector of magnetic dipole of the antenna maintains constant (steady-state phase of the antenna dipole) due to magnetic hysteresis of magnetic material employed for the magnetic core. No power expenditure during the steady-state phase of the magnetic dipole facilitates highly effective generation and fast switching of a large magnetic dipole. The magnetic core also serves as a shield between the antenna coil and any conductive part of the antenna assembly.

Abstract: Earth formations are characterized by using an array of electrodes which can measure streaming potentials in the formation, and by interpreting the data obtained by the electrodes. The electrodes are placed on a wireline tool, a LWD tool, or in a fixed manner about a completed wellbore. The measured streaming potentials are generated by drilling with an overbearing pressure, slitting the mudcake in a borehole, acid injection, or any of various other manners which causes fluid movement. The data obtained is interpreted to locate fractures, measure formation permeability, estimate formation pressure, monitor drilling fluid loss, detect abnormal pressure, etc. Particularly, a streaming potential voltage transient having a double peak profile signifies the presence of a formation fracture.

Abstract: An apparatus for detecting a position of a component in an earth formation is disclosed. The apparatus includes: a transmitter configured to emit a first magnetic field into the earth formation and induce an electric current in the component, the transmitter having a first magnetic dipole extending in a first direction; and a receiver for detecting a second magnetic field generated by the component in response to the first magnetic field, the receiver having a second magnetic dipole extending in a second direction orthogonal to the first direction. A method and computer program product for detecting a position of a component in an earth formation is also disclosed.

Abstract: A method for measuring resistivity variations in the earth comprising passing a transient current between two source electrodes; measuring the transient current at the source electrodes; measuring the resultant transient voltage between at least one pair of receiver electrodes; estimating one or more processing functions for applying to the measured input current to provide a step current profile, and applying the same one or more processing functions to the measured voltage to provide an estimate of the step response voltage between the receivers, using both the step current and the estimated step response voltage to determine the resulting apparent earth resistance, and using the apparent earth resistance to determine the resistivity of the earth.

Abstract: A retrievable tool for steering through an earth formation includes a first tool assembly and a tilted antenna attached to the first tool assembly. The tool also includes a second tool assembly attached to the first tool assembly and a tilted antenna attached to the second tool assembly. The first tool assembly attaches to the second tool assembly so that the antennas are tilted in predetermined directions. The tilted antennas are transmitter antennas or receiver antennas. Each tool assembly is a tubular cylinder with a longitudinal axis running the length of the cylinder, wherein the tubular cylinder has two ends, each end including a rotational attachment mechanism. The tool assemblies attach to each other through their rotational attachment mechanisms. The rotational attachment mechanism may be a screw-on mechanism, press-fit mechanism, or welded mechanism.

Abstract: A method for noise signal analysis and communication with an underground transmitter. The method comprises the steps of measuring a noise floor when no signal is transmitted from a transmitter, detecting a signal when the transmitter is transmitting, and estimating the noise free component of the signal by removing the noise floor measurement. The measurement of the noise floor and detecting the signal from the transmitter may be done using a root mean square technique. The noise floor measurement can be removed from the measured signal by subtracting the noise floor measurement from the measured signal or alternatively by calculating the square root of the difference between the square of the measured signal and the square of the noise floor measurement. The noise estimation technique may be used in connection with a differential phased shift keying communication scheme or other modulation techniques.

Abstract: Structure for deep MWD resistivity measurements suitable for both geo-steering and measurements ahead of the drill bit is disclosed. The structure is capable of extracting information about resistivity of formation in the presence of conductive drill. In one embodiment, ahead-of-bit sensing is achieved via transient electromagnetic measurements when current is switched off in the transmitter loop and the transient signal is measured in the receiver loops placed at some distances from the receiver. To reduce a parasitic effect of the currents in the drill three-coil bucking system with magnetic nonconductive shield in combination with a highly conductive copper shield are applied. Specifically, a short (less than 1 m) copper cover and short (less than 0.2 m) ferrite cover are placed in the vicinity of transmitting and receiving coils. A bucking operation followed by an inversion is performed on received signals to obtain data reflecting parameters of the surrounding subsurface formations.

Abstract: A method for noise signal analysis and communication with an underground transmitter. The method comprises the steps of measuring a noise floor when no signal is transmitted from a transmitter, detecting a signal when the transmitter is transmitting, and estimating the noise free component of the signal by removing the noise floor measurement. The measurement of the noise floor and detecting the signal from the transmitter may be done using a root mean square technique. The noise floor measurement can be removed from the measured signal by subtracting the noise floor measurement from the measured signal or alternatively by calculating the square root of the difference between the square of the measured signal and the square of the noise floor measurement. The noise estimation technique may be used in connection with, a differential phased shift keying communication scheme or other modulation techniques.

Abstract: Structure for deep MWD resistivity measurements suitable for both geo-steering and measurements ahead of the drill bit is disclosed. The structure is capable of extracting information about resistivity of formation in the presence of conductive drill. In one embodiment, ahead-of-bit sensing is achieved via transient electromagnetic measurements when current is switched off in the transmitter loop and the transient signal is measured in the receiver loops placed at some distances from the receiver. To reduce a parasitic effect of the currents in the drill three-coil bucking system with magnetic nonconductive shield in combination with a highly conductive copper shield are applied. Specifically, a short (less than 1 m) copper cover and short (less than 0.2 m) ferrite cover are placed in the vicinity of transmitting and receiving coils. A bucking operation followed by an inversion is performed on received signals to obtain data reflecting parameters of the surrounding subsurface formations.

Abstract: A method for determining a component of electric field response of the Earth's subsurface to a time-varying electromagnetic field induced in the Earth's subsurface is provided. The method includes measuring electric field response along a nonlinear pattern on at least one of the Earth's surface and the bottom of a body of water. The method includes measuring magnetic field response in three directions along the nonlinear pattern on at least one of the Earth's surface and the bottom of the body of water. The method further includes determining an electric field response in a direction normal to the measured electric field response using the electric field response and magnetic field response measurements.

Abstract: A device for guiding energy in a subsurface electromagnetic measuring system is provided, the device including a transmitting member for transmitting an electromagnetic signal into a subsurface medium, an energy-guiding member disposed in magnetic communication with the electromagnetic signal, and a receiving member for receiving a return signal induced from the subsurface medium. A method of guiding energy in a subsurface measuring system is also provided, the method including transmitting an electromagnetic signal into a subsurface medium, modifying the electromagnetic signal using a magnetic field, and then receiving a modified return signal induced from the medium using a receiving member.

Abstract: Measurements made with an induction logging tool are processed to provide a resistivity model of fluid invasion of the formation. Up to five zones can be determined over a radial distance of about 0.6 m. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Abstract: A method for interpreting transient electromagnetic survey data includes imparting an electromagnetic field in the Earth's subsurface by passing electric current through a transmitter antenna. The electric current includes switched direct current at a selected switching frequency. Voltages induced in a receiver corresponding to electromagnetic effects induced in the Earth's subsurface are detected. Frequency domain electromagnetic response of the Earth's subsurface is determined from the detected voltages and transient electromagnetic response of the Earth's subsurface is determined from the detected voltages.

Abstract: A method for filtering spurious resonances from an NMR dataset comprises the steps of: (a) creating a first, non-oscillating magnetic field of a predetermined field strength across a sample, (b) intermittently exposing the sample to a second, oscillating magnetic field orthogonal to the first to generate an NMR signal, (c) detecting the NMR signal from the sample, (d) adjusting the first magnetic field to a different predetermined field strength and repeating steps (a) to (c), and (d) comparing the detected signals to obtain an NMR dataset from the sample from which spurious resonances have been filtered.

Abstract: An induction logging tool is used on a MWD bottom hole assembly. Due to the finite, nonzero, conductivity of the mandrel, conventional multi frequency focusing (MFF) does not work. A correction is made to the induction logging data to give measurements simulating a perfectly conducting mandrel. MFF can then be applied to the corrected data to give formation resistivities.

Abstract: A method and apparatus for minimizing direct coupling between transmitters and receivers on a downhole logging tool are disclosed. One embodiment includes a transmitter, a bucking device, and a plurality of receivers, where signals may be directly coupled from the transmitter into the receivers and signals may be indirectly coupled from the transmitter into the receivers through the formation and borehole environment. The bucking device minimizes the magnitude of the signals that are directly coupled from the transmitter into multiple receivers within the plurality. By varying the current in the bucking device, the bucking device minimizes the magnitude of the directly coupled signal of each receiver in the plurality, and each receiver may utilize a common bucking device.

Abstract: A method and apparatus locates buried objects in conductive soil by creating a direct current in a transmitting loop, periodically terminating the direct current in the transmitting loop to create an eddy current in the conductive soil using time domain induction, receiving a magnetic field resulting from the eddy current running through the conductive soil, and locating the buried object using the received magnetic field.

Abstract: The invention relates to a method of mapping subsurface resistivity contrasts by making multichannel transient electromagnetic (MTEM) measurements on or near the earth's surface using at least one source, receiving means for measuring the system response and at least one receiver for measuring the resultant earth response. All signals from the or each source-receiver pair are processed to recover the corresponding electromagnetic impulse response of the earth and such impulse responses, or any transformation of such impulse responses, are displayed to create a subsurface representation of resistivity contrasts. The invention enables subsurface fluid deposits to be located and identified and the movement of such fluids to be monitored.

Abstract: The invention relates to a method of mapping subsurface resistivity contrasts by making multichannel transient electromagnetic (MTEM) measurements on or near the earth's surface using at least one source, receiving means for measuring the system response and at least one receiver for measuring the resultant earth response. All signals from the or each source-receiver pair are processed to recover the corresponding electromagnetic impulse response of the earth and such impulse responses, or any transformation of such impulse responses, are displayed to create a subsurface representation of resistivity contrasts. The invention enables subsurface fluid deposits to be located and identified and the movement of such fluids to be monitored.

Abstract: A metal detector with a transmit coil which transmits a magnetic field, transmit timing control circuitry, and receive signal circuitry and receive signal processing circuitry, and a low voltage and a high voltage power supply. The timing sequence generated within the transmit timing control circuitry produces control signals such that there are at least two different transmit periods, a short and a long period, and such that there are periods when no current flows through the transmit coil. The timing sequence is such that an average transmit coil energy at termination of the long periods is similar to that of an average transmit coil energy at termination of the short periods.

Abstract: Metal detection apparatus wherein a transmit coil will transmit magnetic pulses, and the processing circuitry will weight a receive signal more heavily soon after a transmit pulse transition and less heavily after a longer period following the transmit pulse transition.

Abstract: A unique time-domain electromagnetic system and data processing technique which, using low frequency electromagnetic fields, can localize, in three-dimensions, the position of buried metallic objects is disclosed. The measurement system uses time-domain electromagnetic techniques on a scanning frame similar to a X-Y plotter. The system collects magnetic data over a large area above the buried object. The spatial information of the field detected on the ground is then processed with an unique ‘nearfield holographic’ data processing method to reconstruct the field image of the buried object.

Abstract: An inspection system include a transmitter and a receiver configured for communication with a remotely positioned processing means. The transmitter and receiver are arranged as a mobile apparatus configured for insertion into any duct, conduit, pipeline, mining shaft, or the like, or any diameter or cross section. The transmitter is configured to transmit an electromagnetic signal to induce an electromagnetic response in the duct and the electromagnetic response is detected by the receiver. The mobile apparatus is self-powered and processes the electromagnetic response prior to communicating the processed response to the remotely positioned processing means as a discrete signal.

Abstract: A process is described to detect conducting objects buried in the ground by sending a series of electromagnetic pulses and the return signal. The signal characteristics stored in the database are sets of numerical data which each define characteristics of decreasing curves of the values of previously-received signals then, in a search phase, the numerical values of samples ranked 1, 2, . . . n are recorded, representing a real decreasing curve of a received signal. The average real decreasing curve is created by determination of the average value of the samples, each of which represents the average value of the values of the samples of the same rank. A value representing the difference between the set of characteristics of the real average decreasing curve and each of the sets with the same database characteristics is calculated. The smallest of the differences is compared with the threshold value.

Abstract: A method is disclosed for discriminating electromagnetic responses of metallic objects in soil to application of an electromagnetic pulse from superposed responses due to magnetic susceptibility of the soil, comprising substantially eliminating, from at least a portion of the response, any component having a power law decay characteristic with an exponent which is characteristic of the soil.

Abstract: A unique time-domain electromagnetic system and data processing technique which, using low frequency electromagnetic fields, can localize, in three-dimensions, the position of buried metallic objects is disclosed. The measurement system uses time-domain electromagnetic techniques on a scanning frame similar to a X-Y plotter. The system collects magnetic data over a large area above the buried object. The spatial information of the field detected on the ground is then processed with an unique `nearfield holographic` data processing method to reconstruct the field image of the buried object.

Abstract: A back-up proximity sensor for a vehicle is formed with an array of sensor pairs. Each sensor pair includes a lower passive infrared sensor (PIR) having a first field of view and an upper PIR having a second field of view. Each lower PIR and upper PIR is vertically mounted with respect to one another. The lower PIR and upper PIR of each sensor pair are angularly directed such that the respective fields of view intersect, thereby establishing a detection zone in a region behind a vehicle. The sensor pairs are arranged in a substantially adjacent, semicircular configuration to provide a continuous area of coverage behind a vehicle. A detection circuit receives output signals from each sensor pair and generates an output signal indicative of a warm body being detected by both the upper and lower sensors in a selected sensor pair, eliminating false alarms generated by warm bodies outside the region of the desired detection zone.

Abstract: In a time domain electromagnetic mapping technique of the type using transmitter pulses of half-sinusoidal waveform, with the half sinusoids being segments of a sinusoidal waveform having a frequency and corresponding to a resonant frequency of the transmitter coil, an improved current fall time at the end of each pulse is obtained by forming each transmitter pulse of plural immediately successive half sinusoids, the transmitter coil being tuned to an appropriately increased resonant frequency relative to the pulse repetition rate. Circuits for generating the improved pulse waveforms are disclosed.

Abstract: An inductive proximity sensor determines if a metallic object is in close proximity. An inductor is placed near the object. Several switches control the direction of the voltage passing through the inductor. During a first time period, the voltage flows through the inductor to induce a magnetic field in the object. During the second time period, the voltage is reversed in the inductor to quickly eliminate any current in the inductor. The decaying magnetic field in the object induces a voltage in the inductor which is measured during a third time period and compared to a reference value to determine the proximity of the object to the sensor.

Abstract: A method of geophysical analysis includes transmitting an electromagnetic signal into the earth and measuring the resulting transmission of that signal through the earth to a plurality of spaced recording units. The values of the transmitted signal are locally digitized and stored at each recording unit. The stored data from each recording unit is subsequently transmitted through a telemetric link to a central processing or analyzing unit, the stored data being transmitted from one recording unit at a time and in a preselected sequence. The data may be transmitted from each recording unit in a block and stored in the central processing unit. The digitizing and storing of the measured values at each unit is accomplished through a yield point amplifier. Automatic drift correction processing may also be applied to the measured values obtained from each recording unit.