Abstract: This invention provides a pulse induction metal detector where a coil transmits a pulsed magnetic field to energize metal objects that are often buried or hidden in a matrix (ground) containing ferromagnetic minerals. A difficult challenge is to detect and identify the metal object while ignoring the ferromagnetic matrix. Techniques are presented for achieving this.

Abstract: Locate information relating to use of a locate device to perform a locate operation may be acquired from one or more input devices, logged/stored in local memory of a locate device, formatted in various manners, processed and/or analyzed at the locate device itself, and/or transmitted to another device (e.g., a remote computer/server) for storage, processing and/or analysis. In one example, a locate device may include one or more environmental sensors and/or operational sensors, and the locate information may include environmental information and operational information derived from such sensors. Environmental and/or operational information may be used to control operation of the locate device, assess out-of-tolerance conditions in connection with use of the locate device, and/or provide alerts or other feedback. Additional enhancements are disclosed relating to improving the determination of a location (e.g.

Abstract: An apparatus for non-invasive subsoil inspection used for verifying the presence of any underground facilities includes a mobile support structure (2) which can be moved in at least one horizontal direction and which supports antennas (A) adapted to transmit an electromagnetic signal towards the soil and to receive the response echoes. An electronic processing unit is adapted to analyze the data acquired by the antennas and to reconstruct an image of the subsoil portion scanned by the machine.

Abstract: A technique utilizes the acquisition of data from desired subterranean regions via a logging system. The logging system is constructed for use in a wellbore and comprises a transmitter module having a transmitter antenna. Additionally, the logging system utilizes a receiver module spaced from the transmitter module and having a receiver antenna. The transmitter antenna and the receiver antenna are oriented to enable sensitivity in desired directions, such as ahead of the logging system.

Abstract: A stray-wire sensor includes a vertical magnetic gradiometer (VMG) carried over the surface by ground vehicles or by low-flying aircraft. The VMG has a spot of sensitivity on the ground which stays nadir to the VMG itself. A Faraday shield surrounding the VMG screens out the near field electric dipole signals, and a ferrite rod core and winding inside act as an antenna sensitive to the near-field magnetic dipole signals which radiate from horizontal lying stray wires on the ground surface in the dirt of hidden by ground cover. The VMG depends on it being moved around over the ground so that magnetic signal gradients and reversals can be measured point-by-point. The nadir points which fall over a point along a long horizontal wire will express characteristic signatures in the signal gradients and phase reversals measureable in the antenna.

Abstract: Buried object locators including an omnidirectional antenna array and a gradient array are disclosed. A locator display may include information associated with a buried object based on both omnidirectional antenna array signals and gradient antenna array signals.

Abstract: Metal detectors use graphical displays offering many analysis methods and user options which were not possible before. The new graphical detector displays allow new ways to display target information that enable better methods of analyzing and viewing target data. Graphical detectors have menu structures with dozens of operating parameters which can be modified by the user. Some of these parameters are able to be changed on-the-fly without having to suspend detector operation.

Abstract: A portable device and associated method are described for use with a system in which a locating signal is transmitted from within the ground during an operational procedure. The locating signal includes a transmission frequency that is selectable from a group of discrete transmission frequencies in a frequency range and the region includes electromagnetic noise that can vary. The portable device includes a receiver having a bandwidth that includes the transmission frequency range and is operable for measuring the electromagnetic noise in the transmission frequency range to establish a frequency content of the electromagnetic noise for use in selecting one of the discrete transmission frequencies that is subsequently transmitted as the locating signal during the operational procedure. The locating signal can be transmitted from a boring tool, a pullback arrangement or an inground cable. A predicted maximum operational depth for a transmitter can be determined prior to the operational procedure.

Abstract: A self-calibrating magnetic field monitor is disclosed. In one embodiment, a magnetic field sensor repeatedly generates an electronic signal related to the magnetic field. In addition, a calibration module generates a relative baseline signal based on an average value of the electronic signals for a given time period. A comparator compares the electronic signal with the relative baseline signal and generating an output signal if a difference in the comparing is greater than or equal to a threshold.

Abstract: Buried object locators including an omnidirectional antenna array and a quad gradient array are disclosed. A locator display may include information associated with a buried object based on both omnidirectional antenna array signals and quad gradient antenna array signals.

Abstract: A high-Q human-portable, battery-powered self-correcting tunable resonator in a transmitter apparatus for inducing alternating currents of high quality in buried conductors to facilitate their location is disclosed. The transmitter apparatus may employ an FET-driven capacitive tuning circuit and a coil design that achieves high precision, high-quality transmission signals, and which may be equipped with a high-voltage booster for facilitating fault-localization applications.

Abstract: A device for detecting objects such as mines placed in a zone to be explored, the device being placed on a vehicle moving at a velocity V and including a panel on which a radiation set is arranged to transmit signals at an illumination frequency and to receive signals reflected from the zone, and a processing circuit to provide information about the presence of the objects after processing of the reflected signals, wherein the radiation set includes an alignment of antennas arranged transverse to the velocity V of displacement of the vehicle.

Abstract: A device is described for use as part of a system in which a transmitter is moved through the ground while transmitting a signal that can be used to locate the transmitter. The device includes a receiver for receiving the signal to generate certain information about the position of the transmitter relative to the position of the device based on the signal. A processor establishes a current location of the transmitter and records the current location as one of a series of recorded locations of the transmitter based on the certain information and, at a time of recording the current location, electronically records a time stamp that designates at least the time at which the current location was recorded as part of the series of recorded locations of the transmitter.

Abstract: A ground tracking system including a ground follower assembly for use with a locator or other device for determining position, motion, and/or orientation information is disclosed. The ground follower assembly may include a wheel assembly coupled to a locator and configured to swivel and/or pivot relative to an antenna node of the locator to generate signals for use in determining position information during a locate operation, such as from a sonde array.

Abstract: Locate information relating to use of a locate device to perform a locate operation may be acquired from one or more input devices, logged/stored in local memory of a locate device, formatted in various manners, processed and/or analyzed at the locate device itself, and/or transmitted to another device (e.g., a remote computer/server) for storage, processing and/or analysis. In one example, a locate device may include one or more environmental sensors and/or operational sensors, and the locate information may include environmental information and operational information derived from such sensors. Environmental and/or operational information may be used to control operation of the locate device, assess out-of-tolerance conditions in connection with use of the locate device, and/or provide alerts or other feedback. Additional enhancements are disclosed relating to improving the determination of a location (e.g.

Abstract: A device rotates at least one static magnetic field about an axis, producing a rotating magnetic dipole field, and is movable in relation to the surface of the ground. The field is periodically sensed using a receiver to produce a receiver output responsive to the field. A positional relationship between the receiver and the device is monitored using the output. In one aspect, changing the positional relationship, by moving the device nearer to a boring tool which supports the receiver, causes an increase in accuracy of depth determination. In another aspect, determination of an actual overhead position of the boring tool, and its application, are described. Use of a plurality of measurements over at least one-half revolution of each magnet is disclosed. Establishing a surface radial direction toward a boring tool and resolution of multi-valued parameters is described. Calibration techniques, as well as a three transmitter configuration are also described.

Abstract: A steering tool is movable by a drill string to form an underground bore along an intended path. A sensing arrangement of the steering tool detects its pitch and yaw orientations at a series of spaced apart positions along the bore, each position is characterized by a measured extension of the drill string. The steering tool further includes a receiver. At least one marker is positioned proximate to the intended path, for transmitting a rotating dipole field to expose a portion of the intended path to the field for reception by the receiver. The detected pitch orientation, the detected yaw orientation and the measured extension of the drill string are used in conjunction with magnetic information from the receiver to locate the steering tool. The steering tool may automatically use the magnetic information when it is available. A customized overall position determination accuracy can be provided along the intended path.

Abstract: Exemplary apparatus include locate devices that generate, store and/or transmit electronic records of locate information relating to detection of underground facilities. An exemplary method for analyzing and processing locate information includes a computer-implemented method for visually rendering (e.g., in a display field of a display device) various aspects of locate operations. In one implementation, an output stream of data packets may be provided, wherein each data packet includes one or more flag fields that are set or reset upon at least one actuation of an actuation system of a locate device, and wherein at least some of the data packets include locate information relating to a locate operation.

Abstract: The present disclosure relates to determining the attenuation of an electromagnetic signal passing through a conductive material. An antenna is provided and placed in relatively close proximity to the conductive material. An alternating current is passed through the antenna and the impedance of the antenna is measured. The attenuation is determined using the measured impedance. A single frequency measurement may be made, or multiple measurements using different frequencies may be made. Grouped parameters based on properties of the material and the frequency of the current are used to relate the coil impedance to the attenuation. A current frequency for which the ratio of the antenna's resistive part of the impedance to the angular frequency of the current is substantially insensitive to at least one of the parameters is preferred.

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: An electronic metal detector having, a transmit coil arranged and adapted to transmit an alternating magnetic field associated with a reactive transmit coil voltage, the transmit coil being connected to transmit electronics arranged and adapted to generate a transmit signal, the transmit electronics having at least two power sources, a first power source and a second power source, wherein the first power source is adapted and arranged to connect to the transmit coil for at least a first period, and the second power source is adapted and arranged to connect to tie transmit coil for at least a second period, the said transmit electronics including at least one servo control negative feedback loop, a first servo control negative feedback loop, which is adapted and arranged to monitor a transmit coil current for at least part of the said first period, and to control at least part of the said transmit signal, the transmit electronics being adapted and arranged to control the transmit signal to produce the reactive

Abstract: A surface-conforming obscured feature detector includes a plurality of sensor plates flexibly connected together, each having a capacitance that varies based on the dielectric constant of the materials that compose the surrounding objects and the proximity of those objects. A sensing circuit is coupled to the sensor plates to measure the capacitances of the sensor plates. A controller is coupled to the sensing circuit to analyze the capacitances measured by the sensing circuit. One or a plurality of indicators are coupled to the controller, and are selectively activated to identify the location of a relative high capacitance, which can be indicative of an obscured feature behind a surface.

Abstract: A receiver and tracking system for identifying a location of a magnetic field source. In a preferred embodiment a plurality of tri-axial antennas are positioned at three distinct points on a receiver frame. Each antenna detects a magnetic field from a source and a processor is used to determine a location of the source relative to the frame using the antenna signals. Each tri-axial antenna comprises three windings in each of three channels defined by a support structure. The windings each define an aperture area. The windings have substantially identical aperture areas and have a common center point. The receiver may to display to the operator the relative location of the field source or may direct the operator to a spot directly above the field source.

Abstract: Included are embodiments of a method for communicating user preferences to at least one environment. At least one embodiment includes receiving a request from an environment for preference information related to a user and receiving a user identifier from the environment, the user identifier obtained via a portable user device. Other embodiments include determining at least one user preference related to the user, determining capabilities related to the environment, and communicating at least one user preference to the environment.

Abstract: A pulse-induction type metal detector using a transmitter coil energizing pulse that selectively reduces the amplitude of background signals from conductive soils, ores and salt water. The detector can be operated with higher amplification of the received signals than conventional detectors, without driving the input amplifier into saturation. This makes it possible to detect land mines, tramp metal and gold in media whose characteristics make detection with conventional metal detectors difficult.

Abstract: A method for localizing a person in surroundings equipped with fixed electrical appliances includes measuring an electromagnetic field radiated by one or more of these fixed electrical appliances with a magnetometer carried by the person, identifying a fixed appliance operating near the magnetometer by comparing the measured field with pre-recorded magnetic signatures. Each pre-recorded magnetic signature is associated with an electrical appliance present in the surroundings. The person is then localized at least in part based on pre-recorded items of information that correspond to localization, in the surroundings, of the fixed electrical appliance as identified by its magnetic signature.

Abstract: Methods and apparatus for detecting a presence or absence of an underground facility and generating electronic records of locate operations are described herein. An exemplary apparatus includes an actuator and at least one receiver antenna to detect a magnetic field from the underground facility. The apparatus further includes a processor coupled to a memory, which may at least be further coupled to the at least one receiver antenna. Upon execution of processor-executable instructions stored in the memory, the processor logs in the memory locate information relating at least in part to operation of the at least one receiver antenna. The processor logs the locate information in response to actuation of the actuator and/or at least one event based at least partially on a characteristic of the magnetic field detected by the at least one receiver antenna.

Abstract: A metal detector for detecting a metallic target in a soil including: transmit electronics for generating a repeating transmit signal cycle, the repeating transmit signal cycle including at least one receive period and at least one non-zero transmit coil reactive voltage period; a transmit coil connected to the transmit electronics for receiving the repeating transmit signal cycle and generating a transmit magnetic field; a receive coil for receiving a receive magnetic field during the at least one receive period and providing a receive signal induced by the receive magnetic field; and receive electronics connected to the receive coil for processing the receive signal during the at least one receive period to produce an indicator output signal, the indicator output signal including a signal indicative of a presence of the metallic target when under an influence of the transmit magnetic field; wherein the repeating transmit signal cycle is generated such that a waveform of the repeating transmit signal cycle i

Abstract: A method for detecting electrically conductive targets in soil including the steps of: generating a transmit magnetic field for transmission into the soil based on a transmit signal; receiving a receive magnetic field; providing a receive signal induced by the receive magnetic field; selecting at least two models, each approximating a form of a signal due to a different type of source; processing the receive signal using the at least two models to produce at least two independent signals, each representing a component of the receive signal due to a different type of source; and producing, based on at least two independent signals, an indicator output signal indicative of the presence of the electrically conductive target.

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: A spot indicating metal detector apparatus rides on a motorized platform having a rotary framework having a plurality of metal detectors mounted thereon with a plurality of metal detector coils positioned adjacent the ground below. The metal detector apparatus has a plurality of spray heads each associated with one metal detector detector coil for spraying a fluid onto the earth at the position the metal detector detects the presence of a metallic object.

Abstract: An underground tunnel detection system does not employ radar. Instead, an automatic frequency control is used to keep a continuous wave (CW) transmission tuned to the resonant frequency of a resonant microwave patch antenna (RMPA). Changes in loading and the bulk dielectric constant of the mixed media in front of the RMPA will affect its resonant frequency and input impedance. A significant shift in the measured input impedance is interpreted as a possible tunnel, and the phase angle of the measured input impedance tends to indicate a slightly forward or aft position relative to the detection system rolling over it on the ground surface.

Abstract: A service tee marker fixture comprises a disk marker and a cylindrical attachment sleeve fastened concentrically to the disk marker and constructed of a flexible material which provides a releasable friction fit with a service tee cap. For certain sleeve materials a stiffener plate is used to secure an end portion of sleeve adjacent to the disk marker. Detents are formed inside the attachment sleeve to grip matching ribs on the cap. An integrally formed inwardly-extending annular flange at an open end of the sleeve helps retain the sleeve on the cap. When installed the wire coil is horizontal and the marker shields the tee, and is further centered over a centerline of the main pipe. A novel method is also disclosed for using the service tee marker fixtures to survey and locate service line end points.

Abstract: Methods and apparatus for providing on a display device an electronic rendering of a locate operation to detect a presence or an absence of an underground facility. One or more electronic detection marks are displayed in a display field of the display device, based at least in part on locate information generated by a locate device used for the locate operation. The locate device includes a receiver antenna to detect a magnetic field from the underground facility. The locate information includes magnetic field information based on the detected magnetic field, and geographic information indicating at least one location of the locate device during the locate operation. One or more characteristics of the electronic detection mark(s) is/are based on the magnetic field information, and one or more positions in the display field at which the electronic detection mark(s) is/are displayed is/are based on the geographic information.

Abstract: A method for improving a sensitivity of a metal detector by reducing an unwanted magnetic field generated by at least one electrically conductive element of the metal detector, the metal detector transmitting a transmit magnetic field into a soil and a possible target within the soil which in response generate a response magnetic field, the method including the step of: redirecting at least a portion of the response magnetic field from entering the at least one electrically conductive element, wherein otherwise the at least one electrically conductive element within an influence of the response magnetic field generates the unwanted magnetic field due to a change in an intensity of the response magnetic field entering the at least one electrically conductive element, the redirecting adapted to reduce or eliminate the unwanted magnetic field generated by the at least one electrically conductive element thereby improving the sensitivity of the metal detector.

Abstract: A device for detecting an object in a subsurface, including a transmitting unit having a transmitting element designed to emit a transmission signal into the subsurface, a receiving unit having two or more receiving elements designed to receive a reception signal which is a function of the transmission signal and the properties of the object and of the subsurface, a control and evaluation unit which is designed to control the transmitting unit and receiving unit and to evaluate the reception signals, and a display unit which is designed to display the reception signals evaluated by the control and evaluation unit. The transmitting unit has at least one further transmitting element which is designed to emit at least one further transmission signal into the subsurface, and the transmitting elements of the transmitting unit are controllable independently of one another by the control and evaluation unit. A method is also provided.

Abstract: The present disclosure relates to determining attenuation factors relating to an electromagnetic signal passing through, a conductive material seen by a real sensor. A sensor is provided and disposed proximate to the material. An alternating current is passed through the sensor and the impedance of the sensor is measured. The impedance of an ideal coil is obtained from the measured impedance using electromagnetic modeling combined with a circuit analysis of the coil impedance, and the attenuation factors for the real coil in straight or feedback mode are determined by electromagnetic modeling of casing attenuation factors and impedance of an ideal coil combined with equivalent circuit modeling of the sensor transfer functions. The attenuation factors seen by the real sensor may be determined in real-time or post-survey. The material may be magnetic or non-magnetic.

Abstract: A training set including a target object set and a clutter object set is accessed. It is determined that the training set includes multiple types of targets or multiple types of clutter. The target feature value of a type of target is compared with the clutter feature value. The type of target is associated with the non-target object based on the comparison. A classifier is trained using the target feature value and the clutter feature value of the associated type of target and the non-clutter object. A feature value associated with an unknown object is applied to multiple classifiers to generate a set of metrics for the unknown object. The metrics are aggregated into an overall metric. Whether the unknown object is included in the target set is determined based on the overall metric.

Abstract: The invention relates to an apparatus for detecting a conductive object (5). The apparatus comprises at least one transmitting device (2), which is operative to generate a first changing magnetic flux (11, 12), and at least one receiving device (10), which is operative, in use, to receive a second changing magnetic flux (9) generated by the conductive object (5) in dependence upon the first changing magnetic flux. In addition, the at least one transmitting device and the at least one receiving device are disposed in relation to each other so as to attenuate the first changing magnetic flux (11, 12) received directly by the at least one receiving device (10) from the at least one transmitting device (2).

Abstract: A method for generating electromagnetic waves in the ELF/ULF comprising the steps of using a ground-based Horizontal Electric Dipole (HED) antenna to send electromagnetic pulses upwardly in the E-region of the ionosphere to form an oscillatory or pulsed electric field; allowing said pulsed electric field to interact with magnetized plasma of the lower ionosphere to generate a pulsed horizontal and vertical current which have associated Horizontal and Vertical Electric Dipole moment; and allowing them to radiate.

Abstract: A method for operating of a metal detection system may comprise a balanced coil system with a transmitter coil that is connected to a transmitter unit, which generates transmitter signals having a transmitter frequency that is selected from a group of at least two transmitter frequencies, and with a first and a second receiver coil that provide output signals to a signal input of at least one amplifier unit included in a receiver unit, wherein the output signals compensate each other so that the system is in balance. A system adapted to operate according to an exemplary method is also provided.

Abstract: A system and method for locating buried cables, pipes and other utilities includes a man portable receiver/locator which is linked by a wireless mesh connection to a transmitter which either directly applies, or induces, a signal onto a buried utility.

Abstract: A highly flexible real-time metal detector platform which has a detection capability for different targets and applications, where the operator is able to alter synchronous demodulation multiplication functions to select different types or mixtures of different types to be applied to different synchronous demodulators, and also different waveforms of the said synchronous demodulation multiplication functions; examples of the different types being time-domain, square-wave, sine-wave or receive signal weighted synchronous demodulation multiplication functions. The operator can alter the fundamental frequency of the repeating switched rectangular-wave voltage sequence, and an operator may alter the waveform of the repeating switched rectangular-wave voltage sequence and corresponding synchronous demodulation multiplication functions.

Abstract: A cable detection device is provided for measuring underground cable conditions. In one embodiment, a detection device is provided, including a handle for detecting underground cables; a digging component for digging, wherein the component is attached to a bottom of the handle; a panel attached on the bottom of the handle; a set of sensors attached to the panel, where the sensors are for detecting presence of cables by magnetic fields before digging occurs or during digging when the digging component undergoes operation, and where the sensors are tunneling magnetoresistance (TMR) sensors that are small in size, and where each sensor is placed evenly on the panel as an n by n array orientation, in order to maximize the sensitivity of the magnetic waves transmitted by the TMRs.

Abstract: The present invention relates to a method for detecting an electrically conducting target in soil, including the steps of generating a repeating transmit signal cycle of a fundamental period using transmit electronics, the repeating transmit signal cycle including a first period and a second period within each fundamental period; generating a transmit magnetic field using a magnetic field transmitter, based on the repeating transmit signal cycle, for transmission into the soil; receiving a receive magnetic field using a magnetic field receiver; producing a receive signal induced by the receive magnetic field; arranging for a current flowing through the magnetic field transmitter to flow to a first potential through a damping resistor during the second period for providing a damping effect on the current flowing through the magnetic field transmitter; arranging for the current flowing through the magnetic field transmitter to flow to a second potential, predominantly through an alternative path with a lower re

Abstract: A boring tool is moved through the ground within a given region along a particular path. The boring tool is moved in cooperation with moving a portable locator to establish a series of boring tool locations of the boring tool on the particular path. As at least one location of the series of locations is established, the location and a time stamp are electronically recorded to designate at least a time at which the location was recorded.

Abstract: An integrated mine detection system includes a ground penetrating metal detector and a ground penetrating radar detector. The integrated mine detection system includes an integrated search device housing a radio-wave transmitter of the radar detector and a coil of the metal detector. The radio-wave transmitter includes an antenna. The integrated search device includes a radio-wave receiver in the form of a pair of receiving antennas.

Abstract: A method for generating a transmit signal for transmission including the steps of a) generating at least two selected rectangular wave signals, each having a different fundamental frequency; b) mixing the selected rectangular wave signals to produce a driving signal; and c) driving a switching circuit using the driving signal for generating a transmit signal for transmission, wherein the Fourier transform of the transmit signal contains frequency components of relatively high magnitude, at frequencies corresponding to the convolution of the fundamental frequencies of the said at least two selected rectangular wave signals, as compared to other frequency components across the frequency spectrum of the Fourier transform, and wherein the rectangular wave signals are selected such that the frequency components of relatively high magnitude are substantially the same in magnitude, and spaced from each other in the frequency spectrum in a predetermined manner.

Abstract: The invention concerns a proximity detection of buried conductive structures before or while digging in areas being excavated. By means of the enclosed methods, devices, and setups, the ability and accuracy of the detection of underground structures, such as conduits, pipes, etc. is improved by conductively applying a current into the structure through the soil. The thereby emitted electromagnetic field is detected by a movable detection- unit over ground. According to this electromagnetic field the detection-unit can determine the proximity of the structure and issue a warning signal. This warning signal helps an operator of an earth moving machine to avoid a collision with the structure.

Abstract: A sensor for the location of metallic objects and also an associated method comprise a plurality of transmitting coils (2.1, 2.2) and at least one receiving coil (1.9) which are arranged such as to be inductively coupled to one another and overlap to a partial extent for the purposes of decoupling the interaction therebetween, whereby there can be obtained a point of optimal cancellation of the interaction. Due to the fact that a flow of current is passed through the transmitting coils (2.1, 2.2) by a sensor electronic system, equal flows of current through the transmitting coils have an effect upon the at least one receiving coil (1.9) which results in a local point of optimal cancellation which moves in a first direction when there is a flow of current in a first transmitting coil (2.1), whereas it moves in another direction when there is a flow of current in a further transmitting coil (2.