Abstract: Methods, systems and locators for detecting faults in an insulation layer of an insulated conductor buried beneath a ground surface are described. The locator comprises a magnetometer arranged to detect a magnetic field generated by the alternating current and to generate a current signal on the basis of the detected magnetic field, and an Alternating Voltage Gradient receiver comprising a pair of probes arranged to make electrical contact with the ground surface, which is arranged to generate a voltage signal indicative of a voltage between the pair of probes. A processor is configured to substantially synchronously sample the current signal and the voltage signal. This enables improved detection of faults in the insulation layer of the insulated conductor.

Abstract: A locator for determining the location and/or orientation of a concealed conductor, comprising a reference field detector operable to detect an alternating magnetic field along a reference axis; a first field detector operable to detect an alternating magnetic field along a first axis; and a processor operable to calculate an in-phase component of a signal detected by the first field detector, the in-phase component being in phase with a signal detected at the reference field detector and to calculate a signal indicative of a position of the concealed conductor relative to the locator using at least the in-phase component.

Abstract: A locator for locating a concealed conductor comprises a first field detector operable to detect an alternating magnetic field along a first axis parallel to a primary axis of the locator; a second field detector, displaced from the first field detector and operable to detect an alternating magnetic field along a second axis parallel to the primary axis of the locator; and a processor operable to calculate a difference between a field detected by the first detector and a field detected by the second detector, and to calculate an indication of the lateral displacement of the concealed conductor from the primary axis of the locator using the difference.

Abstract: A detector for calculating the distortion of an electromagnetic field produced by a buried current carrying conductor comprises three antennas B, M, T. Outputs of two pairs of antennas are compared and the depth of the buried conductor is calculated using two different methods. If there is a significant difference in the two calculated depths then it is deemed that the electromagnetic field produced by the buried current carrying conductor is significantly distorted by the material in which the conductor is buried.

Abstract: A detector for calculating a depth of a buried conductor is provided. The detector includes a plurality of antennas for detecting an electromagnetic field radiated by the conductor and one or more signal processors for calculating the depth of the conductor based on the field detected by the antennas. The calculated depth of the conductor is displayed when one or more predetermined criteria are satisfied.

Abstract: A detector for detecting a buried conductor comprises a plurality of antennas B, T. Each antenna B, T has a winding wound around the antenna, the winding being connected to a current source for providing a predefined current in the winding. When the predefined current is applied to the winding an electromagnetic field is generated at the antenna which induces a test current in the antenna. The test current is compared to calibration data stored in the detector to validate the correct operation of the detector.

Abstract: A system for detecting a buried conductor comprises a transmitter for producing an alternating test current in the buried conductor and a receiver for detecting an electromagnetic field produced by the test current in the buried conductor. A communication link is provided between the receiver and the transmitter. The receiver measures the signal to noise ratio, SNR, of the electromagnetic field produced by the test current and if the SNR is below a threshold then the receiver controls the transmitter to set frequency and/or power characteristics of the test current.

Abstract: A system for detecting a buried conductor comprises a transmitter for generating a test signal in the buried conductor and a detector for detecting an electromagnetic signal resulting from the test signal flowing in the buried conductor. The transmitter comprises a waveform generator for generating a drive waveform signal, a power supply, an amplifier, connected to the power supply and the waveform generator for producing an output drive signal based on the drive waveform signal and an output circuit for acting on the output drive signal to generate an output signal having a current and a voltage. In-phase and quadrature components of the current and voltage of the output signal are fed back for controlling the amplifier.

Abstract: A system for detecting a buried conductor comprises a transmitter for producing an alternating test current in the buried conductor and a receiver for detecting an electromagnetic field produced by the test current in the buried conductor. A communication link is provided between the receiver and the transmitter. The test current comprises first and second components of different frequency. The receiver monitors the phase creepage of the first and second components and controls the transmitter to reset the phase difference between the first and second components as phase creepage increases.

Abstract: The present invention provides a method of time domain reflectometry including transmitting a test signal along a cable under test from one end and sensing and recording a reflected signal from the cable at that end, using the recorded, reflected signal to estimate the distance, Ldist, from the one end to a discontinuity on the cable, separating a test signal component from the remainder, Vr, of the reflected signal; estimating the impedance, Zfault, of the discontinuity from known, predetermined values of the characteristic impedance, Zline, and of the characteristic gain, T, of a reference cable, and from the said separated test signal and reflected signal components, calculating the estimation error as a difference between the model reflection signal, Vrmod, expected of the cable under test based on the characteristic impedance and characteristic gain and the estimated impedance, Zfault and distance, Ldist, and the actual reflection signal Vr, choosing new estimated values of Ldist and Zfault in accordance

Abstract: A detector 1 for detecting a buried current carrying conductor comprises a digital homodyne receiver. The receiver processes field strength signals induced in a pair of vertically spaced antennae 3, 5. The analogue to digital converter is an audio-grade stereo CODEC 11.

Abstract: A detector for locating a sonde is comprised of a plurality of antennas, a corresponding number of signal isolator modules 1 and a geometrical evaluation module. The magnetic signal generated by the sonde has a fundamental frequency and harmonic frequencies. A frequency spectrum analyzer 29 which forms part of the signal isolator module 1 has frequency bins which are aligned with the fundamental frequency and a plurality of harmonic frequencies of the magnetic signal produced by the sonde. The frequency bins follow variations in the frequency of the magnetic signal produced by the sonde which allows the detector to detect the sonde at a separation of up to 30m.

Abstract: A detector 1 for detecting a current carrying conductor determines the presence of a current carrying conductor one or more of passive or active modes. In the passive modes, the detector 1 detects either very low frequency radio signals re-radiated from a conductor or electromagnetic radiation produced by a conductor as a result of mains voltage carried in the conductor, or in a nearby conductor. In the active mode, an alternating signal from a dedicated signal generator is coupled into the buried conductor. Signals are induced in a pair of antennae 3, 5 in the detector 1, and the signals are processed in each of these modes simultaneously. The outputs of each of the modes are convolved to produce an audio and/or visual alert if a current carrying conductor is detected by any of these modes.

Abstract: A detector 1 for detecting a current carrying conductor has a pair of vertically spaced antennae 3, 5 to detect the magnetic radiation produced by a current carrying conductor as a result of one or both of the mains power supply or an electromagnetic signal which is induced in the conductor by a dedicated signal transmitter. The detector 1 continuously calculates the depth of a buried conductor and if the buried conductor is above a predetermined minimum depth then the detector 1 triggers an audio and/or visual alarm. By reducing the sensitivity of the antennae 3, 5, the lateral offset range for which the alarm sounds is reduced and the location of a buried conductor can be determined.

Abstract: A security system for controlling access to an enclosed conduit along which runs fiber optic cable, the conduit having a cover for access to the cable, the system having a communications receiver and a modulator responsive to an output of the receiver for coupling non-intrusively to the fiber optic cable adjacent the cover, the communications receiver being responsive to the presence or absence of an access authorization signal from an operator to cause the modulator to introduce a signal to the fiber optic cable indicative of the authorization status.

Abstract: A radio mode selectivity block 41 for a detector 1 for detecting a buried current carrying conductor comprises a plurality of beat frequency oscillators 53 to center the bandwidth of detection of the detector 1 on target very low frequency (VLF) frequency bands. The frequencies of the beat frequency oscillators are chosen to fall within the VLF frequency bands used in a number of countries, so that the detector 1 can be used in radio mode in these countries without the need for local configuration.

Abstract: A cable detection apparatus is disclosed having a filter, the filter transmitting components of a signal detected substantially at certain harmonics of a first frequency. The filter may also attenuate the signal at certain even harmonics thereof. A method of detecting and/or locating cables in the same manner is also disclosed.