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 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 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 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.

Abstract: In order to control the sonde of an underground object, such as an underground boring tool, a predetermined sequence of rotation steps is applied to the object and that sequence is detected. The detection of the appropriate sequence causes the sonde to change its function, for example by changing the carrier frequency of the signal transmitted by the sonde on to change the data output sequence or transfer rate, or to change output power. While it is possible to use a single rotation step, the use of more than one step, with each step to be carried out within a predetermined time, reduces the risk of error.

Abstract: A method and apparatus includes filter for removing a non-tracer gas from detection system and control unit for detecting the presence a low concentration tracer gas in the atmosphere.

Abstract: Transmitted magnetic field signals useable for locating an underground object, and methods and systems for generating the same. The magnetic field signal has desired spectral characteristics. More specifically, the transmitted magnetic field signal includes a carrier component useable for locating an underground object. The carrier component has a carrier component frequency substantially equal to an integer multiple of 300 Hz. This guarantees that the carrier component frequency is substantially equal to an integer multiple of both 50 Hz and 60 Hz. Such a carrier component allows use of maximum information sidebands in environments that often include harmonically derived interference signals at regular 50 Hz (±0.1 Hz) or 60 Hz (±0.1 Hz) intervals caused by power lines. The transmitted magnetic field signal may also include at least one information sideband including sideband energy.

Abstract: A data recovery subsystem for use in a receive system configured to receive a magnetic field signal, the magnetic field signal including a carrier component usable for locating an underground object and at least one modulation sideband. The data recovery subsystem includes a first mixer to mix a Radio Frequency (RF) signal with a first Local Oscillator (LO) signal to produce an Intermediate Frequency (IF) signal representative of the magnetic field signal. A Phase Locked Loop (PLL) phase-locks a second LO signal to an IF carrier component of the IF signal. A second mixer synchronously mixes the IF signal with the second LO signal to produce a baseband signal including a demodulated sideband.

Abstract: A data sonde for use in horizontal directional drilling comprising a battery housing to receive a power supply from an internal battery, a connector to receive a power supply from an external power supply cable, and an antenna to emit radiation, is provided, wherein the antenna is arranged to receive operative power from an external power supply when one is connected to the connector, and from a battery housed in the battery housing if no external power supply is connected to the connector. A method of operation of the same is also provided.

Abstract: Methods and systems for producing an encoded information signal having attenuated low frequency spectral components and a substantially constant average energy. An M bit code word is produced for each N bits of an information signal according to the following conditions: (a) each code word includes an equal number of logic zero bits and logic one bits; (b) each code word includes no more than two consecutive identical bits; and (c) M is greater than N. For example, M equals eight and N equals four. Such an encoded information signal is especially useful for generating a magnetic field signal usable for locating an underground object. This is in part because information sidebands of the magnetic field signal to have desired spectral characteristics that are useful in environments that often include harmonically derived interference signals at regular 50 Hz (±0.1 Hz) or 60 Hz (±0.1 Hz) intervals caused by power lines.

Abstract: In order to control the sonde of an underground object, such as an underground boring tool, a predetermined sequence of rotation steps is applied to the object and that sequence is detected. The detection of the appropriate sequence causes the sonde to change its function, for example by changing the carrier frequency of the signal transmitted by the sonde on to change the data output sequence or transfer rate, or to change output power. While it is possible to use a single rotation step, the use of more than one step, with each step to be carried out within a predetermined time, reduces the risk of error.

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.

Abstract: A cable detection or location device is disclosed having a detection stage to produce a detection signal, a decimating filter having an input and an output, the input being coupled to the receiving stage to filter the detection signal and output a down-sampled filtered signal with a decimation ratio of N, and an output stage, coupled to the output of the decimating filter, to output an indication signal based upon the down-sampled filtered signal. The decimating filter used is a Finite Impulse Response (FIR) filter having a frequency response corresponding to that of a cascade of m SINC filters, wherein m is an integer greater than 1. A method of decimating a signal in a device is also disclosed.

Abstract: Cathodic protection voltages are used to resist the damage to pipes or cables from electrolytic effects. However, localized fields can lead to stray currents and may result in corrosion and it is therefore desirable to detect and analyse those stray currents. Frequently there are several pipes in the area of interest and so it is necessary to distinguish between those pipes. Therefore the cathodic voltage on the pipes is modulated, with different pipes having different modulations. This modulation may be applied using an interrupter. Orthogonal modulations with non-unitary aspect ratios improve the discrimination between the pipes while maximizing the energy content of the modulation pattern. The analysis is improved when the interrupters are synchronized with each other and so repeating on the same time-base. This synchronization may be achieved using an external time signal such as GPS. An interrupter which can be used in this regard is also proposed, and may be powered from the cathodic voltage itself.

Abstract: A method and apparatus includes a multi-position valve that restricts the air flow when the valve is placed in one position. Pressure tap valves are located are the inlet and outlet ports to measure the pressure differential and thereby determine the airflow rate.