Abstract: A monitoring device defines a boundary for movement of an underground object such as a booring tool. The underground object generates a magnetic field which is detected by the monitoring device. The monitoring device then determines the position of the underground object relative to itself, and hence to the boundary. The movement of the underground object can then be controlled so that it does not cross the boundary. The monitoring device may therefore define a protection zone so that a buried object within that protection zone will not be contacted by the moveable underground object.

Abstract: A system for tracing routes of conductors has a transmitter (10) for applying an alternating signal (11) to the conductor to be traced (12), and the field produced by this signal is detected remotely from the conductor. In order to distinguish between the field produced by the conductor being traced and the fields produced by nearby conductors (14) due to capacitive coupling (17), the alternating signal has phase-locked first and second components with frequencies F1 and F2 respectively, related by N×F1=M×F2, where N and M are non-adjacent integers greater than 1, one of which is odd and one of which is even, having no common factors. The field is detected at a plurality of positions. The phase relationship of the detected signals is investigated to determine unambiguously the position of the object concerned.

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: Method and systems for reducing effects of magnetic field interference that may interfere with a magnetic field signal generated at or near an underground object, where the magnetic field signal is used to monitor the location of the underground object. At least two different moving averages of a plurality of samples that are representative of a detected magnetic field signal strength are produce. Each of the different moving averages is a moving average of a different number of the plurality of samples. A respective quality metric (e.g., variance) is then determined for each of the different moving average. One of the moving averages is selected based on the determined quality metrics. Further signal processing is then performed using the selected moving average. For example, the selected moving average is used to monitor the location of the object.

Abstract: In order to identify a fiber optic cable (10) a beam (14) of polarised light is caused to pass down the cable to a first site (A) at which an electromagnetic field (24) is applied to the cable (10). The electromagnetic field (24) traverses the cable (10) in an essentially transverse direction and has a time-varying component orientated along the length of the cable (10) at the first site (A), with the component varying so that the line integral thereof along the cable (10) is non-zero. This results in a variation in the polarisation of the light, which can the be detected by a polarisation discriminator (20) at a second site (B), thereby to identify the cable (10).

Abstract: In order to locate an inaccessible object such as an underground boring tool, the inaccessible object having means, for example a solenoid, to generate a magnetic field, a locator is provided with a detector for detecting the generated magnetic field. The detector may be an aerial array of three mutually perpendicular coils. When the locator is moved from a first position to a second position errors may arise in the measurements due to misalignment of the locator. In order to minimise such errors, a magnetic compass is provided on the locator to ensure that the locator can be maintained in the same position relative to the Earth's magnetic field. The magnetic compass is not affected by the magnetic field generated by the solenoid as this magnetic field is an A.C. magnetic field.

Abstract: Apparatus for detecting a leak in a pipe, and determining the location of that leak, comprises a cover plate for an opening into the pipe to be tested, such as an end cap for threading onto the end of a pipe, the cover plate having an aperture through which extends a flexible hose having an inflatable bladder at its free end. The hose is calibrated from its free end and is pushed into the pipe through the aperture for a known distance, whereafter the bladder is inflated by air supplied under pressure to the hose, so as to seal the pipe between the bladder and the cover plate. Air under pressure is then supplied to the sealed portion of the pipe and the pressure drop within that sealed portion is monitored over a period of time. By repeatedly performing the method but each time moving the hose further into the pipe, the location of the leak may accurately be determined.

Abstract: A method of locating a concealed conductor is performed by generating a magnetic field with a direction in which the field is a maximum. The magnetic field is rotated until that direction is directed towards the conductor. In this way, a signal is induced in the conductor which has a maximum value when that direction is directed towards the conductor. The induced signal is detected in the conductor, using a detector arranged to determine the direction of the conductor relative to the detector. The detector detects when the induced signal has the maximum value.

Abstract: In order to identify a cable buried underground, a very low frequency voltage signal is applied to the cable and an electric field sensor is brought into proximity with the cable. The sensor thus detects the voltage signal on the cable and so identifies the cable. The sensor is unaffected by one or more additional cables carrying voltage signals, which are proximate the cable of interest, as the electric filters from such additional cables do not pass to the cable of interest. The sensor is mounted on a probe which is mounted into a bore in the soil around the cable of interest. The probes may also carry a magnetometer for detecting magnetic fields generated by low frequency alternating current signals on the cable of interest.

Abstract: If a solenoid is mounted on an underground object, such as a boring tool, magnetic fields generated by an electric current flowing through that solenoid can be detected by a suitable detector at or above the surface. If the axis of the solenoid is tilted, the maximum value of the field is not directly above the solenoid. Therefore, the present invention makes use of measured values of horizontal and vertical components of the magnetic field to determine the separation of the detector and the solenoid, and also, by making use of a tilt sensor associated with the solenoid to derive a prediction of the ratio of the horizontal and vertical components of the field at a position vertically above or below the solenoid. If that predicted value of the ratio is then compared with the measured value of the ratio, the two will coincide when the detector is vertically above the solenoid. Thus, by moving the detector until such coincidence is obtained, the position of the solenoid can be determined.

Abstract: A locator such as a ground penetration probe (24) has spaced antennae (21,22,23) therein which detect electromagnetic signals from an object (26) such as a buried cable. By analyzing the electromagnetic signals using a suitable processor (25) it is possible to determine the separation of the locator and object (26), both in terms of the direction (X) corresponding to the spacing of the antennae (21,22,23) and the perpendicular direction (Y) to the object (26). This then permits a display to be generated showing visually the separation of the locator and the object (26). If the locator incorporates a tilt sensor, the processor (25) can then compensate for tilting of the locator, and determine the vertical and horizontal separation of the locator and the object (26).

Abstract: In order to locate an inaccessible object, such as an underground boring tool (30), a solenoid (10) on or in the tool generates a magnetic field which is detected at two measuring locations (20, 21). Information relating to the relationship between the axial and radial components of the field from the solenoid (10) are stored, and comparison of the measured values of the axial and radial components at the measurement locations (20, 21) enables the direction of the solenoid (10) from the measurement locations (20, 21) to be determined. The known attenuation of the magnetic field from the solenoid (10) enables the distance between the solenoid (10) and the measurement locations to be determined from the absolute value of the field at the measurement locations (20, 21) and the direction to the solenoid (10).

Abstract: Two vertical, parallel, horizontally spaced signal coils are connected in series but in opposite phase across an a.c. source. Thus a buried conductor located centrally beneath the coils experiences an alternating magnetic field whose strength is due to the addition of the fields induced by the two coils. The field strength may be further enhanced by one or more of: providing a ferromagnetic flux diverter between the upper ends of the coils; placing a conductive nonmagnetic screen between them; connecting a tuning capacitor in parallel with the coils; or providing a tuning circuit having series-connected secondary coils which are flux-linked to respective signal coils and are in parallel with a capacitor. There may be a switch arrangement for switching the signal coils to in-phase connection, for use when they are oriented horizontally.

Abstract: An angular displacement sensor for limited angle applications (e.g., for sensing automotive throttle positions) comprising first (14) and second (16) relatively rotatable components arranged to confront each other axially. The first component (14) provides a plurality of poles (14A, B, C) which are angularly disposed about the rotation axis and extend towards the second component. These poles (14A, B, C) have axes which extend in the same direction as the rotation axis. Some poles have windings (14A, B), while others (14B) provide flux return paths. The second component comprises an inductance affecting component (16) which overlies only some of the wound poles at any given time, the relative rotation varying the poles which are overlaid. The sensor includes an output unit (17) for providing output signal data related to the inductances of the excitation poles and thus related to the rotary configuration of the components.

Abstract: Geographical positional data is obtained for an underground object by locating the object using a device that locates underground objects. An apparatus that receives data from a global position system ("GPS") provides data identifying global position of the device, and thus also of the located underground object. A data storage unit stores such positional data, which may be used in the future to re-locate the underground object. The GPS-data receiving apparatus can preferably receive data from at least one overhead GPS satellite and from a secondary stationary receiver. Data from the secondary stationary receiver may be modulated on to a signal transmitted along a detected underground cable object.

Abstract: An elongate vessel, preferably cylindrical, is partially filled with a conductive and/or ferromagnetic fluid. At least two coils are wound on the vessel in longitudinally different regions so that tilting the vessel varies the amount of the fluid inside the coils differently. This affects their inductances. The variation in inductances is monitored, directly or indirectly, e.g. by applying an AC signal to the coils and monitoring the voltage drops across them. This provides an electrical output related to the inclination of the sensor's axis. It is unaffected by rotation about the axis. Thus the sensor can be used to monitor the orientation of the axis of a drilling tool, e.g. a mole, which rotates about its axis.

Abstract: An inductive displacement sensor has first and second elements which define a path for movement. The first element has coil portions which interact with an inductance affecting part of the second element so that the inductances of the coil portions vary with movement of the inductance affecting part, only some of the coil portions being affected by the inductance affecting part at any time. The coil portions are arranged in two series connections, each series connection being at least two coil portions electrically connected in series. Coil portions of the two series connections are then arranged alternately. In this way, substantially sinusoidal output signals may be obtained.

Abstract: A system for tracing routes of conductors is disclosed. An alternating signal is applied to the object to be traced (12), and the field produced by this signal is detected remotely from the object. In order to distinguish between signals produced by the object being traced and those produced by nearby conductors (14) due to capacitive coupling, the alternating signal has first and second components, related in frequency and phase, and the field is detected at a plurality of positions. The phase relationship of the detected signals is investigated to determine unambiguously the position of the object concerned. In one embodiment, the second frequency component is a harmonic of the other. In another embodiment the frequency of the second component is the frequency of the first, plus or minus a sub-harmonic of the first.

Abstract: Displacement along a linear or rotary path causes relative displacement of a pair of elements (101,102) that confront each other across the path. One element (101) provides a series of coil portions (AB,BC), while the other (102) has a portion which increases the inductance of the fraction of the coil portions that it lies adjacent at any instant. The coil portions are homopolar. Typically each coil portion has an axis which intersects the path, and all are wound in the same sense about their axes. They are generally connected in series as a single winding on a core (101). The core has unwound portions (104) for providing a flux return path.