Location tracking system

Abstract

The present disclosure relates a location tracking system comprising a base unit and a remote device. The base unit comprises at least one electrical wire, an AC current source configured for supplying an AC current flowing through the at least one electrical wire so as to generate an alternating magnetic field, and a first and a second ground terminal. The remote device comprises a magnetic field detector and a signal transmitter configured for transmitting a modulated electrical signal via the earth to the base unit, and wherein the modulated electrical signal comprises encoded data specifying at least one or more magnetic field properties detected and / or specifying one or more quantities derived from the one or more magnetic field properties detected. The base unit further comprises a signal receiver coupled with the first and the second ground terminal and configured for detecting the modulated electrical signal transmitted by the signal transmitter.

Description

[0001] Title: Location tracking system

[0002] FIELD OF DISCLOSURE

[0003] The invention relates to a location tracking system, more precisely a system that allows to remotely track a location of an object. The object can be located underground or above ground.

[0004] BACKGROUND

[0005] The present disclosure relates to a location tracking system for tracking the location of a remote object, i.e. the object to be tracked is located at a distance with respect to for example a base station that needs to know the location of the object with respect to the base station. Various types of location tracking systems for tracking a location of an object are available on the market.

[0006] Some known tracker systems use a global position system based on a GPS device that can receive radio signals broadcasted by a global satellite system. Basic GPS systems have generally an accuracy of a couple of meters. More advanced systems wherein the GPS is using for example the Real-Time Kinematic, RTK, technique, can obtain accuracies in the cm range. A remote device, also named tracker, comprising a GPS can be attached to the object to be tracked and the location of the remote device can for instance wirelessly be transmitted to a base station as an RF signal.

[0007] However, a drawback of a GPS based position system is its inability to work indoors, underground or zones with limited satellite coverage. Further, the GPS can also be impacted by atmospheric related situations. A further drawback is that a GPS based system generally also uses quite some energy for acquiring the satellite signals, which can be a problem for battery powered tracking devices.

[0008] Underground object localization is for instance required for the mining industry or for underground boring. For example, when drilling a hole underground it is important to maintain the boring assembly correctly positioned and oriented in order to assure that the hole is formed in the required location and direction.

[0009] An example of a known drilling system for underground installations is a HDD rig system for drilling tunnels, e.g. required for installing pipelines. These systems make use of a rod assembly comprising a sequence of rods coupled on one end to a drill head located below ground and coupled to another end to a drill rig generally installed above ground, sometimes below ground. During the drilling process it is important to track the location of the drill head in order to be able to make steering corrections when needed, e.g. when the path followed by the drill head is deviating from the planned path.

[0010] For underground drilling, various types of sensors have been proposed to help localize the drilling head such as the use of gravity, magnetic, pressure, inclination, acceleration sensors and the use of gyroscopes. However, the use of these sensors and detection techniques for localization purposes might result in more costly and more complex and possibly less precise position determining systems.

[0011] In the field of bore hole drilling, location tracking systems using powerful magnets and / or solenoids located either above or below ground for generating varying magnetic fields that can be detected above or below ground with a probe are also known in the art. One of the problems with these systems is however the drop of the magnetic field with distance and hence the need to use high currents for generating the magnetic field. Additionally, for systems using for instance two solenoids, also the positioning of the coils with respect to each other may be important as the field may differ at the same distance for different positions of both solenoids.

[0012] Hence, there is room for improving location tracking systems, more specifically location tracking systems that not only can determine locations of objects located above ground but also for objects located below ground. SUMMARY

[0013] It is an object of the present disclosure to provide a robust, powerful and cost-effective location tracking system.

[0014] The present disclosure is defined in the appended independent claims. The dependent claims define advantageous embodiments.

[0015] According to an aspect of the present disclosure, a location tracking system comprising a base unit and a remote device is provided. The base unit comprises at least one electrical wire, an AC current source configured for supplying an AC current flowing through the at least one electrical wire so as to generate an alternating magnetic field, and at least a first and a second ground terminal.

[0016] The remote device comprises at least: a) a magnetic field detector configured for detecting one or more magnetic field properties of the alternating magnetic field, and wherein the one or more magnetic field properties comprises at least a magnetic field strength and / or a magnetic field orientation; and b) a signal transmitter configured for transmitting a modulated electrical signal via the earth to the base unit, and wherein the modulated electrical signal comprises encoded data specifying at least the one or more magnetic field properties detected and / or specifying one or more quantities derived from the one or more magnetic field properties detected.

[0017] The base unit further comprises a signal receiver electrically coupled with the at least first and second ground terminal and configured for detecting the modulated electrical signal transmitted by the signal transmitter.

[0018] Advantageously, by providing a remote device with a signal transmitter transmitting a modulated electrical signal and a corresponding signal receiver at the base station for receiving the modulated electrical signal, no cabling is required for transmitting the magnetic field data or derived positioning data. Indeed, the modulated electrical signal may propagate from the signal transmitter through the earth towards the ground terminals, which in turn are electrically coupled with the signal receiver.

[0019] In embodiments, the location tracking system comprises two ground terminals, a first and a second ground terminal. In other embodiments, the location tracking system may comprise two or more ground terminals, for example 3 or more ground terminals.

[0020] In embodiments, the first and the second ground terminal may be terminals for establishing a return path through the earth for the AC current flowing through the at least one electrical wire, i.e. the first and second ground terminal are configured for establishing a return path through the earth.

[0021] Advantageously, by providing a base unit that is generating a magnetic field using an electrical wire that is coupled with ground terminals to the earth for forming an earth return path, a somewhat circular magnetic field is created that is somewhat dropping linearly in strength with distance.

[0022] Advantageously, by providing a base unit that is producing a magnetic field based on the single-wire-earth-return principle, a simple and cost effective base unit can be manufactured.

[0023] Advantageously, the ground terminals of the base station that are used for forming the earth return path for the AC current flowing through the electrical wire for creating the magnetic field, may also be used for receiving the modulated electrical signal from the signal transmitter of the remote device.

[0024] In embodiments, the at least one electrical wire, that is used for generating the alternating magnetic field, may be configured for also receiving the modulated electrical signal. Generally, in these embodiments, the signal receiver is coupled with the at least one electrical wire for detecting the modulated electrical signal received through the at least one electrical wire. In further embodiments, the location tracking system may further comprise a receiving electrical wire configured for receiving the modulated electrical signal. Generally, in these embodiments, the signal receiver is coupled with the receiving electrical wire for detecting the modulated electrical signal received through the receiving electrical wire. The receiving electrical wire is forming a connection wire electrically connecting the signal receiver 3b with the ground terminals for receiving the MES signal.

[0025] Generally, the signal transmitter comprises a first transmission electrode for making a first electrical contact with the earth and a second transmission electrode electrically insulated from the first transmission electrode for making a second electrical contact with the earth.

[0026] Preferably, the AC current from the AC current source has a frequency in a range between 3 Hz and 30 kHz.

[0027] Generally, the current source supplying the AC current is configured to provide a current amplitude having a value between 100 mA and 5 A, preferably between 0.5 A and 5 A, more preferably between 0.5 A and 3 A.

[0028] Generally, the modulated electrical signal has a carrier frequency comprised in a range between 3 Hz and 30 kHz, preferably the carrier frequency is different from the frequency of the AC current supplied by the AC current source.

[0029] In embodiments, the signal receiver is configured for receiving the modulated signal as a signal propagating through the electrical wire, preferably the signal receiver is configured for detecting the modulated signal propagating through the electrical wire as a voltage variation.

[0030] In embodiments, the signal transmitter comprises a control unit configured for generating the modulated electrical signal. Preferably, the control unit is configured for applying a modulated AC voltage between the first and second transmission electrode. In embodiments, the modulated AC voltage has a maximum amplitude in range between 1 V and 24 V, preferably between 1 V and 10 V, more preferably between 5 V and 10 V.

[0031] In embodiments, the control unit comprises a signal generator for generating a carrier waveform and a signal modulator configured for modulating the carrier waveform.

[0032] In embodiments, the magnetic field detector comprises at least a magnetic field sensor, an amplifier and filter unit for amplifying and filtering signals detected with the magnetic field sensor, and a processing unit for generating a sequence of data to be transmitted to the base unit.

[0033] In embodiments, the one or more quantities derived from the one or more magnetic field properties detected comprises one or more coordinates specifying a location of the magnetic field detector or a location of a device the magnetic field detector is attached to.

[0034] In embodiments, the remote device comprises a housing configured for supporting and housing the magnetic field detector and the signal transmitter. Preferably, the housing comprises a main body and an internal body, and wherein the main body has an inner bore and the internal body is inserted through the inner bore of the main body.

[0035] In embodiments, the internal body comprises a channel configured for transmitting air or a drilling fluid from a first end to a second end of the internal body.

[0036] In embodiments, the internal body comprises a cavity configured for at least receiving electronic components of the signal transmitter and / or receiving components of the magnetic field detector. Preferably wherein the electronic components of the signal transmitter comprise at least a control unit and / or wherein the components of the magnetic field detector comprises at least the magnetic field sensor, the amplifier and filter unit and the processing unit. Generally, the cavity is separated from the channel such that no air or drilling fluid can enter the cavity.

[0037] In embodiments, an electrically conductive sleeve electrically insulated from the main body and surrounding at least a part of an outer side of the main body is forming the first transmission electrode. Preferably, wherein at least a portion of the main body or a conductive element attached to the main body is forming the second transmission electrode.

[0038] In embodiments, an inner side of the electrically conductive sleeve is electrically insulated from the main body by an isolating glue and / or by one or more O-rings, preferably at least two O-rings. Optionally, a first and a second lateral side of the electrically conductive sleeve is electrically insulated from the main body by respectively a first and a second ringshaped insulator.

[0039] According to a second aspect of the present disclosure, a drilling system for drilling a hole or a tunnel comprising at least a drill rig 6 that may be positioned on the earth surface, a drill head, a drill rod assembly for connecting the drill head with the drill rig and a location tracking system are provided. In embodiments, the remote device of the location tracking system is coupled between an end portion of the drill rod assembly and the drill head.

[0040] In embodiments, the drilling system comprises a drill controller configured for calculating a steering correction for adjusting a drill direction of the drill head, and wherein the calculation of the steering correction is based on the encoded data received from the signal transmitter.

[0041] SHORT DESCRIPTION OF THE DRAWINGS

[0042] Further aspects of the present disclosure will be explained in greater detail by way of example and with reference to the accompanying drawings in which: Fig.l shows a schematic representation of an example of an embodiment of a location tracking system for underground location tracking according to the present disclosure;

[0043] Fig.2 shows a system according to the present disclosure comprising two parallel wires for generating a first and a second magnetic field;

[0044] Fig.3 and Fig.4 show schematic representations of drilling systems for drilling a hole comprising a location tracking system according to the present disclosure;

[0045] Fig.5 schematically illustrates a distance and angular deviation detection;

[0046] Fig.6 schematically illustrates a bottom hole assembly of a drilling system comprising a drill head and a remote device according to the present disclosure comprising a magnetic field detector and a signal transmitter;

[0047] Fig.7 is a cross-section of an embodiment of a remote device that is attachable to a drill head;

[0048] Fig.8 schematically illustrates a transmission of a modulated electrical signal from a remote device attached to a drill head located below ground to a base unit located above ground;

[0049] Fig.9 schematically illustrates a transmission of a modulated electrical signal from a signal transmitter coupled to drill rods;

[0050] Fig.10 shows a schematic representation of a further example of an embodiment of a location tracking system wherein the straight wire is positioned vertically with respect to the ground level;

[0051] Fig.11 shows a schematic representation of a further example of an embodiment of a base unit of a location tracking system according to the present disclosure;

[0052] Fig.12 shows a schematic representation of a further example of an embodiment of a location tracking system for underground location tracking according to the present disclosure, wherein at least a portion of the electrical wire for generating the magnetic field is non-insulated;

[0053] Fig.13 shows a schematic representation of another example of an embodiment of a location tracking system for underground location tracking according to the present disclosure wherein the electrical wire for generating the magnetic field is forming one or more loops, and wherein via the ground terminals a return path for the AC current is established through the earth;

[0054] Fig.14 shows a schematic representation of a further example of an embodiment of a location tracking system for underground location tracking according to the present disclosure wherein the electrical wire for generating the magnetic field is forming one or more loops, and wherein in addition to a return path through the earth ground via the ground terminals, a second return path above ground for the AC current is provided;

[0055] Fig.15 shows a schematic representation of a further example of an embodiment of a location tracking system according to the present disclosure, wherein the electrical wire for generating the magnetic field is forming one or more loops and wherein a separate receiving wire is coupled between the ground terminals such that the modulated electrical signal may propagate to the signal receiver of the base unit via the separate receiving wire;

[0056] Fig.16 shows a schematic representation of a further example of an embodiment of a location tracking system according to the present disclosure, wherein the electrical wire for generating the magnetic field is separated from a receiving wire coupled between the ground terminals;

[0057] Fig.17 shows a schematic representation of a further example of an embodiment of a location tracking system according to the present disclosure, wherein three ground terminals are provided; Fig.18 shows a schematic representation of a further example of an embodiment of a location tracking system according to the present disclosure, wherein the signal receiver and AC current source are located at different locations above ground;

[0058] Fig 19 schematically illustrates an embodiment of a location tracking system used for underground mining applications.

[0059] The drawings of the figures are neither drawn to scale nor proportioned. Generally, identical components are denoted by the same reference numerals in the figures.

[0060] DETAILED DESCRIPTION OF EMBODIMENTS

[0061] With reference to Fig.l, Fig.2, Fig.10, Fig.11, and Fig.13 to Fig.18, examples of embodiments of a location tracking system according to the present disclosure are schematically shown.

[0062] The location tracking system 1 for tracking a location of an object comprises at least a base unit 3 and a remote device 4.

[0063] In Fig.l, an example of an embodiment is shown wherein the remote device 4 is located underground. An example of an application that may use the location tracking system according to the present disclosure is a drilling system for drilling a hole. With reference to Fig.3, Fig.4, Fig.8, Fig.9 and Fig.12 embodiments of a drilling system using a location tracking system according to the present disclosure, are schematically shown. In these examples, the drilling system comprises a drill rig 6 positioned on the earth 20 surface, a bottom hole assembly 28 positioned underground and comprising at least a drill head 8, and a drill rod assembly 7 for connecting the drill rig 6 with the bottom hole assembly. In this example the remote device 4 and the drill head 8 may be forming the bottom hole assembly 28. In other embodiments the bottom hole assembly may comprise additional components. Drilling systems may use a location tracking system according to the present disclosure wherein the remote device 4 is for instance located between an end portion of the drill rod assembly 7 and the drill head 8, as illustrated on Fig.8. In this way, as the remote device is coupled to the drill head, the location of the drill head can be tracked during operation of the drill head.

[0064] The location tracking system of the present disclosure is however not limited for use with a drilling system, it can be used for any device that needs to be tracked, especially a device that is located underground.

[0065] As illustrated on Fig.l, the base unit 3 of the location tracking system 1 according to the present disclosure comprises an electrical wire 2 and an AC current source 3a configured for supplying an AC current flowing through the electrical wire 2. The base unit 3 further comprises a first ground terminal Pl and a second ground terminal P2. In the embodiment shown on Fig.l, the first Pl and second P2 ground terminal are configured for establishing an earth return path for the AC current flowing through the electrical wire 2. In this way, the single-wire-earth-return principle is used for having a current flowing through the electrical wire.

[0066] The location tracking system 1 is further provided with a remote device 4, located underground, that comprises a magnetic field detector 4a configured for detecting one or more properties of the magnetic field generated by the electrical wire 2 and a signal transmitter 4b configured for transmitting a modulated electrical signal MES via the earth 20 to the base unit, as will be discussed in more detail below.

[0067] In further embodiments, as schematically illustrated on Fig.14, the electrical wire 2 is coupled with the ground terminals Pl, P2 for forming a return path through the earth 20 and, at the same time a return path RP above ground is provided as well. In this embodiment, the alternating magnetic field is generated both by a contribution from a first current using the earth as return path and a contribution from a second current using the other return path RP above ground. In this example shown on Fig.14, the electrical wire 2 is also forming loops.

[0068] In other embodiments, as schematically shown on Fig.15 to Fig.18, the electrical wire 2 is not using a return path through the earth 20, via the ground terminals, as is the case for the embodiment shown for instance on Fig.l, but instead uses its proper return path RP, i.e. a return electrical wire, above ground coupled to the AC current source. Advantageously, with the embodiment shown on Fig.15 to Fig.18, there is no return path through the earth and hence no current through the earth for generating the alternating magnetic field. In this way, potential disturbances for transmitting the modulated electrical signal with the signal transmitter may be avoided. Further, when using a return path through the earth 20, the resistance between the ground pins and the soil may limit the amount of current through a single wire for a given power source. Advantageously, by using a wire in a loop, the resistance is much lower and a higher current may be used and hence a higher magnetic field for a similar power source may be reached.

[0069] In embodiments, the ground terminals Pl, P2 are ground pins or ground rods insertable in the earth 20. The ground pins can for example be made of copper. The ground pins may be in any shape or form suitable for connection with the earth. In other embodiments, ground pins or grounding facilities already existing or already installed for other purposes may be used.

[0070] In some embodiments, as schematically shown for example on Fig.4 and Fig.8, when the location tracking system is used for tracking a location of a drill head 8 while drilling a hole under the earth surface, a drilling anchor 9 anchoring a drilling rig 6 located on the earth surface can be used as one of the ground terminals Pl for forming the single-wire-earth-return. Further, in embodiments, the drill rod assembly, also named drill string, of the drill system may act as a ground terminal. The present disclosure is not limited to a specific location for placing the electrical wire. The electrical wire may be located on the earth surface, in the air or below the earth surface.

[0071] In embodiments, as schematically illustrated on Fig.l, the electrical wire 2 may for example be resting on the earth 20 surface. In other embodiments the electrical wire may be resting or at least partly be resting on a riverbed.

[0072] In further embodiments, as schematically illustrated on Fig.10, the electrical wire may be positioned through a reference bore hole 35 made through the earth 20. In this example, the reference bore hole 35 is a vertical hole and a first ground terminal P 1 is located near the earth surface and a second ground terminal P2 is located on the bottom side of the bore hole. In embodiments, the at least one electrical wire 2 of the location tracking system may be a single conductive wire or cable.

[0073] Further, the electrical wire 2 is not necessary elongating along a straight line as for example schematically shown on Fig.l, but the electrical wire 2 may also be elongated along a curved line or a combination of a straight and curved line. For example, in embodiments the electrical wire may be aligned along an essentially straight line and in case a physical obstacle occurs on the straight line, a turn around the obstacle with the electrical wire can be made.

[0074] In the embodiments shown on Fig.13 to Fig.18, the electrical wire is forming one or more loops, similar to a loop antenna. Such a configuration wherein the wire 2 for generating the magnetic field is forming loops, results in a magnetic field strength that may be multiple times larger when compared to a magnetic field generated by a straight single wire.

[0075] In embodiments, the electrical wire 2 may comprise a first end E 1 and a second end E2 and the first ground terminal Pl is electrically connectable to the first end E 1 and the second ground terminal P2 is electrically connectable to the second end E2. As schematically shown on Fig.5, the electrical wire 2 may have a wire length L, measured between the first end El and second end E2, and the wire length L is generally in a range between 1 meter and 2000 meter or even longer, preferably between 2 meter and 1000 meter, more preferably between 10 meter and 1000 meter.

[0076] The electrical connection of the ground terminals with the ends of the electrical wire 2 may be directly or indirectly. A direct connection has to be interpreted as a connection wherein an end of the electrical wire is directly attached to a ground terminal. As for example schematically illustrated on Fig.l, the second end E2 is directly connected to the second ground terminal P2. An indirect connection has to be interpreted as a connection wherein an intermediate part is making the electrical connection with the end of the electrical wire and the ground terminal. For example, as shown on Fig.l, the first end El of the electrical wire is connected to the current source 3a, which in turn is connected to the first ground terminal Pl. In other embodiments, the intermediate part connecting an end of the electrical wire 2 to a ground terminal may also be an auxiliary wire extension wire. In Fig.11 an example is shown wherein the first and second end of the electrical wire 2 are directly connected to respectively the first and second ground terminal and wherein the current source 3a is located between the first and second end of the electrical wire 2.

[0077] By generating an AC current through the electrical wire 2 an alternating magnetic field B is generated having somewhat circular magnetic field lines around the electrical wire. Remark that the magnetic field lines in the figures of the present disclosure are only shown schematically for illustration purposes, for instance the magnetic field lines of a straight wire are located in a plane perpendicular to the wire.

[0078] Typically, the AC current from the AC current source 3 a has a frequency in a range between 3 Hz and 30 kHz so as to generate an alternating magnetic field at the same frequency. In embodiments, the current source 3a is configured to provide a current amplitude having a value between 100 mA and 20 A, preferably between 0.1 A and 5 A, more preferably between 0.5 A and 3 A. In embodiments, the current source is controlled for supplying a constant current amplitude such that the amplitude of the magnetic field is also maintained constant. As a magnetic field signal is used as a tracking signal it is important to provide a constant current in order to have an adequate tracking performance.

[0079] Generally, for safety regulations, the current source operates at low voltage and the current source may for example be configured for operating at a maximum voltage of 48 V.

[0080] The remote device 4 comprises a magnetic field detector 4a configured for detecting one or more properties of the magnetic field generated with the electrical wire 2. The one or more properties of the magnetic field comprise at least a magnetic field strength and / or a magnetic field orientation.

[0081] In embodiments, the magnetic field orientation may be detected by measuring one or more vector components, also named coordinates, of the magnetic field. In embodiments, two or three vector components with respect to a reference coordinate system, e.g. a 3D orthogonal coordinate system, associated to for example the magnetic field detector 3a, may be measured.

[0082] In embodiments, the magnetic field detector may be a combination of multiple magnetic field sensors e.g. 3 sensors in a XYZ configuration.

[0083] In embodiments, as schematically shown on Fig.6, the magnetic field detector 4a comprises a magnetic field sensor 11 for sensing signals, e.g. analog signals, comprising information with respect to the magnetic field properties, an amplifier and filter circuit 12 for amplifying and filtering the signals, e.g. analog signals, detected with the magnetic field sensor 11, and a processing unit 13 for generating a sequence of data, e.g. serial data, to be transmitted to the base unit.

[0084] In embodiments, the magnetic field sensor is a magnetometer, for example a rotating coil magnetometer known in the art wherein the magnetic field induces a sine wave in the rotating coil. From the induced sine wave signal, both the magnetic field strength and the magnetic field orientation can be obtained.

[0085] The remote device 4 further comprises a signal transmitter 4b configured for transmitting a modulated electrical signal MES via the earth 20 to the base unit. The modulated electrical signal MES comprises encoded data specifying at least the one or more magnetic field properties detected with the magnetic field detector and / or specifying one or more quantities derived from the one or more magnetic field properties detected. As will be further discussed below in more detail, an example of derived quantities from the magnetic field properties are one or more coordinates determining the location of magnetic field detector or the location of a device the magnetic field detector is attached to, such as for example a drill head. In embodiments, further information may be part of the encoded data, such as for example a temperature measurement or any other quantity processed.

[0086] In embodiments, the modulated electrical signal MES has a carrier frequency comprised in a range between 3 Hz and 30 kHz. Preferably the carrier frequency is selected to be different from the frequency of the AC current supplied by the AC current source 3a for generating the alternating magnetic field.

[0087] As schematically illustrated in the embodiments shown on Fig.l, Fig.2, Fig.10, Fig.11, and Fig.13 to Fig.18 , the signal transmitter 4b generally comprises a first transmission electrode TE 1 for making a first electrical contact with the earth 20 and a second transmission electrode TE2 electrically insulated from the first transmission electrode for making a second electrical contact with the earth 20. The transmission electrodes TE1, TE2 are made of a conductive material, e.g. a metal. They can have any shape or form and can be in contact with the earth through insertion, buried, just laying on top of the surface or a combination of the above.

[0088] In some embodiments, as schematically illustrated on Fig.19, wherein the location tracking device is for example used in the domain of underground mining, the transmission electrodes TE 1 and TE2 may be moved through a tunnel using a transportation device 40, such as a truck. In this example, a first transmission electrode TE1 may make contact and glide along an upper portion of the tunnel and a second transmission electrode may make contact and glide along the lower portion of the tunnel. In this example, the remote device 4, may be located or be part of the transportation device 40.

[0089] With reference to Fig.8, Fig.9, and Fig.12 to Fig.16, the modulated electrical signal MES transmitted by the signal transmitter 4b to the signal receiver 3b is schematically indicated by arrows, and, as schematically shown, the modulated electrical signal MES is transmitted through the earth 20 from the transmission electrodes TE1, TE2 of the signal transmitter towards the ground terminals Pl, P2 of the base unit.

[0090] In embodiments, the signal transmitter 4b further comprises a control unit 10 configured for generating the modulated electrical signal. Typically, the control unit 10 comprises a signal generator for generating a carrier waveform, e.g. a sin waveform, and a signal modulator for modulating the carrier waveform with a modulation signal comprising the data to be transmitted.

[0091] In embodiments the modulation may be an analog modulation wherein an analog modulation signal is impressed on the carrier wave. In other embodiments, the modulation may be a digital modulation wherein a digital modulation signal representing a sequence of binary digits is impressed on the carrier wave. In embodiments, the control unit 10 of the signal transmitter 4b is configured for applying a modulated AC voltage between the first TE 1 and second TE2 transmission electrodes so as to generate the modulated electrical signal as a current that can flow from the transmission electrodes TE1, TE2 through the earth towards the ground electrodes Pl, P2.

[0092] Generally, the modulated AC voltage applied between the first TE 1 and second TE2 transmission electrode has a maximum amplitude in the range between 1 V and 24 V, preferably between 1 V and 10 V, more preferably between 5 V and 10 V. The voltage applied depends on the type of battery and voltage conversion that is used for powering the signal transmitter.

[0093] In embodiments, the remote device 4 comprises one or more batteries for powering the magnetic field detector 4a and the signal transmitter 4b.

[0094] The base unit 3 further comprises a signal receiver 3b configured for detecting the modulated electrical signal MES transmitted by the signal transmitter 4b. Thereto, the signal receiver 3b is electrically coupled with the first P 1 and the second P2 ground terminal for receiving the modulated electrical signal MES transmitted through the earth.

[0095] In embodiments, as for example schematically shown on Fig.8 and Fig.9, the at least one electrical wire 2 that is used for generating the alternating magnetic field is also used as a receiving wire for receiving the MES signal. Hence, in these embodiments, the at least one electrical wire 2 is configured for receiving the modulated electrical signal MES. Generally, in these embodiments, the signal receiver 3b is coupled with the at least one electrical wire 2 for detecting the modulated electrical signal MES received through the at least one electrical wire 2. In other words, the electrical wire 2 is also forming a connection wire for electrically connecting the signal receiver 3b with the ground terminals such that the modulated electrical signal MES may propagate through the electrical wire 2. Advantageously, in these embodiments no extra wires are needed and a single wire may be used for generating the alternating magnetic field and for receiving the MES signal.

[0096] In other embodiments, as schematically shown on Fig.14 to Fig.17, a receiving electrical wire 2-r, in addition to the electrical wire 2 for generating the alternating magnetic field, may be provided that is configured for receiving the modulated electrical signal. Generally, in these embodiments, the signal receiver 3b is coupled with the receiving electrical wire 2-r for detecting the modulated electrical signal MES received through the receiving electrical wire 2-r. In other words, the receiving wire 2-r is forming a connection wire electrically connecting the signal receiver 3b with the ground terminals for receiving the MES signal.

[0097] With reference to the embodiment shown on Fig.14, the receiving wire 2-r and the electrical wire 2 are connected such that, as mentioned above, when the AC current source is supplying an AC current for generating the magnetic field, there are two magnetic field contributions, a first contribution resulting from current using the earth as a return path and a second contribution from current using the return path RP, schematically shown on Fig.14, above ground. In other words, in the embodiment shown on Fig.14, the receiver wire 2-r and electrical wire are forming a parallel circuit. As further schematically shown on Fig.14, a filter circuit FC may be provided to ensure that the signal received through the receiver wire is not interfering or being interfered by the transmitting signal from the current source 3a.

[0098] In the embodiment shown on Fig.15 to Fig.18, the receiving wire 2- r for receiving the MES signal is separated from the electrical wire 2, in this example forming one or more loops, that is used for generating the alternating magnetic field. The receiving wire 2-r may in this way electrically couple the signal receiver 3b with the ground terminals Pl, P2. In embodiments, the receiving wire 2-r and the electrical wire 2 for forming the magnetic field may be bundled.

[0099] As discussed above, in order to form a transmission path for the MES signal, at least two ground terminals Pl, P2 need to be provided. In embodiments, as will be recognized by the skilled person, more than two ground terminals may be provided, and wherein the two or more ground terminals may be electrically coupled with the signal receiver 3b . For instance, in Fig.17 an example of an embodiment of a location tracking system is shown wherein three ground terminals Pl, P2 and P3 are provided, and wherein the three ground terminals Pl, P2, P3 are electrically coupled with signal receiver 3b.

[0100] The at least one electrical wire 2 of the location tracking system may be an insulated electrical wire or a non-insulated wire.

[0101] In embodiments wherein the MES signal is received through the at least one electrical wire 2, this electrical wire 2 may advantageously be a non-insulated wire, or this electrical wire 2 may comprise a non-insulated electrical wire portion 2-ni, as schematically illustrated on Fig.12. Advantageously, by providing a non-insulated wire or wire portion 2-ni, the receiving area for receiving the modulated electrical signal MES might be increased. Indeed, by using a non-insulated electrical wire, the modulated electrical signal MES is not only receivable at the ground terminal, but the entire length of the non-insulated electrical wire may receive the MES signal that is transmitted through the earth.

[0102] Similarly, for embodiments as shown on Fig.14 to Fig.18, which are comprising an additional receiving electrical wire 2-r, this additional receiving electrical wire 2-r may either be insulated or non-insulated. When non-insulated, the receiving wire 2-r has the advantage mentioned above that a larger receiving area is created for receiving the MES signal.

[0103] In embodiments, the MES signal transmitted by the signal transmitter 4b is a modulated voltage signal propagating through the earth and further propagating through the electrical wire 2 and / or the additional receiving wire 2-r towards the signal receiver. This voltage signal in the electrical wire 2 and / or additional receiving wire 2-r may be detected by the signal receiver 3b, for instance as a modulated voltage signal. Generally, the internal resistance of the signal transmitter is specified to have a sufficient sensitivity for detecting the modulated electrical signal.

[0104] In embodiments, the signal receiver 3b may be configured for detecting the modulated electrical signal MES as a voltage variation between the first P 1 and second P2 ground terminal.

[0105] In embodiments, as illustrated on Fig.l, the signal receiver 3b may be electrically coupled in parallel with the current source 3a.

[0106] In further embodiments, as schematically shown on Fig.18, wherein the circuit for generating the alternating magnetic field is electrically separated from the circuit for receiving the modulated electrical signal, the signal receiver 3b may be located at a different location when compared to the location of for instance the AC current source 3a.

[0107] By making use of the earth as a conductor for transmitting the modulated electrical signal MES from the signal transmitter 4b, e.g. located underground, to the signal receiver 3b, e.g. located above ground, a wireless signal transmission is obtained, i.e. no electric cable connecting the signal transmitter with the signal receiver is required.

[0108] In embodiments, the signal receiver 3b comprises a demodulator for extracting the encoded data from the modulated electrical signal received.

[0109] In embodiments, the internal resistance of the signal transmitter 3b is configured for obtaining a sufficient sensitivity for detecting the modulated electrical signal transmitted. The person skilled in the art will adequately select the internal resistance of the signal transmitter such that even for larger distances, the signal transmitter is sufficiently sensitive for detecting the modulated electrical signal. As there is a relation between the magnetic field detected and the location of the magnetic field detector with respect to the electrical wire, the location or a variation of the location of the magnetic field detector with respect to the electrical wire can be determined. Hence, if the magnetic field detector is coupled to an object or device, the location of the object or device with respect to the electrical wire may be determined.

[0110] In embodiments, the base unit 3 or the signal receiver 3b of the base unit comprises a controller configured for determining a location of the magnetic field detector 4a with respect to the electrical wire based on the one or more magnetic field properties detected.

[0111] In these embodiments wherein location determination is performed by the base unit, the information contained in the modulated electrical signal MES may comprises basic data, for instances data specifying an amplitude and / or a phase shift of the sine wave signal measured with a magnetometer.

[0112] In other embodiments, the magnetic field detector 4a comprises a processing unit 13, such as an onboard processor, configured for determining a location of the magnetic field detector with respect to the electrical wire 2 based on the one or more magnetic field properties detected. This location with respect to the electrical wire is an example of a quantity derived from the magnetic field properties that can be transmitted to the base unit. The location can for example be expressed by one or more coordinates. In these embodiments, the modulated electrical signal MES transmitted from the remote device to the base unit comprises the one or more quantities derived.

[0113] In embodiments, the controller of the signal receiver 3b or the processing unit 13 of the magnetic field detector 4a makes use of a mathematical expression or model that specifies for a given current generated in the electrical wire the relation between magnetic field strength and the distance from the magnetic field detector to the electrical wire. In this way, by measuring a magnetic field strength, the distance to the electrical wire can be calculated. Alternatively, a calibration can be used that maps for a given current, the magnetic field strength with the distance to the electrical wire.

[0114] In embodiments wherein the magnetic field detector 4a also measures the magnetic field orientation, the controller of the base unit or the processing unit of the remote device may be configured to calculate one or more deviation angles to express an angular deviation of a reference axis R associated to the remote device with respect to the electrical wire. A deviation angle is a further example of a derived quantity from the magnetic field properties.

[0115] For example if the remote device, or at least the magnetic field detector, is attached to a drill head, the reference axis R may be an axis parallel with a longitudinal axis of the drill head indicating a direction of drilling.

[0116] With reference to Fig.5, a distance D and a deviation angle Au between a reference axis R of the magnetic field detector and an electrical wire elongating along a straight line SL is schematically shown. As schematically illustrated on Fig.5, a deviation angle Au equal to 0° may correspond to the reference axis R being parallel with the straight line SL.

[0117] In embodiments wherein the remote device is located below the ground surface, the deviation angle of the reference axis R of the remote device with respect to the straight line SL may be determined by two deviation angles Au and AB, for respectively determining a pitch and jaw angular deviation of the reference axis R. The pitch angular deviation may reflect an up-down deviation, while the jaw angular deviation may reflect a left-right deviation.

[0118] In embodiments, the base station 3 is housing a display for displaying the data received from the signal transmitter 4b. Hence the display may display the one or more coordinates specifying the location of the magnetic field detector or the location of a device the magnetic field detector is attached to, e.g. the drill head. For example the following coordinates may be displayed: depth, deviation, pitch, jaw, and drillhead rotation. The operator of the drilling machine can use these coordinates to make steering decisions. The display may be a separate display or a display of a phone or tablet.

[0119] In other embodiments, which may be named an autonomy option, the base station 3 may comprise a drill controller configured for calculating a steering correction for adjusting a drill direction of the drill head. The calculation of the steering correction is based on the encoded data received from the signal transmitter 4b of the remote device 4.

[0120] With reference to Fig.6, a schematic representation is shown of a bottom hole assembly 28 of a drilling system. The bottom hole assembly 28 comprises a drill head 8, which is generally an end part of the bottom hole assembly 28. In the embodiment shown on Fig.6, the remote device 4 is coupled between an end portion of the drill rod assembly 7 and the drill head 8. An insulator 14 separating a first transmission electrode TE1 from a second transmission electrode TE2 is schematically shown.

[0121] In embodiments, the remote device 4 comprises a housing 30 configured for supporting and housing both the magnetic field detector 4a and the signal transmitter 4b.

[0122] In other embodiments, the remote device 4 comprises a housing 30 configured for housing and supporting only the signal transmitter 4b as schematically illustrated on Fig.9. In embodiments, the remote device may additionally comprise a detector housing dedicated for supporting and housing the magnetic field detector 4a, and wherein the detector housing is separated from the housing 30 of the transmitter. Hence, in these embodiments wherein the magnetic field detector has a separate housing, the magnetic field detector 4a may be located at a distance from the signal transmitter 4b. In this way an optimum location can be found for placing the signal transmitter independently from the location of the magnetic field detector.

[0123] With reference to Fig.7, an example of a housing 30 is shown that may be used for either housing the signal transmitter 4b together with the magnetic field detector 4a or alternatively for housing only the signal transmitter 4b. In this example, the housing has a cylindrical shape.

[0124] In embodiments as illustrated on Fig.7, the housing 30 of the remote device comprises a main body 15 having an inner bore and an internal body 25 inserted through the inner bore of the main body 15. In this example, the main body 15 has a shape of a hollow cylinder and the internal body 25 has the shape of a cylinder. Generally, the outer diameter of the internal body 25 is mating with an inner diameter the main body 15 or with at least an inner diameter of a portion of the main body.

[0125] In embodiments, the main body 15 and the internal body 25 may be made of a metal.

[0126] As schematically shown on Fig.7, to hold the internal body 25 attached to the main body 15, one or more lock bolts 22 may be used.

[0127] The drilling systems generally use air or a drilling fluid that is transported from above ground via the drill rod assembly towards the drill head. As the remote device 4 of the location determining system may be located in between the drill rod assembly 7 and the drill head 8, as illustrated on Fig.8, the remote device should be provided with means for transporting the drilling fluid to the drill head. In embodiments, as illustrated on Fig.7, the internal body 25 comprises a channel 18 configured for transmitting air or a drilling fluid from a first end 26a to a second end 26b of the internal body.

[0128] In embodiments, as illustrated on Fig.7, the internal body further comprises a cavity 19 separated from the channel 18. The cavity is for example provided on an outer side of the internal body 25. The cavity 19 is configured for at least receiving electronic components of the signal transmitter 4b and / or components of the magnetic field detector 4a. Preferably, the electronic components of the signal transmitter 4b comprise at least the control unit 10 and / or the components of the magnetic field detector 4a comprises at least the magnetic field sensor 11, the amplifier and filter unit 12 and the processing unit 13.

[0129] As shown on Fig.7, at least two O-rings 21b located between an inner wall of the main body 15 and an outer wall of the internal body 25 are provided. In this way, air or drilling fluid being transported through the channel 18 is prohibited from entering the cavity 19.

[0130] In embodiments, an electrically conductive sleeve 16, illustrated on Fig.7 with a dotted area, is provided that is electrically insulated from the main body 15 and surrounding at least a part of the outer side of the main body 15.

[0131] The electrically conductive sleeve 16 is forming the first transmission electrode TE 1 of the signal transmitter and at least a portion of the main body 15 or a conductive element attached to the main body is forming the second transmission electrode TE2 of the signal transmitter. The conductive element may for example be a contact surface configured for making a contact with the earth.

[0132] In embodiments, an inner side of the electrically conductive sleeve 16 is electrically insulated from the main body 15, more precisely an outer side of the main body, by an insulating glue. In embodiments, as shown on Fig.7, one or more O-rings 21a, in this example two O-rings, may additionally be provided to insulate the inner side of the electrically conductive sleeve 16 from the main body 15. The O-rings 21a also prevent fluid that is surrounding the bottom hole assembly while drilling to enter the cavity 19 through the hole 23.

[0133] In embodiments, as shown on Fig.7, optionally, a first and a second lateral side of the electrically conductive sleeve 16 may electrically be insulated from the main body 15 by respectively a first 14a and a second 14b ring-shaped insulator.

[0134] As further shown on Fig.7, a hole 23, forming an electric throughput for a conductor, may be provided through the main body 15 to connect the electrically conductive sleeve 16 with for instance the control unit of the signal transmitter located in the cavity 19.

[0135] As further illustrated on Fig.7, the main body 15 is extending from a first end portion 17a to a second end portion 17b and the first end portion 17a has a first connecting element 27a for making a connection to a drill rod assembly 7 of a drilling system and the second end portion 17b has a second connecting element 27b for making a connection with a drill head 8 of the drilling system. The connecting elements 27a, 27b may for example be threads provided on an inner side of the main body 15 to make a threaded coupling on one side of the housing 30 with the drill rod assembly 7 and a threaded coupling on the other side of the housing with the drill head 8. More specifically, the first 27a and second 27b connecting element may be a threads formed in an inner side of the end portions 17a, 17b of the main body 15.

[0136] In embodiments the housing 30 has an overall length measured from a first end to a second end of the housing of 30 cm to 100 cm, preferably 40 cm to 80 cm, more preferably 50 cm to 60 cm.

[0137] In embodiments, the main body 15 of the housing 30 has a cylindrical shape and has an outer diameter of 80 mm to 250 mm, preferably 80 mm to 200 mm, more preferably 100 mm to 150 mm.

[0138] In embodiments, as illustrated on Fig.9, the housing 30 is positioned between a first 7a and a second 7b portion of the drill rod assembly of the drilling system. The housing 30 may house at least a signal transmitter 4b for transmitting encoded data to the base station. In these embodiments, the first 17a and second 17b end portion of the main body 15 of the housing 30 may have respectively a first 27a and a second 27b connecting element configured for connecting with respectively the first 7a and the second 7b portion of the drill rod assembly of the drilling system.

[0139] The location tracking system of the present disclosure is not limited to a system having a single electrical wire for generating a magnetic field. In embodiments more than one electrical wire may be provided. For example, as illustrated on Fig.2, two electrical wires may be installed in parallel to generated respectively a first Bl and a second B2 magnetic field.

[0140] In the embodiment shown on Fig.2, the base unit 3 comprises a switching device 5 configured for alternately supplying an AC current with the current source 3a to the first 2a and the second 2b electrical wire so as to alternately generate a first B 1 and a second B2 magnetic field. In other embodiments, the base unit 3 may comprise a second current source for supplying an AC current through the second electrical wire. The base unit further comprises one or more further ground terminals configured for establishing an earth return path for the current in the second electrical wire 2b. In this example shown on Fig.2 a third ground terminal P3 is provided.

[0141] Advantageously, by providing more than one electrical wire for producing more than one magnetic fields, the performance and precision of the location tracking may be improved.

[0142] According to a further invention presented in this disclosure, a signal transmitter 4b is provided for transmitting a modulated electrical signal through the earth from a location underground to a base station located above ground. Generally, the base station comprises a signal receiver for receiving the modulated electrical signal transmitted by the transmitter.

[0143] The signal transmitter 4b is for example located underground and may be coupled to a drilling system, as schematically illustrated on for example Fig.l and Fig.3. The signal transmitter 4b may be separated from an external device that is generating the data that need to be transmitted to the base station. For example the external device may be a bottom hole assembly generating data and these data can be send wirelessly or through a cable to the signal transmitter, which in turn then transmits the data received from the external device through the earth as a modulated electrical signal receivable by the base station.

[0144] The components of the signal transmitter have been discussed above in the context of the first inventive aspect of the present disclosure.

[0145] The signal transmitter comprises for instance a first transmission electrode TE1 for making a first electrical contact with the earth 20 and a second transmission electrode TE2 electrically insulated from the first transmission electrode for making a second electrical contact with the earth.

[0146] The signal transmitter 4b further comprises a housing 30 configured for housing and supporting the signal transmitter 4b.

[0147] With reference to Fig.7, a housing 30 for the signal transmitter is shown wherein the housing 30 comprises a main body 15 and an internal body 25, and wherein the main body 15 has an inner bore and the internal body 25 is inserted through the inner bore of the main body 15.

[0148] In embodiments, the internal body 25 may be attached to the main body 15 by one or more lock bolts 22.

[0149] In embodiments, the internal body 25 comprises a cavity 19 configured for at least receiving electronic components of the signal transmitter 4b, preferably wherein the electronic components of the signal transmitter 4b comprise at least the control unit 10 configured for generating the modulated electrical signal.

[0150] In embodiments, the internal body 25 comprises a channel 18 configured for transmitting air or a drilling fluid from a first end 26a to a second end 26b of the internal body 25. In this way, in embodiments, the signal transmitter 4b may be installed in between two drill rod portions 7a, 7b of a drill rod assembly 7 of a drilling system while maintaining a continuous flow of air or drilling fluid towards the drill head 8 of the drilling system, as schematically shown on Fig.9. In other embodiments, the signal transmitter that is housed in the housing 30, may be installed between an end portion of the drill rod assembly 7 and the drill head 8, as schematically shown on Fig.8.

[0151] In embodiments, the main body 15 of the housing 30 of the signal transmitter 4b is extending from a first end portion 17a to a second end portion 17b and wherein the first and second end portions have respectively a first 27a and a second 27b connecting element configured for making a connection with respectively a first 7a and a second 7b drill rod portion of a drill rod assembly 7 of a drilling system. Preferably the first and second connecting element is a thread formed in an inner side of the end portions 17a, 17b of the main body 15. In this way, the signal transmitter can be coupled in between two drill rod portions of a drill rod assembly 7 of a drilling system.

[0152] In other embodiments, the main body 15 is extending from a first end portion 17a to a second end portion 17b and wherein the first end portion has a first connecting element 27a for making a connection to a drill rod assembly 7 of a drilling system and the second end portion has a second connecting element 27b for making a connection with a bottom hole assembly 28, or more specifically with a drill head 8, of the drilling system. Preferably the first and second connecting element is a thread formed in an inner side of the end portions 17a, 17b of the main body 15. In this way, the signal transmitter can be coupled between an end portion of the drill rod assembly 7 and a bottom hole assembly 28, or more specifically a drill head 8.

[0153] Generally, the channel 18 in the internal body 25 is separated from the cavity 19 such that no air or drilling fluid can enter the cavity 19. In embodiments, the housing 30 comprises one or more sealing elements, such as O -rings, configured to prohibit air or drilling fluid from entering the cavity 19.

[0154] For example, in the exemplary embodiment shown on Fig.7, two O- rings 21b located between an inner wall of the main body 15 and an outer wall of the internal body 25 are provided to prohibit air or drilling fluid transported through the channel 18 from entering the cavity 19. Additionally, one or more O-rings 21a, in this example two O-rings, may be provided between the inner side of the electrically conductive sleeve 16 and the outer side of the main body 15 to prevent fluid that is surrounding the bottom hole assembly while drilling to enter the cavity 19 through the hole 23 which is forming an electrical throughput from the cavity to the sleeve.

[0155] In embodiments, an electrically conductive sleeve is surrounding at least a part of an outer side of the main body 15, and the electrically conductive sleeve 16 is forming one of the first TE1 or second TE2 transmission electrodes. In embodiments, the electrically conductive sleeve 16 is forming the first transmission electrode TE1 and at least a portion of the main body 15 is forming the second transmission electrode TE2.

[0156] In embodiments, the signal transmitter may comprise an interface for receiving data from an external device, and wherein the signal transmitter transmits the data received from the external device to the base station by generation a modulated electrical signal comprising encoded data specifying the data received from the external device. The external device may be a device located underground and which is a device generating data that needs to be transmitted to the base station above ground. The external device may for example be a bottom hole assembly of a drilling system. The interface may be a cable connection for a cable connecting the signal transmitter with the external device. In this example, the signal transmitter may be coupled between two portions of the drill rod assembly and the signal transmitter may receive data from the bottom hole assembly through a cable or wirelessly. The signal transmitter then encodes the data for forming a modulated electrical signal that can be transmitted through the earth to the base station.

[0157] According to the further invention discussed above related to a signal transmitter, a number of clauses can be defined as outlined below, wherein the clauses comprise characterizations indicating a variety of options, features, and feature combinations that can be used in accord with the teachings of the present disclosure with respect to a signal transmitter as discussed above. The following clauses could for instance be claimed for the signal transmitter:

[0158] 1. A signal transmitter (4b) for transmitting a modulated electrical signal through the earth from a location underground to a base station located above ground, comprising a housing (30) configured for housing and supporting said signal transmitter (4b), and wherein the housing comprises an internal body (25) having a cavity (19) configured for at least receiving electronic components of the signal transmitter (4b).

[0159] 2. The signal transmitter according to clause 1 wherein the electronic components of the signal transmitter (4b) comprise at least a control unit (10) configured for generating the modulated electrical signal.

[0160] 3. The signal transmitter (4b) according to clause 1 or 2 comprising a first transmission electrode (TE 1) for making a first electrical contact with the earth (20) and a second transmission electrode (TE2) electrically insulated from the first transmission electrode for making a second electrical contact with the earth.

[0161] 4. The signal transmitter according to any of clauses 1 to 3 wherein the housing (30) comprises a main body (15) and wherein the main body (15) has an inner bore and the internal body (25) is inserted through the inner bore of the main body (15), preferably wherein the internal body (25) is attached to the main body (15) by one or more lock bolts (22).

[0162] 5. The signal transmitter according to clause 4 wherein the internal body (25) further has a channel (18) configured for transmitting air or a drilling fluid from a first end (26a) to a second end (26b) of the internal body (25).

[0163] 6. The signal transmitter according to clause 5 wherein the cavity (19) is separated from the channel (18) such that no air or drilling fluid can enter the cavity, preferably the housing comprises one or more sealing elements, such as O-rings, configured for sealing the cavity from the channel.

[0164] 7. The signal transmitter according to any of clauses 1 to 6 wherein the main body (15) of the housing (30) of the signal transmitter (4b) is extending from a first end portion (17a) to a second end portion (17b) and wherein the first and second end portions have respectively a first (27a) and a second (27b) connecting element configured for coupling the signal transmitter in between a first (7a) and a second (7b) drill rod portion of a drill rod assembly (7) of a drilling system.

[0165] 8. The signal transmitter according to any of clauses 1 to 6 wherein the main body (15) of the housing (30) of the signal transmitter (4b) is extending from a first end portion (17a) to a second end portion (17b) and wherein the first and second end portions have respectively a first (27a) and a second (27b) connecting element configured for coupling the signal transmitter between a drill rod assembly (7) and a bottom hole assembly (28), or more specifically between a drill rod assembly (7) and a drill head (8).

[0166] 9. The signal transmitter according to clause 7 or clause 8 wherein said first and second connecting element is a thread formed in an inner side of the end portions (17a, 17b) of the main body 15.

[0167] 10. The signal transmitter according to any of clauses 3 to 9 wherein an electrically conductive sleeve (16) is surrounding at least a part of an outer side of the main body (15) and wherein said electrically conductive sleeve (16) is forming one of said first (TE1) or second (TE2) transmission electrodes. 11. The signal transmitter according to clause 10 wherein said electrically conductive sleeve (16) is forming said first transmission electrode (TE1) and at least a portion of said main body (15) is forming said second transmission electrode (TE2).

[0168] 12. The signal transmitter according to any of previous clauses wherein the modulated electrical signal comprises encoded data.

[0169] 13. The signal transmitter according to any of previous clauses comprising an interface for receiving data from an external device, and wherein the modulated electrical signal generated by the signal transmitter comprises encoded data specifying the data received from the external device, preferably wherein the interface is configured for wirelessly receiving the data from the external device or wherein the interface is configured for receiving the data from the external device through a cable.

[0170] The present disclosure has been described in terms of specific embodiments, which are illustrative of the disclosure and not to be construed as limiting. It will be appreciated by persons skilled in the art that the present disclosure is not limited by what has been particularly shown and / or described and that alternatives or modified embodiments could be developed in the light of the overall teaching of this disclosure. The drawings described are only schematic and are non-limiting.

[0171] Use of the verb "to comprise", as well as the respective conjugations, does not exclude the presence of elements other than those stated. Use of the article "a", "an" or "the" preceding an element does not exclude the presence of a plurality of such elements.

[0172] Furthermore, the terms first, second and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the disclosure described herein are capable of operation in other sequences than described or illustrated herein.

[0173] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiments is included in one or more embodiment of the present disclosure. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one ordinary skill in the art from this disclosure, in one or more embodiments.

[0174] REFERENCE NUMBERS

[0175]

Claims

CLAIMS1. A location tracking system (1) comprising a base unit (3) and a remote device (4), and wherein the base unit (3) comprises at least one electrical wire (2), an AC current source (3a) configured for supplying an AC current flowing through said at least one electrical wire (2) so as to generate an alternating magnetic field (B), and at least a first (Pl) and a second (P2) ground terminal, and wherein said remote device (4) comprises at least: a) a magnetic field detector (4a) configured for detecting one or more magnetic field properties of said alternating magnetic field (B), and wherein said one or more magnetic field properties comprises at least a magnetic field strength and / or a magnetic field orientation; and b) a signal transmitter (4b) configured for transmitting a modulated electrical signal (MES) via the earth (20) to the base unit, and wherein said modulated electrical signal comprises encoded data specifying at least the one or more magnetic field properties detected and / or specifying one or more quantities derived from the one or more magnetic field properties detected; and wherein said base unit (3) further comprises a signal receiver (3b) electrically coupled with said at least first (Pl) and second (P2) ground terminal and configured for detecting the modulated electrical signal transmitted by the signal transmitter.

2. The location tracking system according to claim 1 wherein the AC current from the AC current source (3a) has a frequency in a range between 3 Hz and 30 kHz.

3. The location tracking system according to any of previous claims wherein said current source (3a) is configured to provide a currentamplitude having a value between 100 mA and 20 A, preferably between 0.1 A and 5 A, more preferably between 0.5 A and 3 A.

4. The location tracking system according to any of previous claims wherein said current source is configured for operating at a maximum voltage of 48 V.

5. The location tracking system according to any of previous claims wherein the modulated electrical signal (MES) has a carrier frequency comprised in a range between 3 Hz and 30 kHz, preferably the carrier frequency is different from the frequency of the AC current supplied by the AC current source (3 a).

6. The location tracking system according to any of previous claims wherein said modulated electrical signal (MES) is a modulated voltage signal.

7. The location tracking system according to any of claims 1 to 6 wherein the signal receiver (3b) is configured for receiving the modulated electrical signal (MES) as a signal propagating through the electrical wire (2), preferably the signal receiver (3b) is configured for detecting the modulated electrical signal propagating through the electrical wire (2) as a voltage variation.

8. The location tracking system according to any of previous claims wherein the signal receiver (3b) is configured for detecting the modulated electrical signal (MES) as a voltage variation between the first (Pl) and second (P2) ground terminal.

9. The location tracking system according to any of previous claims wherein the signal transmitter (4b) comprises a first transmission electrode (TE1) for making a first electrical contact with the earth (20) and a second transmission electrode (TE2) electrically insulated from the first transmission electrode for making a second electrical contact with the earth.

10. The location tracking system according to claim 9 wherein the signal transmitter (4b) comprises a control unit (10) configured for generating said modulated electrical signal.

11. The location tracking system according to claim 10 wherein said control unit (10) is configured for applying a modulated AC voltage between said first (TE1) and second (TE2) transmission electrode.

12. The location tracking system according to claim 11 wherein the modulated AC voltage has a maximum amplitude in range between 1 V and 24 V, preferably between 1 V and 10 V, more preferably between 5 V and 10 V.

13. The location tracking system according to any of claims 10 to 12 wherein said control unit (10) comprises a signal generator for generating a carrier waveform and a signal modulator configured for modulating the carrier waveform.

14. The location tracking system according to any of previous claims wherein said magnetic field detector (4a) comprises at least a magnetic field sensor (11), an amplifier and filter unit (12) for amplifying and filtering signals detected with the magnetic field sensor (11), and a processing unit (13) for generating a sequence of data to be transmitted to the base unit.

15. The location tracking system according to any of previous claims wherein said remote device (4) comprises a housing (30) configured for supporting and housing said magnetic field detector (4a) and said signal transmitter (4b).

16. The location tracking system according to claim 15 wherein said housing (30) comprises a main body (15) and an internal body (25), and wherein the main body (15) has an inner bore and the internal body (25) is inserted through the inner bore of the main body (15).

17. The location tracking system according to claim 16 wherein the internal body (25) is attached to the main body (15) by one or more lock bolts (22).

18. The location tracking system according to claim 16 or claim 17 wherein said main body (15) has a shape of a hollow cylinder and the internal body (25) has the shape of a cylinder, preferably an outer diameter of the internal body (25) is mating with an inner diameter the main body (15) or at least with an inner diameter of a portion of the main body (15).

19. The location tracking system according to any of claims 16 to 18 wherein the internal body (25) comprises a channel (18) configured for transmitting air or a drilling fluid from a first end (26a) to a second end (26b) of the internal body (25).

20. The location tracking system according to any of claims 16 to 19 wherein the internal body (25) comprises a cavity (19) configured for at least receiving electronic components of the signal transmitter (4b) and / or receiving components of the magnetic field detector (4a), preferably wherein the electronic components of the signal transmitter (4b) comprise at leastthe control unit (10) and / or wherein the components of the magnetic field detector (4a) comprises at least the magnetic field sensor (11), the amplifier and filter unit (12) and the processing unit (13).

21. The location tracking system according to claim 20 wherein the cavity (19) is separated from the channel (18) such that no air or drilling fluid can enter the cavity.

22. The location tracking system according to claim 20 or 21 wherein the housing (30) comprises at least two O-rings (21b) located between an inner wall of the main body (15) and an outer wall of the internal body (25) and configured to prohibit air or drilling fluid from entering the cavity (19).

23. The location tracking system according to any of claims 16 to 22 wherein an electrically conductive sleeve (16) electrically insulated from the main body (15) and surrounding at least a part of an outer side of the main body (15) is forming said first transmission electrode (TE1), preferably wherein at least a portion of said main body (15) or a conductive element attached to said main body is forming said second transmission electrode (TE2).

24. The location tracking system according to claim 23 wherein an inner side of the electrically conductive sleeve (16) is electrically insulated from the main body (15) by an insulating glue and / or by one or more O-rings (21a), preferably a first and a second lateral side of the electrically conductive sleeve (16) is electrically insulated from the main body (15) by respectively a first (14a) and a second (14b) ring-shaped insulator.

25. The location tracking system according to any of claims 16 to 24 wherein said main body (15) is extending from a first end portion (17a) to asecond end portion (17b) and wherein the first end portion has a first connecting element (27a) for making a connection to a drill rod assembly (7) of a drilling system and the second end portion has a second connecting element (27b) for making a connection with a drill head (8) of the drilling system, preferably said first and second connecting element is a thread formed in an inner side of the end portions (17a, 17b) of the main body (15).

26. The location tracking system according to any of claims 16 to 24 wherein said main body (15) is extending from a first end portion (17a) to a second end portion (17b) and wherein the first and second end portions have respectively a first (27a) and a second (27b) connecting element configured for making a connection with respectively a first (7a) and a second (7b) drill rod portion of a drill rod assembly (7) of a drilling system, preferably said first and second connecting element is a thread formed in an inner side of the end portions (17a, 17b) of the main body (15).

27. The location tracking system according to any of previous claims wherein said electrical wire (2) comprise a first end (El) and a second end (E2) and wherein said first ground terminal (Pl) is electrically connectable to said first end (El) and said second ground terminal (P2) is electrically connectable to said second end (E2).

28. The location tracking system according to any of previous claims wherein said magnetic field orientation is detected by measuring one or more vector components of said magnetic field, preferably by measuring two or three vector components with respect to a reference coordinate system preferably associated to said magnetic field detector (4a).

29. The location tracking system according to any of previous claims wherein said one or more quantities derived from the one or more magneticfield properties detected comprises one or more coordinates specifying a location of the magnetic field detector or a location of a device the magnetic field detector is attached to.

30. The location tracking system according to any of previous claims wherein said magnetic field detector (4a) comprises a processing unit (13) configured for determining a location of said magnetic field detector, or a location of a device the magnetic field detector is attached to, with respect to said electrical wire based on said one or more magnetic field properties detected, and wherein said one or more quantities derived from the one or more magnetic field properties comprise at least said location.

31. The location tracking system according to any of claims 1 to 29 wherein said signal receiver (3b) comprises a controller configured for determining a location of said magnetic field detector (4a), or a location of a device the magnetic field detector (4a) is attached to, with respect to said electrical wire (2) based on said one or more magnetic field properties detected.

32. The location tracking system according to any of claims 29 to claim 31 wherein said location is expressed as a distance between the magnetic field detector and the electrical wire and / or by an angular deviation with respect to the electrical wire of a reference axis (R) associated to the magnetic field detector.

33. The location tracking system according to any of previous claims wherein said signal receiver (3b) is electrically coupled in parallel with said current source (3 a).

34. The location tracking system according to any of previous claims wherein the signal receiver (3b) is configured for demodulating the modulated electrical signal received.

35. The location tracking system according to any of previous claims wherein said magnetic field detector (3b) is coupled to the signal transmitter (3 a) through a cable connection or through a wireless connection for supplying magnetic field data.

36. The location tracking system according to any of previous claims wherein said electrical wire (2) is configured for generating circular magnetic field lines around the electrical wire.

37. The location tracking system according to any of previous claims wherein said electrical wire (2) is elongating along a straight line, a curved line or a combination of both, preferably wherein the electrical wire is located on the earth surface, in the air or below the earth surface.

38. The location tracking system according to any of claims 1 to 36 wherein said at least one electrical wire (2) is forming one or more loops, preferably wherein the at least one electrical wire is located on the earth surface, in the air or below the earth surface.

39. The location tracking system according to any of previous claims wherein the first (Pl) and the second (P2) ground terminal are configured for establishing a return path through the earth (20) for said AC current flowing through said at least one electrical wire (2).

40. The location tracking system according to any of previous claims wherein said at least one electrical wire (2) in a non-insulated electrical wireor the at least one electrical wire (2) comprises a non-insulated electrical wire portion (2-ni).

41. The location tracking system according to any of previous claims wherein the at least one electrical wire (2) is configured for receiving the modulated electrical signal, preferably wherein the signal receiver (3b) is coupled with the at least one electrical wire for detecting the modulated electrical signal (MES) received through the at least one electrical wire (2).

42. The location tracking system according to any of claims 1 to 40 further comprising a receiving electrical wire (2-r) configured for receiving the modulated electrical signal, preferably wherein the signal receiver (3b) is coupled with the receiving electrical wire (2-r) for detecting the modulated electrical signal (MES) received through the receiving electrical wire (2-r).

43. The location tracking system according to any of previous claims wherein said base unit (3) comprises a display for displaying the data received from the signal transmitter (4b), preferably a display for displaying one or more coordinates specifying a location of the magnetic field detector or a location of a device the magnetic field detector is attached to.

44. A drilling system for drilling a hole or a tunnel comprising at least a drill rig (6) positionable on the earth surface, a drill head (8), a drill rod assembly (7) connecting the drill head with the drill rig and a location tracking system (1) according to any of claims 1 to 43, and wherein said remote device (4) is coupled between an end portion of the drill rod assembly (7) and the drill head (8).

45. A drilling system for drilling a hole or tunnel comprising at least a drill rig (6) positionable on the earth surface, a drill head (8), a drill rod assembly (7) connecting the drill head with the drill rig, and a locationtracking system (1) according to any of claims 1 to 43, and wherein said signal transmitter (4b) is located in between two portions (7a, 7b) of said drill rod assembly (7).

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