Through-the-earth transmission in a blasting system

Abstract

A method of transmitting a TTE signal to each of a plurality of detonator assemblies in a blasting system wherein the method includes the step of simultaneously transmitting the TTE signal from each of a plurality of transmitters which are configured to function in synchronism such that a first TTE signal from a first transmitter received by a detonator assembly should be in phase with a second TTE signal from a second transmitter which is received by the same detonator assembly, to within half a wavelength at an operating frequency which is the same for all the transmitters.

Description

THROUGH-THE-EARTH TRANSMISSION IN A BLASTING SYSTEMBACKGROUND OF THE INVENTION

[0001] This invention relates to a blasting system wherein communication to each of a plurality of detonator assemblies is achieved using through-the-earth (TTE) signals.

[0002] A blasting system can include thousands of detonator assemblies which are controlled, at least for ignition purposes, by means of a TTE signal. The extent of a geographical area which is occupied by a blasting system is dependent, at least, on the number of detonator assemblies in the system and on the spacing between boreholes in which the detonator assemblies are respectively positioned.

[0003] If the blasting system includes several thousand detonator assemblies then the geographical area occupied by the blasting system can be large.

[0004] The capability of a TTE signal to be transmitted reliably through a particular distance is dependent on a number of factors including the power output of a transmitter, the size of an antenna which is used to transmit the TTE signal and on the geology at the blasting site. If the blasting system is of a unidirectional nature then it is not possible for the individual detonator assemblies to transmit signals to a blasting controller to confirm, for example, that a TTE signal which originated at the blasting controller has been reliably received at the detonator assembly. This means that the configuration of the blasting system must be such that for practical purposes there is certainty that a TTE signal from a blasting controller will, in fact, be received by each detonator assembly.

[0005] By way of example a typical transmitter in use in a blasting system of the kind described may have an effective through-the-earth transmission range of about 300 metres for an antenna with a rectangular size of 2x8 metres. If the antenna size is increased to 4x50 metres then the transmission range is increased to 500 metres. Theoretically, a through-the-earth transmission range of about 2 kilometres can be achieved using an antenna in a square configuration of 280 metres x 280 metres. Although a two-kilometre distance is substantial, in a very large blasting system this range might be inadequate. Additional restrictions arise due to the available power output of the transmitter and on the area available for antenna deployment. These factors effectively limit the number of detonator assemblies which can be reliably included in a TTE blasting system.

[0006] An object of the present invention is to provide a technique whereby the number of detonator assemblies in a blasting system of the kind described can be reliably increased.SUMMARY OF THE INVENTION

[0007] The invention provides a method of transmitting a TTE signal to each of a plurality of detonator assemblies in a blasting system wherein the method includes the step of simultaneously transmitting the TTE signal from each of a plurality of transmitters.

[0008] The blasting system may be configured so that each transmitter can reliably transmit a TTE signal to a respective number of the detonator assemblies. The number of transmitters, and the positions of the transmitters, are chosen to ensure that the TTE signals reach all of the detonator assemblies. It is not possible though to ensure that a TTE signal from a first transmitter will reach only a specific number of detonator assemblies, and that the signal willnot reach any of the remaining detonator assemblies. The transmitters are therefore operated to ensure that they function simultaneously i.e. the transmitters are configured to function in synchronism.

[0009] Thus in the blasting system a first TTE signal from a first transmitter received by a detonator assembly must be in synchronism with a second TTE signal which is transmitted by a second transmitter and which is received by the same detonator assembly. Timing of the signals in this respect is necessary to ensure that the TTE signals which are transmitted by two or more transmitters and which are received by one or more detonator assemblies do not overlap with one another in a way which causes jamming or distortion of any of the signals. To achieve this objective the degree of synchronisation must be such that a first TTE signal from a first transmitter received by a detonator assembly should be in phase with a second TTE signal from a second detonator, received by the same detonator assembly, to within half a wavelength at the operating frequency which is the frequency of each TTE signal. The various TTE signals are identical and the signals contain the same commands and data.

[0010] In the blasting system a signal originated at or enabled by a blast controller may be transferred to all the transmitters which are configured to operate in synchronism with another.

[0011] In one technique a signal which is subsequently to be transmitted by each transmitter is originated at the blast controller and is then transmitted wirelessly or via a shared signal bus line to each of the transmitters.

[0012] In another approach each transmitter, suitably programmed beforehand, is enabled to transmit a TTE signal in synchronism with the other transmitters by means of a command or enabling signal sent from the blast controller, wirelessly or via a bus line.

[0013] In each case, if is known from preceding tests that there are meaningful time delays (different transmission periods) between some transmitters and some detonator assemblies, then suitable time delay factors can be included in the signals or commands sent from the blast controller to ensure the subsequent synchronised transmission of the TTE signals by the transmitters, in the sense referred to i.e. different signals received by a single detonator assembly have a phase difference which is less than 180° and preferably less than 90°.

[0014] Each transmitter, and particularly those transmitters which are relatively far from the blast controller, may include an amplifier to boost the strength of the TTE signal which is to be transmitted by the transmitter. Thus in the blasting system each transmitter transmits a respective TTE signal which preferably is boosted and which is initiated or derived from a command or an originating TTE signal sent by the blast controller via a suitable medium e.g. a bus line.

[0015] Each transmitter is connected to a respective antenna.

[0016] Each detonator assembly includes a respective receiver which is capable of receiving a signal which is transmitted through the earth i.e. a TTE signal.

[0017] The invention further extends to a blasting system which includes a blast site, a plurality of detonator assemblies which are respectively positioned in boreholes at the blast site, and aplurality of transmitters which are configured to transmit, in synchronism, respective TTE signals from respective antennas, and wherein each detonator assembly in a first group of detonator assemblies receives a first TTE signal, containing predetermined information, data or commands, from a first transmitter and each detonator assembly in a second group of detonator assemblies receives a second TTE signal which is in synchronism with the first TTE signal, which contains the same predetermined information, data or commands, from a second transmitter.

[0018] Due to uncertainties which are associated with through-the-earth signal transmission attributable for example to physical variations such as geological structures in the ground through which the TTE signals propagate it is not possible to configure the blasting system to ensure that for example a detonator assembly in the first group receives the first TTE signal only, and does not receive the second TTE signal as well. To cater for the situation in which a detonator assembly receives two or even more TTE signals from different transmitters, more or less at the same time, the transmitters are configured to work in synchronism i.e. the transmitters are configured to ensure that the phase difference between any two TTE signals received by a single detonator assembly is less than 180° and preferably is less than 90°.

[0019] As a part of the establishment of the blasting system, in respect of any particular configuration or layout of components at the blast site, test routines may be implemented using test signals to assess whether the various transmitters transmit the respective TTE signals in synchronism (in the manner described) and to obtain an indication of time delays which can affect signal propagation through rock due for example to distances, geographical and geological factors and so on. To ensure that the maximum phase difference between any tworeceived TTE signals is less than 180°, and preferably is less than 90°, appropriate corrective measures are taken may be required. For example, if necessary through the use of suitable delay lines or time delay techniques, each of the transmitters is configured to ensure that TTE signals which are received by the various detonators are essentially in phase. BRIEF DESCRIPTION OF THE DRAWING

[0020] The invention is further described by way of example with reference to the accompanying drawing which is a schematic representation of a blasting system according to the invention in which the transmission of identical through-the-earth (TTE) signals from different transmitters is synchronised. DESCRIPTION OF PREFERRED EMBODIMENT

[0021] The accompanying drawing illustrates a blast site 10 at which a number of boreholes (not shown) are drilled. A detonator assembly of any suitable kind is loaded into each borehole which is charged with explosive in a conventional manner. Various protocols essential for the safe operation of the blast site are carried out. These aspects are known and thus are not further described herein.

[0022] Each detonator assembly includes a respective receiver(not shown) which is capable of receiving a signal which is transmitted through the earth i.e. a TTE signal.

[0023] A blast controller 14 is used to control the blasting process at the blast site 10. The blast controller is connected to a transmitter 16 which transmits a through-the-earth signal froma suitably designed antenna 16A. For various reasons, including those described hereinbefore, the transmitter 16 and the antenna 16A have an effective range, or envelope of operation, 16B which is of limited size. The envelope 16B is indicated in dotted outline and encloses various detonator assemblies 16.1 , 16.2 ...16.N. The detonator assemblies which are not inside the envelope 16B cannot reliably be communicated with via the transmitter 16.

[0024] To address this the blast controller is also connected via a signal bus line 26 to additional transmitters 28, 30 and 32 etc which are installed at various spaced apart locations taking into account factors such as signal transmission strength, geological and geographical characteristics, and the like, which can affect the transmission of a TTE signal. These transmitters are configured to transmit TTE signals via respective antennas 28A, 30A and 32A. These antennas have respective operating envelopes 28B, 30B and 32B indicated in each case by means of a dotted line. These envelopes can intersect with one another and also with the envelope 16B of the transmitter 16 as shown in the drawing.

[0025] Instead of the bus line 26 a blast controller could communicate with each transmitter using a wireless technique.

[0026] In some cases, different reference numerals are used in the drawing to designate the same detonator assembly. This is to enable the association between each operating envelope (16B, 22B, 30B and 32B) and the associated detonator assemblies, to be clearly illustrated. An inspection of the drawing shows that in some cases some of the detonator assemblies fall into each of two partially overlapping operating envelopes. It is possible though for a detonator assembly to fall into more than two operating envelopes.

[0027] The envelope 28B extends to and includes detonator assemblies 28.1 , 28.2, 28.3, 28.4,28.5 and 28.6. The detonator assemblies 28.2 and 28.3 are the same as the detonator assemblies 16.6 and 16.5 which are inside the envelope 16B.

[0028] The envelope 30B extends to and covers detonator assemblies 30.1 , 30.2, 30.3, 30.4 and 30.5. The detonator assembly 30.5 is the same as the detonator assembly 16.2 i.e. that detonator assembly falls inside the scope of each of the envelopes 28B and 16B.

[0029] The envelope 32B extends to and covers detonator assemblies 32.1 to 32.4. The detonator assembly 32.3 is the same as the detonator assembly 30.3. It is apparent therefore that in some instances the envelopes of the various antennas overlap to some extent with one another. However the occurrences and the degrees of those overlaps are not predictable, and it is this aspect which is addressed by the invention.

[0030] Each operating envelope is shown as being of a circular shape. This is exemplary only and non-limiting.

[0031] An originating through-the-earth signal, which is generated at or by the blast controller 14, is transmitted simultaneously via the signal bus 14 to each of the transmitters 16, 28, 30 and 32. These input signals are received by the various transmitters essentially simultaneously. However if there is a time delay in signal transmission then this would be established beforehand using test signals and test protocols, and corrective measures are then taken to ensure that, thereafter, in response to the input signals, the transmitters transmit identical TTE signals essentially at the same time, in synchronism so that, upon reception by a detonator assembly there is a maximum phase difference between any two TTE signals of180° and preferably the phase difference is less than 90°. This has the result that two or more of these signals, from different transmitters, received by any single detonator assembly, are processed at that detonator assembly as a single TTE signal.

[0032] A possible operating protocol, adopted for enhanced security and reliability of operation, involves the transmission (as aforesaid) by the blast controller of an originating or enabling (command) signal to each of the transmitters and for the receipt of that signal to be confirmed by each transmitter sending a receipt signal to the blast controller. Thereafter, having established that all the transmitters are functionally operative, a further signal (wireless or via a bus line) from the blast controller initiates the transmitters to transmit the TTE signals, with time delays as may be appropriate to ensure synchronism.

[0033] The aforementioned synchronisation process which is based on the use of multiple transmitters which are linked to one another allows for the establishment of a blast site with a large number of detonator assemblies and for the effective and safe operation of the blast site particularly in respect of firing signals.

Claims

CLAIMS1 . A method of transmitting a TTE signal to each of a plurality of detonator assemblies in a blasting system wherein the method includes the step of transmitting the TTE signal from each of a plurality of transmitters which are configured to function in synchronism such that a phase difference between a first TTE signal from a first transmitter of said plurality of transmitters received by a detonator assembly and a second TTE signal from a second transmitter of said plurality of transmitters, received by the same detonator assembly is less than 180°.

2. A method according to claim 1 wherein the transmitted TTE signals are identical to one another.

3. A method according to claim 2 wherein the blasting system includes a blast controller which sends the TTE signal to said plurality of transmitters which are configured subsequently to transmit the TTE signals in synchronism with one another.

4. A method according to claim 3 wherein the blast controller sends the TTE signal to each transmitter via a wireless connection or a bus line.

5. A method according to claim 2 wherein the blasting system includes a blast controller which sends an enabling signal to said plurality of transmitters which are configured subsequently to transmit the TTE signals in synchronism with one another.

6. A method according to claim 5 wherein the blast controller sends the enabling signal to each transmitter via a wireless connection or a bus line.

7. A method according to claim 1 which includes the step of associating time delays with the first transmitter and the second transmitter, as may be necessary, to ensure said phase difference is less than 180°.

8. A blasting system which includes a blast site, a plurality of detonator assemblies which are respectively positioned in boreholes at the blast site, and a plurality of transmitters which are configured to transmit, in synchronism, respective TTE signals from respective antennas, so that at least each detonator assembly in a first group of detonator assemblies receives a first TTE signal, containing predetermined information, data or commands, from a first transmitter of said plurality of transmitters and so that at least each detonator assembly in a second group of detonator assemblies receives a second TTE signal which is in synchronism with the first TTE signal, which contains the same predetermined information, data or commands, from a second transmitter of said plurality of transmitters.

9. A blasting system according to claim 8 wherein the plurality of transmitters are configured to ensure that a phase difference between any two or more TTE signals received by a single detonator assembly is less than 180° and preferably is less than 90°.

10. A blasting system which includes a blast site, a plurality of detonator assemblies which are respectively positioned in boreholes at the blast site, and a plurality of transmitters which are configured to transmit, in synchronism, respective TTE signals from respectiveantennas, so that a phase difference between a first TTE signal, containing predetermined information, data or commands, from a first transmitter of said plurality of transmitters received by a detonator assembly and a second TTE signal which contains the same predetermined information, data or commands, from a second transmitter of said plurality of transmitters received by the same detonator assembly is less than 180°.

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