VELOCITY OF DETONATION MEASUREMENT

Abstract

A method of obtaining velocity of detonation (VOD) information from a borehole wherein an explosive in the borehole is ignited by initiation of a detonator, the method including the steps of using a control circuit which obtains a measurement of the VOD and which is subsequently destroyed by ignition of the explosive, and of transmitting from the borehole a wireless signal which contains the VOD measurement and data which identifies the borehole before the control circuit is destroyed.

Claims

1-15. (canceled)

16. A blasting system which includes a plurality of detonator assemblies, a blast controller and at least one receiver wherein each detonator assembly includes a detonator which, in use, is positioned inside a borehole which is charged with an explosive, a communication module and conductors which connect the detonator to the communication module, wherein the detonator in response to a fire command signal from the blast controller received by the detonator at a time A is initiated at a time B thereby to cause ignition of the explosive in the borehole, and wherein the communication module includes a control circuit which is configured to obtain a measurement of the velocity of detonation (VOD) of the explosive and a transmitter for transmitting to the receiver a wireless signal which contains the VOD measurement and identification information which identifies the detonator assembly from which the wireless signal was transmitted before the transmitter is destroyed by the ignited explosive.

17. A blasting system according to claim 16 wherein in respect of each detonator assembly the respective control circuit, in response to receipt of the fire command signal from the blast controller, transmits the fire command signal at the time A to the detonator.

18. A blasting system according to claim 16 wherein the fire command signal is transmitted to the detonator from the blast controller using a through-the-earth signal.

19. A blasting system according to claim 16 wherein in respect of each detonator assembly the respective identification information comprises at least one of the following: a modulation technique, on the wireless signal, which is uniquely related to the detonator assembly; a data packet which contains the wireless signal and which is uniquely linked to the detonator assembly; the inclusion in the detonator assembly of a unique identifier and the inclusion of the unique identifier in the wireless signal which contains the VOD measurement.

20. A blasting system according to claim 16 wherein in respect of each detonator assembly transmission of the respective wireless signal commences at the time B and is maintained until such time as at least a predetermined length of the conductors is consumed by the ignited explosive, and wherein the duration of the time period for which the wireless signal is transmitted is indicative of the VOD measurement.

21. A blasting system according to claim 16 wherein in respect of each detonator assembly the respective wireless signal is transmitted for the duration of a time period it takes for a predetermined length of the conductors to be consumed by the ignited explosive.

22. A blasting system according to claim 16 wherein in respect of each detonator assembly the respective VOD measurement is based on at least one of the following: a resistance which is presented by the conductors to the control circuit; an instantaneous rate at which a resistance which is presented by the conductors to the control circuit decreases.

23. A blasting system according to claim 16 wherein said wireless signals which are transmitted simultaneously or in identical time slots by said transmitters from said plurality of detonator assemblies are multiplexed to enable such wireless signals to be distinguished from one another.

24. A method of obtaining velocity of detonation (VOD) information from each of a plurality of boreholes in a blasting system wherein each borehole is respectively charged with an explosive which is ignited by initiation of a respective detonator in the borehole in response to a fire command signal from a blast controller, the method including the steps, at each borehole, of using a respective control circuit which is associated with the respective detonator to obtain a measurement of the VOD and of transmitting from the borehole a respective wireless signal which contains the VOD measurement and data which identifies the borehole before the control circuit is destroyed by the ignited explosive.

25. A method according to claim 24 wherein in respect of each borehole the respective VOD measurement is made by measuring at least one of the following: a value of a resistance which is presented to the control circuit by conductors which are connected to the detonator; an instantaneous rate at which a value of a resistance presented to the control circuit by conductors which are connected to the detonator changes; a frequency of oscillation of an oscillator in which a value of a resistance presented to the control circuit by conductors, which are connected to the detonator, determines the frequency of operation of the oscillator, or the rate of change of said frequency of oscillation.

26. A method according to claim 24 wherein each said wireless signal is modulated to enable the wireless signal to be distinguished from any other wireless signal which contains a VOD measurement and which is simultaneously transmitted.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The invention is further described by way of examples with reference to the accompanying drawings in which:

[0046] FIG. 1 illustrates aspects of a blasting system according to the invention,

[0047] FIG. 2 illustrates in block diagram form some components of a detonator assembly according to the invention, and

[0048] FIG. 3 is a graphical depiction of different inventive techniques upon which the generation and transmission of VOD measurements from detonator assemblies in the blasting system can be based.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0049] FIG. 1 of the accompanying drawings schematically illustrates aspects of a blasting system 10 at which the principles of the invention are implemented.

[0050] The blasting system 10 includes a blast site 12 at which are formed a plurality of boreholes 16A, 16B . . . 16N at predetermined locations. Each borehole is charged with an explosive 18, as is known in the art.

[0051] The blasting system 10 includes a plurality of detonator assemblies 20A, 20B . . . 20N. Each detonator assembly is located in a respective borehole 16 exposed to the explosive 18 in the borehole.

[0052] The blasting system 10 includes a blast controller 22 and a receiver 24. The receiver 24 may be one of a number of similar receivers which are positioned at predetermined remote locations around the blast site 12. Alternatively the receiver 24 is located at, or forms a part of, the blasting controller 22. Another possibility is to configure one or more detonator assemblies 20, selected for the purpose, so that each can then act, at least to the extent required for the implementation of the invention, as a receiver 24.

[0053] The detonator assemblies 20 are physically substantially identical to one another although the operations thereof are not necessarily identical.

[0054] Referring to the detonator assembly 20A it includes a communication module 34A which is configured to be positioned at a mouth 36A of the borehole 16A in which it is positioned. The communication module 34A is connected by conductors 38A to a detonator 40A which is positioned in accordance with a blast plan for the blasting system 10 at a known depth in the borehole, exposed to the explosive material 18.

[0055] FIG. 2 shows in block diagram form a detonator assembly 20.

[0056] The communication module 34 includes a power source 42, a signal generator 44, a transmitter/receiver module 46 with a transmitter 46A and a receiver 46B, and a control circuit 48. The listing of these components is not exhaustive and is given to enable the principles of the invention to be understood. In one embodiment an identifier 50 which uniquely identifies the detonator assembly 20 is stored in a memory unit 52 in the communication module 34.

[0057] The blast controller 22 is used to execute a blasting sequence in the blasting system according to predefined protocols. After all prescribed initial checking and programming steps have been taken a stage is reached at which the blast controller 22 transmits a blast signal 56 to the various detonator assemblies 20A . . . 20N. The blast signal 56 is received by the receiver 46B and validated by the control circuit 48 and, in accordance with predetermined rules, the control circuit 48 then transmits a fire command signal 58 via the conductors 38 to the detonator 40. The fire signal 58 causes the detonator 40 to initiate at a predetermined time and the explosive 18 exposed to the detonator is ignited.

[0058] Subsequently, as is described hereinafter, a wireless signal 62, which contains a VOD measurement of the explosive 18, is sent to the receiver 24.

[0059] The length of the conductors 38 between the communication module and the detonator 40 is known. From that value, and from the time which is taken for the conductors to be consumed, the VOD for the explosive exposed to the conductors can be determined.

[0060] The wireless signal 62 also includes the identifier 50 which uniquely identifies the detonator assembly 20. Additionally, the identifier 50 is linked to an identifier of the borehole 16 at which the detonator assembly 20 is used. The borehole 16 can be numerically designated or it can be designated by means of its geographical position i.e. through the use of appropriate coordinates. That information is kept in a database which is accessible by a control computer, not shown, linked in any suitable way to the blast controller 22 and to the receiver 24.

[0061] The wireless signal 62 is produced in a controlled manner by the function of the control circuit 48 which actuates the signal generator 44. A signal produced by the signal generator is subjected to a modulation technique by a modulator 66, as is described hereinafter. The resulting modulated signal 68 is applied to the control circuit 48 and combined with the identifier 50 to produce a signal 70 which then, via the transmitter 46A, is included in the wireless signal 62 which is transmitted from the detonator assembly.

[0062] In a variation the modulation technique used for the transmission of the VOD signal can be configured so that it uniquely identifies the originating detonator assembly.

[0063] At a blast site which includes a large number of boreholes and detonator assemblies, of the order of several thousand, technical challenges arise in distinguishing a wireless signal 62X sent from a detonator assembly 20X from a wireless signal 62Y sent from a detonator assembly 20Y. The difficulty is compounded when the respective wireless signals, possibly from a large number of detonator assemblies, are sent simultaneously or substantially simultaneously i.e. with only a very small time interval between the actual transmission times of the wireless signals.

[0064] Despite this difficulty the transmission of a wireless signal from a detonator which contains a VOD measurement of the explosive exposed to the detonator is of significant value in forming an assessment of blasting efficiency and for quality control purposes.

[0065] FIG. 3 graphically depicts different methods for generating and transmitting a wireless signal which contains data relating to a VOD measurement. Inherently there are time constraints in measuring the VOD which can be as high as 7000 mps. By way of a non-limiting example only, and depending inter alia on measurement techniques employed, in order to measure this parameter an explosive front in the borehole under consideration should travel for at least 10 meters so that there is sufficient time to make, and then to process, relevant input data. This means that it would take about 1.5 milliseconds to gather the information required to provide a VOD calculation. The control circuit 48 can then calculate the velocity of detonation and include the VOD value and the identifier 50 in the signal 70. That information is then transmitted in the wireless signal 62.

[0066] FIG. 3 shows a horizontally extending timeline with spaced apart transversely extending dotted lines marked A, B, C and D respectively. In respect of any given detonator assembly 20 the time A is the time at which the fire command signal 58 is sent by the control circuit 48 via the conductors 38 to and received by the associated detonator 40.

[0067] The time B is the time at which the detonator 40 is initiated and consumed (destroyed) in response to the fire command signal 58.

[0068] The time C is the time at which the communication module 34 has been consumed after ignition of the explosive 18.

[0069] The time D is a parameter used to mark the end of a time interval after the time B during which time interval a predetermined length of the conductor 38 has been consumed and which time interval is of sufficient duration to enable a VOD measurement to be made.

[0070] In a first method M1 the transmitter 46A is kept inoperative until such time as VOD data has been obtained. At the time D a signal 621 with the VOD data and the identifier 50 is transmitted by the transmitter 46B. Clearly this must be before the time C for at the time C the detonator assembly 20 is destroyed by the ignited explosive 18.

[0071] In a second method M2 transmission of a wireless signal 622 commences at the time B and ends at the time D. The VOD measurement, once calculated, is included with the identifier in the wireless signal 622. This is not necessarily the case for the VOD measurement could be obtained from the expression (length of conductor 38 consumed)/(duration of signal). Thus if the length of the conductor is a known quantity the duration of the signal is sufficient to convey the VOD data. No additional data is required to be sent during the transmission although data such as an identifier for the detonator assembly could be sent.

[0072] In a method M3 transmission of a first signal 623A commences at or after the time A but before the time B. Transmission of the signal 623A ends at the time B. Thereafter a second signal 623B is transmitted from the time B up to the time D at which time the measurement of the VOD has been completed and this measurement and the identifier are then included in the signal 623B.

[0073] The signals 623A and 623B can be distinguished from each other through the use of an appropriate modulation technique (MOD1, MOD2). For example the signal 623A may comprise an up-chirp signal while the signal 623B may comprise a down-chirp signal which is modulated with the VOD and identifier information. The signals 623A and 623B can be distinguished from each other in any other suitable way e.g. by using different frequencies for their transmissions.

[0074] FIG. 3 thus graphically depicts different ways in which a wireless signal can be transmitted from a detonator assembly to transfer information relating to the VOD measurement and the respective identifier. The VOD measurements for each of the explosive charges in the respective boreholes are transferred to a control location for subsequent assessment and processing.

[0075] In a large blasting system with several thousand detonators the VOD signals coming from the various detonator assemblies must be distinguished from one another even though at least some of such signals may be transmitted at the same time or within closely spaced time intervals from one another. To achieve this type of discrimination the wireless signals 62 coming from the different detonator assemblies are orthogonal or multiplexed using various techniques. Use is made of orthogonal frequency division multiplexing techniques as referred to hereinbefore.

[0076] In the method M1 the VOD data is transmitted in the signal 621 only after a full calculation has been made thereof.

[0077] In the method M2 the signal 622 is transmitted from the time B and it is transmitted continuously while the conductors 38 are being consumed. Once the conductors are fully consumed, or after consumption of a predetermined length of the conductors, transmission of the signal 622 is terminated. Thus the duration of the time period for which the signal 622 is transmitted is, in itself, indicative of the VOD, for the lengths of the conductors from the module 34 to the detonator 40 are known.

[0078] In the method M3 a first signal 623A is transmitted for other communication purposes not related to the VOD measurement, up to the time B. Thereafter a signal 623B is transmitted. This signal essentially corresponds to the signal 622 in that it endures for a period from the time B until such time as the conductors 38 have been consumed. The signals prior to the time B and after the time B are differentiated from one another to avoid confusion and to enhance discrimination, by transmitting the signals at different frequencies or by using different modulation techniques on the signals. In each case the transmitted signal 62 does carry the unique identifier for the detonator assembly in question.

[0079] A technique which finds particular value in measuring VOD is to measure the rate of change of a parameter which is dependent on VOD.

[0080] While the conductors 38 are being consumed it is possible to calculate the instantaneous rate at which this occurs. One approach is to measure the resistance presented by the conductors 38 to the control circuit 48. This resistance changes as plasma resulting from initiation of the explosive 18 creates a conductive path between the conductors 38. The rate at which the resistance changes, due to the plasma effect, is then indicative of the VOD. An instantaneous rate of change of resistance value can be obtained in a shorter period than the period which is taken for the conductors from the module 34 to the detonator 40, or a predetermined length of these conductors, to be consumed.

[0081] The resistance which is presented by the conductors 38 could alternatively be regarded as being linked to a resistor which is included as an active element in an oscillating circuit e.g. an L/R/C circuit in which the frequency of oscillation is dependent at least on the value of the resistance. As the resistance changes, in the manner described, the frequency of oscillation also changes. The instantaneous rate at which the frequency changes is indicative of the VOD and a signal containing data on the rate of change of the frequency, collected at a remote point, enables the VOD data for the particular borehole to be logged. A similar result can be achieved by monitoring the amplitude of oscillation (not the frequency of oscillation), and the rate of change of the amplitude.

[0082] FIG. 3 shows a method M4 which is similar to M3. Transmission of a first signal 624A commences at or after time A and is continued up to the time B. Thereafter signal transmission is stopped, i.e. there is radio silence, for a time interval K of duration which is less than (B-D). At the end of the time interval K transmission of a second signal 624B commences and continues until the time D i.e. after a velocity of detonation measurement has been made, or after a predetermined set time which ends before the time C. The signals 624A and 624B do not necessarily have to be distinguished from each other in that the receiver 24 associated with the blast controller 22 has the capability to detect the stop-start in the transmission i.e. the stopping of the transmission of the signal 624A at the time B and the starting of the transmission of the signal 624B at the time B+K.