DETONATION SYSTEM.

Abstract

A detonation system comprising a detonation site with a perimeter surrounding the detonation site, a plurality of detonation pits spaced at the detonation site, a plurality of detonator assemblies, each detonator assembly positioned in a respective detonation pit, each detonator assembly including a respective receiver that responds to a magnetic signal transmitted from a control device and received by the receiver, a plurality of magnetic field strength meters (MFSMs) located at spaced points around the perimeter; each MFSM including a respective unique identifier; each MFSM, in response to a magnetic signal detected by the MFSM, producing a respective data signal that depends on the intensity of the detected magnetic signal and that includes said unique identifier, and a communication device for transmitting said data signals from said MFSMs to a data collection point.

Description

DETONATION SYSTEM BACKGROUND OF THE INVENTION The present invention relates to a detonation system based on the use of signal transmission through the ground. In a detonation system of the type described, detonator assemblies placed in various detonation pits within a detonation area receive commands transmitted via magnetic signals. The signal transmission process is unidirectional if the detonator assemblies lack sufficient energy to transmit signals back to a detonation control center. To address this, a pre-detonation inspection of the detonation area is conducted to ensure that the deployed detonator assemblies are correctly positioned and that the detonation system is such that command signals from the detonation control center are reliably received. Magnetic field strength meters (MFSMs) are used at various locations to monitor the magnetic field strength for prospecting purposes.MFSMs are also deployed shortly before detonation to monitor magnetic signals, as it has been established that varying conditions at the detonation site can affect the intensity of these signals. The MFSMs record information during the initial survey, and the resulting data are subsequently consulted to determine the optimal location of the detonator assemblies and the optimal deployment of an antenna to transmit the magnetic signals. In one technique, MFSMs are deployed in blast pits following a pattern that covers the entire detonation zone. A transmitter at the control center then operates in test mode for a predetermined period while the MFSMs record test messages to determine the degree of magnetic field propagation through the ground. The MFSMs are then retrieved and interrogated, for example, using a tagger with an NFC (near-field communication) interface. The acquired data can be analyzed to understand the transmission process through the ground. Furthermore, the data helps identify a fault or weakness in the system, such as a misfire. The aforementioned process is laborious and time-consuming. One object of the invention is to address this aspect. SUMMARY OF THE INVENTION The invention provides a detonation system comprising a detonation site with a perimeter surrounding the detonation site, a plurality of detonation pits spaced within the detonation site, a plurality of detonator assemblies, each detonator assembly placed in a respective detonation pit, each detonator assembly including a respective receiver responding to a magnetic signal transmitted from a control device and received by the receiver, a plurality of magnetic field strength meters (MFSMs) placed at spaced locations within the perimeter, each MFSM including a respective unique identifier, each MFSM in response to a magnetic signal detected by the MFSM, producing a respective data signal dependent on the strength of the detected magnetic signal and including said unique identifier,and a communication device for transmitting said data signals from said MFSMs to a data collection point. The locations where the MFSMs are placed are such that, once the detonators are initiated, the MFSMs are not damaged. The data collection point can be anywhere convenient, but preferably it is located on the control device. The unique identifier associated with each MFSM can be an identity of the MFSM or of the MFSM location. The communication device can be configured to allow data transmission from each MFSM continuously or at regular intervals. Each MFSM can be interrogated using any suitable technique and, in response to an interrogation signal sent, for example, from a transmitter located at the data collection point, the MFSM can transmit the respective data signal to a receiver located at the data collection point. Before a detonation, the control device can transmit a magnetic signal, and the MFSMs, strategically located at the detonation site, can then be used to ensure effective and successful ground communication with the respective detonator assemblies. The data signals from the MFSMs can be transmitted to the data collection point by any suitable method that guarantees the absence of magnetic signals that could inadvertently trigger the individual detonator assemblies. Thus, the MFSMs can transmit their respective data signals using a suitable wireless technique. Alternatively, a fiber optic cable can be used to transmit the data signals from the respective MFSMs to the data collection point.Generally, it would not be appropriate to connect the MFSMs using a current-carrying conductor, as this configuration could lead to the generation of a magnetic field that could interfere with the magnetic signals coming from the control device. The fiber optic cable is positioned so that it will not be damaged during the detonation. One or more sensors can be placed at each selected MFSM location to monitor variable environmental parameters such as temperature, air humidity, precipitation, or seismic activity. In this way, each MFSM, or one or more of the selected MFSMs, could be used to collect data on a range of variables and transmit that data to a data collection point located, for example, at the control device, or in communication with the control device. A major advantage of the above technique is that, using criteria known in the technique, an evaluation of the data produced by the MFSMs on the expected reliability of the detonation system's operation can be made before the firing takes place. Another advantage of the invention is that before, during, and after a detonation, the MFSMs function to monitor various events, including those occurring during and as a result of the detonation. Since the MFSMs and the fiber optic cable are not damaged by the detonation, the MFSMs are able to provide real-time data on the events occurring during the detonation. This capability allows the MFSMs to be deployed to identify a detonation failure so that, once the detonation has taken place, corrective measures can be taken, for example, to retrieve a defective set of detonators. The invention further extends to a method for evaluating the operational reliability of a detonation system comprising a detonation site with a perimeter surrounding the detonation site, a plurality of detonation pits spaced at the detonation site, a plurality of detonator assemblies, each detonator assembly located in a respective detonation pit, each detonator assembly including a respective receiver that responds to a magnetic signal transmitted from a control device and received by the receiver, the method comprising the steps of surrounding the detonation site with a fiber optic cable positioned so that, upon initiation of the detonator assemblies, the fiber optic cable is not damaged, connecting a plurality of magnetic field strength meters (MFSMs) to the fiber optic cable, and transmitting a magnetic signal from the control device through the ground.producing in each MFSM a data signal that depends on the intensity of a magnetic signal detected by the MFSM, transmitting from each MFSM through the fiber optic cable to a data collection point the respective data signal, and using the data signals, received at the data collection point, to evaluate the reliability of the transmission of the magnetic signal through the ground from the control device to the detonator assemblies. BRIEF DESCRIPTION OF THE DRAWINGS The invention is further described by way of example with reference to the accompanying drawings Figures 1, 1A and 1B which respectively schematically represent aspects of a detonation system according to the invention DESCRIPTION OF PREFERRED EMBODIMENT The attached drawings schematically represent aspects of a detonation system 10 according to the invention. The detonation system 10 includes a detonation site 12 surrounded by a loop antenna 14 connected to a transmitter 16 coupled to a control device 20 comprising a data collection point 21 in a detonation control center 22. A plurality of detonation pits 24 are formed at the detonation site. Each detonation pit includes a respective detonator assembly 26, one of which is shown in more detail in Figure 1A. Each detonator assembly includes a receiver 28, a control circuit 30 comprising an ignition element 31, an explosive 32, and a power source 34 used to energize the receiver 28 and the control circuit 30 and, when the receiver 28 receives a firing command and transfers it to the control circuit 30, to provide power to fire the element 31 and thereby initiate the explosive 32. Detonation site 12 has a perimeter 36, indicated by a dotted outline. Magnetic field strength meters (MFSMs) 40 are placed at specific locations along the perimeter. Each MFSM includes a signal generator and a magnetic field strength sensor. Each MFSM also includes a signal generator and a transmitter 42 capable of generating a data signal 44 that depends on the strength of a magnetic field detected by a detector 46 within the MFSM. Each MFSM has a memory device in which a unique identifier 48 is stored (Figure 1B). The identifier 48 can be linked to the MFSM 40 or to the geographical location where the MFSM is installed. The respective sensors 50, 52, etc., can be connected, as required, to one or more selected MFSMs 40. Sensor 50 can be used, for example, to monitor the temperature at the MFSM's location, while sensor 52 can monitor humidity levels. Other variable environmental parameters can also be monitored, as required. The invention is not limited in this respect. The data calculated by sensors 50 and 52 are incorporated, as required, into the data signal 44 produced by the generator and transmitter 42. The MFSM 40 are connected to each other by means of a communication device 60 which in this example comprises a fiber optic cable 62 that is coupled to a transmitter / receiver device 64 in the detonation control center 22. Transmitter 16 is designed to transmit a magnetic signal through the loop antenna 14 via the ground. This signal, detected by the respective receiver 28 of each detonator assembly 26, is used to transmit information to the individual detonator assemblies 26 for synchronization, arming, and firing purposes, as is known in the art. The detonator assemblies cannot return information-carrying signals to the detonation control center 22, as this would require a significant amount of onboard power in each detonator assembly. Therefore, the detonation system 10 is unidirectional. To ensure the reliable operation of the detonation system, it is vital to verify that the magnetic signals for controlling the detonation process, originating from the control center 22, are reliably received by the detonator assemblies 26. The 40 MFSMs are used to meet the aforementioned requirement. Each MFSM is placed on perimeter 36 at a location chosen to ensure that, when the detonation occurs at site 12, the MFSM will not be damaged. Furthermore, the MFSMs are positioned so that, collectively, they can provide an accurate indication of the effectiveness of magnetic signal propagation through the ground from the detonation control center 22. The intention here is to provide a mechanism for assessing whether the signals from transmitter 16 are accurately and completely received by all the detonator assemblies 26 that are surrounded by the loop antenna 14. Similarly, the communication device 60, comprising the fiber optic cable 62 surrounding the detonation site 12, linking the MFSMs together, and the transmitter / receiver device 64, is located out of harm's way to allow continuous use during the detonation and for subsequent retrieval and reuse at a new detonation site. The MFSMs located on perimeter 36 do not need to be moved before detonation and can be used to continuously monitor the magnetic field established by transmitter 16. Each MFSM 40 collects data on at least the magnetic field strength at its location. As mentioned, some or all of the MFSMs are connected to one or more sensors 50, 52 to monitor various environmental or other parameters. Data on the strength of the magnetic signals from transmitter 16 and data produced by sensors 50, 52, collected by each MFSM, are transmitted to the control center 22 via the fiber optic communication mechanism 60. Each MFSM can transmit data continuously or at regular intervals.Each MFSM can also be interrogated by an interrogation signal transmitted from the transmitter / receiver array 64 in the detonation control center 22 via fiber optic cable 62. Alternatively, an interrogation signal could be sent from array 64 using wireless techniques. The data signals from the MFSMs are used, employing techniques known in the art, to form an assessment of the reliability of the detonation system's operation before firing takes place. If an MFSM indicates that, for any reason, the strength of a magnetic signal transmitted from the detonation control center 22 is weak or unreliable, corrective action must be taken. MFSMs are capable of continuously monitoring data, particularly data generated before, during, and immediately after a detonation event. This data can be processed to determine the effectiveness of a detonation and to identify any misfires. Each MFSM detects a magnetic signal that is not necessarily generated by the control device. Consequently, each MFSM produces a data signal in response to any magnetic signal produced by any event other than a magnetic signal transmitted from the control device. For example, if the firing of a detonator and the subsequent ignition of an explosive generate a magnetic signal, an MFSM may detect this signal. The availability of this information can be used to understand the effects of the detonation and, potentially, to identify misfires. The detonation system 10 of the invention can be used in any suitable underground or surface location. In the former application, as an additional safety measure, it is preferable to control the detonation process from a surface location. Typically, a central control point is used, employing a suitable surface detonation controller system that communicates wirelessly with the described detonation system. The detonation system can be controlled from the surface detonation controller for pre-detonation testing and evaluation, as well as for the detonation itself. In this way, the magnetic signal data collected at the detonation control center 22 by the transmitter / receiver 64 can be transmitted to the surface detonation controller as required.The process can be automated and the data transferred from the detonation control center 22 to the surface detonation controller can be recorded and displayed, as needed, to assist in the detonation process, and are also available for post-detonation evaluation purposes. This invention has been described with reference to a detonation system in which a unidirectional magnetic signal transmission through the ground takes place. However, the techniques described herein may be used, if necessary, in a detonation system in which a bidirectional magnetic signal transmission occurs, possibly through the ground.

Claims

1. A detonation system (DS) comprising a detonation site (DS) with a perimeter (36) surrounding the detonation site (DS), an antenna (14), a transmitter (16) in a control device (20) that, through the antenna (14), transmits a magnetic signal, a plurality of detonation pits (24) spaced at the detonation site, and a plurality of detonator assemblies (26), each detonator assembly (26) placed in a respective detonation pit (24), each detonator assembly (26) including a respective receiver (28) that responds to the magnetic signal transmitted from the control device (20) and received by the receiver (28), and characterized in that the detonation system (DS) includes a plurality of magnetic field strength meters (MFSMs) (40) situated respectively at spaced locations on the perimeter (36), each MFSM (40) includes a respective unique identifier (48),Each MFSM (40), in response to a magnetic signal detected by the MFSM originating from the control device (20) and transmitted via the antenna (14), produces a respective data signal (44) that depends, at least, on the intensity of the detected magnetic signal and includes said unique identifier (48), and a communication arrangement (60) for transmitting said data signals (44) from said MFSM (40) to a data collection point (21), thereby enabling the evaluation of the reliability of the magnetic signal transmitted from the control device (20) to the detonator assemblies (26), and characterized in that each MFSM (40) is optionally configured to monitor data at the MSFM location before, during, and after a detonation event.

2. A detonation system according to claim 1, characterized in that the unique identifier (48) associated with each MFSM (40) is an identity of the MFSM or of the MFSM location.

3. A detonation system according to claim 1, characterized in that the communication arrangement (60) comprises an optical fiber cable (62) surrounding the detonation site (12) and connected to each MFSM (40), a respective transmitter (42) in each MFSM (40) for transmitting said data signals (44) via said optical fiber cable (62) to the data collection point (21), and a receiver (64) at the data collection point (21) connected to the optical fiber cable (62) and configured to receive data signals (44) from each MFSM (40).

4. A detonation system according to claim 3, characterized in that the communication arrangement (60) includes a transmitter (64) for transmitting an interrogation signal to an MFSM (40) which, in response, transmits the data signal (44) to said receiver (64).

5. A detonation system according to claim 1 comprising at least one selected MFSM location, at least one sensor (50, 52) for monitoring an environmental parameter, and characterized in that the data signal (44) produced in said MFSM (40) includes data produced by the sensor (50, 52).

6. A detonation system according to claim 1, characterized in that the antenna is a loop antenna (14) surrounding the detonation site (12).

7. A method for evaluating the operational reliability of a detonation system (10) comprising a detonation site (12) with a perimeter (36) surrounding the detonation site (12), an antenna (14), a transmitter (16) in a control device (20) which, through the antenna, transmits a magnetic signal, a plurality of detonation pits (24) spaced at the detonation site, a plurality of detonator assemblies (26), each detonator assembly (26) positioned in a respective detonation pit (24), each detonator assembly (26) including a respective receiver (28) which responds to the magnetic signal transmitted from the control device (20) and received by the receiver (28), the method being characterized by the steps of surrounding the detonation site (12) with an optical fiber cable (62), connecting at spaced locations a plurality of magnetic field strength meters (MFSM) (40) respective to the fiber optic cable (62),transmitting a magnetic signal through the antenna from the control device (20) through the ground, producing in each MFSM (40) a data signal (44) that depends at least on the intensity of a magnetic signal detected by the MFSM, transmitting from each MFSM through the fiber optic cable (62) to a data collection point (21) the respective data signal (44), and using the data signals (44), received at the data collection point (21), to evaluate the reliability of the transmission of the magnetic signal through the ground from the control device to the detonator assemblies (26) prior to detonation.

8. Method according to claim 7, characterized in that the data signal (44) from an MFSM (40) is transmitted in response to an interrogation signal from the control device (20).

9. A method according to claim 7, comprising the step of including in the data signal (44) from an MFSM (40), data relating to the identity of the MFSM and, optionally, data relating to a predominant environmental parameter at the location of the MFSM.

10. A method according to claim 7 comprising the step of using the data signals (44) received at the data collection point (21) to monitor events occurring during, and after, the detonation as a result of the detonation.

11. A method according to claim 7 comprising the step, after the detonation takes place at the detonation site, of recovering, for reuse, the MFSMs and the fiber optic cable.

12. A method according to claim 7 comprising the step of transmitting the magnetic signal from the transmitter (16) to the control device (20) through a loop antenna (14).

13. A method according to claim 7 characterized in that the data signals (44) are automatically relayed to a detonation controller to assist in a detonation process.

14. A method according to claim 7 characterized in that said data signals (44) of the MFSMs are transmitted continuously.

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