ZA200802718B - Centralised blasting system - Google Patents

Description

~ 200870274

INTRODUCTION AND BACKGROUND

This invention relates to a blasting system for causing a multi-shot blast and more particularly to a centralized blasting system for use in causing a multi-shot blast, for example in deep underground mines.

Blasting systems for causing multi-shot blasts are known in the art. At least some of the known systems comprise electronic detonators, which are programmable, either from a central control station or by means of a portable programming tool, with digital data relating to a respective delay time after reception of a common firing signal when the programmed detonator is configured to cause an associated charge to be initiated. These known systems are complex in their operation, are expensive and often not safe enough for at least some applications.

OBJECT OF THE INVENTION

Accordingly, it is an object of the present invention to provide a centralised blasting system, parts thereof and associated methods with which the applicants believe the aforementioned disadvantages may at least be alleviated.

SUMMARY OF THE INVENTION

,

According to the invention there is provided a centralized blasting system comprising:

- a central blast controller; - the controller being connectable to a communications backbone;

- a plurality of network slave stations connectable to the backbone in distributed manner; - a plurality of detonators connectable by respective electrical links to each of the network slave stations; i. - the system comprising data communications means to enable digital data communications between the central controller and the network slave stations via the backbone, but not between the slave stations and the detonators connected thereto; and - each slave station being configured to sense by means of an analogue signal on the respective link a detonator load connected to the network slave unit. : Each detonator may be an instantaneous detonator.

Alternatively,

each or at least some of the detonators may be a programmable electronic detonator, which is adapted to be programmed with delay time data.

In this specification the term “instantaneous detonator” is used to denote a detonator, which is configured, when a suitable firing signal is received, immediately to initiate a charge associated with the detonator. Hence, such a detonator would not be programmable or comprise delay time means, such as a memory arrangement, for storing data or a signal relating to a delay time after the firing signal is received and before the charge is initiated.

Each of the detonators of the system may be connectable to a respective shock tube assembly. Each shock tube assembly may comprise a further detonator and a delay time providing means incorporated in the assembly.

The central blast controller may be connected to the backbone by a network interface unit. The central blast controller may be connected to the network interface unit by a serial link.

The backbone may comprise a primary network element and a plurality of secondary or branch network elements. The primary network element and the secondary network elements may comprise electrical conductors. In other embodiments, at least the primary network element may comprise optical fiber. In an embodiment wherein the primary network element comprises optical fiber and the secondary i elements comprise electrical conductors, suitable converters may be provided between the primary element and each secondary element.

The network slave stations may comprise an upstream port, a downstream port and at least one detonator port to which at least one detonator is connectable. At least some of the network slave stations may be connected at the upstream port to an upstream part of the backbone and at the downstream port to a downstream part of the backbone, so that each of the at least some slave stations function as a repeater on the backbone. Other network slave stations may be connected to the backbone by the upstream port only.

The electronic detonator may comprise - a main circuit comprising an input, a fusehead and a switch; - a charge storage device connected in the circuit; - a current limiting device upstream of the charge storage device for limiting to below a no-fire current of the fusehead, a current flowing from the input and through the fusehead, when the switch is closed; and - the switch being configured to close an initiating circuit comprising the charge storage device and the fusehead when a DC voltage at the input exceeds a predetermined threshold value.

Alternatively or in addition, the electronic detonator may comprise: - Bb - a main detonator circuit comprising an input and a charge storage device; - the charge storage device, a fusehead and a switch being connected in an initiating circuit of the detonator; and - the switch being configured to close the initiating circuit when a DC voltage at the input exceeds a predetermined threshold voltage of at least 50V.

Each network slave station may comprise a local controller, the controller may be connected to the upstream port via suitable protection circuitry, opto-isolation circuitry and an upstream network interface; the controller may be connected to the downstream port via a downstream network interface and the controller may be connected to a keypad provided in a user accessible position on a housing of the network slave station.

Each slave station may comprise a DC voltage generator configured to generate a detonator firing signal in the form of a DC voltage larger than 50V, preferably larger than 100V and even more preferably larger than 135V and a switch means for applying the firing voltage to the detonators connected thereto, thereby to initiate the detonators.

The voltage generator may further be configured also to generate a DC test voltage, which is substantially lower than the aforementioned firing voltage.

Each detonator port of the network slave station may be connected in a respective circuit comprising a first switch of said switch means for connecting a selected one of the threshold voltage and the test voltage to the circuit. The first switch may be controllable by a select signal from the controller. The circuit may also comprise a second switch in series with the first switch and which is controllable by the select signal, to provide at an output of the circuit an analogue signal having a parameter, which is proportional to a detonator load connected to the port. The parameter may be current and be directly proportional to a number of detonators connected in parallel to the port. oo ,

The output may be connected to an analogue to digital converter, which may be connected to provide at a sense input of the controller, digital data relating to detonator load.

The controller may comprise a memory arrangement for storing said digital data.

The data communications means may enable data communications between the central blast controller and a selected one of the network slave stations on a master slave basis, in half-duplex manner and pulse width modulation may be used.

Due to long distances between the blast controller and any network slave station, a relatively slow bit rate may be utilized. The bit rate may typically be in the order of 100bits/sec.

The data communications may be in the form of discrete packets wherein each packet may comprises a header comprising first and second start bits, a data field comprising a plurality of data bits, and at least one parity bit. The first and second start bits may be of opposite polarity, but equal length. The data field may comprise eight (8) data bits and the packet may comprise one parity bit.

Each network slave station may be assigned a respective address falling in a first part of a block of sequential numbers represented by the data bits. The block may comprise a second part of sequential numbers, which may be used to encode respective commands to the slave station and a third part of sequential numbers that may be used as special addresses.

The third part may be sandwiched between the first and second parts.

A protocol whereby the central controller speaks first may be followed. According to this protocol the controller transmits a first packet comprising in the data field an address of a selected network slave station. The selected network slave station responds with a response packet comprising status data in the data field.

Communications is then limited to between the central controller and the selected network slave station, until the controller transmits a packet comprising an address of a next selected network slave station.

Subsequent packets transmitted to the first network slave station may comprise in the data filed encoded commands selected from the second range 104.

. '

The data communications means may comprise a data extractor comprising a comparator comprising a first input for a reference voltage, a second input for a data signal and an output; and a circuit for generating a variable reference voltage at an output thereof which output is connected to the first input, the circuit being configured to generate a reference voltage such that when the generated reference voltage is applied to the first input, output bits at the output of the comparator corresponding to first and second reference bits in the data signal, which are of opposite polarity and of equal length, would be of equal length.

The invention also extends to a network slave station as herein defined and/or described, a data extractor as herein defined and/or described and associated methods as herein defined and/or described, including a data communications method and/or protocol as herein defined and/or described.

More particularly, a method of causing a multi-shot blast may comprise the steps of: - causing a plurality of distributed instantaneous detonators to initiate a respective shock tube assembly connected thereto; and

- causing the shock tube assemblies to initiate the blast.

The method may comprise the steps of applying a DC voltage larger than 50V at an input of each instantaneous detonator, to initiate the instantaneous detonators. >

The method may comprise the step of utilizing respective delay time mechanisms in the shock tube assemblies to cause a sequential blast.

BRIEF DESCRIPTION OF THE ACCOMPANYING DIAGRAMS

The invention will now further be described, by way of example only, with reference to the accompanying diagrams wherein: figure 1 | is a block diagram of a first embodiment of a central blasting system according to the invention; figure 2 is a similar block diagram of a second embodiment of the system; figure 3 is a block diagram of a detonator forming part of the system according to the invention; figure 4 is a block diagram of part of a network slave station (NSS) forming part of the system; figure 5 is a block diagram of a detonator interface forming part of a NSS;

figure 6 is a time diagram of typical half-duplex digital communications on the backbone; figure 7 is a more detailed time diagram; figure 8 is a map of addresses, special addresses and commands that my be used in a digital communication system on a backbone of the central blasting system utilizing an eight (8) bit data word; figure 9 is a block diagram of a adaptive threshold data extractor forming part of a network interface unit and /or the network slave station of the central blasting system; and figures 10(a) to 10{c) are time diagrams illustrating a method of extracting data from a signal received by means of the data extractor.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

In figure 1 there is shown a first embodiment of a centralized blasting system 10 according to the invention.

The system 10 is typically deployable at a deep under ground mine 12, to cause a multi-shot blast. The system comprises a control computer or central blast controller 14 normally located at an above ground control station 16. The control computer is connected to a communications backbone 18 via a network interface unit (NIU) 20.

The control computer 14 is connected to the NIU by a serial link 22. ~ The backbone comprises a primary network element 24 which may be in the order of 6km in length extending downwardly into the mine to various levels. A plurality of secondary network elements 26.1 to 26.n may be connected to the primary element. The secondary elements may also be in the order of 6km in length.

A plurality of network slave stations (NSS) 28.1 to 28.m are connectable in distributed manner to the backbone 18. Referring to

NSS 28.1, each NSS comprises an upstream port 30 which is : connectable to the backbone and a downstream port 32 which may also be connected to the backbone as shown in the case of NSS 28.1, so that the NSS serves the purpose of a repeater on the backbone. In other cases the downstream ports may be unused, so that the NSS’s are connected in parallel, as is the case with NSS 28.4 to 28.m.

Referring again to NSS 28.1, each NSS also comprises a plurality, preferably six, detonator ports 34.1 to 34.6. At least one instantaneous detonator 36 is electrically connectable by a respective link or blasting cable 38 to each port. In some embodiments, a connector unit 40 comprising an extension lead 42 and a plurality of terminals may be connected to at least some detonator ports.

Typically three to five detonators may then be connected in parallel to the terminals.

In the embodiment of figure 2, at least the primary network element 24 comprises an optical fibre cable, which is connected to the secondary elements 26.1 to 26.n by suitable optical fibre to conductor converters 44. In other embodiments, at least some of the secondary network links may comprise optical fibre cables.

Referring to figure 1, each instantaneous detonator 36 is connectable to a respective shock tube assembly. The shock tube assembly may embody any delay time element required to cause a sequential multi- shot blast in the mine 12.

In figure 3 there is shown a circuit diagram of an instantaneous detonator 36. The detonator is described in more detail in the provisional specification of the applicant's South African patent application 2008/01145 entitled “Instantaneous electronic starter detonator for shock tube assembly” and the contents of which are incorporated herein by this reference. An important feature of this detonator is that the detonator does not comprise any memory arrangement for storing data relating to a delay time after a firing signal is received and before the detonator initiates an explosive charge associated with the detonator. Once a DC threshold voltage

V4, falling in a particular voltage range is applied to an input 52 of the detonator, the switch 54 closes, causing the fuse 56 to initiate the explosive charge. The range is selected such that it comprises DC voltages that are not normally found in a mining environment. The threshold voltage may be larger than 50V, preferably larger than 100V and more preferably larger than 135V.

In figure 4 there is shown a block diagram of a NSS 28. The NSS : comprises a microprocessor-based controller 60. The controller 60 is connected to the aforementioned upstream port 30 via an upstream network interface 62, opto-isolation circuitry 64 and protection circuitry 66 configured to protect the NSS against lightning and stray signals. The aforementioned downstream port 32 is connected to the controller via a downstream network interface 68. A keypad 69 is also connected to the controller. A power supply circuit 70, which is connectable to mains power, generates a DC output voltage, to power the various circuits of the NSS. The DC output voltage is also connected to a firing voltage and test voltage generator 72. The firing voltage is the aforementioned threshold voltage V, required to initiate a detonator and the test voltage V: is a substantially lower DC voltage generated to sense a detonator load and/or test the integrity and/or status of a connection of any detonator or connector unit 40 connected to the NSS. The controller has six SELECT outputs S, to Sg one for each detonator port 34.1 to 34.6 of the NSS and a common

SENSE input to receive a signal relating to the detonator load connected to a selectable detonator port of the NSS. The generated voltage output signal V, the SELECT outputs S1 to S6 and a SENSE’ input are connected to a detonator interface 80 shown in figure 5.

For each of the ports 34.1 to 34.6, the detonator interface 80 comprises a respective circuit 82.1 to 82.6. Each circuit comprises a pair of switches, such as switches 84.11 and 84.12 in circuit 82.1, controlled by a respective signal from S, to Sg, to enable selection of the circuit and for electronic determination of a detonator load, i.e. in the sense of how many detonators there are connected in the circuit.

The determination is performed by, while the switches 84.11 and 84.12 of the selected circuit 82.1 are closed, the test voltage V; is applied to the circuit 82.1. The resulting current |; in the circuit 82.1 is proportional to the detonator load or number of detonators connected in parallel to the port. More particularly, the current is directly proportional to the number of detonators connected in parallel to the : port. Referring to figure 4, the signal at SENSE’ is amplified and converted to digital data by A/D 74. The data represents the number of detonators connected to the circuit, is read at the SENSE input of the controller and is stored in a memory arrangement associated with the controller 60. This data may be communicated to the central controller 14 as will hereinafter be described. .

The central blasting system 10 utilizes half-duplex digital communications for communications on the backbone between the central control computer 14 as master and the NSS’s 28.1 to 28.m as slaves, as will hereinafter be described. Referring to figure 6, the master transmits during a master transmit time an 11-bit message 90 comprising first and second start bits 90.1 and 90.2 of opposite polarity, but equal lengths, followed by eight data bits 90.3 to 90.10 and a parity bit 90.11. After a suitable turn around time 92, an addressed NSS responds during a slave transmit time with a similarly configured 11-bit answer 94. Due to the long distances between the master and slave, typically 4 to 8 km, the bit rates that are used are preferably slow and in the order of 100 bits/sec.

A more detailed time diagram is shown in figure 7. It indicates that after transmission of a message 90, the NIU is configured to expect to start to receive a response from a NSS during a period T,, which period starts after a first minimum period T,., after the end of message 90 and ends a second period T,,, after the end of message 90. The NIU is then configured to forward the received response to the controller 14, a period T, after the response is received.

Referring to figure 8, with the aforementioned eight data bits, a block 100 of 256 sequential and different words may be formed. Words in a } first part 102 of the block may be used as respective addresses for

NSS’s 28.1 to 28.m. Words in a second part 104 may be utilized to code commands to be transmitted from the control computer 14 to an addressed NSS. A third part 106 may be reserved for special addresses.

During preparation for a blast, each NSS 28.1 to 28.m is assigned a unique primary address in the first part 102. A list of such assigned addresses is stored in an inventory in a memory arrangement of the

NSS. It is possible that the address assigned to a particular NSS and stored in the NSS may become corrupted, so that the actual address stored in that NSS would fall outside of range 102. In such a case, the controller 60 of that NSS is configured automatically to sense the error and to reassign to itself a new address falling in the special address range 106. The control computer 14 is configured to poll the NSS’s by sending out commands comprising addresses in the special address range and to identify from an answer received from said NSS the new address, and to update the inventory.

Due to various causes, it may also happen that two or more NSS's incorrectly remain programmed with the same primary address, which of course is an undesirable situation. During polling of the NSS’s, such

NSS’s would answer simultaneously with the same address, which answers, due to the nature of the system, would interfere with one another. The control computer is configured to instruct those NSS’s by an appropriate command in the data field, to randomise their respective addresses. The said NSS’s are configured in response to the command to derive by means of a suitable random number generator and to reassign to itself a respective new primary address in the special address range 106. The intention is that the so reassigned addresses would be different from one another, so that the NSS’s may be addressed individually.

In addition to the aforementioned primary address, each NSS may also be assigned a secondary address. The primary and secondary addresses may during preparation for the blast be associated with a respective physical location in the mine 12 for that NSS. Hence,

should an NSS be caused to reassign to itself a primary address as hereinbefore described, the physical location of that NSS may still be determined and/or known from the secondary address.

Other commands that may be transmitted by the control computer 14 to the NSS’s, may include: answer with primary status data; answer with secondary status data; answer with data entered via a keypad 69 associated with the NSS; answer with a checksum relating to program memory in the microprocessor forming part of the controller 60; and answer with multi-byte messages.

The primary status data may be encoded in and derived from the state of the eight bits in a primary status answer byte received from the

NSS. Bit DB, may indicate whether a message entered via the keypad 69 is available or not; bit DB, may indicate whether a mine panel configuration has changed or not; bit DB, may indicate whether the

NSS is disabled or not; DB; may indicate whether the NSS is locked or not; DB, may indicate whether the NSS is armed or not; DBs may indicate whether the NSS has an error or not; and DB, may give an indication of the quality of communications, for example.

Co 20

The data communications between the NIU 20 and the network slave stations is based on a protocol in terms whereby the NIU sends a message comprising the address of a selected NSS. The selected NSS responds with its address and thereafter all communications are between the NIU and the selected NSS until a message 90 comprising an address of a next selected NSS is transmitted. The messages 90 between messages with address data may comprise selected commands falling in the command range 104 as hereinbefore described.

Due to the long lengths of the primary link 24 and secondary links 26.1 to 26.n and the associated impedance of these lines, a signal 90 that is transmitted by NIU 20 to an NSS may be distorted. The same would happen in the opposite direction with a signal 94 that is transmitted by the NSS to the control computer 14. The signal in figure 10(a) is a representation of a signal as transmitted by the NSS, at the NSS. Figure 10(b) is a representation of the transmitted signal as received at the NIU 20. With such distortion, it may become difficult if not impossible to extract data from the signal.

An adaptive threshold data extractor is generally designated by the reference numeral 120 in figure 9. The extractor comprises a comparator 122 having a first input 123 for a variable threshold signal

Vim. Which is generated as hereinafter described The distorted signal oo 130 on primary link 24 is connected to a second input 124. Data 132 extracted from the signal at second input 124 is available at output 126.

In an example embodiment and as shown in figure 10(b), the variable threshold voltage V,, is generated by a reference voltage generating circuit connected to the first input 123 at a voltage level such as to ensure that the pulses 134 and 136 derived at output 126 from reference bits (normally the first and second start bits of a packet) are of equal length as shown at 138 and 140. However, any other suitable reference bits may be used for this purpose.

It will be appreciated that there are many variations on the invention herein defined and/or described without departing from the scope and spirit of this disclosure.

Claims (46)

RI RLY CLAIN..——

1. A centralized blasting system comprising: - a central blast controller; - the controller being connectable to a communications backbone; - a plurality of network slave stations connectable to the backbone in distributed manner; - a plurality of detonators connectable by respective electrical links to each of the network slave stations; - the system comprising data communications means to enable digital data communications between the central controller and the network slave stations via the backbone; and - each slave station being configured to sense by means of an analogue signal on the respective link a detonator load connected to the network slave unit.

- 2. A central blasting system as claimed in claim 1 wherein each detonator is an instantaneous detonator.

3. A central blasting system as claimed in claim 1 or claim 2 wherein each of the detonators of the system is connectable to a respective shock tube assembly.

4, A central blasting system as claimed in claim 3 wherein each shock tube assembly comprises a further detonator and a delay time providing assembly incorporated in the shock tube assembly.

5. A centralized blasting system as claimed in any one of claims 1 to 4 wherein the central blast controller is connectable to the backbone by a network interface unit and wherein the central blast controller is connected to the network interface unit by a serial link.

6. A centralized blasting system as claimed in any one of claims 1 to 5 wherein the backbone comprises a primary network element and a plurality of secondary or branch network elements connected to the primary element.

7. A centralized blasting system as claimed in claim 6 wherein the primary network element and the secondary network elements comprise electrical conductors.

8. A centralized blasting system as claimed in 6 wherein at least the primary network element comprises optical fiber.

9. A centralized blasting system as claimed in any one of claims 1 to 8 wherein each network slave station comprises an upstream port, a downstream port and at least one detonator port to which at least one detonator is connectable by the respective electrical link.

10. A centralized blasting system as claimed in claim 9 wherein at least one network slave station is connected at the upstream : port to an upstream part of the backbone and at the downstream port to a downstream part of the backbone, so that said network slave station functions as a repeater on the backbone.

11. A centralized blasting system as claimed in any one of claims 1 to 10 wherein each of said detonators comprise

- a main circuit comprising an input which is connectable to the respective link, a fusehead and a switch; - a charge storage device connected in the circuit; - a current limiting device upstream of the charge storage device for limiting to below a no-fire current of the fusehead, a current flowing from the input and through the fusehead, when the switch is closed; and - the switch being configured to close an initiating circuit comprising the charge storage device and the fusehead when a DC voltage at the input exceeds a predetermined threshold value.

12. A centralized blasting system as claimed in any one of claims 1 to 10 wherein each of said detonators comprise: - a main detonator circuit comprising an input which is connectable to the respective link and a charge storage device; - the charge storage device, a fusehead and a switch being connected in an initiating circuit of the detonator; and - the switch being configured to close the initiating circuit when a DC voltage at the input exceeds a predetermined threshold voltage of at least 50V.

13. A centralized blasting system as claimed in any one of claims 9 to 12 wherein each network slave station comprises a local controller, the controller being connected to the upstream port via protection circuitry, opto-isolation circuitry and an upstream network interface; the controller being connected to the downstream port via a downstream network interface and the controller being connected to a keypad provided on a housing of the network slave station.

14. A centralized blasting system as claimed in any one of claims 1 to 13 wherein each network slave station comprises a DC voltage generator configured to generate a detonator firing signal in the form of a DC voltage larger than 50V and a switch means for applying the firing voltage to the detonators connected thereto, thereby to initiate the detonators.

15. | A centralized blasting system as claimed in claim 14 wherein the voltage generator is configured also to generate a DC test

. voltage, which is substantially lower than the aforementioned firing voltage.

16. A centralized blasting system as claimed in 16 wherein each detonator port of the network slave station is connected in a respective circuit comprising a first switch of said switch means for connecting a selected one of the threshold voltage and the test voltage to the circuit.

17. A centralized blasting system as claimed in claim 16 wherein the first switch is controllable by a select signal from the controller, wherein the circuit further comprises a second switch in series with the first switch and which second switch is controllable by the select signal, to provide at an output of the circuit an analogue signal having a parameter, which is proportional to the detonator load connected to the port.

18. A centralized blasting system as claimed in claim 17 wherein the parameter is directly proportional to a number of detonators connected in parallel to the port.

19. A centralized blasting system as claimed in claim 17 or claim 18 wherein the output is connected to an analogue to digital converter, which converter is connected to provide at a sense input of the controller, digital data relating to the detonator load. 28 | Co

® 2008/ 02718

20. A centralized blasting system as claimed in claim 19 wherein the controller comprises a memory arrangement for storing said digital data.

21. A centralized blasting system as claimed in any one of claims 1 to 20 wherein the data communications means supports data communications between the central blast controller and a selected one of the network slave stations on a master slave basis, in half-duplex manner and with pulse width modulation.

22. A centralized blasting system as claimed in claim 21 wherein data is transmitted at a bit rate of in the order of 100bits/sec.

23. A centralized blasting system as claimed in any one of claims 21 16 and 22 wherein the data communications is in the form of discrete packets, wherein each packet comprises a header comprising first and second start bits, a data field comprising a plurality of data bits, and at least one parity bit.

24. A centralized blasting system as claimed in claim 23 wherein the first and second start bits are of opposite polarity, of equal length, wherein the data field comprises eight (8) data bits and the packet comprises one parity bit.

25. A centralized blasting system as claimed in any one of claims 23 and 24 wherein each network slave station is assigned a respective address falling in a first part of a block of sequential numbers represented by the data bits, the block comprising a second part of sequential numbers, which is used to encode respective commands to the slave stations and a third part of sequential numbers that is used as special addresses.

26. A centralized blasting system as claimed in claim 25 wherein the third part is sandwiched between the first and second parts.

27. A centralized blasting system as claimed in any one of claims 21 to 26 wherein the communications is in accordance with a protocol whereby the central blast controller talks first.

28. A centralized blasting system as claimed in claim 27 wherein the central blast controller transmits a first packet comprising in a data field an address of a selected network slave station, wherein said network slave station responds with a response packet comprising status data in a data field and wherein communications is then limited to between the central blast controller and the selected network slave station, until the central blast controller transmits a packet comprising an address : of a next selected network slave station in the data field.

29. A centralized blasting system as claimed in claim 28 wherein subsequent packets transmitted to the first network slave station after said first packet comprise encoded commands in the data filed.

30. A centralized blasting system as claimed in any one of claims 21 to 29 wherein the data communications means comprises a data extractor comprising a comparator comprising a first input for a reference voltage, a second input for a received data signal ‘ and an output; and a circuit for generating a variable reference voltage at an output thereof which output is connected to the first input, the circuit being configured to generate a reference voltage such that when the generated reference voltage is applied to the first input, output bits at the output of the comparator corresponding to first and second reference bits in

: the data signal, which are of opposite polarity and of equal length, would be of equal length.

31. A method of causing a multi-shot blast comprising the steps of: - causing a plurality of distributed instantaneous detonators to initiate a respective shock tube assembly connected thereto; and - causing the shock tube assemblies to initiate the blast.

32. A method of causing a multi-shot blast as claimed in claim 31 comprising the step of applying a DC voltage larger than 50V at an input of each instantaneous detonator, in order to initiate the instantaneous detonators.

. 15 33. A method of causing a multi-shot blast comprising the step of utilizing respective delay time mechanisms in the respective shock tube assemblies, to cause a sequential blast.

34. A network slave station comprising a local controller, the controller being connected to an upstream network port. via protection circuitry and an upstream network interface; the controller being connected to a downstream network port via a downstream network interface; and the controller being connected to at least one detonator port.

35. A network slave station as claimed in claim 34 wherein the controller is connected to a keypad provided on a housing of the network slave station.

36. A network slave station as claimed in claim 34 or claim 35 comprising a DC voltage generator for generating a DC firing voltage larger than 50 V and which generator is connectable to a the at least one detonator port.

37. In a centralized blasting system comprising a central blast So controller, a plurality of network slave stations connected to the central blast controller via a backbone and data communications means supporting data communications between the central blast controller and a selected one of the network slave stations, a data extractor comprising a comparator comprising a first input for a reference voltage, a second input for a received data signal and an output; and a circuit for generating a variable reference voltage at an output thereof which output is connected to the first input, the circuit being configured to generate a reference voltage such that when the generated reference voltage is applied to the first input, output bits at the output of the comparator corresponding to first and second reference bits in the data signal, which are of opposite polarity and of equal length, would be of equal length. :

38. In a centralized blasting system comprising a central blast controller and a plurality of network slave stations connected to the central blast controller via a backbone, data communications means supporting data communications between the central blast controller and a selected one of the network slave stations on a master slave basis, in half-duplex manner and with pulse width modulation. E 15

39. A data communications means as claimed in claim 38 wherein the data communications is in the form of discrete packets, wherein each packet comprises a header comprising first and second start bits, a data field comprising a plurality of data bits, and at least one parity bit.

40. In a centralized blasting system comprising a central blast controller, a plurality of network slave stations connected to the central blast controller via a backbone and data communications means supporting data communications between the central blast controller and a selected one of the network slave stations, a protocol whereby the central blast controller talks first and wherein the central blast controller transmits a first packet comprising in a data field an address of a selected network slave station, wherein said network slave station responds with a response packet comprising the address in a data field and wherein communications is thereafter limited to be between the central blast controller and the selected network slave station, until the central blast controller transmits a packet comprising an address of a next selected network slave station in the data field.

41. A centralized blasting system substantially as herein described with reference to the accompanying diagrams.

42. A method of causing a centralized blast substantially as herein described with reference to the accompanying diagrams.

43. A network slave station substantially as herein described with reference to the accompanying diagrams. oo 35

44. A data extractor for use in a centralized blasting system, substantially as herein described with reference to the accompanying diagrams.

45. A data communications means for use in a centralized blasting system, substantially as herein described with reference to the accompanying diagrams.

46. A protocol for use in a centralized blasting system, substantially as herein described with reference to the accompanying diagrams. +t Dated this al day of Narety 0O¥ Patent Ny / Agent for the Applicant