BLASTING SYSTEM

Field of the invention

The invention relates to an electronic blasting system and to a method of safely applying a firing voltage to a detonator, for testing purposes, in an electronic blasting system. The invention also relates to a detonator for use in such a system and/or method.

Background to the invention

Detonators are employed in the blasting of rock for the extraction of minerals or other valuable components, the quarrying of rock and in civil engineering projects that require rock blasting. Blasting is generally done by drilling a pattern of boreholes, priming each borehole with a detonator and a booster and filling the hole, in accordance with the design, with commercial explosives. Types of detonators used include those attached to a pyrotechnic fuse (fuse head), electric detonators, shock-tube initiated detonators and, in the last 20 years or so, electronic detonators.

Wired electronic blasting depends on electrical leads from a blaster unit (usually near the blast) to every hole that has been supplied with an electronic detonator. The surface wiring system may comprise a lead-in line which connects to lines running along each row of holes. Connectors, usually insulation displacement connectors (IDCs), are used to connect the lead-in line or trunk line electrically to the row lines. Similar connectors may be used to connect the detonator leg wires to the row lines.

Each detonator typically comprises a metal tube containing a sealing plug, a crimp, an electronic module, a fuse head connected to the electronic module and an explosive charge.

The electronic module of modern detonators typically comprises a microprocessor, a power supply to supply regulated power to the microprocessor, a firing capacitor and a bleed resistor which acts as a shunt and drains the firing capacitor to safe voltage levels after a period of time. During preparations for a blast, one or more detonators is/are placed in each hole. The detonators are then logged, during which the operator applies a hand-held device, commonly referred to as a “logger” to the detonator to generate an association between the detonator’s unique electronic identity and the borehole into which it is deployed. Logging commonly also includes programming the detonator by writing a firing time for the hole in question into the detonator’s memory, testing the detonator for its readiness to fire, and recording all relevant details of the detonator in the memory of the logger.

Since logging and testing of detonators is typically done while personnel are on a loaded blast pattern, a very high degree of safety is demanded for this operation. Many systems achieve this by communicating between detonators and loggers at a low, non-firing voltage (as opposed to a higher, firing voltage used to transmit blast commands) which renders the operation inherently safe.

However, while low voltage logging has significant safety advantages, it has the disadvantage of not testing detonators at the voltage that will be used during firing. This can result in problems, especially when leakage between the wires of the circuit is exacerbated at higher voltage. Leakage is commonly caused by water ingress at a connector or at a point of damage to wire insulation. Current leakage lowers the line voltage at the detonators furthest from the blaster unit, and often adversely affects two-way communication between the blaster unit and the detonators. For example, a circuit that functions perfectly at a low testing/programming voltage may exhibit problems in the form of one or more detonators failing the communications test at the firing voltage. It will be appreciated that having to delay a blast because leakage has only been discovered at firing time may result in a high cost to and wasted time in the mining or other blasting operation.

In some systems, to overcome the issue of leakage, logging is conducted at the firing voltage. Such systems are not inherently safe, but may achieve acceptable levels of safety by design. Specifically, the detonator in these systems may include two capacitors: a logic capacitor, which powers up sufficiently to allow the detonator to communicate with the logger, but which is too small to fire the detonator, and a firing capacitor, which carries enough energy to fire the detonator. During logging only the logic capacitor is charged, and not the firing capacitor. These systems typically rely on the integrated circuitry inside the detonator to prevent the firing capacitor from becoming charged during logging and testing. It will be appreciated that the consequences of the circuitry failing can be severe.

Embodiments of the present invention aim to address or alleviate the issues identified above, at least to some extent.

Summary of the invention

In accordance with a first aspect of the invention, there is provided a detonator for use in an electronic blasting system, the detonator comprising an electronic module including: a logic circuit which includes a processor and a logic capacitor, the logic circuit being responsive to logging and testing at a range of voltages ranging from a lower, non-firing voltage to a higher, firing voltage, wherein the logic circuit is configured to respond in a limited operational mode when a supply voltage is in a lower range and in a fully operational mode when the supply voltage is in a higher range; and a firing circuit which includes a firing capacitor configured to fire a fuse head of the detonator, wherein the supply of energy to the firing circuit is controlled by the logic circuit such that the firing capacitor cannot be charged during logging or testing of the detonator despite the voltage applied to the detonator being above the non-firing voltage or substantially equal to the firing voltage.

In some embodiments, the firing circuit is separated from the logic circuit by a firing capacitor charging switch controllable by the logic circuit such that the firing capacitor cannot be charged during logging or testing of the detonator despite the voltage applied to the detonator being above the non-firing voltage or substantially equal to the firing voltage.

In some embodiments, the logic circuit only allows the firing capacitor to be charged in response to receiving an arm command from an external unit. The external unit may be a blaster unit, a control unit and/or a portable logging device. The firing capacitor charging switch may be closed by the logic circuit in response to receiving the arm command.

The logic circuit and the firing circuit may thus be separate circuits. The lower voltage may be below about 10 V, preferably around 9V, and the higher voltage may be above about 18 V, preferably around 24V.

The lower voltage may be referred to as an inherently safe voltage as it is lower than what is required to charge the firing capacitor for the purposes of firing the fuse head of the detonator.

The logic circuit may be housed within an application specific integrated circuit (ASIC) which is capable of safely receiving a wide range of voltage and which controls the power supply to the logic circuit. The detonator may include a low-voltage power supply configured to supply power to the ASIC at a level which is insufficient to fire the fuse head.

The logic circuit may be configured to respond to a supply voltage range of from about 5 V to about 26 V without requiring input from an external device connected to the detonator to select specific, narrower voltage ranges.

In some embodiments, depending on the voltage or voltage range supplied to the logic circuit within the ASIC, the logic circuit may either respond in the fully operational mode, or in the limited operational mode, based on digital logic designed into the ASIC.

The logic circuit may be configured to respond in the limited operational mode when the supply voltage is in the range of about 5 V to about 10 V (the lower range), in which mode it ignores any commands received from an external device connected to the detonator to calibrate, charge and/or fire the detonator.

The ASIC is thus able to select functionality based on the voltage or voltage range applied to it.

The logic circuit may be configured to respond in the fully operational mode to a supply voltage ranging from about 18 V to about 26 V (the higher range). In the fully operational mode, the logic circuit may respond to commands from an external device connected to the detonator to calibrate, charge and/or fire the detonator. In accordance with a second aspect of the invention, there is provided an electronic blasting system comprising: at least one blaster unit; a plurality of detonators substantially as described above, connected or connectable to the at least one blaster unit via a wire network and positioned or positionable according to a blast design; a control unit configured to communicate with the at least one blaster unit for controlling the calibration, charging, arming and/or firing processes of the detonators; and a portable logging device configured to log and test each detonator at the lower, non firing voltage and only to permit testing to be conducted at the higher, firing voltage once safe functioning of the logic circuit has been established.

The portable logging device is also referred to as a “logger” in this specification.

The detonators may form a multiple detonator circuit, in use.

In accordance with a third aspect of the invention, there is provided a method of safely applying a firing voltage to a detonator for testing purposes in an electronic blasting system, the method comprising, prior to testing the detonator at a firing voltage, testing the detonator at a lower, non-firing voltage to establish safe functioning of a logic circuit or processor of the detonator, wherein the testing is conducted prior to operations being halted for blasting.

The detonator may be the detonator as defined above and may form part of an electronic blasting system as defined above.

The testing may be carried out to test for leakage in wires connecting the detonator to a blaster unit, which leakage may be apparent at the higher, firing voltage, but not at an inherently safe, lower, non-firing voltage.

Brief description of the drawings

An embodiment of the invention is described below, by way of example only, and with reference to the following drawings, in which: Figure 1 is a schematic diagram of an electronic blasting system according to the invention; Figure 2 is a schematic drawing of a detonator of the electronic blasting system;

Figure 3 is a schematic drawing of a logger connected a detonator of the electronic blasting system;

Figure 4 is a schematic drawing of a logger connected to a number of detonators of the electronic blasting system;

Figure 5 is a block diagram illustrating parts of an embodiment of a detonator according to the invention, including an ASIC thereof; and

Figure 6 is a flow diagram depicting exemplary steps in a method/process for testing at firing voltage.

Detailed description with reference to the drawings

The following description is provided as an enabling teaching of the invention, is illustrative of principles associated with the invention and is not intended to limit the scope of the invention. Changes may be made to the embodiment/s depicted and described, while still attaining results of the present invention and/or without departing from the scope of the invention. Furthermore, it will be understood that some results or advantages of the present invention may be attained by selecting some of the features of the present invention without utilising other features. Accordingly, those skilled in the art will recognise that modifications and adaptations to the present invention may be possible and may even be desirable in certain circumstances and may form part of the present invention.

Referring to Figure 1 , an example embodiment of an electronic blasting system (10) is shown. The system (10) comprises multiple detonators (12) connected via connectors (14) to a surface harness wire network (16) and to a blasting machine, also known as a blaster unit (18) or (19). Multiple blaster units (18, 19) are connected wirelessly, via suitably configured modems and antennas (21 ), to a control unit (20) that controls the detonators (12) through their powering, programming, calibration, arming and firing processes. In some cases, blaster units (18, 19) may be connected to each other via a two-wire cable (22) as shown in Figure 1 , e.g. for signal integrity and synchronization between units.

In use, at a blast site, a pattern of boreholes is drilled according to a blast design, where the parameters of each hole, including its position and firing time, are pre-assigned. Each borehole is then primed with one or more detonators (12). The detonator (12) may be inserted into a booster (not shown) to create a primer that initiates the explosive charge, alternatively the detonator (12) may directly initiate certain explosives itself. The detonator (12) is then lowered into the borehole and the hole is filled with a predetermined quantity of explosives.

Each detonator (12) in the network is connected to the surface harness wire (16) via a two- core cable (24) and a connector (14).

Referring to Figure 2, each detonator (12) comprises a sealing plug (26), a crimp (28), an electronic module (30), a fuse head (32) and an explosives charge (34) which are contained inside a metal shell (36).

In this example embodiment, each electronic module (30) comprises electrostatic discharge and over-voltage barriers (38), a low-voltage power supply (40) to supply regulated power to an application specific integrated circuit (ASIC) (42) (containing non-volatile memory and a firing switch). The power supplied by the low-voltage power supply (40) to the ASIC (42) is insufficient to fire the fuse head (32) and this prevents accidental firing thereof. The electronic module (30) further includes a bleed resistor (44) and a firing capacitor (46), which is separated from the low-voltage power supply (40) and the ASIC (42) by a firing capacitor charging switch (70) (shown in Figure 5) located inside the ASIC (42). The bleed resistor (44) acts as a shunt to drain the firing capacitor to safe voltage levels after a period of time.

The ASIC (42) has non-volatile memory that allows data to be written to and read from it during manufacturing, during programming, during testing and during the initiation of the detonator.

Referring to Figure 3, detonators are programmed by writing a firing time and relative position into the detonator’s non-volatile memory by means of a portable logger (60) connected to the detonator, either via the connector (14) which connects to the logger’s connector port (62) or directly from the cable (24) to the cable ports (64) (not depicted). The logger (60) registers each detonator’s unique identity/identifier (ID), and other details already stored in the detonator’s ASIC (42), and programs a firing time into the detonator (12), based on the detonator’s position in the blast design. Additional information, including the fact that the detonator has been positively tested at low (non-firing) voltage, detonator position, date and time and logger ID may also be recorded on the detonator’s (12) non-volatile memory. The logger (60) also tests each detonator for current consumption, and confirmation that it has been successfully programmed, and may request further information from the detonator, including environmental measurements.

Referring now to Figure 4, once the logging of the detonators is complete, the harness wire (16), that connects all the detonators, is connected to the logger (60) at the cable ports (64) to verify that all logged detonators are present and functioning. This test may also involve searching for detonators that have accidentally not been logged.

An issue that is experienced when leakage occurs at firing voltage, is that communication between detonators and blaster units may be compromised and unwanted and costly delays are caused at the critical blasting time in trying to determine what is causing the leakage. It is valuable, therefore, to be able to identify firing voltage leakage before the blast time, when there is extra time during the programming and testing of the detonators and addressing issues is less costly.

Referring to Figure 5 which shows parts of the detonator (12) in more detail, the voltage received by the firing capacitor (46) of the detonator (12) is regulated and controlled by an ASIC-managed firing capacitor charging switch (70) which allows or prevents charging of the firing capacitor (46). None of the energy supplied to the logic circuit, which comprises a logic capacitor (72) and a processor in the form of a digital core (76), reaches the firing capacitor (46), unless the switch (70) is closed.

The digital core (76) is configured to control the functionality of the switch (70), and is thus able to prevent charging of the firing capacitor (46) to allow for safe high voltage testing.

The line to the firing capacitor (46) is only activated when the “arm” command is issued from a blasting unit (18/19), and the switch (70) is closed, otherwise no energy is provided to the firing capacitor (46) and the detonator (12) is inert.

In a preferred example, the driver of the charging switch (70) is grounded during power-up, testing, programming and calibration phases. The switch (70) is then powered at the last moment before the charging phase, for security reasons, ensuring the gate of the charge switch (70) is well grounded. The charge/storage management can only be activated when a correct command(s) sequence is received from the system (10).

In this example, the logic circuit will respond to a supply voltage range of from 5 V to 26 V without requiring input from an external device connected to the detonator to select specific narrower voltage ranges (the external device being a blaster unit, control unit or logger).

Depending on the voltage range supplied to the logic circuit within the ASIC (42), the logic circuit will either respond in a fully operational mode, or in a limited operational mode based on the digital logic designed into the ASIC (42). The ASIC (42) thus has built-in logic allowing it to carry out mode selection based on the voltage applied to the detonator (12). For instance, the logic circuit may respond in a limited operational mode when the supply voltage is in the range of 5 V to 10 V, in which mode it will ignore any commands received from an external device connected to the detonator (12) to calibrate, charge and/or fire the detonator (12). In such cases, the logic circuit may then respond in a fully operational mode to a supply voltage ranging from 18 V to 26 V. In fully operational mode, the logic circuit responds to commands from an external device to calibrate, charge and/or fire the detonator (12).

Embodiments of the invention provide a method of safely applying a firing voltage to a detonator (12) for the purposes of testing for leakage in the wires (16) connecting the detonator to a blaster unit (18/19), which leakage may be apparent at firing voltage, but not at an inherently safe low non-firing voltage. At a high level, this method comprises the steps of testing the detonator (12) at an inherently safe non-firing voltage to establish its safe functionality/functioning, before testing at firing voltage (such testing being conducted before operations are halted for blasting).

Turning to the flowchart (78) in Figure 6, some of the steps in the process are shown. The logger (60) is configured to log and test each detonator (12) at the inherently safe non-firing voltage. Only once the detonator (12) has been successfully tested as having a functioning microprocessor (ASIC (42)) circuit, will the logger (12) allow a firing voltage test to be undertaken. Each logger (60) has voltage and current limiting components and will only communicate with the logic circuit (logic capacitor (72) and digital core (76)) of the detonator (12) at a low, safe non-firing voltage and current that will not allow the fuse head (32) to fire, even if the logger (60) accidentally connects directly to the fuse head (32) (see stage (80)). In this example, this test voltage for communication purposes is less than 10 V, e.g. 9 V.

Once the logger (60) has connected to the detonator (12) at the safe voltage, it proceeds to read a previous test and/or logging result from the detonator’s memory (stage (82)). If the detonator (12) was previously tested as being functional at low safe non-firing voltage, the logger (60) will bypass the voltage limiting functionality and test the detonator circuit at the higher firing voltage, e.g., of more than 9 Volts (stage (84)). In this condition, leakage on the lines (16) and (24) at high firing voltage may be detected by failure in communication.

If the detonator (12) was previously tested as not being functional at the low voltage, testing at firing voltage is not allowed and only low voltage testing is allowed. See stages (86) and (88) in Figure 6 in this regard.

If the logger (60) does not read any previous test result from the detonator (12) it indicates that there was no previous test (or some failure occurred). Then, the logger (60) proceeds to test and program the detonator (12) at the low voltage (stage (90)) and then records either a negative test result at stage (92) or a positive test result at stage (94) in the detonator memory. Again, if there is a negative test result in the detonator memory, only low voltage testing will be allowed in future (stage (96)). On the other hand, at stage (98), if a positive test result is recorded, the ASIC (42) is in the fully operational/functional condition described above and future testing at high voltage is allowed.

The invention therefore provides a novel apparatus and method for safely testing and/or programming detonators whilst addressing the impact of higher leakage problems at firing voltages.

The configuration of the detonator not only provides a split in the design of electronic components, e.g. logic capacitor and firing capacitor, but also provides an intelligent ASIC capable of carrying out a selection process internally to the ASIC which selects the operational mode according to the voltage level the detonator is supplied with at the time of testing or programming.

Embodiments of the invention may reduce or obviate the need to delay a blast because leakage has only been discovered at firing time. This may lead to cost savings and/or greater efficiency in mining or other blasting operations.