ZA200701067B

ZA200701067B - Detonator

Info

Publication number: ZA200701067B
Application number: ZA200701067A
Authority: ZA
Inventors: Koekemoer Andre Louis; Burrows John Francis
Original assignee: Detnet South Africa Pty Ltd
Priority date: 2004-11-22
Filing date: 2007-01-30
Publication date: 2008-05-28
Also published as: WO2006055991A1

Description

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DETONATOR

BACKGROUND OF THE INVENTION

[0001] This invention relates generally to a detonator and more particularly is concerned with a detonator which misfires during use.

[0002] A blasting system may make use of a large number of detonators which are individually activated or initiated under controlled conditions to fire explosives. Due to manufacturing, environmental or other factors a detonator may misfire. When this occurs a potentially dangerous situation arises in that the detonator may well be set off thereafter by secondary factors e.g. during mining operations. A similar consideration applies in respect of the explosive which is associated with the detonator which can be inadvertently fired by external factors. Clearly this type of situation should be avoided.

[0003] Wt is however not easily possible particularly in a large and complex blasting operation, to identify or locate a misfired detonator. The blasting system may make use of hundreds or even thousands of detonators which are installed in respective blast holes over a large area and the appearance of the area may be modified substantially as the result of explosion caused by those detonators which are successfully ignited.

SUMMARY OF INVENTION

[0004] The invention provides, in the first instance, a detonator which includes a housing, at least a primary explosive in the housing, a control circuit for controling the initiation of the primary explosive, and a locating circuit which, when activated, emits a locating signal which is associated with the detonator.

[0005] The locating signal may be emitted wirelessly at any suitable frequency.

[0008] The locating signal may be encoded in a manner ‘which provides a unique association between the locating signal and the detonator. The locating signal may for example be encoded with a unique identifier which may be in the form of a digital or other code. The unique identifier may be derived from, or be the same as, an identifier which is held or stored in suitable memory of the control circuit.

[0007] In a variation of the invention the locating signal is at a predetermined frequency. The locating signal may be emitted continuously or intermittently.

[0008] The locating signal may be emitted in response to an interrogating signal.

[0009] The locating circuit may be in the nature of a transponder which may be active or passive. In the latter case the locating circuit has no specific on-board energy circuit.

[0010] The invention also extends to a method of detecting a misfire in a blasting system which includes a plurality of detonators each of which is arranged, upon activation, to detonate a respective quantity of explosives, the method including the step of generating, in respect of each detonator which has not fired, a locating signal which enables the misfired detonator to be located.

[0011] The locating signal may be generated in accordance with any suitable set of predetermined criteria. For example the method may include the step, after activation of the plurality of detonators, of generating at least one interrogating signal which, if received by a detonator which has misfired, causes a locating circuit which is associated with the detonator to emit a locating signal which is associated with the detonator.

[0012] In a variation of the invention a detonator, when armed, is supplied with energy which is stored at least in two energy storage devices. Energy from a first storage device is used to initiate an explosive. If the explosive is successfully initiated then the detonator, in the resulting explosion, is destroyed. If the explosive is not initiated then the energy in the second energy storage device remains in the energy storage device and this can be used, at least for a limited time period, to power a transmitter which enables the misfired detonator to be identified or located.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention is further described by way of example with reference to the accompanying drawings in which:

Figure 1 is a schematic view in cross section of a detonator according to the invention,

Figure 2 shows a part of a typical blasting system; and

Figure 3 illustrates a part of a circuit of the detonator of the invention and the use thereof to locate a misfired detonator.

DESCRIPTION OF PREFERRED EMBODIMENT

[0014] Figure 1 of the accompanying drawings illustrates a detonator 10 which includes a housing 12 in which is located a primary explosive 14, an electronic detonating circuit 16 and a locating circuit 18.

[0015] Wires 20 are connected at least to the circuit 16 and are used to power and control the arming and firing of the detonator in a conventional manner which is not further described herein.

[0016] Typically the circuit 16 includes a bridge component 22 which is directly exposed to the primary explosive 14 and which, when fired, causes the primary explosive to initiate.

[0017] Figure 2 illustrates a part of a typical blasting system 30. A plurality of boreholes 32 are formed at respective predetermined locations in ground 34 which is to be blasted. A secondary explosive 36 is placed in each borehole together with an associated detonator 10. The wires 20 which extend from the detonators are connected to a blasting harness 38 which extends from blast control equipment, not shown, in a manner which is known in the art.

[0018] When the blasting system 30 is fired it can happen that at least one of the detonators 10 is not initiated. In the process however a substantial part or all of the harness 38 is destroyed and the ground 34, which is blasted, is loosened to an extent that its appearance may be substantially altered. It can therefore be extremely difficult, visually, to locate or detect a misfired detonator.

[0019] Figure 3 illustrates a part of circuitry 42 in the detonator 10. In one example of the invention the locating circuit 18 is in the nature of a passive transponder and includes a receiver 44 which is connected to a small antenna 46, an energy circuit 48 and a transmitter 50. The transmitter may be connected to or embody an oscillator 52.

[0020] Also shown in Figure 3 are blocks designated 54, 56, 58 and 60. These blocks, the nature and function of which are further described hereinafter, form part of a second embodiment of the invention and do not play a role in the understanding of the embodiment which is currently described.

[0021] If a misfired detonator is detected or suspected then, after the blasting process has been completed, a search unit 66, see Figure 3, is employed. The search unit includes a battery 68 which powers a transmitter/receiver unit 70 which is connected to an antenna 72. When the transmitter is energised it emits a signal which is received by the antenna 46 of the misfired detonator, and passed to the receiver 44 which transfers the signal to the energy unit 48. A circuit which normally is in the form of a plurality of coils, with a rectifier, extracts energy from the received signal and converts the extracted energy to a form which is suitable for powering the transmitter 50. The transmitter 50 automatically functions when power is applied to it and, in this example, the oscillator 52 which is embodied in the transmitter then generates a signal at a predetermined frequency which is emitted via the antenna 46.

[0022] The circuit 42 thus functions as a passive transducer in that it emits a distinct signal, which is readily identifiable, in response to an interrogating signal transmitted by the search unit 66. The emitted signal is detected by the antenna 72 and applied to the receiver 70 which processes the signal and outputs a suitable indicating signal to a unit 80 which may include a display 82 or a sound generator or any other appropriate indicating device 84.

[0023] The search unit 66 may be a relatively low power device so that it must be brought fairly close to a misfired detonator in order to activate the corresponding transmitter 50. This ensures that the location of the misfired detonator is readily ascertainable and, if there are two or more misfired detonators, it normally will be possible easily to distinguish the misfired detonators from each other.

[0024] In a variation of the invention which is applicable particularly to programmable electronic detonators, the detonator control circuit 16, which corresponds in substance to the block 56 in Figure 3, includes a module 54 in which is held a code which is a unique identifier for the detonator. If the detonator misfires then the module 54 is not destroyed and the code is preserved. The code can be applied to the transmitter 50 so that the same identifier which is used during the programming of the detonator is emitted in response to an interrogating signal to enable the identity of the misfired detonator and its location to be ascertained.

[0025] In a blasting system of the type shown in Figure 2 energy from the blast control equipment is normally transferred to each of the detonators during testing, programming and arming modes. Once a detonation sequence commences the on- board energy held at each detonator is used to fire the corresponding bridge circuit

[0026] In a variation of the invention energy which is made available during the testing, programming and arming modes, is effectively divided into two in that a first quantity of energy is stored in the module 58 while a second quantity of energy is stored in the module 60. The energy which is stored in the module 58 is used to power the circuit 16 and fire the bridge 22 when necessary. If the detonator is successfully fired then, clearly, the detonator is destroyed. However if a misfire takes place then although the energy in the module 58 may be depleted the energy in the module 60 is preserved. This energy can be used, automatically, after the elapse of a predetermined time period, which may be varied according to requirement, to power the transmitter 50. Thus, in respect of each detonator which has been misfired, the detonator may automatically emit one or more locating signals after a predetermined period of time has elapsed from the time at which the detonator would have fired if the firing process had been successful. This signal can be at the frequency of the oscillator 52 or it may contain the unique identifier held in the module 54.

[0027] The signal can be generated independently and automatically to alert an operator to the fact that a misfire has occurred and the operator can then, if necessary, make use of the search unit 66 to locate the misfired detonator in the manner which has already been described.

Claims

1. A detonator which includes a housing, at least a primary explosive in the housing, a control circuit for controlling the initiation of the primary explosive, and a locating circuit which, when activated, emits a locating signal which is associated with the detonator.

2. A detonator according to claim 1 wherein the locating signal is emitted wirelessly.

3. A detonator according to claim 1 or 2 wherein the locating signal is encoded to provide a unique association between the locating signal and the detonator.

4. A detonator according to any one of claims 1 to 3 wherein the locating circuit includes a transponder which is responsive to an interrogating signal to emit the locating signal.

5. A detonator according to claim 1 which includes a first energy storage device for powering the control circuit, a transmitter, and a second energy storage device for powering the transmitter if the detonator has misfired.

8. A method of detecting a misfire in a blasting system which includes a plurality of detonators each of which is arranged, upon activation, to detonate a respective quantity of explosives, the method including the step of generating, in respect of each detonator which has not fired, a locating signal which enables the misfired detonator to be located.

7. A method according to claim 6 which includes the step, after activation of the plurality of detonators, of generating at least one interrogating signal which, if received by a detonator which has misfired, causes a locating circuit which is associated with the detonator to emit a locating signal which is associated with the detonator.

8. A method according to claim 6 which includes the step of using energy, in a storage device in a misfired detonator, to power a transmitter which enables the misfired detonator to be identified or located.