WO2005005921A1

WO2005005921A1 - Detonator fuse status detection

Info

Publication number: WO2005005921A1
Application number: PCT/ZA2004/000078
Authority: WO
Inventors: Andre Louis Koekemoer; Albertus Abraham Labuschagne
Original assignee: Detnet South Africa Pty Ltd
Current assignee: Detnet South Africa Pty Ltd
Priority date: 2003-07-15
Filing date: 2004-07-13
Publication date: 2005-01-20
Anticipated expiration: 2006-01-15
Also published as: AR046498A1; PE20050561A1; ZA200600350B

Abstract

A detonator (10) which includes a fuse (60), a control unit (30), a current generator (36) which, in response to a signal from the control unit (30), passes a test current, the magnitude of which is below the magnitude of an actuating current, through the fuse (60) and a memory device (32) in which is stored a status signal which is dependent on the magnitude of a voltage produced by the passage of the test current.

Description

DETONATOR FUSE STATUS DETECTION

BACKGROUND OF THE INVENTION

[0001] This invention relates to detecting or testing the status of a fuse in an electronic detonator.

[0002] As used therein the word "fuse" includes an energy dissipating element which, when current of a predetermined magnitude passes through the element, releases sufficient energy to enable a primary explosive to be initiated. Typically this type of element includes a fusible link although it is known to make use of other elements which generate sufficient energy to cause explosive initiation.

[0003] In a blasting system it is of vital importance to establish the integrity of a detonator which is to be used in the system. The fuse in a detonator is an essential component which is used to transfer energy from an energy source to an explosive. It is however not possible to test the integrity of a fuse, in an assembled detonator, on a fully functional basis for the passage of a full design current through the fuse will cause explosive detonation.

SUMMARY OF INVENTION

[0004] The invention provides a method of testing a fuse in a detonator which includes the steps of passing a test current, the magnitude of which is below the magnitude of an actuating current, through the fuse, generating a status signal which is dependent on the magnitude of a voltage which is produced by the passage of the test current and storing the status signal in a memory device. [0005] The time period for which the test current is passed may be limited, or controlled, for a predetermined time according to known criteria.

[0006] As used herein the phrase "actuating current" means the minimum current which is necessary to cause initiation of the detonator.

[0007] Preferably the voltage is produced across the fuse. The voltage may alternatively be produced across a component which is serially connected to the fuse.

[0008] The memory device is preferably in the detonator. The test current is preferably automatically generated when power is applied to the detonator.

[0009] The test current is preferably generated within the detonator, as opposed to being generated by means which is external to the detonator.

[0010] The status signal may be produced by comparing the voltage to a reference voltage.

[0011] The detonator may be one of a plurality of detonators in a blasting system and the respective fuses in the detonators may be tested substantially simultaneously.

[0012] The status signal may be accessed by a control system, according to requirement, to obtain an indication of the fuse status at a remote location.

[0013] The status signal may be compared to a reference signal at a remote location. [0014] The invention also provides a detonator which includes a fuse, a control unit, a current generator which, in response to a signal from the control unit, passes a test current, the magnitude of which is below the magnitude of an actuating current, through the fuse, and a memory device in which is stored a status signal which is dependent on the magnitude of a voltage produced by the passage of the test current.

[0015] The voltage may be produced across the fuse.

[0016] The detonator may include a comparator which compares the voltage to a reference voltage and which, in response thereto, produces the status signal.

[0017] The status signal may be directly proportional to the voltage.

[0018] The memory device may be accessible by a blast controller or similar device, via a connection which is made to the detonator.

1 ] A high input resistance device may be positioned between the comparator and the fuse.

[0020] The current generator may be a constant current source of any suitable design or, in a variation of the invention, a current sink.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The invention is further described by way of examples with reference to the accompanying drawings in which: Figure 1 illustrates a detonator according to a first form of the invention connected to a blast controller; Figure 2 illustrates a detonator according to a second form of the invention; and

Figure 3 illustrates a detonator according to a third form of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0022] Figure 1 of the accompanying drawings illustrates a portion of a detonator 10 according to one form of the invention connected to a blast controller 12. The detonator 10 is not described in detail hereinafter for the principles of the invention can, within reason, be used with most electronic delay detonators which are known in the art. Only those aspects which are necessary for an understanding of the invention are described_f hereinafter.

[0023] The detonator 10 may be one of a plurality of similar detonators each of which is connected to a harness 16 by means of a respective connector 18 and wires 20, to make up a blasting system with a desired configuration. These aspects are known in the art.

Ϊ24] The detonator 10 includes a control unit 30, indicated in dotted outline, which contains a memory device 32 such as solid state memory, or the like, a control circuit

34 which includes a voltage or any other power detection or sensing component 35, a current generator which, in this example of the invention, is a constant current source 36, and a comparator circuit 40.

[0025] The comparator circuit includes an operational amplifier, analogue comparator or any similar device 42 with an output 44 which is connected to the control circuit 34, a first input 46 which is connected to a voltage dividing network made up of resistors 48 and 50, and a second input 52. The function of this network is to provide a stable and accurate reference voltage for the purpose described hereinafter. A 'similar function can be achieved by using any appropriate device in place of the network e.g. a solid state device which generates a suitable reference voltage.

[0026] A fuse 60 in the detonator has a first terminal connected to the current source 36 and a second terminal 64 connected to one end of the voltage dividing network. The input 52, to the amplifier 42, is connected to the first terminal via a high input resistor 66.

[0027] The operation of the constant current source 36, which may be of any suitable design, is controlled by the control circuit 34.

[0028] At the commencement of a test or verification phase, the application of power from the blast controller to the control circuit 30 via the harness is detected by the sensing component 35. The detonator is then automatically advanced through a power on/reset cycle by means of the control circuit 34 which responds to the component 35. At the end of the cycle the control circuit 34 automatically outputs a control signal which is applied to, and which is used to actuate, the current source 36 which then passes a test current of known magnitude through the fuse 60. The control circuit 34 could be hardware based, or it could include processing or logic devices, where necessary running suitable software, to implement its functions. The

magnitude of the test current is low, particularly compared to the actuating current which is required under normal conditions to actuate the fuse ie. to cause detonation of a primary explosive (not shown) associated with the fuse. The designed magnitude of the test current, apart from being smaller than the magnitude of the actuating current for safety reasons, is calculated taking into account, at least, the expected resistance or impedance of the fuse, assuming the fuse is in a sound condition, so that a resulting volt drop across the fuse (due to the passage of the test current) will be of an acceptable and usable value.

[0029] A series resistor 61 is included between the current source and the fuse to act as a current limiting device and reduce the likelihood of inadvertent fuse actuation in case of circuit failure.

[0030] The time period for which the test current is passed through the fuse is controlled according to known criteria for example to ensure that the fuse is not damaged by the current and so that there is adequate time for taking measurements.

[0031] The test current flows through the fuse and a test voltage is produced across the fuse. In accordance with the Ohm's Law the magnitude of the test voltage is directly related to the resistance value of the fuse. The test voltage is applied to the input 52 of the amplifier 42 via the high' input resistor 66 to ensure that,^' as far as is possible, the amplifier is isolated from the circuit associated with the fuse 60. The test voltage is compared by the amplifier to a reference voltage at the input 46 which is produced by applying a controlled, stable voltage, generated by the control unit 34, to a terminal 68 of the voltage dividing network which includes the resistors 48 and 50. A status signal which is produced by the amplifier on the output 44 is indicative of the comparison process.

[0032] The reference voltage can be produced in any appropriate way and, depending in circumstances, may be within a defined range, or window, with upper and lower limits which sets acceptable tolerances.

[0033] As the constant current source produces a current of predetermined magnitude the magnitude of the voltage across the fuse is dependent on the characteristics 'of the fuse 60. For example if the fuse is open-circuited the voltage will be zero whereas if the fuse has a high resistance the voltage will be increased.

Conversely if the fuse has a resistance which is lower than its designed value the voltage across the fuse will be reduced.

[0034] The status signal, produced by the comparator circuit 40, is transferred by the control circuit 34 to, and is stored in, the memory device 32. The memory device can be interrogated remotely by the blast controller 12, when required, to obtain an indication of the status of the fuse 60. If the fuse is faulty then appropriate action can be taken.

[0035] Figure 2 shows a detonator 10A according to a second form of the invention which is similar to the detonator 10 and, consequently, components which are the same have the same reference numerals. The current source 36 is however replaced by a current sink 36A connected, in this instance, to the fuse 60 via a serially connected, current limiting resistor 62.

[0036] At the start of a test phase, when power is applied by the blast controller 12 to the harness 16, a test current is automatically enabled by the control circuit 34 in a manner similar to what has been described. The test current flows through the resistor 62 which has a high value and which therefore provides a current limiting protective effect in the event of a malfunction, and the fuse 60 to the current sink 36A. The voltage drop over the fuse 60 is directly related to the resistance of the fuse. If the current through the fuse drops below a predetermined value, which indicates that the resistance of the fuse is unacceptably high eg. the fuse connection to the fuse is "high-resistance" or open-circuited, the comparator switches to indicate a "high-resistance" or "no-fuse" condition. This information is stored in the memory device 32 and 'can be accessed, from the blast controller 12, using communication techniques which are known in the art. If the fuse status is defective appropriate remedial action can be taken.

[0037] The test current can be generated in any appropriate way and the invention is not limited in this respect. As indicated the test current is automatically generated at the start of a power-on phase and the fuse-status information is stored in an appropriate memory. If a blasting circuit includes a large number of detonators then, essentially, all the fuses in the detonators are simultaneously and automatically tested, a feature which can result in a substantial saving of time. According to requirement each memory device could store an indication of a defective fuse, or of a sound fuse. Merely by way of example a data bit could be switched from a logical 0 to a logical 1 to indicate a faulty fuse, and the data bit could remain at the logical 0 if the fuse is sound.

[0038] A further possibility is to test each detonator, in a plurality of detonators, separately from the other detonators. If the test data (status signal) arising from a test is to be stored remotely, e.g. at the blast controller, then this technique, which is executed in real time, can be adopted. If the test data is stored at each respective detonator then the simultaneous testing of all the detonators is preferred for, as noted, this technique offers a significant saving of time.

[0039] Clearly if the detonator fuses are to be tested in real time in succession, then the detonators must be individually addressable. This can be done either by giving each detonator a unique address or identity data, or by distinguishing a detonator, from other detonators, by virtue of its position in a detonator string connected to the harness. A command signal can then be addressed to each detonator in succession, with respective' current generator in each detonator then being separately actuated.

The resulting test data, sent to the controller, is then uniquely linked to the respective detonator.

[0040] If a blasting system includes a large number of detonators then it should be possible to associate the status information of each fuse with the appropriate detonator. This can be done in different ways. For example the detonators could be interrogated in a predetermined sequence which is based on the detonator layout, or each detonator could be individually identifiable, eg. have a unique identifier included in the memory device 32, or be otherwise associated with the control unit 34, so that the fuse status information is uniquely linked to the respective detonator.

[0041] Figure 3 illustrates a detonator 10B further variation of the invention. Again components which are similar to those which hav already been described bear like reference numerals.

[0042] A constant current source 36, upon power up of a blast system, applies a test current of predetermined magnitude to the fuse 60. A voltage which is developed across the fuse is directly applied to an analogue to digital converter, or any similar device 70, and data on the magnitude of the voltage across the fuse is passed by the control circuit 34 to the memory device 32. The status signal can be interrogated remotely by the blast controller 12, when required, and the data can then be transferred to the blast controller 12 where a further comparison step can be carried out, if required.

[0043] It is to be understood that the voltage across the fuse, in the described circumstances, is directly indicative of the resistance or impedance of the fuse. The status signal, in turn, can be a digitised form of the voltage. This digital data can then be accessed from a remote point (the blast controller 12) and manipulated as required. In particular it is possible to compare the digitised data to reference data thereby to test whether the resistance or impedance of the fuse is of an acceptable value or lies above or below the acceptable value and then to store a status signal, which depends on the comparison, in a memory device which is remote from the detonator, eg. in or at the blast controller 12. Again if the fuse status is defective, appropriate remedial action can be taken.

Claims

1. A method of testing a fuse in a detonator which includes the steps of passing a test current, the magnitude of which is below the magnitude of an actuating current, through the fuse, generating a status signal which is dependent on the magnitude of a voltage which is produced by the passage of the test current and storing the status signal in a memory device.

2. A method according to claim 1 wherein the voltage is produced across the fuse.

3. A method according to claim 1 or 2 wherein the magnitude of the voltage is dependent on the impedance of the fuse.

4. A method according to any one of claims 1 to 3 wherein the status signal is produced by comparing the voltage to a reference voltage.

5. A method according to claim 4 wherein the reference voltage lies within a defined range with an upper limit and a lower limit.

6. A method according to any one of claims 1 to 5 wherein the test current is generated within the detonator.

7. A method according to any one of claims 1 to 6 wherein the test current is automatically generated when power is applied to the detonator.

8. A method according to any one of claims 1 to 7 wherein the memory device is in the detonator.

9. A ethod according to claim 8 which includes the step of accessing the status signal from a location which is remote from the detonator.

10. A method according to any one of claims 1 to 7 wherein the memory device is remote from the detonator.

11. A method according to any one of claims 1 to 9 wherein the detonator is one of a plurality of detonators connected to a harness in a blasting system, and wherein the fuses in the respective detonators are tested substantially simultaneously.

12. A method according to claim 10 wherein the detonator is one of a plurality of detonators connected to a harness in a blasting system, and wherein the fuses in the respective detonators are individually tested in succession.

13. A detonator which includes a fuse, a control unit, a current generator which, in response to a signal from the control unit, passes a test current, the magnitude of which is below the magnitude of an actuating current, through the fuse and a memory device in which is stored a status signal which is dependent on the magnitude of a voltage produced by the passage of the test current.

14. A detonator according to claim 13 wherein the voltage is produced across the fuse.

15. A detonator according to claim 13 or 14 which includes a comparator which compares the voltage to a reference voltage and which, in response thereto, produces the status signal.

16. A tietona'tor according to claim 13 or 14 wherein the status signal is directly proportional to the voltage.

17. A detonator according to claim 16 which includes an analogue to digital converter to produce the status signal.

18. A detonator according to claim 15 which includes a high input resistance device between the comparator and the fuse.

19. A detonator according to any one of claims 13 to 18 wherein the current generator is selected from a current source and a current sink.

20. A detonator according to any one of claims 13 to 19 which includes a detector which senses the application of power to the detonator and wherein the control unit, in response thereto, actuates the current generator.

21. A detonator according to any one of claims 13 to 20 which includes a high value resistor between the current generator and the fuse.

22. A detonator which includes a fuse, a control unit, a current generator which, in response to a signal from the control unit, passes a test current, the magnitude of which is below the magnitude of an actuating current, through the fuse and a device for producing a status signal which is dependent on the magnitude of a voltage produced by the passage of the test current.

23. A detonator according to claim 22 wherein the device which produces the status signal is an analogue to digital converter.

24. A detonator according to claim 22 or 23 which includes a detector which senses the application of power to the detonator and wherein the control unit, in response thereto, actuates the current generator.

25. A detonator according to any one of claims 22 to 24 wherein the current generator is selected from a current source and a current sink.

26. A detonator according to any one of claims 22 to 25 which includes a high value resistor between the current generator and the fuse.

27. A blasting system which includes a plurality of detonators, each detonator being according to any one of claims 13 to 21 , a blast controller and a harness which connects the detonators to the blast controller and wherein, when power is applied, via the harness, by the blast controller to the detonators, the respective current generators pass the respective currents through the respective fuses, in each of the detonators, substantially simultaneously.

28. A blasting system which includes a plurality of detonators, each detonator being according to any one of claims 22 to 26 and being directly addressable, a blast controller and a harness which connects the detonators to the blast controller and wherein the blast controller actuates the respective current generators in each of the detonators in succession by means of a respective command addressed to the respective detonator, whereby the respective current is passed through the respective fuse, and each detonator then transmits a respective status signal to the blast controller.