[0002] Extensive use is made of shock tubes in blasting operations. In some situations a so-called black powder fuse is used to ignite a shock tube which, in turn, then propagates an ignition signal to one or more detonators.

[0003] A black powder fuse is based on the use of high quality carbon and factors such as the size of particles in the carbon and the moisture content of the carbon play a role in determining the carbon quality.

[0004] The procurement of specification-compliant carbon is becoming increasingly demanding. Accordingly it is an object of the present invention to provide an alterative device for igniting a shock tube.

SUMMARY OF INVENTION

[0005] The invention provides a shock tube igniter which includes a housing which contains, at least, an electrical energy source at a first voltage, a timer arrangement, a voltage conditioning circuit, output contacts, a switch, an energy storage device, at least one signal generator and an actuator, and wherein, in response to operation of the actuator:

a) the voltage conditioning circuit transfers energy from the source to the energy storage device;

b) the timer arrangement commences timing of a predetermined timing period; and

c) the signal generator is operated, and at the end of the timing period, the switch is closed to connect the energy storage device to the output contacts.

[0006] The electrical energy source may provide electrical energy at a first voltage. The voltage conditioning circuit may transfer electrical energy to the storage device so that electrical energy is stored in the storage device at a second voltage which is greater than the first voltage.

[0007] The signal generator can produce an audible sound or a visible light or any other appropriate signal. Preferably a sound signal and a light signal are produced. The nature of each signal which is produced may vary with passage of the timing period. For example a sound signal may increase in intensity with passage of the timing period. Alternatively or additionally the sound signal may be in the form of pulses and the pulse frequency may be increased with passage of the timing period. If a light signal is produced then the intensity of the light signal may be increased with passage of the timing period. Alternatively or additionally the light signal may be in the form of a pulse train and the pulse frequency may be increased with passage of the timing period.

[0008] The timing period may be preset, for example under factory conditions. This contributes to the safety of operation and helps to make the igniter more resistant to tampering. Alternatively the timing period may be set at the time of usage. For example an operator may select a timing period from a number of possibilities. The invention is not limited in this respect.

[0009] In a preferred form of the invention the timing arrangement includes two timers which are operated in parallel and which run independently of each other. The execution of the predetermined timing period by each timer is then required before detonator initiation can take place. This "redundancy" approach enhances security of operation. For example if only a single timer is used then, conceivably, the timer could malfunction and provide a signal that the predetermined period has been executed whereas a shorter period, as a matter of fact, may have been executed. Premature initiation could then take place and this could have serious adverse safety consequences. Thus, unless signals are received from both timers within a predetermined time interval indicating that each timer has successfully executed the timing of the predetermined time interval, initiation of the shock tube cannot take place.

[0010] Preferably a sensing device is used to detect the connection of an external component such as a detonator to the output contacts. The timing arrangement is rendered inoperative unless the component is connected to the output contacts. This means that, in practice, the shock tube igniter is not functional unless it is properly installed. The likelihood that the timer arrangement could commence execution of the predetermined timing interval before the shock tube igniter is correctly connected to a detonating arrangement, is obviated. This feature safeguards against the timing arrangement starting timing of the timing period (whether inadvertently or as a consequence of user intervention) and then, prior to completion of the timing period, being connected into a blasting system. If this were to occur the timing period could be completed shortly after, say, a detonator is connected to the output contacts and initiation thereof could take place while an operator is still within range of the explosive in question.

[0011] The actuator may include an appropriate switch. The actuator may be accessible on an external surface of the housing. Preferably the shock tube igniter includes a cover over the actuator. The arrangement is preferably such that the cover must be removed to expose the actuator to enable the actuator to be operated.

[0012] The electrical energy source may comprise one or more batteries.

[0013] The switch may be any appropriate device and, for example, may be a relay or a semiconductor switch. The invention is not limited in this respect.

[0014] The signal generator may be powered directly from the electrical energy source.

[0015] In use the shock tube igniter may be provided in combination with an electric detonator which is connected, when appropriate, to the output contacts. The electric detonator is preferably not ignitable at the first voltage. This provides a degree of intrinsic safety to the combination.

[0016] As used herein "electric detonator" includes an electric, and an electronic, detonator.

BRIEF DESCRIPTION OF THE DRAWING [0017] The invention is further described by way of example with reference to the accompanying drawing which illustrates in block diagram form a shock tube igniter according to the invention in an installed mode.

DESCRIPTION OF PREFERRED EMBODIMENT

[0018] The accompanying drawing schematically illustrates a shock tube igniter 10 which is connected to an electric detonator 12 which, in turn, is connected to a shock tube 14. [0019] The shock tube forms part of a blasting system and extends to a plurality of detonators, not shown, of any suitable kind.

[0020] The shock tube igniter 10 includes a housing 20 which is made from an inexpensive yet durable plastics material. Preferably the housing is sealed or otherwise closed so that the contents of the housing are not directly accessible.

[0021] The housing contains an electrical energy source 22 which consists of one or more batteries, a voltage conditioning circuit 24, an energy storage device 26 such as a capacitor, a timing arrangement 28, a first switch 30, a second switch 32, a sound generator 34, a light source 36, a sensor 38 and output contacts 40. The detonator 12 has contacts 42 which are connected directly or via suitable leads, not shown, to the contacts 38, when required.

[0022] An actuator 44 is positioned between the electrical energy source 22 and the components 24 to 30. The actuator may be of any suitable kind and is schematically illustrated as including a switch 46, which is normally open, and which is operable by means of a switch lever 48 which is positioned on an outer surface of the housing. A removable cover 50 overlies the switch lever. The arrangement is such that unless the cover is removed or displaced from the housing the switch lever is not accessible and the switch 46 is therefore not operable.

[0023] The switches 30 and 32 are normally open. The switch 32 is provided in combination with a controller which regulates the working action of the switch.

[0024] The timer arrangement 28 includes a first timer 28A and a second timer 28B. These timers run independently of each other and are designed to work in parallel. Each timer provides an independent output to the switch 32. [0025] The sensor 38 is custom-made and is designed to detect the connection of the detonator 12 to the contacts 40 i.e. it detects when the contacts 42 are electrically connected to the contacts 40. If this type of connection is not made then the sensor renders the timing arrangement 28 inoperative. The timers 28A and 28B are only able to execute predetermined timing periods if a detonator with predetermined electrical characteristics is connected across the contacts 40.

[0026] The igniter 10, in an installed configuration, is connected to the electric detonator 12 i.e. the contacts 40 are connected to the contacts 42. The electric detonator requires a predetermined amount of electrical energy delivered at a voltage in excess of a specified level and within a predetermined time interval in order to be successfully ignited. Preferably the energy source 22 provides energy at a voltage V1 which equals the battery voltage and which is less than the ignition voltage of the detonator 12. The function of the voltage conditioning circuit 24 is such as to store energy in the capacitor 26 at a voltage V2 which is above the specified initiating voltage of the detonator 12. The capacitor 26 is capable of storing a quantity of energy in excess of that required for firing the detonator 12.

[0027] When the arrangement is to be activated the cover 50 is removed to expose the switch lever 48. The switch 46 is then closed by an operator. The sensor 38 continuously monitors the status of the contacts 40. The sensor thus detects if the detonator 12 is connected to these contacts.

[0028] If the sensor detects the absence of the detonator across the contacts 40 the timers 28A and 28B are kept inoperative. If the detonator connection is in place then the sensor allows the timers 28A and 28B in the timer arrangement 28 independently to commence respective timing periods, each of a predetermined duration, for example 60 minutes. The conditioning circuit 24, which is typically in the nature of a step-up circuit, transfers energy from the battery 22 to the capacitor 26. The capacitor, when fully charged, has a voltage V2 and holds a quantity of energy, at the voltage V2, which is adequate for firing the detonator 12.

[0029] The timer arrangement 28, once the timers commence respective timing periods, causes closure of the switch 32. The switch can be closed permanently or it can be repeatedly closed and opened at a varying frequency. Upon closure of the switch energy from the battery 22 is applied to the light source 36 and to the sound generator 34. In one arrangement the light 36 is caused to flash initially at a low frequency and at a low intensity. As each of the timers 28A and 28B further executes its respective timing period the light intensity is increased and the frequency of the light pulses is also increased. A similar situation applies to the sound generator which, initially, generates audible sounds at a low level and in pulses at a fairly low frequency. The pulse repetition rate is increased and the sound level is increased as the timers go through their respective timing periods. Towards the end of the timing periods the sound may for example be continuous and at a high level or pitch.

[0030] It is to be noted that if either timer fails, operation of the igniter 10 is automatically terminated. The switch 32 is only operative in response to signals which must be produced by the timers 28A and 28B in parallel. The absence of one signal automatically inhibits the operation of the switch 32. Similarly, if the detonator 12 is not connected to the contacts 40, operation of the timing arrangement 28 is automatically inhibited. [0031] At the end of the timing periods the timer arrangement 28 causes the switch 30 to close. The switch thereby connects the capacitor 26 to the electric detonator and electrical energy passes to the detonator and immediately initiates the detonator. The shock tube 14 is thereby ignited and a signal is transmitted by the shock tube to detonators which are connected downstream to the shock tube.

[0032] The timer arrangement 28 can be set under factory conditions to enable each timer 28A and 28B to execute a timing period which is known to be safe and which is not alterable. For example, the timing period may be of the order of 60 minutes. This is exemplary only and non-limiting. In a variation of the invention though the user is given a facility of being able to vary the timing period. As the detonator 12 is initiated at the end of the timing period the duration of the timing period should be such that safety aspects are not compromised. Thus it is possible, in a variation of the invention, by way of example only, for a user to actuate the timer arrangement 28 to execute a timing period selected from a number of possible periods e.g. of 60 minutes, 45 minutes and 30 minutes (say).

[0033] The igniter 10 is a self-contained, non-reusable and throw-away device. It is sealed so that its contents are not accessible. The cover 50, once removed, is preferably not replaceable. This helps to prevent tampering with the igniter.

[0034] The cover 50 can take on any appropriate form. The cover adds a degree of water resistance to the housing. The cover additionally functions as a safety mechanism. A user for example, is only able to access the contacts 40, to make a connection to a detonator string, if the cover is partially removed. To achieve this, the cover may have lines of weakness or be otherwise designed so that the cover comes off the housing, in stages. In a first stage the contacts 40 are exposed. Further displacement of the cover will allow the switch lever 48 to be accessed.

[0035] Provision may be made in the cover for openings so that sound from the sound generator 34 is not unduly attenuated, or for a diagnostic test port. The light source 36 is also carefully positioned so that, although the source is protected against risk and damp, light emission is not attenuated. The light source 36 could for example comprise two or more light emitting diodes, one of which is green and another of which is red. The green diode is energised for an initial interval of the timing period. The red diode would then be energised as the timing period comes to finality. Different variations are of course possible.

[0036] The provision of two timers in the timing arrangement means that failure of one timer results in a failsafe situation of the igniter. Additionally the igniter can only be rendered operative if it is correctly connected to a detonator in a blasting system. This aspect, as noted, is monitored by the sensor 38. It is therefore not possible for the timing period to be initiated before connection of the igniter into the blasting system has taken place.

[0037] The igniter is preferably designed for single usage. An objective in this respect is that, for safety reasons, a user should not be encouraged to attempt to retrieve the device so that it can be re-used.