The use of electrical/electronic devices is growing rapidly in commercial blasting operations. For example, some detonators now rely on Integrated circuits to provide functionality. Providing electrical power to such devices is therefore necessary. This could be achieved in, for example wireless initiation devices, using a built-in battery or charged capacitor but providing the devices “live” presents significant safety concerns since the device may itself contain an explosive (detonators include a small charge of explosive) or be positioned within or in proximity to an explosive during use. Addressing these concerns by specifically designed safety systems, such as multiple layers of control at the level of circuit design, is possible. However, this adds to design complexity and operation and, in turn, this has implications with respect to cost, efficiency and application. Furthermore, safe operation is compromised if the safety system itself fails.
The possible problems of providing an explosive-containing initiation device with a built-in power supply can be overcome by supplying the device in multi-component form, with the power supply containing component being distinct from any component containing explosive material. However, in such cases, the use of a built-in power supply, such as a battery or other charge storage device, can limit the shelf life of that component due to unintended (bleeding of) electrical discharge. This may occur by a number of mechanisms, including chemical and physical mechanisms. An embodiment of this invention seeks to avoid the problem of shelf life limitation that may be associated with on-board power supplies such as batteries.
Further, in a blasting operation it is sometimes desirable to leave electrical devices in a borehole for a long time. In such cases the use of an on-board battery may limit the sleep time of such devices, i.e. the period for which the device can be left in the bore hole before intended use. In an embodiment, the invention seeks to provide a power source that can easily be scaled to provide very long sleep times in the borehole.
Against this background it would be desirable to provide an alternative approach to providing electrical energy for electrical/electronic devices used in commercial blasting operations.