Ammunition and explosives – Igniting devices and systems – Ignition or detonation circuit
Patent
1987-02-26
1989-09-26
Jordan, Charles T.
Ammunition and explosives
Igniting devices and systems
Ignition or detonation circuit
102206, F42C 1100, F42C 1912
Patent
active
048691712
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a detonator.
BACKGROUND ART
Known detonators usually comprise a housing containing an explosive charge with a pair of fusehead conductors; passage of a current through these conductors causes the detonator to explode. Whilst this construction of detonator has the advantage of simplicity, it has very serious disadvantages from the point of view of safety and also from the point of view of ease of unauthorised use.
The main problem from the point of view of safety is that the detonators are susceptible to inadvertent operation because the fusehead conductors can pick up stray electromagnetic radiation or induced currents due to magnetic or electric fields. Handling of known detonators can therefore be somewhat hazardous.
From the point of view of security, known detonators suffer from the disadvantage that they can be actuated by any electrical device which supplies sufficient electrical current to the fusehead conductors. Thus, the detonators can be used for illegal purposes if they fall into the wrong hands.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide a detonator which is incapable of actuation unless control signals of a predetermined form are applied thereto. Further objects of this invention are to provide a detonator of a particular construction and a blasting system which utilises such detonators.
According to the present invention there is provided a detonator comprising housing means, an explosive charge located within the housing means, fusehead conductors extending from the explosive charge, conditioning means in the fusehead conductors, the conditioning means being operable, in a normal state, to render the fusehead conductors incapable of carrying a voltage or current sufficient to cause explosion of the explosive charge, and control means responsive to control signals applied thereto and operable to change the state of the conditioning means to an armed state, in response to receipt of a predetermined control signal, wherein the fusehead conductors are capable of carrying a voltage or current sufficient to cause explosion of the explosive charge.
Most of the components of the detonator according to this invention are well-known to the art. For example, the housing may be constructed from any material known to be suitable for this purpose, such as aluminum, steel or carbon-filled rubber. The explosive charge used normally in the detonator can again be any type of explosive used for such purposes, for example, lead azide, lead styphnate or pentaerythritol tetranitrate. Mixtures of one or more of these explosives are used by the art and may also be used in the detonators according to this invention.
The fusehead conductors are of conventional type and are joined within the explosive charge by a fusible element. When an electric current is passed between the conductors, the element fuses and sets off the explosive. Other initiating fuseheads include exploding bridge-wire and "flying-plate" types.
The conditioning means operates such that in a normal, i.e. non-armed, state, the detonator cannot be accidentally or deliberately fired without first putting the conditioning means in an armed state by a predetermined control signal. It does this by rendering the fusehead conductors incapable of carrying an electric current. This can be achieved in a number of ways. For example, the conditioning means may short-circuit the fusehead conductors by connecting them to an earth wire, or more simply (and preferably) to the housing means.
The change to the armed state thus requires that the short circuit be removed. The selection of a particular type of short circuiting means will determine how this is achieved. For example, the conditioning means may comprise a relay the contacts of which are connected in the fusehead conductors and the operating coil of which is responsive to the control means. Preferably, the contacts connect the fusehead conductors to the housing in the normal state, and in the armed state form an electrical lin
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D J Moorhouse and S T Deeley
Jordan Charles T.
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