Ammunition and explosives – Igniting devices and systems – Ignition or detonation circuit
Patent
1990-02-13
1992-07-28
Johnson, Stephen
Ammunition and explosives
Igniting devices and systems
Ignition or detonation circuit
102207, 1022022, 102201, 102218, F42C 1102
Patent
active
051332574
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of initiating, i.e. starting, an electronically delayed ignition system for explosive charges, which is entirely protected from electromagnetic waves. The invention relates to a design of such shielded ignition system.
BACKGROUND OF THE INVENTION
In the employment of electric ignition systems for initiating explosive charges, nearby radio and radar stations, as well as other sources of radiation, constitute potential risks, since they could give rise to sufficiently powerful induced currents in the ignition wiring to cause accidental initiation of the charges. This is a serious drawback which is inherent in all electric ignition system and because of this drawback, in electrical ignition systems intended for military applications, it has been necessary to incorporate complex anti-disturbance systems, since, in field-service use it cannot be anticipated, as in civilian blasting operations using electrical ignition systems, that all use of radio, radar or other radiation transmitters in the vicinity of the explosion site can be prevented.
It has previously been common to provide electrically initiated blasting cartridges (blasting caps), when necessary, with pyrotechnical delay charges of conventional type. However, electronic delayed action igniters with very good performance as regards precise and well-known ignition intervals and small outside dimensions have recently become available at highly attractive prices.
These electronic delayed action igniters constitute a further argument in favor of choosing an electric instead of a non-electric ignition system in the initiation of explosive charges. However, as soon as an electric ignition system is employed in which the electric wires are of sufficient length to run the risk of induced currents in the wires, there will be the additional requirement of accurate and therefore also complex and expensive disturbance shielding of the entire ignition system.
Consequently, it would in many cases be desirable to have access to a non-electric ignition system which could occur the same exact time lag as the electronic time igniters and which could never be achieved using even the best pyrotechnical delay charge.
SUMMARY OF THE INVENTION
The present invention relates to a disturbance-shielded, electronically delayed ignition system for explosive charges in which the ignition system is initiated by detonation, or high-energy combustion, for instance of a pyrotechnical charge or the like, triggered in the immediate vicinity of the ignition system. According to one embodiment of the present invention, the initiating effect on the ignition system is achieved by means of a detonating fuze fired in its vicinity. The effect initiating the ignition system may then, in accordance with another embodiment of the present invention, be amplified by or replaced by, for instance, a slower burning pyrotechnical charge. According to the present invention, at least a portion of the energy generated on detonation or combustion is converted into electric current of sufficient power to energize an electronic time igniter which, in turn, initiates the desired detonation after a preset time interval.
By employing a detonating fuze such as a pentyl fuze or a low-energy fuze of the type which consists of a tube interiorly coated with a primary explosive for initiating the electrically delayed igniter, access will thus be created according to the present invention to an ignition system which is entirely free of disturbance in respect of induced currents in the ignition system, at the same time as the electronic delayed action, with its extraordinarily high precision, gives an ignition time precision which today is impossible to achieve by using time exclusively pyrotechnical igniters.
Detonating fuzes of the pentyl fuze type, or the low-energy fuze briefly described in the foregoing will, on firing, always give rise, to a greater or lesser extent, to both a shock wave and to heat and light generation. According to the present inve
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