Imperial Chemical Industries Limited

Eirwyn Jones

Michael I Mitchell

A control circuit for firing an electrically actuable igniter in response to a firing signal having predetermined characteristics. For protection from inadvertent or accidental actuation, the control circuit includes at least one inductor in series with the fuse wire of the igniter and at least one inductor in parallel with the source of the firing signal. The series and parallel inductors are electromagnetically coupled to one another through a ferrite bead and are electrically connected so as to generate opposed magnetic effects when current flows through them. Electric detonators incorporating the control circuit are also detailed.

Selectively actuable electrical circuit

An ignition system for the firing of a plurality of electrically actuable igniters (16) and methods for construction and use of the assembly. The ignition leading wire (17) of each electrically actuable igniter (16) is formed from a continuous length of insulated wire connecting its two electrical connection terminals. The leading wire is looped around a transformer core (14) having a movable portion (15) that is opened to admit the loop. A firing cable (12) coupled to a source of electrical firing energy (11) is also looped around the transformer core completing the formation of a transformer for coupling electrical firing energy from the source to each of the igniters to be fired. A plurality of transformer cores can be coupled to a single firing energy source by looping a continuous wire from the source, through each transformer and then back to the source, thereby electromagnetically coupling firing energy to each transformer. In an alternate configuration, the igniter leading wires (17) are each loop coupled to a toroidal core (20) which is in turn electromagnetically coupled to a transformer (19 ) by a single loop of insulated wire looped through the core of the transformer and each toroidal core. The construction method includes connecting the two ends of a continuous length of insulated wire (17) to the two electrical connection terminals of each igniter (16) to be fired, or further including the looping of each continuous length of insulated wire (17) from an igniter around a toroidal core (20) to form an ignition assembly for coupling to a transformer (19) just prior to firing of the igniters. The method for use of the ignition assembly includes either the looping of the continuous wire (17) connected to each igniter around the transformer (14) having a movable portion (15) or coupling the toroidal cores (20) to a transformer (19) so that firing energy can be transferred from the source of electrical firing energy (11) to the igniters (16) to be fired.

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Alloway, United Kingdom

Eirwyn Jones