Rf immune firing circuit employing high-impedance leads

Abstract

High-impedance leads in a firing circuit prevent radiofrequency induced currents from prematurely detonating the electroexplosive device. A capacitor across a serial arrangement of an electroexplosive device and an SCR permits the use of a standard size power source to detonate the (EED) electroexplosive device, notwithstanding the impedance introduced by the interference preventing leads.

Claims

1. A firing circuit for an electroexplosive device which is immune from radiofrequency induced currents comprising: an energizing source; an electroexplosive device; a current control means operatively connected to said electroexplosive device; and high impedance carbon impregnated plastic leads for transmitting energy from said energizing source to said current control means. 2. The firing circuit of claim 1 wherein said current control means comprises: an energy storage capacitor operatively connected to said energizing source by means of said high impedance leads; a current path between said energy storage capacitor and said electroexplosive device; and switch means in said current path responsive to energy buildup on said capacitor to close said current path, whereby said electroexplosive device is actuated. 3. The firing circuit of claim 2 wherein said switch means comprises: a zener diode responsive to said energy buildup so as to breakdown at a predetermined energy level; and a silicon controlled rectifier connected in series with said electroexplosive device and responsive to breakdown of said zener diode to close said circuit path whereby said electroexplosive device is actuated. 4. The firing circuit of claim 3 wherein said switch means further comprises a variable reactance interposed between said energy storage capacitor and said zener diode permitting manual control of the energy level required on said capacitor to cause said zener diode to breakdown. 5. The firing circuit recited in claim 3 wherein said electroexplosive device and said current control means are packaged in a package comprising: a tubular enclosure of minimum size; an explosive charge occupying an end portion of said enclosure; said electroexplosive device arranged in intimate contact with said explosive charge; said zener diode and silicon controlled rectifier connected into a circuit with said electroexplosive device and arranged in close proximity to said electroexplosive device; and said energy storage capacitor connected into the circuit with said electroexplosive device and arranged to seal said previous elements into said enclosure, said capacitor also connected to said energizing source by means of high impedance leads, whereby said charge, electroexplosive device, diode, rectifier and storage capacitor are all contained within said tubular enclosure. 6. The firing circuit recited in claim 1 wherein said high impedance leads comprise: a pair of metal wires operatively connected to said energizing source; a pair of carbon impregnated plastic wires operatively connected to said current control means; and a pair of crimp-on connectors electrically connecting said metal wires with said plastic wires, whereby an impedAnce mismatch occurs at the splice. 7. The firing circuit recited in claim 6 wherein said high impedance leads further comprise a capacitor shunting said metal wire pair whereby a great impedance mismatch occurs at the splice.
1 [54] RF IMMUNE FIRING CIRCUIT EMPLOYING HIGH-IMPEDANCE LEADS [72] Inventors: John T. Petrlck; Reginald I. Gray, both of Fredericksburg, Va. The United States of America as represented by the Secretary of the Navy [22] Filed: Sept. 12,1969 [2]] ,AppLNo; 857,443 [73] Assignee: [ 1 Feb. 8, 1972 3,225,695 12/1965 Kapp etal ..1o2/76.2 3,543,493 9/1967 Auldsetal ..102/70.2 Primary Examiner-Verlin R. Pendegrass AttorneyEdgar J. Brower and Thomas 0. Watson, Jr. [ ABSTRACT High-impedance leads in a firing circuit prevent radiofrequency induced currents from prematurely detonating the electroexplosivc device. A capacitor across a serial arrangement of an electroexplosive device and an SCR permits the use of a standard size power source to detonate the (EED) electroexplosive device, notwithstanding the impedance introduced by the interference preventing leads. 1521 u.s.c1. 102/28 511 1111.01 F42b3/18 5s] FieldofSearch ..1o2/2s,70.2 4 [56] References Cited UNITED STATES PATENTS 2,754,757 7/1956 MacLeod ....,..,.,...102 21; HIGH /2 I3 v 21522;, CAPACITOR iggfgg c DEVICE PATENTED Fm BIHTZ l6 ELECTRO EXPLOSIVE DEVICE HIGH /2 l3 IMPEDANCE ENERGY LEADS STORAGE \Vx CAPACITOR CAPACITOR & FIG. 3 CRIMP ON CONNECTOR WIRE STUB INVENTORS JOHN Z PETE/6W REGINALD GREY BY $4,. 0. Lua ATTORNEY The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. BACKGROUND OF THE INVENTION This invention pertains to firing circuits in general and more particularly to firing circuits that are designed to eliminate accidental ignition of electroexplosive devices by radiofrequency induced currents. The problem of accidental ignition of electroexplosive actuated ordnance has been approached in many ways. Shielding of the firing circuit by a continuous metal surface provides one method for diminishing the probability of accidental ignition. Filtering out the hazardous radiofrequencies induced in the circuit is another method employed. These methods, although effective in reducing the hazards of accidental ignition, contribute bulk and weight to the ordnance employing these embodiments. Also, in situations where firing circuit connections to a weapon must be accomplished in high energy fields, as on an aircraft carrier, for example, these methods are not completely satisfactory in diminishing radiofrequency induced currents. SUMMARY OF THE INVENTION The invention provides by means of high resistance leads a lightweight RF immune firing circuit requiring a minimum of space. By causing an energy buildup on a storage capacitor at the EED, a conventional firing source may be used. The energy storage capacitor and electronic switch required to fire the EED by means of a standard firing source through high resistance leads are compact and packageable so as to be capable of replacing the EED without housing modifications. OBJECTS OF THE INVENTION An object of this invention is to provide a radiofrequency immune firing circuit that prevents the induction of radio frequency currents into the cables of the firing circuit. A further object of this invention is to provide a radio frequency immune firing circuit that is lightweight and compact so as to be capable of replacing the standard firing circuit and EED presently used in the art by simply substituting one for the other. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates, in circuit diagram form, one embodiment of the invention; FIG. 2 illustrates pictorially one packaging method that may be used for the invention; FIG. 3 is a cross-sectional view of FIG. 2 illustrating the interior of the packaged invention and the arrangement of the various elements; FIG. 4 is an illustration of another embodiment of the invention; FIG. 5 is an illustration of a still further embodiment of the invention; FIG. 6 is an illustration, in circuit diagram form, of another embodiment of the invention; and FIG. 7 is an illustration, in circuit diagram form, of still another embodiment of the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates the basic concept of the invention. By using high impedance leads 10 and 11 for distributing power from the power source V to the electroexplosive device 16 the hazard of radiofrequency currents being induced into these leads i's-very much diminished. Energy storage capacitor 12 is required to collect sufficient energy to actuate the electroexplosive device 16. Because of the very high impedance of leads l0 and 11, which may be carbon impregnated wire with an insulating sheath, a very high power source would be required if the energy storage capacitor 12 and other control equipment were not used to actuate the EED. The power source required to actuate an EED without the use of an energy storage capacitor would dissipate sufficient power in the wire to melt them before the EED was actuated. By use of energy storage capacitor 12 a standard power source may be used. Capacitor 12 is charged over a period of time by a standard voltage source. When the charge reaches a predetermined firing level the EED 16 will be actuated. Variable resistor 13 determines at what energy level of capacitor 12 EED 16 is actuated. When storage capacitor 12 reaches this energy level, zener diode 14 will break down causing a current to be injected into silicon controlled rectifier 15. This current will in effect cause SCR 15 to close the circuit between capacitor 12 and EED 16. Capacitor 12 will then discharge its energy through EED 16 causing it to actuate. The invention functions equally well when the electroexplosive device is either a carbon bridge type or the hot wire bridge type of device. FIGS. 2 and 3 illustrate packaging the circuit components can be seen from FIG. 2, energy storage capacitor 18, circuit 19 and the explosive charge 20 which is actuated by the electroexplosive device located within circuit 19 forms a very compact package with a tubular enclosure. FIG. 3 illustrates the internal arrangement of the components within the package. Energy storage capacitor 22 is connected to leads 21, which may be carbon impregnated plastic with an insulating sheath. Capacitor 22 is also connected to resistor 24 which will control break down of zener diode 26 which in turn causes silicon controlled rectifier 25 to close the circuit between capacitor 22 and electroexplosive device'27 thereby detonating charge 28. As can be seen the component parts of the circuit, resistor 24, zener diode l6, and SCR 25 are all located within the circuit module 23. FIG. 4 illustrates an embodiment of the invention directed towards alleviating the time delay inherent in the operation of the embodiment shown in FIG. 1. In order to decrease the time required for energy storage capacitor to charge to the requisite energy level, metal wire pairs 30 may be used to replaceija portion of high impedance leads 32. Metal wire pairs 30 are connected to the high impedance pair 32 by means of crimp-on connectors 31 which create an impedance mismatch between the two wire pairs thereby preventing radio frequency induced currents in metal wire pair 30 from getting to the electroexplosive device within package 33. FIG. 5 illustrates a modification of FIG. 4 which will allow a more satisfactory filtering of radiofrequency currents. A greater impedance mismatch between the two cable pairs joined by connectors 36 is created by using capacitor 35 in conjunction with connectors 36. This arrangement will prevent to a greater degree the application of radio frequency induced currents in metal wire pair 34 to the EED package 38. FIG. 6 illustrates yet another embodiment of the invention which is directed towards alleviating the long time delay inherent in the operation of FIG. 1. The EED 44 of the circuit will be actuated as soon as capacitor 41 is charged by means of source V through high impedance leads 40 to a level sufficient to cause zener diode 42 to breakdown which in turn will cause SCR 43 to conduct. FIG. 7 illustrates another embodiment of the invention which is also directed towards alleviating the time delay inherent in the operation of FIG. 1. When energy storage capacitor 46 reaches an energy level of a certain amplitude, capacitors 47 and 48 also reach that energy level. If it is sufficient to cause zener diode 49 to breakdown thereby injecting current into silicon controlled rectifier 50, the circuit between energy storage capacitor 46 and the EED 51 is closed. Energy storage capacitor 46 will, of course, discharge through EED 51 causing it to actuate. Capacitors 47 and 48 allow for adjustment of the energy buildup on capacitor 46 without the disadvantage of increasing the time delay. Obviously many modifications and variations of the present invention are possible in the light of the above teachings. What is claimed is: l. A firing circuit for an electroexplosive device which is immune from radiofrequency induced currents comprising: an energizing source; an electroexplosive device; a current control means operatively connected to said electroexplosive device; and high impedance carbon impregnated plastic leads for transmitting energy from said energizing source to said current control means. 2. The firing circuit of claim 1 wherein said current control means comprises: an energy storage capacitor operatively connected to said energizing source by means of said high impedance leads; a current path between said energy storage capacitor and said electroexplosive device; and switch means in said current path responsive to energy buildup on said capacitor to close said current path, whereby said electroexplosive device is actuated. 3. The firing circuit of claim 2 wherein said switch means comprises: a zener diode responsive to said energy buildup so as to breakdown at a predetermined energy level; and a silicon controlled rectifier connected in series with said electroexplosive device and responsive to breakdown of said zener diode to close said circuit path whereby said electroexplosive device is actuated. 4. The firing circuit of claim 3 wherein said switch means further comprises a variable reactance interposed between said energy storage capacitor and said zener diode permitting manual control of the energy level required on said capacitor to cause said zener diode to breakdown. 5. The firing circuit recited in claim 3 wherein said electroexplosive device and said current control means are packaged in a package comprising: a tubular enclosure of minimum size; an explosive charge occupying an end portion of said enclosure; said electroexplosive device arranged in intimate contact with said explosive charge; said zener diode and silicon controlled rectifier connected into a circuit with said electroexplosive device and arranged in close proximity to said electroexplosive device; and ' said energy storage capacitor connected into the circuit with said electroexplosive device and arranged to seal said previous elements into said enclosure, said capacitor also connected to said energizing source by means of high impedance leads, whereby said charge, electroexplosive device, diode, rectifier and storage capacitor are all contained within said tubular enclosure. 6. The firing circuit recited in claim 1 wherein said high impedance leads comprise: a pair of metal wires operatively connected to said energizing source; a pair of carbon impregnated plastic wires operatively connected to said current control means; and a pair of crimp-on connectors electrically connecting said metal wires with said plastic wires, whereby an impedance mismatch occurs at the splice. 7. The firing circuit recited in claim 6 wherein said high impedance leads further comprise a capacitor shunting said metal wire pair whereby a great impedance mismatch occurs at the splice.

Description

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