U.S. patent number 3,640,224 [Application Number 04/857,443] was granted by the patent office on 1972-02-08 for rf immune firing circuit employing high-impedance leads.
This patent grant is currently assigned to The United States of America as represented by the Secretary of the Navy. Invention is credited to Reginald I. Gray, John T. Petrick.
United States Patent |
3,640,224 |
Petrick , et al. |
February 8, 1972 |
RF IMMUNE FIRING CIRCUIT EMPLOYING HIGH-IMPEDANCE LEADS
Abstract
High-impedance leads in a firing circuit prevent radiofrequency
induced cents 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.
Inventors: |
Petrick; John T.
(Fredericksburg, VA), Gray; Reginald I. (Fredericksburg,
VA) |
Assignee: |
The United States of America as
represented by the Secretary of the Navy (N/A)
|
Family
ID: |
25326011 |
Appl.
No.: |
04/857,443 |
Filed: |
September 12, 1969 |
Current U.S.
Class: |
102/202.2;
102/220 |
Current CPC
Class: |
F42B
3/188 (20130101) |
Current International
Class: |
F42B
3/188 (20060101); F42B 3/00 (20060101); F42b
003/18 () |
Field of
Search: |
;102/28,70.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Pendegrass; Verlin R.
Claims
What is claimed is:
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.
Description
STATEMENT OF GOVERNMENT INTEREST
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 radiofrequency
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 is 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 10 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 so as to
allow the replacement of the electroexplosive device presently used
in ordnance with the package illustrated. As 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 26, 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 replace a 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.
* * * * *