US3613592A

US3613592A - Electronic delay cartridge

Info

Publication number: US3613592A
Authority: US
Inventors: William J Brown; Robert F Butler; Smith E Hedden; Janis Jablovskis
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1969-07-07
Filing date: 1969-07-07
Publication date: 1971-10-19
Anticipated expiration: 1988-10-19

Abstract

An extremely compact electronic cartridge for delaying the delivery of a firing pulse to a squib which initiates a main charge. The delay provided by the circuit is maintained constant with temperature variations by using a thermistor in the circuit, and the original firing pulse is provided by a thermal battery.

Description

United States Patent [72] Inventors William J. Brown King George;

Robert F. Butler, King George; Smith E. Hedden, Dahlgren; Janis Jablovskis, King George, all of Va.

[56] References Cited UNITED STATES PATENTS 2,998,774 9/1961 Gibson 102/702 P 3,099,962 8/1963 Smith 102/702 3,211,057 10/1965 White, Jr. et al. 102/702 3,225,695 12/1965 Kapp et al 102/702 3,343,493 9/1967 Aulds et al.... 102/70.2 3,483,395 12/1969 Sauber 307/141 Primary Examiner-Benjamin A. Borchelt Assistant Examiner-Thomas H. Webb Attorneys Edgar J. Brower and Thomas 0. Watson, Jr.

ABSTRACT: An extremely compact electronic cartridge for delaying the delivery of a firing pulse to a squib hich initiates a main charge. The delay provided by the circuit is maintained constant with temperature variations by using a thermistor in the circuit, and the original firing pulse is provided by a thermal battery.

PATENTEUUCT 19 l97l 3, 6 1 3 5 9 2 T if WILL MM 4. BROWN INVENTORS ROBERT F. BUTLER SMITH E. HEDDON JAN/5 JAB/.OVSK/S ATTORNEY ELECTRONIC DELAY CARTRIDGE GOVERN MENT INTEREST IN THE INVENTION 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 l. Field of the Invention This invention relates generally to devices for delaying the initiation of an explosive charge and more particularly to an electronic delaying device having substantially constant delay time with temperature change.

2. Description of the Prior Art In many applications, such as escape systems, it is desirable to have a delay period between the time initiation action is started and the time the initiation of the main explosive occurs. For such applications, the prior art has generally used pyrotechnic delay cartridges in which the original initiation action ignited a percussion primer which in turn initiated a pyrotechnic delay column. The pyrotechnic delay column was made of slowly burning explosive which would delay the speed with which thedetonation would reach and initiate the main charge. A disadvantage of a pyrotechnic delay cartridge is that the pyrotechnic mix in the delay column must be mixed and pressed under carefully controlled conditions in order to maintain constancy of delay time. Regardless of the care taken in preparing pyrotechnic delay cartridges delay time variations in excess of :25 percent are common, and delays over five seconds are very difiicult to produce.

Electronic delay cartridges have also been proposed in the prior art however these have been bulky and the delay time would vary with temperature changes. Also, the power sources used were normally ordinary batteries whose power would decay with time even if not used.

SUMMARY OF THE INVENTION The disadvantages of the prior art have been overcome by providing an extremely compact electronic delay cartridge activated by a thermal battery and having a thermistor in the delay circuit to maintain the delay time constant with temperature variations.

It is an object of this invention to provide a delayed initiation device to electronically delay the initiation of a charge after starting the initiation process.

It is another object of this invention to provide such a delayed initiation device whose delay time is minimally affected by temperature variations.

It is still another object of this invention to provide such a delayed initiation device which is extremely compact.

A further object of the'invention is to provide an electronic delayed initiation device which can be activated by the application of heat.

It is another object of this invention to provide an electrdiiic delayed initiation device which can be reliably activated long after it has been installed in an explosive system.

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. I shows the basic construction of an electronic delay cartridge according to applicants invention;

FIG. 2 shows applicants delay cartridge when the components are fitted into a casing the size of a 38 caliber shell casing, and the details of the squib initiation system;

FIG. 3 shows the connection between the thermal battery and the printed delay circuit according to applicants invention; and

FIG. 4 shows the electronic delay circuit of applicants device.

2 DESCRIPTION OF THE PREFERRED ahvitiomMENrs FIG. 1 shows the basic construction of the cic'ctr hic'aciay cartridge generally designated by reference numeral Il',c'o'rnprising a casing 12, having therein a thermal battery I4 ;an' electronic delay circuit 15, a squib initiation system 16 and a main charge 18.

Thermal batteries are well known in the art and any, known thermal battery could be used. Activation of the thermal battery can be accomplished in a number of ways for example by means of a percussion primer or by means of an electric match. Upon activation the thermal battery provides a pulse of electricity to the delay circuit. The delay circuit delays delivery of this pulse to the squib a predeten'riined amount (if time, which is set by the circuit parameters. When'the piils'e reaches the squib, the squib is heated and ignitesthe main charge. I -j.

FIG. 2 shows in greater detail certain portions efa-delay cartridge such as that shown in Fig. 1. A ca'sing t9 the a era 38 caliber cartridge contains a thermal battery 20 andan electronic delay circuit 21. The initiation assembly 22 is of eonventional design and contains a bridge wire squib'26sur rounded by lead styphnate 25. Around the bridge wire-and lead styphnate is an ignition mixture 24. The ignition mixture 24 is separated from main charge 28 by spacer I7 having-arr aperture therethrou'gh to allow detonation of the main charge by the ignition mixture. Upon delivery of the electric pulseby! the delay circuit to bridge wire 26 the lead styphria'te is ignited cuit board 35 to a thermal battery 20. Leads 3 2 and Siextn'd through aligned apertures 37 and a9, and $3 arid 38"in'the printed circuit board and the thermal battery to connect the battery to the printed circuit. The p'ririted circuittioard is then" placed adjacent the end of the thermal battery 20 and the assembly is then inserted into casing into abutment with shoulder 23. Member 27, containing the igniter assembly and the bridge wire and ignition mix is then insert nto the cartridge, and leads from the bridge wire 'areplugg'edinto'the printed circuit board. Main charge '28 is than packed into member 27 and enclosure plate 29 is placed over th 'endiof the cartridge. The end of the cartridge 31 is then crimped o'y'er an O-ring 30 to retain the entire assembly within casing.

FIG. 4 shows the novel delay circuit of the invention. Aconventional thermal battery 20 is used to providepower to the circuit. A thermal battery is one which is normally inert but upon application of heat is activated to provide a pulsc r electricity to the circuit. Normally this. is doiie by melting of an electrolyte which then flows into' the battery to activate .it. Since the electrolyte is not normally the battery thermal battery never deteriorates from setting inactive. This meaiis that it is reliable to provide power for initiation of anescape system or the like long after it has been installed, whereas a conventional battery could very well be discharged useless. Upon activation of battery 20, capacitor 37 being charged through resistor 36. Unijunction transistor 38 is normally reverse biased, but after capacitor 37 become suffi: ciently charged, the unijuncton transistor becomes forward biased, thereby effectively shorting capacitor 37 acrossre sistor 39 and the gate to cathode region of a silicon controlled rectifier 42. This pulse applied to thegate of the silicon controlled rectifier turns it on" thus applying power to the bridge wire 26. v v To control the effect of temperature variations on the time delay circuit, a thermistor I was placed in parallel with resister 40 creating an equivalent resistance which varies with temperature. Variations of the resistance of the thermistor 4! with temperature will maintain the time delay between activation of the thermal battery and the supplying of power to bridge wire 26 essentially constant with temperature. The resistance of resistor 40 has an effect on the voltage to which capacitor 37 must build to forward bias unijunction transistor 38. By placing thermistor 41 in parallel with resistor 40, a temperature variable biasing resistance has been provided which compensates for temperature induced variations in other circuit parameters to maintain substantially constant the time necessary for capacitor 37 to charge to the level required to forward bias unijunction transistor 38. Experimentation has shown that the time delay period varies less than :3 percent between the temperatures of -60 and +l60 F.

Thus it can be seen that an extremely compact electronic delay cartridge has been produced which provides a delay time which is substantially constant over a wide range of temperatures.

Obviously, many modifications are possible in view of the above teachings. For example, thyratron circuits could be employed instead of solid a circuitry. Also, this delay circuit could be used in environments other than explosive initiation. It would be useful anytime a temperature independent delay time is desired.

What is claimed is:

1. Means for delayed initiation of an explosive charge comprising:

an electronic delay circuit including means for maintaining time delay constant with temperature variation;

a thermal battery actuable to provide power to said delay circuit; and

means connected to said thermal battery by said delay circuit to initiate said explosive charge.

2. The device of claim 1 wherein said maintaining means comprises a thermistor.

3. The device of claim 1 wherein said electronic delay circuit comprises:

switch means;

means normally biasing said switch means open;

a capacitor which is charged by said thermal battery to overcome the bias on and close said switch means, and to discharge through said switch means to activate said initiation means;

said biasing means including the means for maintaining time delay constant with temperature variation.

4. The device of claim 3 wherein said maintaining means comprises a thermistor.

5. The device of claim 3 wherein said switch means comprises a unijunction transistor and said biasing means comprises resistors connected thereto, said maintaining means comprising a thermistor in parallel with one of said resistors.

6. The device of claim 5 further including a silicon controlled rectifier between said unijunction transistor and said initiating means normally preventing current flow from said unijunction transistor to said initiating means, said silicon controlled rectifier allowing such current flow in response to the discharge of said capacitor through said unijunction transistor.

7. The device of claim 1, wherein said electronic delay circuit comprises:

a first resistor and a capacitor connected in series across said thermal battery;

a unijunction transistor having its emitter connected between said resistor and capacitor;

a first base region of said unijunction transistor being connected through a second resistor across said capacitor;

a silicon controlled rectifier having its gate connected to said first base region and its cathode in parallel with said second resistor, the anode of said silicon controlled recti fier being connected to said initiation means; and

a thermistor connecting said initiation means to a second base region of said unijunction transistor, said second base region and thermistor being in parallel with said first resistor.

8. The device of claim 7 wherein said initiation means comprises a fourth resistor.

9. An electronic delay circuit comprising:

a power source;

switch means;

means normally biasin said switch means open;

a capacitor which is c arged by sa|d power source to overcome the bias on and close said switch means and to discharge through said switch means; and

said biasing means including thermistor means to maintain the time necessary to overcome the bias on said switch means substantially contant with temperature variations.

10. The circuit of claim 9 wherein said switch comprises a unijunction transistor and said biasing means comprises resistors connected thereto, said thermistor maintaining means comprising a thermistor in parallel with one of said resistors.

11. The circuit of claim 10 further including a silicon controlled rectifier between said unijunction transistor and said initiating means normally preventing current flow from said unijunction transistor to said initiation means, said silicon con trolled rectifier allowing such current flow in response to the discharge of said capacitor through said unijunction transistor.

12. An electronic delay circuit comprising:

a power source;

a first resistor and a capacitor connected in series across said power source;

a silicon controlled rectifier having its gate connected to said first base region and its cathode in parallel with said second resistor;

an ultimate current delivery portion, said current delivery portion being connected to the anode of said silicon controlled rectifier; and

a thermistor connecting said current delivery portion to a second base region of said unijunction transistor, said second base region and thennistor being in parallel with said first resistor.

13. The circuit of claim 12 wherein said ultimate current delivery portion comprises a fourth resistor.

Claims

1. Means for delayed initiation of an explosive charge comprising: an electronic delay circuit including means for maintaining time delay constant with temperature variation; a thermal battery actuable to provide power to said delay circuit; and means connected to said thermal battery by said delay circuit to initiate said explosive charge.

2. The device of claim 1 wherein said maintaining means comprises a thermistor.

3. The device of claim 1 wherein said electronic delay circuit comprises: switch means; means normally biasing said switch means open; a capacitor which is charged by said thermal battery to overcome the bias on and close said switch means, and to discharge through said switch means to activate said initiation means; said biasing means including the means for maintaining time delay constant with temperature variation.

4. The device of claim 3 wherein said maintaining means comprises a thermistor.

7. The device of claim 1, wherein said electronic delay circuit comprises: a first resistor and a capacitor connected in series across said thermal battery; a unijunction transistor haVing its emitter connected between said resistor and capacitor; a first base region of said unijunction transistor being connected through a second resistor across said capacitor; a silicon controlled rectifier having its gate connected to said first base region and its cathode in parallel with said second resistor, the anode of said silicon controlled rectifier being connected to said initiation means; and a thermistor connecting said initiation means to a second base region of said unijunction transistor, said second base region and thermistor being in parallel with said first resistor.

9. An electronic delay circuit comprising: a power source; switch means; means normally biasing said switch means open; a capacitor which is charged by said power source to overcome the bias on and close said switch means and to discharge through said switch means; and said biasing means including thermistor means to maintain the time necessary to overcome the bias on said switch means substantially contant with temperature variations.

11. The circuit of claim 10 further including a silicon controlled rectifier between said unijunction transistor and said initiating means normally preventing current flow from said unijunction transistor to said initiation means, said silicon controlled rectifier allowing such current flow in response to the discharge of said capacitor through said unijunction transistor.

12. An electronic delay circuit comprising: a power source; a first resistor and a capacitor connected in series across said power source; a unijunction transistor having its emitter connected between said resistor and capacitor; a first base region of said unijunction transistor being connected through a second resistor across said capacitor; a silicon controlled rectifier having its gate connected to said first base region and its cathode in parallel with said second resistor; an ultimate current delivery portion, said current delivery portion being connected to the anode of said silicon controlled rectifier; and a thermistor connecting said current delivery portion to a second base region of said unijunction transistor, said second base region and thermistor being in parallel with said first resistor.