US 3672303 A
An atmospheric temperature sensing squib firing contrivance for igniting an explosive device at a specific outside temperature, comprising an atmospheric temperature sensor, a time delay safety function that prevents premature ignition, an enabling function that allows ignition when the desired input conditions are met, the ignition function, and an inside temperature sensor that stabilizes the circuits against changing ambient temperature of the explosive device.
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Description (OCR text may contain errors)
United States Patent Brawn  TEMPERATURE SENSING SQUIB FIRING DEVICE John M. Brawn, Ridgecrest, Calif.
 Assignee: The United Stltes of America as represented by the Secretary 0! the Navy  Filed: May 28,1970
 Appl.No.: 41,437
 U.S.Cl. ..l02/70.2R  lnt.-Cl. F42c 11/06, F42c 15/40, F42c 19/06  Field oiSearch ..l02/l9.2, 28, 70.2
 References Cited UNITED STATES PATENTS 3,351,016 11/1967 Simpson ..102/70.2 3,559,582 2/1971 Hrzek ..l02/70.2
POSITIVE SUPPLY [451 June 27,1972
Primary Examiner-Benjamin A. Borchelt Assistant Examiner-Thomas B. Webb Attorney-R. S. Sciascia and Roy Miller  ABSTRACT An atmospheric temperature sensing squib firing contrivance for igniting an explosive device at a specific outside tempera- 1 ture, comprising an atmospheric temperature sensor, a time delay safety function that prevents premature ignition, an enabling function that allows ignition when the desired input conditions are met, the ignition function, and an inside temperature sensor that stabilizes the circuits against changing ambient temperature of the explosive device.
4 Claims, 1 Drawing Figure NEGATIVE SUPPLY PATENTEDJum I972 13. 672. 303
POSITIVE SUPPLY NEGATIVE SUPFLY I N VEN TOR.
JOHN M. BRAWN ROY MILLER ATTORNEY.
1 TEMPERATURE SENSING SQUID FIRING DEVICE 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 The present invention'comprises a squib firing circuit used for igniting an explosive device. The firing circuit senses an outside atmospheric temperature and causes ignition of the explosive device at a predetermined atmospheric temperature. A necessary feature of the firing circuit is that ignition of the explosive device must be prevented for a predetermined time period to provide safe separation from a launching vehicle such as an aircraft. A second feature is that ignition of the explosive device must also be prevented until the atmospheric sensor that initially can be warmer first senses a colder atmospheric temperature than the temperature at which ignition is to occur, i.e., it is intended that the explosive device incorporating the firing contrivance be launched initially into an environment that is colderthan the atmospheric temperature at which ignition occurs.
BRIEF DESCRIPTION OF THE DRAWING The FIGURE is a schematic diagram of the firing circuit.
DESCRIPTION OF THE PREFERRED EMBODIMENT The squib firing contrivance is to be made an integral part of an explosive device that will be ejected from a launching aircraft. The ambient temperature of the explosive device at the time of launch can be either warmer or colder than the atmospheric temperature of the environment into which it is launched. At launch, the atmospheric temperature sensor is instantly exposed to the outside environment that initially must be colder than the temperature at which ignition of the explosive device is to take place. Ignition occurs when the atmospheric temperature warms to the desired predetermined value.
The circuit set forth in the FIGURE incorporates a battery that is an integral part of the explosive device but whose sole purpose is to provide power to this contrivance to effect ignition of the explosive device. The battery must be a special type with characteristics suitable to the particular application, there being two general classifications that are available. (I) The battery can be continuously active and the power turned on to feed the firing contrivance by means'of switch 13-that closes at the instant of launch. The positive side of the battery is connected in series with the switch [3 through connector 11 to the positive supply lead of the firing contrivance. The negative side of the battery is connected through connector 12 directly to the negative supply lead of the contrivance. Thus, full battery power is applied to the supply leads of the contrivance at the instant of launch. (2) The battery can be a type that initially is inert but is made active at the instant of launch. In this case, the switch 13' is omitted and the positive side of the battery 10 is connected directly to the positive power lead of the circuits through connector 11 and the negative side of the battery 10 is connected directly to the negative supply lead of the circuits through connector T2. In either case, power is applied to the positive and negative supply leads of the circuits at the instant of launch.
Connected between the positive and negative supply leads is I an outside atmospheric temperature sensing thermistor T, in series with an adjustable potentiometer 14 which, in turn, is
' connected in series with a parallel combination comprising a The common connection to the baseof transistor l5,-resisto'r R, and signal point A is by-passed through a capacitor C, to the negative supply lead.
Also connected between the positive and negative supply leads is a capacitor charging circuitcomprisinga resistor R in series with a capacitor-C, whose charge voltage having the time constant R C, appears at signal point B. The common connection at signal point B is connected to the collector of transistor 15.
The emitter of transistor 15 is connected through resistor R, to the negative supply lead of the circuits and is also connected to the emitter of the unijunction transistor (UJT) l6 and to signal point C.
Also connected between the positive and negative supply leads of the circuits is a series combination comprising resistor R in series with base 2 of the UJT 16,. the internal inter-base resistance of UJT l6 existing at base 1, in series with resistance R Base 1 of the UJT 16 is'connected to signal point D and to the gate of a Silicon ControlledRectifier (SCR) 17.
Also connected between the positive and negative supply leads of the circuits is a squib 18 for igniting the explosive device, in series with'the anode-cathode portion of the SCR 17. The squib 18 is an integral part of the explosive device and is external to the firing circuit and is connected directly to the positive supply lead through connector 19 and to the anode of the SCR 17 through connector 20. The cathode of the SCR 11 isconnected directly to the negative supply lead.
Operation of the firing contrivance is initiated by closing the switch 13 or activating the battery 10, caused by launch from the aircraft, and simultaneously exposing the atmospheric temperature sensing thermistor T, to the outside environment. Thus power is applied to the circuits at the instant of launch and simultaneously the atmospheric temperature sensing thermistor T,,, being exposed to the outside environment, starts rapidly cooling to the temperature that is colder than the desired trigger temperature. Response of the thermistor T to the sudden change in temperature from its initial ambient level to the different atmospheric level is very rapid so that it starts accurately sensing the atmospheric temperature within a few seconds.
As power is suddenly applied to the positive and negative supply leads at the instant of launch, capacitor C starts charging through resistor R reaching a trigger threshold level at signal point B in a specified time period determined by the time constant R C However, the capacitor C continues to charge until such time as ignition of the explosive device may occur or until ultimately the charge voltage at point B reaches a value essentially equal to the supply voltage. The charge voltage V, at point B constitutes a collector source voltage for transistor 15, conventionally designated V Full forward conduction through the transistor (I cannot take place until the charge voltage V, at point B reaches its trigger threshold level. Excessive charge voltage at point B, i.e., higher than threshold level, has no significant effect on functioning of the transistor 15. Therefore, heavy conduction through the transistor 15 is prevented as long as the charge voltage V, is lower than threshold level but can be enabled when V, at point B reaches or is higher than threshold level.
The atmospheric temperature sensing thermistor T in series with the adjusting potentiometer 14, in series with an inside temperature stabilizing parallel-series network comprising an ambient temperature sensing thermistorv T in parallel with resistor R all in series with resistorR form an adjustable voltage dividing network whose output, V at point A principally varies in proportion to the outside atmospheric temperature. The signal, V at point A is therefore primarily related to sensing the atmospheric temperature. The atmospheric sensing thermistor T, has a negative temperature coefficient such that its resistance increases as the atmospheric temperature decreases. The higher resistance of T, associated with a lower temperature causes V at point A, coupled through resistor R to be lower when the temperature is lower. The atmospheric temperature sense signal V, at point A is therefore proportional to the outside temperature, i.e., conversely, V at point A rises when the outside temperature rises. The discrete signal, V,,, at point A for a given atmospheric temperature is determined by the adjustment of the variable tap of potentiometer 14. An actuation level for V at point A is thereby selectively related to a specific atmospheric temperature at which ignition of the explosive device is desired. The signal V,,, while responding to outside temperature, is modified in such a way as to stabilize the firing contrivance against change in the ambient inside temperature of the explosive device.
The stabilizing ambient temperature sensing thermistor T in parallel with resistor R all in series with resistor R effects a corrective component in the signal V,, at point A that satisfies the changing actuation level requirement at point A when the ambient temperature of the explosive device changes substantially. The needed compensation is lumped for all of the temperature sensitive circuit components, e.g., transistor 15, UJT l6 and SCR 17. The actuation level at point A increases as the ambient temperature gets lower, and vice versa. The negative coefiicient of thermistor T, causes the compensating component of V, at point A to increase when the ambient temperature decreases. The thermistor T, provides the basic compensation while the resistor R connected in parallel therewith linearizes the correction. Resistor R being in series in the compensating network, limits the degree of compensation in the corrective component of V, at point A. Resistor R, therefore controls the slope of error, plotting atmospheric temperature at which triggering occurs vs. ambient temperature of the total device.
Reiterating, the signal at point A is proportional to the atmospheric temperature, rising from a lower value when the atmosphere is initially colder than the desired trigger temperature, reaching the actuation level at point A at the same instant that the atmospheric temperature has warmed to the desired trigger temperature. The adjusted signal at the moveable contact of the potentiometer 14 is coupled through resistor R to signal point A. Resistor R and capacitor C constitute an RF filter that prevents stray signals from appearing at point A that would be due to RF or radar radiations that the atmospheric temperature sensor may be exposed to in the outside environment.
The transistor 15 is configured in a general way as an emitter follower, that is, the emitter signal V, at point C follows or tends to be identical to the temperature sense signal V,, at point A, conditions permitting. However, V at point C can never exceed a value that is approximately 0.6 volt less than V, at point A. This is due to an inherent voltage drop in the base-to-emitter junction of transistor 15. This is conventionally labeled V representing the drop when the base-toemitter diode" is forward biased. The signal at point C therefore follows the signal at point A with an approximate 0.6 volt offset expressed as: V, V, V This is true providing the capacitor charge signal V at point B has reached its threshold level or above. The signal V at point C is prevented from following the signal, V,,, at point A when the charge signal V at point B has not reached threshold level. Thus, the time delay charge signal V at point B enables or disables the transistor 15 in a manner that allows triggering after a specified time interval but prevents triggering before the end of the specified time interval. The transistor 15 also provides an isolating function that prevents interaction between the temperature sense signal, V at point A and the time delay charge signal, V,,, at point B. Such isolation is necessary to prevent the time-charge function from introducing error in the temperature sensing function, and vice versa.
Since the emitter of transistor 15 is connected through signal point C to the emitter of the UJT 16, the trigger actuation level, V,., at point C is established by the critical emitter breakdown voltage V of the UJT 16. The precise level of breakdown is established by the intrinsic stand-off ratio of the UJT 16. The critical point is a function of the series circuit between the positive and negative supply leads comprising resistor R in series with base 2 of the UJT 16, the inter-base resistance of UJT l6 existing at base 1, in series with resistor R-,. The emitter to base 1 portion of the UJT l6 suddenly goes into conduction at the instant that signal V, at point C reaches the critical value of emitter breakdown V; of UJT 16. At the instant of emitter breakdown in UJT 16, a heavy-current discharge path for the charge in capacitor C is formed, comprising the collector-emitter path ts) through transistor 15, the emitter-base-l path (133. through UJT l6, and mainly resistor R However, the gate of the SCR 17 is in parallel with resistor R and therefore also becomes a branch of the high current discharge path for the charge in capacitor C,.
The charge signal V, at point B must have already reached its threshold level before this chain of events can occur, i.e., the transistor 15 must have been enabled for heavy conduction. At the instant of emitter breakdown in the UJT 16, the voltage at point C drops to a value near the negative supply potential, which in turn forces the voltage at the emitter of transistor 15 downward thus enabling transistor 15 into a state of saturated conduction. This dumps the charge of the capacitor C, into the resistor R and the gate of the SCR 17.
The heavy discharge current causes an IR drop across the parallel combination comprising resistor R and the gate of the SCR 17 so as to produce a positive-going trigger pulse at signal point D. Since this pulse also appears at the gate of the SCR 17, the SCR 17 is turned on. The heavy current drawn through the squib 18 when the SCR 17 is in heavy conduction causes ignition of the explosive device. it is clear that the critical breakdown value V, at point C reflects back and establishes the actuation level of V, at point A.
Assuming the worst case where the ambient temperature of the explosive device is warmer than the atmospheric temperature at which triggering is desired, the atmospheric sense signal V, at point A, at time of launch, is already higher than the actuation level at point A. This is because the atmospheric sensor T is sensing the ambient temperature of the device at time of launch and has not yet had time to respond to the atmospheric temperature. Heavy conduction through transistor 15 cannot occur because the capacitor charge signal V,, is near zero potential and the transistor is not enabled. A path of light current flow does exist, however, because the base-emitter diode of transistor 15 is forward biased. The resulting voltage drop across resistor R is insignificant and does not threaten false triggering. Also the current is of small enough magnitude that heating of the atmospheric sensing thermistor T does not occur, T being a part of the current loop.
Immediately following launch, the charge signal V,, at point B starts to rise and will reach threshold level in a prescribed time interval. At the same time, the atmospheric sense signal V, at point A is rapidly falling because the temperature sensor T has been exposed to the atmospheric environment. The thermal response of the atmospheric temperature sensing thermistor T,, must be fast enough that the temperature sense signal V, at point A drops below actuation level before the time delay charge signal V at point B can reach threshold level. The time constant R C, of the charge signal V, is established by selective choice of the capacitor C, and resistor R, values. The time constant is made long enough to accommodate the thermal response of the atmospheric temperature sensor but at the same time short enough that the explosive device can function in its intended manner. For example, the charge time constant would be made 5 or 6 seconds if experience shows the thermal response of the atmospheric temperature sensor T allows the sense signal V, to go below actuation level within 2 or 3 seconds. The time delay charge signal, V at point B is therefore the safety factor because it enables or disables the transistor 15 and the atmospheric sense signal, V,,, at point A is the prime triggering factor.
Finally, the explosive device ignites when a specified amount of supply power is gated into the firing squib 18. The positive-going pulse at signal point D, as the UJT l6 triggers into conduction, causes the anode-cathode section of the SCR 17 to switch into heavy conduction and latch. This causes essentially the entire supply voltage between the positive and further function.
The switch 13 must be of a type that is actuated inertially or is spring loaded and actuates as the explosive device clears its holder, if a continuously live batter is used. Otherwise, the battery 10 must initially be inert, then become activated by an electrical means received from the aircraft during launch, or by a mechanical means inertially during launch from the aircraft.
It is expected that the ambient temperature of the explosive device will remain relatively constant after launch due to its mass and configuration. The thermal response of the stabilizing thermistor T, therefore does not need to be rapid like the requirement of the atmospheric temperature sensor. The
value of resistor R is chosen while adjusting and testing the accuracy of the atmospheric temperature sensor over a wide range of ambient temperature change. Potentiometer 14 is adjust'ed to cause triggering at a specific desired atmospheric temperature which must be done before the firing contrivance is introduced into the explosive device.
What is claimed is:
l. A temperature sensing firing device for use in an environment comprising;
switch means having an input and output;
time delay means operatively connected to said switch means for biasing said switch means off for a predeter mined time interval after said device is released into a cold environment;
input signal means connected to the input of said switch means operative to sense the environmental temperature and output a signal therefrom that varies in accordance with the environmental temperature;
said switch means producing an output pulse when switched to an on condition; and
means operatively coupled to said switch means and responsive to said output pulse therefrom for causing initiation of the firing device.
2. A temperature sensing firing device as set forth in claim 1 wherein;
said input signal means comprises a thermistor responsive to changes in said environmental temperature.
3. A temperature sensing firing device as set forth in claim 2 and further including;
RF filter means connected between said input signal means and said switching means for filtering out RF signals in the environment.
4. A temperature sensing firing device as set forth in claim 1 and further including;
circuit stabilization means connected in series with said input signal means for compensating and linearising the output of said input signal means over a wide temperature range in the environment.