Dual Spectrum Infrared Fire Detection System With High Energy Ammunition Round Discrimination

Abstract

Disclosed is a multichannel fire or explosion detection system wherein an output fire suppression or control signal is generated in response to fires or explosions which radiate power above a predetermined threshold level. The system includes means which discriminate against explosive fires in a fuel tank or other highly combustible material on the one hand and high energy exploding rounds of ammunition per se which do not subsequently cause a large scale fire. Thus, the present detection system will not generate an output fire suppression or control signal in the event a high energy ammunition round explodes in the vicinity of a fuel tank without igniting and exploding it. Additionally, fail safe detection logic means are provided in the present system and generate a time delayed fire suppression enable signal to thereby enable an output signal gate in the event of a delayed or secondary fire or explosion above a predetermined magnitude.

Description

FIELD OF THE INVENTION

This invention relates generally to fire and explosion detection and suppression systems and more particularly to a fast acting long and short wavelength responsive multichannel radiation detector.

BACKGROUND

Fire detection systems which respond to the sudden presence of either a flame or an explosion to thereby generate an output control signal are generally known. Such systems have a very significant utility, for example, in applications with a variety of explosive or fuel transport or storage tanks, and these systems normally function to trigger the operation of a fire suppression mechanism within a few milliseconds after the initiation of a fire or explosion. It is frequently desirable to wire these fire detectors into military armored personnel carrier vehicles which transport various arms and explosives. A possible fire commonly desired to be suppressed by these types of fire detection systems is one which is produced in a fuel tank by a high energy round of ammunition fired into the fuel tank from a remote location.

PRIOR ART

Hitherto, fire detection and suppression systems of the above type employed one or more photon responsive short wavelength photodetectors. These photodetectors sense the energy from radiation emanating from a fire or explosion, such as infrared or ultraviolet radiation in a particular spectral band and characteristic of certain chemical elements or compounds within the fire or explosion. Signals from these photodetectors are properly compared and processed in order to generate a fire control output signal. A disadvantage with this type of prior art fire detection system is that the system is wholly dependent for its proper operation upon receiving the proper photon energy within a given spectral band and from the true source of interest, namely the fire or explosion to be suppressed. As a result, these prior art fire detection systems are frequently subject to false operation in response to extraneous noise or other source radiation which is not associated with a fire or explosion.

Various circuit techniques have been devised to discriminate against these latter sources of extraneous radiation. But these techniques have not been totally practical or satisfactory for all conditions of operation and in the many noisy environments in which the fire detection system must be capable of operating.

In copending application Ser. No. 375,265 filed June 29, 1973 of Robert J. Cinzori, assigned to the present assignee, there is disclosed a basic dual-channel fire and explosion detection system which operates to eliminate the prior art problem of false triggering in response to extraneous noise radiation in a particular spectral band. Briefly, this operation is accomplished in the above Cinzori copending application by the use of a long wavelength-responsive radiation detection channel and a short wavelength-responsive radiation detection channel. These two channels respond respectively to separate wavelength ranges of incident electromagnetic radiation and thereby eliminate the above possibility of false triggering, either by an extraneous noise source or by chopped radiation from a constant energy source, such as the sun. However, the above Cinzori application does not provide means for discriminating between large explosive fires on the one hand and large explosions which cause no fire on the other. The latter could be, for example, explosions of rounds of ammunition which do not subsequently cause a full scale explosive fire. This discrimination capability may obviously be a desirable feature in certain fire detection applications in view of the cost and effort required to suppress large scale fires.

THE INVENTION

The general purpose of the present invention is to provide further novel and useful improvements to the above identified Cinzori invention and particularly to provide a novel fire detection system which features high energy ammunition round discrimination. This purpose is accomplished by the provision of a three channel infrared radiation detection system in which the three radiation responsive channels are interconnected in a novel output logic configuration. This system provides the above described discrimination between large scale explosive fires on the one hand and explosions of high energy ammunition rounds per se which do not subsequently produce full scale fires or explosions on the other. Our novel system includes different levels of discrimination in that initially, a discrimination is made between the energy generated by an exploding ammunition round impeded by burning and combustion of surrounding matter and the energy generated by the round exploding in the atmosphere when no burning or combustion is present. However, after this initial discrimination, fail-safe logic means are provided in each of the three radiation detection channels to thereby respond appropriately to radiation produced by a secondary or delayed fire which may occur after the above described initial discrimination indicates that only an ammunition round has exploded.

The above purposes are specifically achieved by the provision of a detection system which includes a pair of main signal detection and processing channels which are responsive to fires or explosions above a given pan fire threshold level for generating output fire control logic signals. These two main signal detection channels each include a signal delay stage which introduces a time delay into the radiation responsive signals processed in each channel. These time delayed signals are then combined in the system's output logic to control same and to generate a system output fire control or suppression signal in the event the output logic is properly enabled by further signals processed in another, ammunition round threshold energy channel. This ammunition round threshold energy channel, which is also referred to as the "high energy anti-tank (HEAT) round discrimination channel," or for ease of description herein merely as the "round channel," has its input detector coupled to certain round threshold gates which form part of the round channel's output discrimination logic. This output discrimination logic operates to generate the necessary enabling signals for insuring that the detection system produces an output fire control signal only in the event of a full scale explosive fire. The discrimination logic is connected in a novel manner (to be described specifically below) to the system's main signal channels and to the system's output logic. The signal delays in the main signal channels, together with the logic signals generated in the round channel, are combined in the system's output logic in such a manner as to discriminate against round explosions per se which do not produce a full scale explosive fire.

Accordingly, an object of the present invention is to provide a new and improved explosive fire detection system which discriminates between fires and ammunition round explosions which cause no fires.

Another object is to provide a highly sophisticated, accurate and extremely fast acting fire and explosion detection system of the type described which is insensitive to false triggering, either by extraneous noise sources or by chopped radiation from static radiation sources not associated with a fire or an explosion.

A feature of the invention is the provision of a fire and explosion detection system of the type described which includes various levels of infrared radiation discrimination, including an initial discrimination which is made between fires and round explosions which cause no fire. Thereafter, the system operates in a fail-safe manner to respond to secondary fires possibly resulting from the previously sensed ammunition round explosion.

These and other objects and novel features of the present invention will become more fully apparent in the following description of the accompanying drawings.

DRAWINGS

FIG. 1 is a block diagram representation of the multi-channel fire and explosion detection system according to the invention.

FIGS. 2a-2u illustrate a series of twenty-one voltage signal waveforms at various points in the system of FIG. 1 identified as letters "a" through "u" and for the sensed condition where an anti-tank ammunition round hits an explosive target and causes a full scale explosive fire.

FIGS. 3a-3u illustrate a similar series of 21 voltage waveforms at the various points "a" through "u" in the system of FIG. 1 for the two conditions respectively where: (1) the high energy ammunition round misses the combustible target and causes no explosive fire or explosion, and (2) the condition where the ammunition round misses the combustible target, but subsequently causes a secondary fire at the target.

FIGS. 4a-4u illustrate a series of 21 voltage waveforms at the various points "a" - "u" in the system of FIG. 1 for the condition where the ammunition round hits the target, causes an explosive fire, and yet for some reason generates energy thresholds which are initially inconsistent with having caused an explosive fire.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following description of the system of FIG. 1, the term "tank" refers to a fuel tank and will be used interchangeably with the term "target," inasmuch as the present invention has been recently experimentally and successfully tested for its proper operation in response to exploding fuel tanks toward or into which "anti-tank" rounds of ammunition are fired. Thus, the first case (CASE I) to be described below with reference to FIG. 2 is for the condition wherein the round of ammunition hits the tank, causing a full scale fire. CASE II below describes the condition where the anti-tank ammunition round misses the fuel tank, explodes itself, but causes no resultant fire in the fuel tank towards which it was fired. For this condition, the explosion of the ammunition round is outside of the fuel tank, rather than inside, and it will result in a radiated power which rapidly peaks to a maximum (See FIG. 3a) and then drops off rather sharply, all over a relatively short period of time, i.e., considerable energy is dissipated over a short period of time. This latter case will be described below with reference to FIG. 3.

Reference will also be made to FIG. 3 in the description of CASE III below wherein the ammunition round explodes outside of the fuel tank, and yet still produces a delayed or secondary fire. This is possibly caused by the fuel tank fracturing and the leaking fuel igniting at some later time. And CASE IV, which is described below with reference to FIG. 4, describes that condition wherein the ammunition round hits the fuel tank, thus causing a full scale explosive fire but for some reason initially appears to have exploded outside of the fuel tank (an apparent CASE II above). All of these cases are described in detail immediately following the brief identification of the various electronic stages of the functional block diagram in FIG. 1.

Referring now to FIG. 1, the two main radiation detection channels 12 and 14 correspond in general to the two radiation detection channels 12 and 14 in the above-identified Cinzori application. These channels are connected as shown to the system's output logic circuitry 16. A third ammunition round responsive channel 18 is also connected as shown to drive the output logic circuitry 16, and the round channel 18 includes therein certain round discrimination logic 20 to be operationally described in detail.

The two channels 12 and 14 are also referred to herein as "pan fire" channels, inasmuch as these channels do not discriminate between explosive fires and exploding rounds of ammunition, and will, in fact, respond to minimum threshold level or "pan" fires to generate output signals on lines 22 and 24 which lead into the output logic 16. These channels 12 and 14 process, respectively, the 0.9 micron and the 10 micron wavelength radiation which is passed by a pair of optical filters 26 and 28 with these respective wavelength pass bands. These optical filters 26 and 28 are of conventional design and, therefore, are not described in detail herein.

Briefly, the purpose of these two pan fire channels 12 and 14, which are capable of operating in the 0.7 - 1.2 micron and the 7 - 30 micron wavelength ranges, respectively, is to rapidly respond to infrared radiation from relatively low level fires or explosions and in turn generate output enable signals on lines 22 and 24. Simultaneously, these channels 12 and 14 operate to prevent false triggering of the system either by extraneous noise in a certain spectral band or by chopped radiation from a constant energy source. The specific operation of these two channels is discussed in detail in the above Cinzori application. The 0.9 micron pan fire channel 12 includes an input infrared radiation detector 30 which is optically coupled to the 0.9 micron narrow band pass filter 28, and advantageously this detector 30 is a silicon photodiode which has a spectral response in the 0.7 - 1.2 micron range. This photodiode detector 28 is connected to an output amplifier stage 32 which amplifies the detector's small signal detection voltage and applies the amplified signal to the input of an inverter stage 34. The inverter 34 is in turn connected through a threshold gate 36 which drives a time delay stage 38.

The 10 micron pan fire channel 14 advantageously utilizes a thermopile or equivalent detector 40 which is operative to respond to 10 microns of infrared radiation. The detector 40 is optically coupled to the 10 micron filter 26, and this detector 40 typically will have a spectral wavelength response in the range between 7 and 30 microns. The small signal output detection voltage from the detector stage 40 is coupled to a frequency compensating amplifier 44 which, in turn, is coupled to an inverter stage 46. The inverter stage 46 has its output signal coupled through a threshold gate 48 into a time delay stage 50, and the threshold gates 36 and 48 are operative, as will be seen, to generate the step function output pulses 52 and 54 as soon as the rapidly rising input signals applied thereto reach a certain minimum threshold level. These pulses 52 and 54 are also illustrated in FIGS. 2f and 2g, respectively, and the leading edges of these pulses correspond to the pan fire threshold switching levels of gates 48 and 36 respectively. These latter thresholds are noted as PT.sub.1 and PT.sub.2 in FIGS. 2b and 2c respectively. The delayed output pulses from stages 38 and 50 are coupled, as mentioned, into first and second inputs 24 and 22, respectively, of a first output AND gate 56. The third and fourth input connections 58 and 60 of the AND gate 56 are connected as shown to the round channel 18 and controlled thereby in a manner to be described below.

The round channel 18 includes a 0.9 micron wavelength optical radiation filter 62 which is suitably coupled to the input of an infrared radiation detector 64, such as a silicon photodiode. Wavelengths other than 0.9 microns can be used to accomplish the discrimination according to the invention. However, 0.9 microns was chosen because photodefectors with an 0.9 micron peak response are readily available and the maximum HEAT round energy is in the general spectral vicinity of 0.9 microns. The silicon photodiode detector 64 may be identical to the photodiode detector 30, and in fact the stages 28, 30, 32, and 34 can be used in lieu of the stages 62, 64, 66 and 68. However, this scheme involves the use of more costly associated signal processing electronics and it is not the preferred system. The detector 64 has its output signal coupled through an amplifier stage 66 and into an inverter stage 68, and the output signal of the inverter 68 is, in turn, connected to the respective inputs of first and second level round threshold gates 70 and 72, which constitute the input stages of the round discrimination logic 20. The first level threshold gate 70 generates an output pulse 74 when the round detection input voltage signal applied thereto reaches a first preestablished threshold level as will be described. Similarly, the second higher level threshold gate 72 produces an output voltage pulse 76 when the input detection voltage applied thereto crosses a second threshold level which is higher than that of the first level threshold gate 70. The first and second threshold levels of the two gates 70 and 72, respectively, are referenced at points 78 and 80, respectively, in FIG. 3a.

The round channel 18 further includes a direct signal connection 82 between the output of the second level threshold gate 72 and a first AND gate 84, and it also includes a second signal path into the AND gate 84, including a monostable multivibrator 86 and a delay stage 88 connected as shown. A second AND gate 90 is connected as shown between the input and output connections for the monostable multivibrator 86, and the output of the second AND gate 90 is coupled through an inverter stage 92 and into the input of a signal crossover delay stage 94.

The output of the first AND gate 84 is connected to the input of a 25 second timing multivibrator 96 which, in turn, has one of its two digital outputs, Q, directly connected to the fourth input connection 60 of the AND gate 56. The other complementary output Q of the multivibrator 96 is coupled through a delay stage 98 and then to one input 100 of a second output AND gate 102. The other input 104 of the AND gate 102 is directly connected as shown to the output connection for the first level threshold gate 70, and the output connections 106 and 108 of the two AND gates 102 and 56, respectively, are connected to the two input connections for the system's output OR gate 110.

In a functional and operational sense, the portion of the system including the monostable 86, the AND gate 90, the inverter 92 and the delay stage 94 can be considered to constitute a first pulse delay generating means. Similarly, the delay stage 88, the AND gate 84, the monostable 96 and the delay stage 98 can be considered to constitute a second pulse delay generating means.

Upon a careful inspection of the voltage waveform diagrams in each of the FIGS. 2, 3 and 4, the novel round discrimination operation of the detection system of FIG. 1 will become apparent. Some of the voltage waveforms in FIGS. 2, 3 and 4, and appearing at various points in the circuitry of FIG. 1, will not be specifically mentioned in the following description. The consecutive letters a through u denoted in FIG. 1 reference those circuit points in the system of FIG. 1 at which the voltage waveforms in each of FIGS. 2a - 2u, 3a - 3u and 4a - 4u appear for the particular operations (CASE I, CASE II, CASE III or CASE IV) described below. Those voltage waveforms in FIGS. 2, 3 and 4 which are particularly significant to a full and complete understanding of the operation of FIG. 1 will be discussed in some detail hereinafter.

Referring now to both FIGS. 1 and 2, consider a first possible situation, CASE I, where the ammunition round fired hits the fuel tank and causes an explosive fire. For this condition, the slowly rising signal voltage in FIG. 2a corresponds in amplitude to the power radiated from the exploding round and fuel in the tank. Since the round of ammunition is exploding inside a fuel tank, the infrared radiation emitted therefrom begins building relatively slow and this corresponds to an energy transfer from the ammunition round to the fuel and to the combustion taking place therein. This produces a corresponding detection voltage at the output of the detector 64 which, when amplified in stage 66, exceeds neither the first level threshold of the gate 70 nor the second level threshold of the gate 72 within the time required to allow the round channel 18 to respond to this radiation. For this reason, the logic levels in the circuitry section 20 at the outputs of the first and second level threshold gates 70 and 72 remain unchanged, and for this condition, the input connections 58 and 60 of the AND gate 56 are always enabled for a CASE I situation.

Following the initiation of the CASE I explosion in the fuel tank, the radiation responsive signal voltages in FIGS. 2b and 2c at the inputs of the threshold gates 48 and 36, respectively, generate the slightly delayed output pulses 52 and 54 as indicated in FIGS. 2f and 2g respectively. The delays in these pulses correspond, of course, to the pan fire thresholds PT.sub.1 and PT.sub.2 of gates 48 and 36, and for this case, there is no change in the signal levels at points d and e in FIG. 1.

The sharply rising pulses 52 and 54 drive the 4 millisecond delay stages 50 and 38, respectively, to provide the delayed signals illustrated in FIGS. 2i and 2j, respectively. When these voltage signals in FIGS. 2i and 2j swing high to a logical "1" level after the 4 millisecond delay indicated, all of the inputs 24, 22, 58, and 60 of the AND gate 56 are enabled to, in turn, produce an output logical 1 signal (FIG. 2t) on line 108 and at one input of the system's output OR gate 110. For CASE I, the quiescent logic level at the other input 106 of the OR gate 110 is low at a logical "0" and, thus, an output fire suppression or control signal (FIG. 2u) is generated at the output terminal 114 of the OR logic gate 110. During this time, the logic signals in FIG. 2h and in FIGS. 2k through 2s remain unchanged as a result of the signal level stability in the round channel 18. So the output signal in FIG. 2t from the AND gate 56 is generated immediately after the 4 millisecond delays of both of the two signals in FIGS. 2i and 2j, respectively. The output signal voltage in FIG. 2u at the output of the OR gate 110 is processed in electronics (not shown) to trigger a fire suppression or control mechanism (not shown). Such a mechanism may, for example, control a plurality of valves on a pressurized bottle of freon gas.

Consider now the next condition (CASE II) where the round of ammunition misses the fuel tank completely and causes no fire. For this condition, of course, it is desired that no output signal be generated at the output of the OR gate 110, and in a true CASE II condition the explosion per se of the round of ammunition produces no secondary fire. However, in the absence of the round channel 18, this operation would not be possible. For CASE II, the signal at point a in FIG. 1, and shown in FIG. 3a, rises rather sharply as shown up through the first and second round threshold levels 78 and 80, and then begins to taper off rather sharply back through these round threshold levels, as indicated. This signature indicates that the energy from the round is being transferred into the atmosphere or air and not into a combustible medium, such as gasoline or oil. Thus, in this case all of the round explosion energy is dissipated rather quickly.

When the round of ammunition explodes, the "pan fire" voltatages in FIG. 3b and 3c are generated as in the previous CASE I, and these signals, in turn, generate the output pulses 52 and 54, shown also in the voltage waveforms of FIGS. 3f and 3g. These pulses 52 and 54 again initiate the respective switching actions in the 4 millisecond delay networks 50 and 38 which, in turn, produces the delayed pulses shown in FIGS. 3i and 3j, as in CASE I above. Thus, at this point in a CASE II operation, the inputs 24 and 22 of the AND gate 56 are enabled. However, prior to the occurrence of the leading edges 116 and 118 of the delayed pulses in FIGS. 3i and 3j, respectively, the voltage of FIG. 3a crossed the first round threshold level 78 to thereby generate the leading edge 120 of the output voltage pulse in FIG. 3e. This pulse in FIG. 3e appears as the output pulse 74 of the first level threshold gate 70 in the round channel 18, and has a duration corresponding to the time that the signal in FIG. 3a is above the first threshold level 78. Therefore, the input 104 to the AND gate 102 is now enabled.

Now, leaving the operation of the AND gate 102 for the moment, consider the fact that the leading edge 122 of the pulse in FIG. 3d is generated as the signal voltage in FIG. 3a crosses the second round threshold level 80 therein as shown. The leading edge 122 of the square wave pulse in FIG. 3d is followed by its trailing edge 124 thereof, corresponding to the time that the signal in FIG. 3a crosses back through the threshold level 80. The leading edge 122 in FIG. 3d triggers the monostable multivibrator 86, thus creating the 5 millisecond pulse shown in FIG. 3h. Since the logic levels in FIGS. 3d and 3h are at a logical 1, the point k will now swing to a logical 1, be inverted in stage 92 and cause point n to swing to a logical 0. Stage 94 will delay the latter pulse at point n by 0.5 milliseconds and drive point o to a logical zero, thereby disabling the AND gate 56 before the occurrance of leading edges 116 and 118 in FIGS. 3i and 3j. Thus, the AND gate 56 cannot be enabled for the duration of this disabling pulse at the input connection 56 of this AND gate 56.

When the trailing edge 126 of the pulse in FIG. 3o returns this pulse to its high logical level as shown, then the voltage levels in FIGS. 3i, 3j and 3o all place lines 24 and 22 and 58 into the AND gate 56 at a high or a 1 logical level. However, the AND gate 56 is still disabled by reason of the fact that input connection 60 thereto was switched to a logical zero level just 0.2 milliseconds earlier. This can be shown as follows: When the voltage pulse in FIG. 3d triggered the 5 millisecond duration monostable multivibrator 86, the leading edge of the voltage pulse in 3h was delayed for 4.8 milliseconds by he delay stage 88 and then coupled into one of the inputs 128 of the AND gate 84. The outer input 82 of the AND gate 84 is already enabled at ths time by the voltage in FIG. 3d, so the pulses in FIGS. 3-l and 3d now enable the AND gate 84 prior to the time that the voltage in FIG. 3a cross back through the second threshold level 80. At this point in time, the output pulse shown in FIG. 3m is generated to energize the 25 second monostable multivibrator stage 96 so as to drive its output waveform Q in FIG. 3p from a high logical level to a low logical level to thereby maintain the AND gate 56 disabled for at least 25 more seconds. If the detection system in FIG. 1 is now actually seeing a CASE II condition described above, then the voltages in FIGS. 3i and 3j will be returned to their low or zero logical levels by the end of this 25 second period. Thus, in the absence of a secondary fire, it will not be possible for the AND gate 56 to be enabled after the voltage in FIG. 3p returns again to its high logical state after 25 seconds.

Consider now the CASE III situation where the round of ammunition explodes outside the fuel tank to generate the rapidly rising and falling voltage in FIG. 3a, but for some reason causes a delayed or "secondary" fire in the fuel tank. This could be caused, for example, by flack piercing the fuel tank and causing a short delay in the fuel leaking therefrom, which subsequently ignites. This secondary fire will, after some time, return the voltage signal in FIG. 3a back to the first threshold level 78 as indicated at point 130 in FIG. 3a. When this happens, the positive going output pulse 74 (FIG. 3e) at the output of threshold stage 70 will enable the input 104 of the AND gate 102. The Q output of stage 96 goes to a logical 1 level at the beginning of the 25 second pulse duration in FIG. 3q, and the delay gate 98 delays this signal for another 65 milliseconds. This causes the output of stage 98 to subsequently swing to a logical 1 as shown in FIG. 3r, so that the AND gate 102 is now enabled at the leading edge 130 of the pulse in FIG. 3r. The output pulses in FIGS. 3s and 3u are generated for this CASE III situation when the voltage in FIG. 3a once again crosses the first threshold level at point 131.

At the end of the 25 second pulse duration of the monostable multivibrator 96, the Q output of this stage 96 (FIG. 3q) returns to its low logical condition to disable the AND gate 102, and the Q signal on line 60 leading into the AND gate 56 returns to its high logical level to now again enable this input and prepare the fire detection system for another detection operation. Now inputs 58 and 60 of AND gate 56 are again high, so that the main signal processing channels 12 and 14 are now ready to respond to appropriate wavelength infrared radiation to once again enable the AND gate 56.

Referring now to FIG. 4, consider a CASE IV situation wherein an ammunition round hits the fuel tank and causes an explosive fire therein, but for some reason also causes the voltage in FIG. 4a to exceed both the first and second level thresholds as indicated at points 132 and 134 in FIG. 4a. However, for this CASE IV condition, the minimum energy requirement (See FIG. 3a) of CASE II above is not satisfied, since the round did explode in whole or in part in the tank, or at least hit the tank in some fashion. The latter condition causes the signal in FIG. 4a to fall rapidly back through the second and first round threshold levels 78 and 80 as indicated at points 138 and 136, respectively. Thus, for CASE IV, the minimum energy requirement for the "round missed-no fire" CASE II situation above is not satisfied; but the round threshold levels 78 and 80 noted above are exceeded. Thus, the electronics of FIG. 1 must now be capable of generating an output fire control signal (FIG. 4u) for this condition, since a full scale fire and explosion is produced.

For this CASE IV condition, the signals in FIGS. 4b and 4c are generated immediately following the explosion of the round. When the pan fire thresholds PT.sub.1 and PT.sub.2 of channels 14 and 12 are exceeded, as noted in FIGS. 4b and 4c, then the corresponding signal voltages in FIGS. 4f and 4g are driven to a high logical level as indicated. The voltage pulses 52 and 54 (FIGS. 4f and 4g) at the outputs of the threshold gates 48 and 36, respectively, are each delayed 4 milliseconds in the delay stages 50 and 38, and they subsequently appear as the delayed signals in FIGS. 4i and 4j as shown at the input 22 and 24 of the AND gate 56. Thus, at the end of the 4 milliseconds delay indicated in FIGS. 4i and 4j, the lines 22 and 24 leading into AND gate 56 are in the high or "enabled" state.

Consider now the signal level condition on line 58. When the second round threshold level at point 134 in FIG. 4a was initially crossed, the AND gate 90 was temporarily enabled to thereby generate the leading edge 140 of the pulse shown in FIG. 4k. Thus, voltage level in FIG. 4k is temporarily driven high and inverted in stage 92, so that the delayed signal input 58 to AND gate 56 is temporarily disabled for a CASE II situation. Line 60 is also high, so at this time only line 58 into AND gate 56 is disabled. However, upon the return of the signal in FIG. 4a back through the second threshold level 80 and upon the occurrence of the trailing edge 142 of the delayed pulse in FIG. 4o at the output of delay stage 94, the signal level on line 58 is again driven high at a time just prior to the occurrence of leading edges 144 and 146 of the pulses in FIGS. 4i and 4j, respectively. Thus, upon the occurrence of the leading edges 144 and 146 of these latter pulses, all four inputs 22, 24, 58 and 60 of the AND gate 56 are enabled, and output signals will be generated as shown in FIGS. 4t and 4u.

Since the voltage pulse in FIG. 4h is delayed 4.8 milliseconds in the delay stage 88 and appears as the narrow delayed pulse in FIG. 4-l at the input 128 of the AND gate 84, then this pulse in FIG. 4-l first occurs at a time when the voltage pulse in FIG. 4d on line 82 has terminated at its trailing edge 148. This, of course, is the result of the signal in FIG. 4a crossing back through the second round threshold level as noted at point 136. Therefore, the lines 128 and 82 are never simultaneously at a high logical level in CASE IV, and thus the AND gate 84 is not enabled for this operation.

Thus, the AND gate 84 output signal as shown in FIG. 4m remains at a logical 0 level for a CASE IV condition, and the 25 second monostable multivibrator stage 96 is never enabled for this CASE IV condition. Therefore, the output signal voltage in FIG. 4p remains continuously at the high logical level, and the output voltage pulse in FIG. 4t is generated simultaneously with the occurrence of the leading edges 144 and 146 of the pulses in FIGS. 4i and 4j, respectively The pulse in FIG. 4t generates the corresponding output pulse in FIG. 4u at the output of the OR gate 110. Thus, the fire detection system described above is constructed to provide a fire control or suppression signal as shown in FIG. 4u, notwithstanding the fact that the round thresholds at points 132 and 134 in FIG. 4a have been exceeded.

It will be appreciated by those skilled in the art that the present invention is not limited to the particular types of radiation detectors used or to the specific spectral bands disclosed. Furthermore, the particular logic techniques disclosed could obviously be modified by a logic designer to vary the switching response of the system in order to meet certain fire detection application requirements.

It should also be understood that the present invention is not limited in its use to any particular type of output fire suppression means. One suitable technique for suppressing fires and explosions which is most compatible for use with the detection system described above utilizes a plurality of pressurized freon gas bottles, each of which are electro-mechanically driven by a count down register (not shown) at the output of the above described system. Each successive output pulse generated by the system can be utilized to drive the count down register (which is of conventional design), so as to activate a separate bottle each time there is a fire or explosion. In this manner the system can be used to fully guard against a condition where the system operates to extinguish an initial fire, and then is not equipped for further response to a delayed or secondary fire, or even to a second primary fire which occurs later at the same location. As a practical matter, the pressurized bottles of freon are presently commercially available and contain the necessary gas exit orifices, so that the freon gas exits these orifices under a very high pressure and completely empties the bottle in about 20 milliseconds or less.

It is also to be understood and it will be appreciated by those skilled in the digital electronics arts that the novel energy discrimination techniques and concepts of this invention may be carried out using only the round channel of FIG. 1 or some design modification thereof. For example, if it is desired to only discriminate between exploding ammunition rounds whose released energy is unsuppressed (on the outside of the fuel tank) and exploding ammunition rounds whose released energy is totally or partially suppressed (exploding inside the fuel tank or otherwise suppressed in energy by the fuel tank), then the round channel alone is capable of performing this energy discrimination function. Thus, the round channel will either respond to full scale explosive fires and generate an output signal after a predetermined period of time; or the round channel will generate inhibit signals when minimum energy requirements are met and then still produce an output fire control signal after the termination of the inhibit signal in the event that a secondary or delayed full scale explosive fire is caused. In the absence of this full scale explosive fire after the explosion of an unsuppressed ammunition round, then the inhibit signals will properly prevent output fire control or suppression signals from being generated. Of course, when only the round channel 18 is used, then it is subject to false operation; for example, by chopped radiation by a constant energy source, i.e., the sun. This single channel operation may obviously be desirable in certain applications which have other measures for preventing such false operation.

Claims

What is claimed is:

1. A system for making energy dissipation comparisons while detecting fires and explosions above predetermined power thresholds within predetermined time periods including:

a. low threshold radiation channel means responsive to minimum power fires or explosions for generating output enable signals,

b. high threshold radiation channel means responsive to fires or explosions which exceed a predetermined energy threshold for generating inhibit signals of a predetermined time duration or durations, and

c. output logic gate means coupled to both said low and high threshold radiation channel means for receiving both said enable and inhibit signals, said output logic means being operative to generate an output fire control or suppression signal after the removal of said inhibit signals therefrom, whereby relatively short lived fires or explosions within the time duration of said inhibit signals are prevented from triggering an output fire detection or control signal.

2. The system defined in claim 1 wherein said high threshold radiation channel means includes:

a. a threshold gate of a selected switching threshold connected in the signal path of said high threshold channel means and operative to generate logic signals of a time duration dependent upon the energy received from a fire or explosion,

b. first pulse delay generating means connected between said threshold gate and one input of said output logic gate means for generating a first inhibit signal of a first predetermined time duration, and

c. second pulse delay generating means coupled between said threshold gate and another input of said output logic gate means for generating a second inhibit signal of a second predetermined time duration, whereby said output logic gate means is enabled to generate a fire control or suppression signal after the termination of said inhibit signals and in the continued presence of enable signals from said low threshold radiation channel means.

3. The system defined in claim 2 which further includes:

a. a second threshold gate having a second threshold switching level and connected to receive the radiation responsive detection signals from the main signal path of said high threshold channel means to thereby generate enable logic pulses of another, different predetermined time duration, and

b. a second output logic gate means connected to receive both logic signals from said second threshold gate and from said second pulse delay generating means for thereby generating output fire control or suppression signals when said second output logic gate means is enabled, thereby imparting an additional level of energy discrimination to said high threshold radiation channel means.

4. The system defined in claim 3 which further includes an output OR gate connected to receive the output signals from both said first and second output logic gate means for generating the system's output fire control or suppression signals upon receiving enable signals from either of said first and second output logic gate means.

5. The system defined in claim 1 wherein said low threshold radiation channel means includes:

a. long wavelength channel means responsive to radiant energy in a predetermined spectral band of electromagnetic radiation and received from a fire or explosion for generating one output logic signal,

b. short wavelength channel means responsive to radiant energy in another predetermined spectral band and received from said fire or explosion for generating another logic signal, and

c. means coupling said one and another output logic signals to said output logic gate means for properly enabling same during the presence of a fire or explosion above a predetermined minimum threshold level.

6. The system defined in claim 5 wherein said coupling means includes first and second signal delay stages connected in the signal paths of said long and short wavelength channel means, respectively, and further connected to first and second inputs of said first output gate means for providing delayed enable signals thereto, whereby said first output gate means is not immediately enabled after the initiation of said fire or explosion, thereby allowing said high threshold radiation channel means to properly respond to predetermined energy levels of a radiation received from said fire or explosion and thereby temporarily inhibit said first output gate means for predetermined time durations.

7. The system defined in claim 6 wherein:

a. said long wavelength channel means is responsive to radiant energy in a predetermined spectral band above about 6 microns of electromagnetic radiation, and

b. said short wavelength channel means is responsive to radiant energy in a predetermined spectral band less than about 2 microns of electromagnetic radiation.

8. The system defined in claim 7 wherein said long wavelength channel means is responsive to radiation in the 7 - 30 micron range and said short wavelength channel means is responsive to radiation in the 0.7 - 1.2 micron range, and said high threshold channel radiation means is responsive to short wavelength radiation in the 0.7 - 1.2 micron range.

9. The system defined in claim 8 wherein:

a. both said high threshold radiation channel means and said short wavelength radiation channel means includes a photodetector connected at each input thereof, and

b. said long wavelength channel means includes a thermopile detector connected at its input and responsive to a radiation in a spectral band above about 6 microns of electromagnetic radiation.

10. The system defined in claim 9 wherein said high threshold radiation channel means includes:

a. a threshold gate of a selected switching threshold connected in the signal path of said high threshold channel means and operative to generate logic signals of a time duration dependent upon the energy received from a fire or explosion,

b. first pulse delay generating means connected between said threshold gate and one input of said output logic gate means for generating a first inhibit signal of a first predetermined time duration, and

c. second pulse delay generating means coupled between said threshold gate and another input of said output logic gate means for generating a second inhibit signal of a second predetermined time duration, whereby said output logic gate means is enabled to generate a fire control or suppression signal after the termination of said inhibit signals and in the continued presence of enable signals from said low threshold radiation channel means.

11. The system defined in claim 10 which further includes:

a. A second threshold gate having a second threshold switching level and connected to receive the radiation responsive detection signals from the main signal path of said high threshold channel means to thereby generate enable logic pulses of another, different predetermined time duration, and

b. a second output logic gate means connected to receive both logic signals from said second threshold gate and from said second pulse delay generating means for thereby generating output fire control or suppression signals when said second output logic gate means is enabled, thereby imparting an additional level of energy discrimination to said high threshold radiation channel means.

12. The system defined in claim 11 which further includes an output OR gate connected to receive the output signals from both said first and second output logic gate means for generating the system's output fire control or suppression signals upon receiving enable signals from either of said first and second output logic gate means.

13. A fire or explosion detection system for making predetermined energy dissipation comparisons including:

a. threshold radiation channel means responsive to fires or explosions which generate a predetermined amount of energy within a predetermined period of time to in turn generate inhibit signals, and

b. output gate means coupled to said radiation channel means and responsive to said inhibit signals to prevent an output fire suppression from being generated during the presence of said inhibit signals, whereby said channel is operative to generate said fire suppression signals after the termination of said inhibit signals or in the event that no inhibit signals are generated.

14. The system defined in claim 13 wherein said threshold radiation channel means includes logic means for generating an inhibit signal whose time duration is proportional to the time that the radiated power from said fire or explosion is above a predetermined threshold level, whereby the variable duration of said inhibit signals may be logically compared with other fixed signal delays to prevent predetermined energy levels reached in predetermined minimum times from generating an output fire control or suppression signal.