Count discriminating fire detection system

A fire detector senses the change in a physical parameter indicative of a fire such as smoke, heat or the like and produces detection pulses in synchronism with an oscillator circuit when the change in the physical parameter exceeds a predetermined amount. A counting means counts the detection pulses and produces an output which triggers an alarm circuit when a predetermined number of consecutive detection pulses are counted. The count of the counting means is reset by a reset means whenever the detection pulses are nonconsecutive, that is, whenever an oscillator pulse is received without receipt of a corresponding detection pulse. By this means intermittent changes in the physical parameter which indicate some false alarm signal rather than a real fire do not produce the required number of consecutive detection pulses and do not set off the alarm circuit. On the other hand when a real fire occurs the circuit always counts detection pulses from the beginning of the detection of a fire because the counting means is reset each time a series of consecutive detection pulses less than the predetermined number ends.

BACKGROUND OF THE INVENTION 
The present invention relates to a count discriminating fire detection 
system in which a predetermined number of pulses obtained from the output 
of a fire sensor are counted to issue an alarm, and more particularly to a 
system including counting means which is reset whenever a series of 
consecutive detection pulses less than the predetermined number ends. 
A type of prior count discriminating fire detection system uses a capacitor 
which is charged to a predetermined voltage by applying the detection 
output or the pulses produced by a fire sensor to energize an alarm 
circuit. However, various disturbance signals or outputs which may be 
produced from a fire sensor when false alarm triggers arise such as 
smoking, the burning of small pieces of paper, steaming and so on also 
charge the capacitor. Therefore, this capacitor should be periodically 
discharged. Complex circuitry is required to periodically discharge the 
voltage stored in the capacitor thus employed. 
Another type of such a system is disclosed in U.S. Pat. No. 3,842,409, 
which uses a shift registor and a capacitor in combination. A control 
circuit is connected between this capacitor (which is also connected to a 
data terminal of the shift registor) and an output terminal of the fire 
sensor to repetitively charge and discharge the capacitor, so that the 
shift registor may be reset by a clock pulse upon disappearance of the 
data signal at the data terminal in response to the discharge period of 
the capacitor. This system should be improved because of its complexity. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a storage fire 
detection system comprising counting means and reset means in which the 
counting means can be reset by the reset means upon discontinuance of 
continuous detection pulses from a fire sensor at a number smaller than a 
predetermined number. 
It is another object of the invention to provide a storage fire detection 
system in which detection pulses applied to the counting means are 
substantially synchronized with oscillating pulses which reset the 
counting means. 
Still another object of the present invention is to provide a storage fire 
detection system in which the counting means repeats its counting 
operation without time loss after the detection pulses applied to the 
counting means discontinue. 
Distinction between a real fire and above-mentioned false alarm triggers 
which frequently arise is effectively made in a statistical manner in that 
discontinous pulses will ordinarily correspond to false alarms and 
continuous pulses to a real fire. Such pulses are obtained from or 
produced from the output of a fire sensor, which correspond to physical 
changes of more than a predetermined amount in the monitored parameter 
such as smoke, heat and the like. Especially, fire sensors which operate 
with pulse energy can directly produce output pulses suitable for this 
purpose. Moreover, continous pulses of from 3 to 12 in number having pulse 
intervals 2 sec. to 5 sec. may reliably distinguish the detection of a 
fire from various false alarms. The preferred combination of the number of 
continuous pulses and the pulse intervals is selectively set in accordance 
with the location of the respective fire sensors and the possible kinds of 
fires, for example, oil, gas, other ordinary fires and the like. 
The system according to the invention can reset the counting means when the 
pulses applied thereto become discontinuous. Moreover, after a particular 
counting operation of the counting means is stopped and reset by a reset 
pulse, successive counting operations start without loss of any pulse 
supplied from the fire sensor so that all of the pulses are applied to and 
counted by the counting means. 
In the initial stages of a fire during which discontinuous pulses are 
produced, the counting means in repetitively reset and counts the pulse or 
pulses every time the pulses discontinue, and the counting operation 
repeats until the predetermined number of continuous pulses are produced 
and applied thereto. Thus, the predetermined number of continuous pulses 
which are produced for the first time when a fire arises can be counted by 
the counting means without loss of any pulses thereby to issue an alarm. 
Further, the system uses a common oscillator circuit to produce or form the 
pulses for applying to the counting means and to make the reset pulse for 
applying to the counting means, so that the two different pulses can be 
substantially synchronized each other. Although this method causes a time 
difference between the two pulses, it is too small to affect the operation 
of this system.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The storage fire detection system according to the invention illustrated in 
FIG. 1 includes a fire detector 1 which produces a d.c. output when it 
detects a physical change more than a predetermined amount. This detector 
has an amplifying transistor such as a field effect transistor connected 
to an output terminal of a fire sensor such as an ionization smoke sensor. 
An oscillation circuit 2 produces pulses at a constant frequency having a 
pulse interval suitable for detection of the physical changes of a fire 
according to the particular type of sensor. An AND gate 3 has two input 
terminals connected to an output terminal of the fire detector 1 and the 
oscillator circuit 2, respectively and the d.c. output of the fire 
detector 1 is converted into corresponding detection pulses "b" by the 
oscillating pulses "a" according to the logical product of the AND gate 3. 
The detection pulses "b" are applied to a counting means 4. Furthermore, a 
reset circuit 5 is used which has two input terminals connected to the 
oscillator circuit 2 and to the output terminal of the AND gate 3, 
respectively. This reset circuit 5 can not produce a reset pulse when both 
detection pulse "b" and oscillating pulse "a" are applied concurrently 
thereto, but can produce and apply a reset pulse "c" to the reset terminal 
of the counting means 4 when no detection pulse "b" is applied to the 
reset circuit 5 despite the application of a pulse "a". The counting means 
4 can be reset whenever no detection pulse "b" is applied to the reset 
circuit 5. 
The counting means can produce an output "d" effective to energize an alarm 
circuit 6 after it has counted a predetermined number of continuous 
detection pulses "b". This number is selectively predetermined as 
mentioned above, for example, as four in the respective time charts 
illustrated in FIGS. 2, 3 and 4. In FIG. 2 the reset circuit 5 generates 
the reset pulse "c2" and applies it to the counting means 4 when the 
oscillating pulse "a4" enters the reset circuit 5, because only two 
continuous detection pulses "b1" and "b2" enter the counting means but no 
detection pulses are produced thereafter. While no detection pulse "b" is 
applied to both the counting means 4 and the reset circuit 5, the 
oscillating pulses "a4", "a5" and etc. which are applied only to the reset 
circuit 5 continue to reset the counting means 4. This example will 
correspond to false alarm triggers such as smoking, the burning of small 
pieces of paper and etc., since the number of continuous detection pulses 
"b" is less than the predetermined number, that is, the physical change 
detected by the fire sensor is intermittent and only exceeds the 
predetermined amount thereof for a relatively short time. 
When a real fire arises, continuous detection pulses "b1", "b2", "b3" and 
"b4" are successively counted by the counting means as illustrated in FIG. 
3. After counting up to the predetermined number this counting means 4 
produces an output "d" to energize the alarm circuit 6 for developing an 
alarm current "e". The time chart in FIG. 4 illustrates that after a 
discontinuous pulse "b1" due to a disturbance signal or a small fire which 
is not yet identified as a real fire or a false alarm has been produced 
and counted by the counting means 4, the counting means 4 is reset by the 
reset pulse "C2". Immediately the counting means 4 begins to count a first 
detection pulse "b2" of a continuous set of detection pulses "b2", "b3", 
"b4" and "b5" thereby to produce the output "d". Thus, even if randomly 
discontinuous pulses "b" are applied to the counting means 4, the counting 
operation of this counting means does not delay nor miss any first 
detection pulse "b" of continuous sets of pulses. 
The system illustrated in FIG. 5 uses a fire detector 1 which operates with 
pulse energy. This pulse source uses the oscillator circuit 2 so that the 
detection pulse output "b" of this fire detector is substantially 
synchronous with the oscillating pulse "a". Although time differences do 
occur between the detection pulse output "b" and the oscillating pulse 
"a", they are negligible or easily controlled. 
The storage fire detection system according to the invention illustrated in 
FIG. 6 uses a counter or a shift registor as the counting means 4 and also 
an exclusive-OR gate as part of the reset circuit 5. The input-output 
relation of the exclusive-OR gate is as follows: 
______________________________________ 
P Q R 
______________________________________ 
0 0 0 
0 1 1 
1 1 0 
1 0 1 
______________________________________ 
wherein P is the output of the AND gate 3 or the detection pulse "b"; Q is 
the pulse "a" of the oscillator circuit 2; and R is the output of the 
exclusive-OR gate. Since this exclusive-OR gate always receives the 
oscillating pulse "a" as the input Q, this gate produces the reset pulse 
"c" whenever the detection pulse "b" discontinues according to the logical 
truth table. 
A delay circuit comprising a resistor r1 and a capacitor c1 is connected to 
an output terminal of the exclusive-OR gate, and this delay circuit can 
absorb the output that would be accidentally developed due to little time 
difference between the pulse "a" and the pulse "b". An OR gate is 
connected to the output terminal of this delay circuit, and the remaining 
input terminal of the OR gate is connected to an auxiliary reset circuit 
for resetting the system when first turned on. In this arrangement, the 
reset terminal RST of the counting means 4 is connected to the output 
terminal of the OR gate. 
The counter receives the detection pulses "b" on its clock input terminal 
CL, and an output terminal Q.sub.n thereof is connected to the alarm 
circuit 6. A shift register is used as the counting means and a power 
source V.sub.DD is connected to a data terminal D of the shift register. 
The alarm circuit 6 is comprised of a transistor 6a for amplifying the 
output of the counter or the shift register 4, a thyristor SCR having a 
gate connected to an output terminal of the transistor 6a and a relay 6b 
connected in series with the thyristor SCR. When the thyristor SCR 
conducts the relay is energized to actuate various devices.