FIRE ALARM SYSTEM

Abstract: A fire detector which transmits a fire signal with self-holding while detecting a fire phenomenon exceeding the fire level, and which self-holds in response to a control signal transmitted by an accumulation type fire control panel when operated with the fire signal. This fire detector is suitable for connection with an accumulation type fire control panel.

Description: The present invention relates to a fire alarm system comprising a fire detector which is suited for connection with an accumulation type fire control panel. The accumulation type control panel is designed for the purpose of preventing a non-genuine fire alarm from being produced by transient fire (similar) phenomena, and gives a fire indication or alarm on judging that fire has broken out only if it has discriminated that a fire detector is continuously detecting a fire phenomenon exceeding a certain fire detection level for a predetermined length of time. In the case of the accumulation type control panel which continues accumulating operation without resetting the fire detector, however, it is not practicable to use a conventional fire detector having a self-holding function on the following ground. The conventional fire detector, once detected a fire phenomenon (e.g. heat, smoke, light from flame, gas) exceeding the fire level, keeps its fire signal transmission circuit (or the circuit which controls the signal transmission circuit) activated and continues transmitting the fire signal even if the fire phenomenon disappeared immediately after detection. Therefore, the accumulation type control panel, if connected with the above-mentioned fire detector, has such a drawback that it operates on the transient fire phenomenon as well and produces a non-genuine fire alarm. From the above viewpoint it is preferable to connect a non-lock type (nonself-holding type) fire detector to the accumulation type control panel. The non-lock type fire detector outputs the fire signal only while the fire phenomenon is exceeding the fire level and stops outputting the fire signal as the fire phenomenon falls below the fire level. Even if the accumulation type control panel is connected with the non-lock type fire detectors, each equipped with a response indicator lamp to indicate that the fire detection part has operated, there still remains such a problem that one cannot know which fire detector initiated the fire signal to operate the accumulation type control panel because the response indicator lamp is lit only while the fire detector is outputting the fire signal, and goes off as generation of the fire signal is stopped. In view of the above problem the present invention aims at offering a fire detector which is capable of transmitting the fire signal while detecting the fire phenomenon exceeding the fire level and of maintaining its operation when the accumulation type fire control panel has continuously received the fire signal for a predetermined length of time, and operation of the response indicating means such as response indicator lamp. It is a further object of the invention to offer a fire control panel which is capable of controlling the fire detector when the fire control panel has continuously received the fire signal for a predetermined length of time. According to the invention there is provided a fire detecting system comprising a fire detector equipped with a fire detecting means to detect a fire phenomenon; a fire signal transmission means to transmit a fire signal to a fire control panel while the fire detecting means is detecting a fire phenomenon exceeding a predetermined level; a control signal receiving means to receive a control signal transmitted from the fire control panel; a self-holding means which operates when the control signal receiving means has received the control signal and while the fire detecting means is detecting the fire phenomenon exceeding the predetermined level; and an operation indicating means operated by the self-holding means. According to a preferred embodiment of the invention the fire signal transmission means is a device which transmits the fire signal by changing voltage across the input and output terminals connected with the fire control panel to the first predetermined voltage, and the control signal receiving means is a device which detects change of the voltage across the input and output terminals to the second predetermined voltage which differs from the first predetermined voltage. Preferably the first predetermined voltage is a sufficient voltage to maintain the function of the fire detecting means. It is further preferred that the input and output terminals comprise two terminals. According to another preferred embodiment of the invention the operation indicating means also operates an operation of the fire signal transmission means. According to the invention there is further provided a fire control panel equipped with a fire signal detecting means to detect a fire signal transmitted from a fire detector; an accumulation circuit which operates when the fire signal detecting means has detected the fire signal continuously for a predetermined length of time; an alarm circuit which is controlled by output signal from the accumulation circuit; and a control signal transmission circuit which transmits a control signal to control the fire detector when the accumulation circuit has operated. According to a further preferred embodiment of the invention the control signal transmission circuit is caused to produce the control signal by changing the voltage fed to a pair of power supply and signal lines to which the fire detector is connected to a predetermined value. Preferably the accumulation circuit is capable of switching the predetermined time to plural times differing each other. In particular the control signal transmission circuit is controlled by output from the alarm circuit which is controlled by output fron the accumulation circuit. The fire detector according to the present invention transmits a fire signal to a fire control panel when its fire detecting means operated, and continues the operation when it received a control signal from the fire control panel. The invention will now be further described by way of illustrative and non-limiting examples, with reference to the accompanying drawings in which Figure 1 is a circuit diagram showing an embodiment according to the present invention, Figure 2 is a circuit diagram showing an embodiment of the accumulation circuit, and Figure 3 is a block diagram showing another embodiment of the accumulation circuit. The embodiment shown in Figure 1 is composed of an accumulation type control panel RE, a fire detector DE and power supply and signal lines ℓ₀, ℓ₁ which connect the accumulation type control panel RE with the fire detector DE. The accumulation type control panel RE is a control panel which produces alarms in case it has received a fire signal continuously for a predetermined length of time, and is equipped with a fire signal detecting circuit 10, an accumulation circuit 20, an alarm circuit 30, a voltage dropping circuit 40 as control signal transmission means, a power supply B generating a voltage of about 24V, and a reset switch SW. The fire signal detecting circuit 10 is a circuit which detects the fire signal from the fire detector DE, and is equipped with a resistor 11 connected in series with the fire detector DE, and a transistor 12 which switches on when the voltage across the both ends of the resistor 11 has reached a predetermined voltage. The accumulation circuit 20 is a circuit which operates when the above-mentioned fire signal has been accumulated for a predetermined length of time, and is composed of an integration circuit or a timer. The alarm circuit 30 is a circuit which operates on operation of the accumulation circuit 20 and is composed of a transistor 31, a zone relay 32 to operate a fire alarm lamp, zone indicator lamps, an alarm bell etc, which are not shown on the drawing, and a make contact 33 of the zone relay 32. The control signal transmission circuit 40 is a circuit which transmits the control signal by causing the voltage applied across the power supply and signal lines ℓ₀ and ℓ₁ to drop when the alarm circuit 30 has operated, and is equipped with a make contact 41 of the zone relay 32 and a zener diode 42 of about 8V. The above mentioned control signal is a signal which controls the fire detector DE through a pair of power supply and signal lines ℓ₀, ℓ₁. On the other hand the fire detector DE is equipped with a fire detecting part 50, a voltage stabilizing circuit 51, a fire signal transmission circuit 60, a response indicator lamp LED, a voltage detecting circuit 70 as control signal receiving circuit and a self-holding circuit 80. The fire detecting part 50 is a device which detects one or more fire phenomena and comprises one or plural sensor parts responding to heat, smoke (ionization, scattered-light, light obscuration, etc.), radiation or gas, and a detecting part discriminating whether or not the output of the sensor parts has reached a predetermined level. The fire signal transmission circuit 60 is a circuit which transmits a fire signal to the accumulation type control panel RE while the fire detecting part 50 is operating. By changing the voltage across the input and output terminals T₀, T1 to the first predetermined voltage (e.g. 18V) which has no influence upon normal operation of the fire detecting part 50, the fire signal is transmitted to the fire control panel RE. In other words the fire signal transmission circuit 60 allows current to flow through a resistor for signal detection 11 in the fire signal detecting circuit 10 via the power supply and signal lines ℓ₀, ℓ₁ when the fire detecting part 50 has operated. The fire signal transmission circuit 60 is equipped with a transistor 61, zener diodes 62, 63 and a response indicator lamp LED. The response indicator lamp LED serving as operation indicating means also indicates that the fire detecting part is in operation. The voltage detecting circuit 70 is a circuit which detects a voltage drop as control signal caused by the voltage dropping circuit 40 in the accumulation type control panel RE, and is equipped with a bridge circuit comprising a transistor 71, a zener diode 72 and resistor 73, 74, 75, a comparator 76, transistors 78, 79, and voltage dividers R1, R2. The self-holding circuit 80 is a circuit which maintains the operation of the fire detector DE after lapse of an accumulation time of the accumulation type control panel (i.e. the voltage detecting circuit 70 has operated), and yet a fire signal is being produced, and comprises thyrister 81 such as SCR. By operation of the self-holding circuit 80 the response indicator lamp LED is kept lit. Operation of the above embodiment is described below. Assuming that a voltage of 24V is available from the power supply B, and no fire phenomenon has developed, only small current as supervisory current flows through the fire detector DE. Therefore, a voltage of approximately 24V is applied across the input and output terminals T₀ and T1 of the fire detector DE through the power supply and signal lines ℓ₀, ℓ₁. If the fire detecting part 50 has detected a fire phenomenon of a predetermined level, the transistor 61 switches on and the response indicator lamp LED lights, indicating that the fire detecting part 50 is in the operation mode. At the same time the whole fire signal transmission circuit 60 including the zener diodes 62, 63 becomes conductive, allowing current to flow through the resistor 11 in the fire signal transmission circuit 10. In this case a sufficient voltage (the first predetermined voltage, e.g. 18V) for the fire detecting part 50 to continue fire surveillance is applied across the input and output terminals T₀, T1 (2V of the 18V are applied to the voltage stabilizing circuit 51, and remaining 16V are applied to the fire detecting part 50). As current flows through the resistor 11 in the accumulation type control panel RE (i.e. a fire signal has been generated) as described above, the transistor 12 switches on and the accumulation circuit 20 starts accumulating. If the fire signal is generated for a predetermined length of time, the accumulation circuit 20 operates and the transistor 31 switches on. Thus, the zone relay 32 is actuated to operate a fire alarm lamp, a zone indicator lamp and an alarm bell which are not shown on the drawing. At the same time the make contact 41 of the zone relay 32 in the voltage dropping circuit 40 closes, causing the voltage applied to the input and output terminals to decrease down to a voltage (the second predetermined voltage, e.g. 8V) which is determined by the zener diode 42 as control signal. Within the fire detector DE the transistor 71 remains switched on as long as the fire detecting part 50 is in operation, thus the bridge circuit comprising the zener diode 72 and the resistors 73 ∿ 75 is energized, but the comparator 76 outputs no 'High' signal in the case of the first predetermined voltage. However, as the voltage across the input and output terminals T₀, T1 drops to the second predetermined voltage in the above-mentioned case, the voltage on the non-inverting terminal of the comparator 76 becomes higher than that on the inverting input terminal, thus the comparator 76 outputs the 'High' signal. Consequently the transistors 78, 79 switch on, and resultant increase in gate voltage of the thyrister 81 causes the thyrister 81 to turn on and keep the response indicator lamp lit. Since the response indicator lamp LED remains lit while the fire detecting part 50 is in operation, also after the accumulation type control panel has completed accumulation, it is possible to confirm which one of numerous fire detectors in the same zone has caused the accumulation type control panel to operate. Moreover, the response indicator lamp LED does not falsefy operate on transient fire phenomena, that is, the accumulation circuit 20 of the accumulation type control panel RE does not operate on transient fire phenomena. Therefore, the voltage across the input and output terminals T₀, T1 does not reach the above-mentioned second predetermined voltage, the thyrister 81 does not turn on, and the operation of the response indicator lamp LED does not continue. To reset the response indicator lamp LED of the fire detector DE, in other words operation of the self-holding circuit 80, the reset switch SW should be set in the 'OFF' position. In this case, current flowing through the thyrister 81 decreases below the holding current, and the thyrister 81 turns off. While the response indicator lamp LED serves both as response indicating means and a means to indicate the operating mode of the fire detecting part 50 in the above embodiment, a second indicator lamp may be provided as operation indicating means and arranged in such manner that the SCR 81 is connected with the input and output terminal T₀ via the second indicator lamp. For the operation indicating means a mechanical device such as a magnetic indicator plate may be used in place of the indicator lamp. While the self-holding circuit 80 has been referred to as separate member from the voltage detecting circuit 70 in the above embodiment, the self-holding means may be considered in a broad sense to have the voltage detecting circuit 70 and the self-holding circuit 81. It is also possible to separately provide a third signal line ℓ₃ and a terminal to feed the second predetermined voltage, if generated in the control panel RE, to the fire detector DE, and an AND means as control signal receiving means to detect input of the second predetermined voltage and generation of the fire detection signal through the signal line ℓ₃ so that the thyrister 81 may turn on when the AND means has operated. In Figure 2 the accumulation circuit 20 is composed of a transistor 21 which switches on when the fire signal is detected, an integration circuit which accumulates the electric charge with the voltage at the both ends of a resistor 22, and a zener diode 26. The integration circuit is composed of resistors 23a and 23b, a capacitor 25 and a changeover switch 24, and can have different lengths of accumulation times by switching the changeover switch 24. With generation of the fire signal the transistor 21 switches on and a predetermined voltage develops in the resistor 22 and the capacitor 25 is gradually charged with this voltage. When this charging voltage becomes higher thant the zener voltage of the zener diode 26, the alarm circuit 30 operates. The accumulation time of the accumulation circuit 20 is determined by resistance value of the resistor 23a (or 23b) and capacity of the capacitor 25. The diode 26a causes the capacitor 25 to quickly discharge if the fire signal is no longer received during accumulation of the electric charge on the capacitor 25. In lieu of the accumulation circuit 20 a timer which generates output when the fire signal is continuously input for a predetermined length of time, and which is cleared when no signal is input within a predetermined time may be used. In Figure 3 another embodiment of the accumulation circuit is shown. The accumulation circuit 20A is used in such a case that the fire detector DE is the one that outputs pulse signals as fire signal when it has detected a fire phenomenon exceeding a predetermined level (as example a smoke detector using a lamp flashing in a series of pulses may be mentioned.). The counter 27 is a device which counts every time the fire signal is received from the fire signal detecting circuit 10, and outputs on counting, for instance, fifteen signals. The retrigger monostable multivibrator 28 is actuated by the fire signal, and its output time is longer than one repetition period of fire signal pulse but shorter than two repetition periods of the same. Therefore, the monostable multivibrator 28 keeps its output while the fire signal pulses from the fire detector DE is continuously input without interruption. The monostable multivibrator 29 is composed of Schmitt trigger circuit etc. It outputs at the down edge of the retrigger monostable multivibrator 28 and clears the counting of the counter 27. The control signal transmission circuit 40 may be of such composition that transmits, as control signal, a pulse signal or FM . AM signal with specific frequency. In this case a pulse signal of frequency signal detecting circuit should be provided in lieu of the voltage detecting circuit 70 in the fire detector DE. The fire control panel according to the present invention has such an effect that it can properly control the fire detector when it has continuously received the fire signal for a predetermined length of time.

Claims: 1. A fire detecting system comprising a fire detector equipped with a fire detecting means (50) to dedect a fire phenomenon; a fire signal transmission means (60) to transmit a fire signal to a fire control panel (RE) while the fire detecting means (50) is detecting a fire phenomenon exceeding a predetermined level; a control signal receiving means (70) to receive a control signal transmitted from the fire control panel (RE); a self-holding means (80) which operates when the control signal receiving means (70) has received the control signal and while the fire detecting means (50) is detecting the fire phenomenon exceeding the predetermined level; and an operation indicating means operated by the self-holding means (80). 2. A fire detecting system according to claim 1, characterized in that the fire signal transmission means (60) is a device which transmits the fire signal by changing voltage across the input and output terminals connected with the fire control panel (RE) to the first predetermined voltage, and the control signal receiving means (70) is a device which detects change of the voltage across the input and output terminals to the second predetermined voltage which differs from the first predetermined voltage. 3. A fire detecting system according to claim 2, characterized in that the first predetermined voltage is a sufficient voltage to maintain the function of the fire detecting means. 4. A fire detecting system according to claim 2, characterized in that the input and output terminals comprise two terminals. 5. A fire detecting system according to any of claims 1 or 2, characterized in that the operation indicating means also operates on operation of the fire signal transmission means. 6. A fire detecting system according to any of the claims 1 to 5, characterized in that the fire control panel (RE) is equipped with a fire signal detecting means (10) to detect a fire signal transmitted from a fire detector (DE); an accumulation circuit (20) which operates when the fire signal detecting means (10) has detected the fire signal continuously for a predetermined length of time; an alarm circuit (30) which is controlled by output signal from the accumulation circuit (20); and a control signal transmission circuit (40) which transmits a control signal to control the fire detector (DE) when the accumulation circuit (20) has operated. 7. A fire detecting system according to claim 6, characterized in that the control signal transmission circuit (40) in the fire control panel (RE) is caused to produce the control signal by changing the voltage fed to a pair of power supply and signal lines to which the fire detector is connected to a predetermined value. 8. A fire detecting system according to claim 6, characterized in that the accumulation circuit (10) in the fire control panel (RE) is capable of switching the predetermined time to plural times differing each other. 9. A fire detecting system according to any of the claims 6 to 8, characterized in that the control signal transmission circuit (40) in the fire control panel (RE) is controlled by the output from the alarm circuit (30) which in turn is controlled by the output from the accumulation circuit (20).

Inventors: OTSUKA, HIDENORI
Applicants: NOHMI BOSAI KOGYO CO., LTD.
Application year: 1986
Main classification: G08B17
IPC codes: G08B17