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(11) | EP 0 002 868 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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| (54) |
Fire detector Feuerdetektor Détecteur de feu |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
[0001] This invention relates to a fire detector connectable to a control panel by electrical lines and comprising sensor means for sensing a fire phenomenon such as heat, smoke, gas or light and operating switching means short-circuiting the lines and causing an alarm current flowing in the lines to the control panel when a fire has been detected, whereby means for controlling the alarm current are provided.
[0002] In a fire detector of this kind disclosed in US patent Nr. 821 734 the line current control is used for the purpose of differentiating between a fire alarm and a short-circuit of the lines, but whenever one detector has caused an alarm, multiple alarms generated by further detectors can no more be detected with certainty and without overloading the power supply.
[0003] Fig. 1 shows a circuit diagram of a fire alarm system composed from elements disclosed in the Japanese utility model publications sho 49-11672 and sho 50-3108.
[0004] Thereby the fire detectors De may be connected in parallel with each other between a pair of lines 11 and 12 extending to a control panel Re. The operation of this known fire detector is as follows:
[0005] When a sensor, e.g. thermistor Th of the detecting element De has received heat emitted by a fire, the resistance of the thermistor drops and the potential Vb at the junction point b of the thermistor Th and the resistor R, is also reduced. When the potential Vb has reached a voltage less than the emitter potential Ve of the transistor Ti which is determined by the resistances of the resistors R2 and R3, the transistor T, will be turned ON and a thyristor T2 will also be ON by a voltage drop occuring across resistor R4. As a consequence, a current starts to flow from plus terminal of the power source E located in the control panel Re through the reset key Kr, line 12, the parallel circuit of operation indicating lamp La and resistor R5, thyristor T2, line I1, diode D4 and zone relay N operating as signal receiving relay. Then, relay N operates and closes its contacts n1, n2 and n3. By the closed contact n, the operation of the relay N self-holds, through the contact n2 a zone lamp Lf lights up, and further an operation indicating lamp La of the detector De lights up through the contact n3 and the resistor R11. In this case, the diode D4 prevents the lines I, and 12 from short-circuit due to the closing of the contact n1.
[0006] When such fire detectors De are used for a fire alarm system, in the event of a fire, a large current nearly equal to the short-circuit current flows through the lines I1 and 12 via the thyristor T2. Furthermore, if any further detector connected with the detector lines (not shown in the circuit diagram) is actuated successively, there is the possibility of coming short of the capacity of the power source E located in the control panel Re. Also, such a fire alarm system could have the disadvantage that when a detector connected between lines I1 and 12 has been actuated, no other detector connected to the same lines is able to detect a fire because the voltage between lines I1 and 12 will drop to a voltage nearly equal to the short-circuit voltage which could be insufficient for operating the other fire detectors.
[0007] This invention aims at obtaining a fire detector avoiding the above mentioned drawbacks of prior art and whereby even if fire detectors connected to plural detector lines are operated successively, there is no possibility of coming short of the capacity of the power source in the control panel, and whereby even after one detector in a detector line has been operated, fire detection by other detectors connected to the same detector line is still possible.
[0008] This object is achieved by providing a timer circuit arranged in one of said lines having a predetermined switching time during which the alarm circuit is allowed to pass to the control panel in order to operate signal receiving relay and after lapse of which the line current is reduced to a smaller value sufficient for holding the operation of said switching circuit.
[0009] Embodiments of this invention are described hereinafter in connection with the drawings in figures 2-6.
[0012] Fig. 4 and Fig. 5 show circuit diagrams of two kinds of control panels connected with embodiments of this invention.
[0014] Fig. 2 shows a circuit diagram of an embodiment of a fire detector of this invention. This fire detector De consists of a fire detecting . circuit 1, a switching circuit 2 operated by the output of the circuit 1, a timer circuit 3 which is so constructed that when the circuit 2 has operated a large current nearly equal to the short-circuit current flows through the signal receiving relay N located in the control panel via the circuit 2 for a sufficient time for operating the said relay, an operation indicating circuit 4 which forms an oscillation circuit for lighting up the operation indicating lamp upon completion of the operations of the circuit 3, and a power source voltage stabilizing circuit 5. The fire detecting circuit 1 and the switching circuit 2 are the same as the corresponding circuits shown in Fig. 1, the timer circuit 3 and the operation indicating circuit 4 are arranged side by side and connected in series to the line 12, and the power source voltage stabilizing circuit 5 is connected between the lines I1 and 12 extending to the control panel Re, shown in fig. 4.
[0015] The operation of this fire detector is described hereinafter in connection with a control panel shown in fig. 4 and the time charts shown in fig. 3. In supervisory condition, a small supervisory current flows from the line 12 to the line I1 through resistors R8 and R9 in the circuit 4, a parallel circuit consisting of resistor R1, thermistor Th and resistors R3, R2 in the circuit 1, and a diode D3. Since the current is very small, the voltage produced between both ends of the series circuit of resistors R8 and R9 is also rather low.
[0016] When the thermistor Th has received heat emitted by a fire, the resistance of the thermistor will decrease and the potential Vb at the junction point b will drop as shown in fig. 3 (a). When the potential Vb has dropped lower than the emitter voltage Ve of the transistor T1, the transistor T, will be turned ON, a voltage nearly equal to the power source voltage will be applied to both ends of the timer circuit 3 and the operation indicating circuit 4, and a charge current of the condenser C1 arranged in the timer circuit 3 will flow through the emitter and the base of transistor T3 via resistor R6 which causes transistor T3 to turn ON.
[0017] Condenser C2 in circuit 4 will be charged in an instant via transistor T3 and relay A which has a small internal resistance and is used for operating auxiliary devices, e.g. for driving an interlocked controller to close an air conditioning duct in the room in fire. When the charge voltage of the condenser C2 has exceeded the gate voltage of the N-gate thyristor T4, the thyristor T4 will be ON. The state of operations of the transistor T3 and the relay A is shown in fig. 3 (c).
[0018] When the thyristor T4 has been ON, a large signal current being nearly equal to the short-circuit current will flow from the line 12 to the line I, via T3, A, T4 and light emitting diode D2 working on the signal receiving relay located in the control panel to operate it. When the relay N has been operated it will perform the first control such as stopping of air conditioner etc. in the zone in fire, and at the same time the contacts n,, n2 and n3 will be closed and the operation of the relay N will become self-hold, the zone lamp Lf will be lit by the contact n2, and a current for lighting up the operation indicator D2 of the detector De will be supplied to the operation indicating circuit 4 through the contact n3 and the resistor R11. In this case while a large signal current flows through the lines I1 and I2, the transistor T5 in ON by a voltage produced in the resistor R11 via the load resistance R13, and the counter circuit C counts "one" by a voltage produced in the resistor R13. But at this time no output is produced by the counter circuit C and the transistor T6 cannot be ON, and accordingly, the relay B for performing the second control such as to control the smoke ventilator etc. cannot be operated.
[0019] Time t1 while the transistor T3 located in the timer circuit 3 of the detector De is ON can be determined to be a desirable value by the time constant determined by the resistance of the resistor R5 and the capacity of the condenser C,. In this case the resistance or the resistor R6 shall be sufficiently larger than that of the resistor R5. When the transistor T3 has been OFF, the N-gate thyristor T4 located in the operation indicating circuit 4 which forms the oscillation circuit will be OFF, and the circuit 4 will begin to oscillate normally with a regular frequency given by the time constant determined by the resistance of the resistor R7 and the capacity of the condenser C2. Hereafter the diode D2 is flickering as shown in fig. 3 (d). Furthermore, when the transistor T3 has been OFF, the current flowing in the lines through the thyristor T2 will be changed-over to a smaller value just above the minimum self-holding current for maintaining the self-holding of the thyristor T2. This minimum self-holding current flows through the resistors R8 and R9, and the line voltage applied to the actuated detector De is reset to the almost normal voltage. Fig. 3 (e) shows the change with time of the line current II flowing through the lines I1 and 12, and fig. 3 (f) shows a periodical change of the line voltage V between the lines I, and 12.
[0020] Now, when another detector connected with the same detector circuit has actuated, the line voltage VI will drop during the time t, soon after the actuation to a voltage nearly equal to the short-circuit, but the minimum self-holding current of the thyristor T2 of the previously actuated detector is supplied by the discharge current of the condenser C3 located in the power supply stabilizing circuit 5 through the resistors R8 and R9. The transistor T5 located in the control panel is ON by the voltage produced again in resistor R11 by the actuation of this other deteetor, and the counter circuit C counts "two" and the transistor T6 is also ON by the output of the switching circuit 2 at that time, thus, relay B is operated to perform the second control such as to control the smoke ventilator etc.
[0021] Fig. 5 shows a circuit diagram of another control panel Re which may be used in connection with the detectors De according to fig. 2. What differs in this control panel from that shown in fig. 4 is merely the fact that the driving part D of an electromagnetic rotary switch unit F is driven by every ON of the transistor T5 and the wiper W of the rotary switch RS is advanced on the contacts No. 0 to No. 3 step by step, and when the wiper W arrives at the contact No. 2, a circuit to perform the second control is formed.
[0022] Fig. 6 shows a circuit diagram of the timer circuit 3 and the operation indicating circuit 4 in which an amperemeter-type operation indicator M is used instead of the light emitting diode D2 located in the operation indicating circuit 4 of the fire detector De shown in fig. 2. The embodiment shown in fig. 6 is just the same as that shown in fig. 2 except the operation indicating circuit 4. In this circuit a diode Ds for protecting the amperemeter-type operation indicator M is connected in parallel with a series circuit of the amperemeter-type operation indicator M and a resistor R,4 and further a resistor R7 is connected in series with the parallel circuit. The operation indicating circuit 4 is connected with the timer circuit 3 as shown in fig. 6. In this embodiment, in the event of fire, when the thyristor T2 of the detector De has been ON, the large signal current flowing through the transistor T3 and the relay A mainly flows through the diode Ds. The supervisory current in the supervisory condition and the self-holding current of the thyristor T2 flows through the resistors R7, R14, and the indicator M. The indicator M is operated by a part of the large signal current and is self-held by the self-holding current of the thyristor T2.
[0023] It should be noted that the heat sensing thermistors in the above described embodiments of the invention could be replaced by other sensing elements responding to other fire phenomena such as smoke, gas or light. For example the sensing circuit of the detector De may comprise an ionization chamber in series with a refernce element, a photo-electric element or a semiconductor gas sensing element, instead of a thermistor.
[0024] As above-mentioned, this invention has the merit that when these fire detectors are used in a fire alarm system, a large current flowing through the detector once operated is promptly reduced to a small current, and the line voltage to which the detectors are connected is promptly returned from a voltage nearly equal to the short-circuit voltage to a voltage nearly equal to the normal voltage, and accordingly even if the fire detectors connected to plural detector lines are operated successively, there is little possibility of addition of the large currents flowing through these detectors and therefore there is no possibility of coming short of the capacity of power source located in the control panel, and the detection of fire by another detector is possible even after an already actuated detector connected is with the same detector line.
1. Fire detector connectable to a control panel (Re) by electrical lines (I1, 12) and comprising sensor means (Th) for sensing a fire phenomenon such as heat, smoke,
gas or light and operating switching means (T2) short-circuiting the lines and causing an alarm current to flow in the lines to
the control panel when a fire has been detected, whereby means for controlling the
alarm current are provided, characterised by a timer circuit (3) arranged in one of
said lines and having a pre-determined switching time (t,) during which the alarm
current is allowed to pass to the control panel in order to operate a signal receiving
relay (N) after which the line current is reduced to a smaller value sufficient for
holding in operation said switching means (TZ).
2. A fire detector as claimed in claim 1, wherein operation indicating means (D2) are provided for an indication of the line current and an oscillation circuit (4)
producing a pulsating current in the lines when the line current has been reduced
to said smaller value by said timer circuit (3), said pulsating current being sufficient
for operating said indication means (D2).
3. A fire detector as claimed in claim 1, wherein said timer circuit (3) comprises
relay means (A) for operating an external auxiliary device within said predermined
switching time (t,)..
1. Détecteur d'incendie connectable à une station de contrôle (Re) par des lignes
électriques (I1, I2) et comprenant des moyens capteurs (Th) sensibles à un phénomène d'incendie comme
la chaleur, la fumée, le gaz ou la lumière et actionnant des moyens de commutation
(T2) court-circuitant les lignes et générant la circulation d'un courant d'alarme
dans les lignes à la station de contrôle lorsqu'un incendie a été détecté, dans lequel
des moyens sont prévus pour régler le courant d'alarme, caractérisé par un circuit
d'interruption (3) disposé dans une des lignes et possédant un temps (tl) de temporisation
prédéterminé pendant lequel le courant d'alarme est permis de circuler à la station
de contrôle pour actionner un relais (N) de réception de signal et après l'expiration
de la dite temporisation le courant dans les lignes est réduit à une valeur plus petite
suffisante pour maintenir actionné le dit moyen de commutation (TZ).
2. Détecteur d'incendie selon revendication 1 dans lequel moyens d'indication d'actionnement
(D2) sont prévus pour l'indication d'un courant de ligne, et un circuit d'oscillation
(4) générant un courant de pulsation dans les lignes lorsque le courant de ligne a
été réduit à une valeur plus petite par le dit circuit d'interruption (3), dans lequel
le courant de pulsation est suffisant pour actionner les dits moyens d'indication
(D2).
3. Détecteur d'incendie selon la revendication 1 dans lequel le dit circuit d'interruption
(3) comporte des moyens de relaise (A) pour actionner un dispositif auxiliaire externe
dans l'espace du dit temps (tl) de temporisation prédéterminé.
1. Branddetektor, der mittels elektrischer Leitungen (I1, 12) an eine Kontrollstation (Re) anschliessbar ist und Sensor-Mittel (Th) für ein Brand-Phänomen,
wie Hitze, Rauch, Gas oder Licht aufweist und Schaltmittel (T2) zum Kurzschliessen der Leitungen und zur Verursachung eines in den Leitungen zu
der Kontrollstation fliessenden Alarmstromes betätigt, wenn ein Brand detektiert wurde,
wobie Mittel zur Regelung des Alarmstromes vorgesehen sind, gekennzeichnet durch einen
Zeitschaltkreis (3) der in einer der Leitungen angeordnet ist und eine vorgegebene
Schaltzeit (t,) aufweist, während der der Alarmstrom zur Kontrollstation fliessen
kann, um ein Signalempfangs-Relais (N) zu betätigen, und nach der der Leitungsstrom
auf einen kleineren Wert herabgesetzt wird, der ausreichend ist, um die besagten Schaltmittel
(T2) betätigt zu halten.
2. Branddetektor nach Anspruch 1, in welchem Betätigungs-Anzeigemittel (D2) vorgesehen sind, um einen Leitungsstrom anzuzeigen, und ein Oszilatorkreis (4),
der einen pulsierenden Strom in den Leitungen erzeugt, wenn der Leitungsstrom durch
den besagten Zeitkreis (3) auf den besagten niedrigeren Wert herabgesetzt worden ist,
wobei der besagte pulsierende Strom ausreichend ist, um die besagten Anzeigemittel
(D2) zu betätigen.
3. Branddetektor nach Anspruch. 1, in welchem der besagte Zeitkreis (3) Relaismittel
(A) zur Betätigung eines externen Hilfsgerätes innerhalb der vorgegebenen Schaltzeit
(t,) aufweist.