EP0071752B1

EP0071752B1 - Fire alarm system

Info

Publication number: EP0071752B1
Application number: EP19820105866
Authority: EP
Inventors: Hideo C/O Nohmi Bosai Kogyo Co. Ltd. Itoh
Original assignee: Nohmi Bosai Kogyo Co Ltd
Current assignee: Nohmi Bosai Ltd
Priority date: 1981-07-02
Filing date: 1982-07-01
Publication date: 1986-12-10
Also published as: JPS585896A; EP0071752A1; DE3274690D1; JPS6355120B2

Description

The present invention relates to a fire alarm system having a plurality of fire detectors connected in parallel across a pair of lines wherein the fire deter .or, actuated by fire, includes means for sending an alarm signal and an identification signal to a central control panel which including circuits in response to the signal gives both a fire alarm and an identification of the actuated fire detector.
In conventional fire alarm systems, a plurality of fire detectors are connected in parallel across a pair of lines for every area, and the lines are shortcircuited when a physical phenomenon such as heat or smoke caused by fire has reached a predetermined value to transmit fire signals to the control panel at a central location. Therefore, the area where fire has broken out could be indicated only roughly by the control panel. In other words, it is not possible to indicate which fire detector has worked or the change of its output, and it is not possible to indicate the burning condition. Namely it is not possible to suitably control equipment for preventing or expelling the smoke, or to suitable control fire extinguishers.
The UK Patent application GB 2 030 336 describes an emergency alarm system including a plurality of fire detectors connected in parallel by a common cable to a monitor arranged in a central location. A fire detector sends an identification signal to the monitor using DC-pulses signalling on the common cable when the fire detector is actuated by hand. The monitor renders both an alarm signal and an identification signal of the actuated fire detector. The disadvantages of the known emergency alarm system are both the requirement of two pairs of conductors (for power supply and signalling) in the common cable and two signals (alarm and identification signals) are derived from one signal, emitted from the actuated fire detector. Where the emergency alarm system encircles a large surveillance area, a large quantity of signal lines is necessary. Further, in cases of influences on the conductors by interfering electromagnetic fields the single signal transmitted through the conductors can be amended so that in the monitor false signals are derived from the amended signal.
The objects of the present invention are to reduce the wasteful use of the electrical conductors between the fire detectors and the central control panel, and to eliminate the undesired influence on the electrical signals by electromagnetic interfering fields. In the first mentioned case . only one pair of conductors is used. In achieving the second mentioned case a fire alarm signal, a fire quantity signal and an identification signal are emitted from the actuated fire detector and are transmitted to the control panel at the central location, such that the area where fire has broken out, the quantity or condition of the fire and the actuated fire detector are indicated by the control panel.
The invention is characterized by the combination of the features defined in the characterizing portion of claim 1.
Embodiments of the invention will be described in the connection with the drawings in which,

Fig. 1 is a circuit diagram illustrating connections of fire detectors and a control panel in a fire alarm system according to the present invention;
Fig. 2 is a circuit diagram of a fire detector of Fig. 1;
Fig. 3 is a circuit diagram of a control panel of Fig. 1;
Fig. 4 is a diagram showing voltage waveforms for illustrating the present invention.

In Fig. 1, symbols D₁₁ to D_1n and D_n1 to D_nn denote fire detectors that are connected in parallel across a pair of lines I₁ and I through to a pair of lines In to I covering every area, and Re denotes a control panel. The fire detectors connected in parallel in each area have been constructed in the same way except for a decoder that is provided to generate an address signal specific to the detector. Therefore only the detector D₁₁ will be described below with reference to Figs. 2 and 3, in which reference numeral 1 denotes a fire detector circuit which consists of a fire detector portion 2, and a comparator 3 such as operational amplifier A that detects a predetermined output of the detector portion 2. The fire detector portion 2 has an inner ion chamber CH, and an outer ion chamber CH₂ connected in series, and an FET which detects the change in potential at a middle point between the inner ion chamber and the outer ion chamber. Reference numeral 4 denotes an inhibit circuit whose input is connected to the output of the comparator 3, and whose inhibit input is connected to a line voltage detector circuit 5 which detects a predetermined voltage drop across a pair of lines I, and I. The detector circuit 5 consists of a transistor T_i, a Zener diode Z,, and resistors R₁, R₂. Under the supervisory condition, the Zener diode Z, is rendered conductive, whereby the transistor T, is rendered conductive. When other detectors connected in parallel across the lines l₁ and I have worked to decrease the line voltage, the Zener diode Z, is rendered non-conductive, whereby the transistor T, becomes non-conductive. Reference numeral 6 denotes a latch circuit consisting of an RS flip-flop circuit, the set terminal being connected to the inhibit circuit 4, and the output terminal being connected to a switching circuit 7 and to a delay circuit 8. The switching circuit 7 is connected across the pair of lines l₁, I to produce fire signals, and consists of a Zener diode Z₂ having a Zener voltage smaller than that of the Zener diode Z_i, and a transistor T₂. The base of the transistor T₂ which serves as an input terminal is connected to the output of the latch circuit 6. The delay circuit 8 so works that the output of the latch circuit 6 is produced being delayed by a predetermined period of time, and consists of a resistor R₃ and a capacitor C,. The output of the delay circuit 8 is sent to an astable multivibrator 11 via a Schmitt trigger inhibit circuit 9 and an OR circuit 10. Reference numeral 12 denotes a counter which counts pulse outputs produced by the multivibrator 11, and 13 denotes a decoder which produces an output at a predetermined counted value of the counter 12. In the case of this detector D₁₁, the output is produced when "1" is counted. As for other detectors (see Fig. 1) connected in parallel across the lines I₁ and I, for example, as for the detector D₁₂, the decoder produces an output when "2" is counted. As for the detector D_1n, the decoder produces an output when "n" is counted.
Reference numeral 14 denotes a latch circuit which consists of an RS flip-flop circuit, the set terminal thereof being connected to the output of the decoder 13, and the output terminal thereof being connected to the inhibit input of the inhibit circuit and to a clear terminal of the counter 12 via the OR circuit 15. Reference numeral 16 denotes a switching circuit which is connected across the lines I₁ and I like the switching circuit 7, and which works to send the address and fire detection quantity signal of the detector D₁₁. The switching circuit 7 consists of a Zener diode Z₃ having a Zener voltage smaller than that of the Zener diode Z₂, and a transistor T₃, the base of the transistor T₃ which serves as an input terminal being connected to the output of the astable multivibrator 11. Reference numeral 17 denotes a delay circuit which is connected to the output of the latch circuit 14, which consists of a resistor R₄, a capacitor C₂ and a Schmitt trigger circuit B, and which has a delay time that is sufficiently longer than the time for sending address signals. Reference numeral 18 denotes a nonstable multivibrator which operates responsive to the output of the delay circuit 17, and which has a pulse width and a period longer than the time for sending the fire detection quantity signals to the control panel Re via the multivibrator 11. The output of the astable multivibrator 18 is connected to the non-stable multivibrator 11 via a flip-flop circuit 19 and the OR circuit 10. Reference numeral 20 denotes an analog-to-digital converter of which the analog input is connected to the source of the FET in the fire detector portion 2, of which the digital output is supplied to one input of a digital coincidence circuit 21, and of which the strobe input is connected to the output of the astable multivibrator 18. The digital coincidence circuit 21 consists of a magnitude comparator, wherein another input for comparison is connected to the output of the counter 12, and the coincidence output is supplied to the clear terminal of the counter 12 via the OR circuit 15, and is also supplied to the reset terminal of the flip-flop circuit 19 via OR circuit 22. Reference numeral 23 denotes a reset circuit which consists of resistors R₅ to R₇, a capacitor C₃, and a transistor T₄, that are provided on the output side of the constant-voltage circuit 24. The collector of the transistor T₄ which produces an output is connected to the clear terminal of the counter 12 and to the reset terminal of the flip-flop circuit 19 via the OR circuits 15 or 22, and to reset terminals of the latch circuits 6, 14.
Reference numeral 25 denotes a fire signal receiver circuit in the control panel Re, which consists of resistors R₈ to R₁₁, a Zener diode Z₄, a transistor T₅ which becomes conductive upon receipt of a fire signal from the fire detector, and a self- holding circuit made up of a transistor T_s, a relay N, and a contact point n,. Reference numeral 26 denotes a circuit which receives addresses and fire detection quantity signals, and which consists of resistors R₈, R₁₂ to R₁₄, a Zener diode Z₄, and a transistor T₇ which is rendered conductive responsive to a pulse such as an address signal from the fire detector. Reference numeral 27 denotes an alarm indicator circuit which indicates the section where fire has broken out, and which consists of a lamp L that will be turned on when a contact n₂ of a relay N is closed. Reference numeral 28 denotes an AND circuit which consists of a contact n₃ of a relay N, a transistor T₈ of which the base is connected to the collector of the transistor T₇, and a resistor R₁₅, that are all connected in series, 29 denotes a counter which counts the number of pulses sent through the AND circuit 28 as address signals and fire detection quantity signals, and which assumes the form of a four-bit binary counter like the counter 12 in the detector, 30 denotes a pulse generator circuit which consists of resistors R₁₆, R₁₇, a capacitor C₄ and a contact n₄ of a relay N. The pulse generator circuit 30 is connected to inputs of the AND circuit 32 via a flip-flop circuit 31 together with the output of the counter 29, such that only the number of pulses in the form of address signals is stored in a register 33 of a subsequent stage. Further, reference numeral 34 denotes a decoder which converts binary values stored in the register 33 into different values, e.g., which converts binary numbers into decimal numbers. Reference numeral 35 denotes an address indicator circuit which indicates a detector that is operated by the output of the decoder 34, and which consists of numeral display tubes. Reference numeral 36 denotes a timer circuit which produces a single pulse after a predetermined period of time has passed from the reception of a fire signal, an address signal or a fire detection quantity signal produced by the fire detector. The timer circuit 36 consists of a monostable multivibrator M, of which the input is connected to the collector of the transistor T_s, an OR circuit OR₁ of which the inputs are connected to the emitter of the transistor T and to the output of the vibrator M_i, respectively, a timer T, and a monostable multivibrator M₂. The output of the timer circuit 36 is connected to the clear terminal of the counter 29 via OR circuit 37, connected to the reset terminal of the flip-flop circuit 31, and is connected to the set terminal of a flip-flop circuit 38. The output of the flip-flop circuit 38 is connected to the inputs of an AND circuit 39 together with the output of the counter 29, such that the number of pulses in the form of fire detection quantity signals is temporarily stored in a register 40 in a subsequent stage. Further, reference numeral 41 denotes a decoder which converts binary numbers stored in the registers 40 into different values, e.g., which converts binary numbers into decimal numbers, 42 denotes a fire detection quantity indicator circuit which indicates a fire detection quantity depending upon the output of the decoder 41, and which consists of numeral display tubes, 43 denotes a pushbutton switch for restoration, and 44 denotes a reset circuit which consists of resistor R,₈ to R_2o, a capacitor C_s, and a transistor Tg. The collector of the transistor Tg which produces output is connected to the flip-flop circuit 38 and to the reset terminal of the register 33, and is further connected to the clear terminal of the counter 29 and to the reset terminal of the register 40, respectively, via OR circuits 37 and 45, and another input of the OR circuit 45 is connected to the output of the timer circuit 36.
Operation of the circuit will be described below. In Fig. 2, if smoke produced by fire enters into the ion chamber CH₂ in the fire detector portion 2 of a fire detector D₁₁ among a multiplicity of fire detectors D₁₁ to D_1n connected in parallel across the lines I, and I, the source potential of FET rises, whereby the comparator 3 operatives at a predetermined value, and the output is sent to the inhibit circuit 4. In this case, other sensors D₁₂ to D_1n connected in parallel between the lines I, and I do not operate, the line voltage detector circuit 5 is inoperative, and the inhibit input of the inhibit circuit 4 assumes the low level. Therefore, the output from the fire detector circuit 1 sets the flip-flop circuit which works as a latch circuit 6 via inhibit circuit 4, and is further transmitted to the switching circuit 7 and to the delay circuit 8.
Responsive to this output, the switching circuit 7 renders the transistor T₂ conductive. Therefore, a voltage Vq across the lines l₁, and I is dropped to a value V_F as determined by the Zener diode Z₂, as shown in Fig. 4(a), and the thus obtained fire signal is sent to the control panel Re. Accordingly, the voltage drops across the resistor R_s in the fire signal receiver circuit 25 in the receiver Re, whereby the transistor T₅ is rendered conductive, the monostable multivibrator M, in the timer circuit 36 is operated to energize the timer T through OR circuit OR, and to actuate the relay N so that its operation is maintained by the closure of its contact n_i. Consequently, the contact n₂ in the alarm indicator circuit 27 is closed to turn the lamp L on. Thus, it is indicated that fire broke out in the area where the detectors D_", D₁₂ to D_1n are connected in parallel between the lines l₁ and I.
Further, while the fire signals are being received by the control panel Re, outputs of the latch circuit 6 delayed through the delay circuit 8 drive the astable multivibrator 11 via inhibit circuit 9 and OR circuit 10, such that pulse outputs are generated. The pulses are counted by the counter 12. When a pulse number "1" is counted, the decoder 13 operates, whereby the flip-flop circuit that works as latch circuit 14 is set, the inhibit input of the inhibit circuit 9 assumes the high level, the astable multivibrator 11 is stopped through the OR circuit 10, the counter 12 is cleared through the OR circuit 15, and the output is sent to the delay circuit 17. Furthermore, the transistor T₃ in the switching circuit 16 operates for a short period of time responsive to a pulse output from the multivibrator 11, and the voltage across the lines l₁ and I is dropped to V_A as shown in Fig. 4(a), such that the address signal in the form of a pulse produced by the detector D₁₁ is sent to the receiver Re. In the control panel Re, the transistor T₇ in the circuit 26 which receives address signals and fire detection quantity signals, operates responsive to the pulse and is turned on through the contact n₃ in the AND circuit 28 where the transistor T₈ has already been closed, and a pulse number "1" is counted in the counter 29. In the pulse generator circuit 30, furthermore, the contact n₄ in the relay N is switched and the flip-flop circuit 31 is set. The value counted by the counter 29 therefore is temporarily stored in the register 33 through AND circuit 32, and "1" is displayed on the numeral display tube of the address indicator circuit 35 through decoder 34, to indicate that the first detector has operated, i.e., to indicate that the fire detector D₁₁ has operated. Thereafter, the timer T which operates after a predetermined period of time has passed produces an output which causes the monostable multivibrator M₂ to operate, and the flip-flop circuit 31 is reset by the pulse, the counter 29 is cleared through the OR circuit 37, and the flip-flop circuit 38 is set. While the address signals are being received by the control panel Re, outputs of the latch circuit 14 delayed by the delay circuit 17 in the fire detector D₁₁ drive the non-stable multivibrator 18 so that it will periodically produce pulses having a long pulse width. Responsive to the pulses introduced through the flip-flop circuit 19 and the OR circuit 10, the astable multivibrator 11 and the analog-to-digital converter 20 are intermittently actuated. The number of pulses generated by the multivibrator 11, i.e., the value counted by the counter 12, and the fire detection quantity of the fire detector portion 2, i.e., the output of the analog-to-digital converter 20, are compared in the digital coincidence circuit 21 which produces an output when the analog quantity produced by the fire detector portion 2 is in agreement with the value counted by the counter 12. This output resets the flip-flop circuit 19 through OR circuit 22, stops the astable multivibrator 11 through OR circuit 10, and clears the counter 12 through OR circuit 15. Therefore, the astable multivibrator 11 produces pulses of a number corresponding to the fire detection quantity of the fire detection portion. The flip-flop circuit 19 is set responsive to pulses generated successively from the astable multivibrator 18, to actuate the astable multivibrator 11 and the analog-to-digital converter 20. Being controlled by the digital coincidence circuit 21, therefore, the pulses are continuously produced by the astable multivibrator 11 in a number corresponding to the fire detection quantity of that time. Responsive to the thus produced pulses, the transistor T₃ in the switching circuit 16 operates for short periods of time, such that the voltage across the lines I, and I is dropped to V_A twice and then thrice as shown in Fig. 4(a). Thus, fire detection quantity signals are sent to the receiver to indicate that the output of the fire detection portion 2 is increasing, for example, to 2 volts and then 3 volts. In the control panel Re, the transistor T₇ in the circuit 26 which receives address signals and fire detection quantity signals, operates responsive to the pulses, whereby the transistor T_s in the AND circuit 28 is intermittently rendered conductive twice, the timer circuit 36 is energized, the counter 29 counts the pulse number "2", the counted value is temporarily stored in the register 40 through AND circuit 39, and "2" is displayed on the numeral display tube of the detection quantity indicator circuit 42 via decoder 41, to indicate that the output of 2 volts is produced by the fire detection portion 2 in the fire detector D_". The monostable multivibrator M₂ is then operated by the output of the timer T which operates after a predetermined time has passed, the counter 29 is cleared through OR circuit 37, and the register 40 is reset through OR circuit 45. The fire detection quantity signals are then received by the receiver circuit 26, and "3" is displayed in the detection quantity indicator circuit 42, to indicate that the output produced by the fire detector D" has risen to 3 volts. The above operation is performed repetitively, and the fire detection quantity produced by the detector D_" is displayed on the control panel Re with the lapse of time. As for other detectors D₁₂ to D_1n connected in parallel across the lines l₁ and I, the transistor T, in their circuit 5 for detecting line voltage remains non-conductive, the inhibit input of the inhibit circuit 4 assumes the high level, and no output is transmitted from the fire detector circuit 1. Namely the detectors D₁₂ to D_1n remain in the inoperative condition.
When the fire detector D₁₂ has operated instead of the fire detector D_", the astable multivibrator 11 of the detector is stopped by the output of the decoder 13 under the condition in which two pulses are sent. Therefore, two pulses are sent through the switching circuit 16 as shown in Fig. 4(b). When the fire detector D_1n has operated, n pulses are sent as shown in Fig. 4(c). In the control panel Re, therefore, the pulses are counted by the counter 29, and the address indicator circuit 35 indicates that the second detector or the n-th detector has operated. When a fire detector D_n1 of other area has operated, a fire signal receiver circuit 25 (which is not shown) operates to indicate the area where fire has broken out, and the pulse number "1" produced by the detector as an address signal is detected by the circuit which receives address signals and fire detection quantity signals, whereby it is indicated that the first detector has operated. Moreover, the output of the detector is indicated relying upon the fire detection quantity signals that are introduced subsequently. When a button switch 43 for restoring the control panel Re is depressed for a short period of time, the reset circuit 23 in the detector and the reset circuit 44 in the control panel Re operate; i.e., the detector and the control panel are restored to normal condition. Although ion chambers are employed as the fire detector portion 2 in the above-mentioned embodiment, it is of course allowable to employ a fire detector portion of the photoelectric type which detects the light scattered by the smoke or of the thermal type such as thermistors.
The invention is constructed and operates as mentioned above. Namely, the invention provides a fire alarm system which is capable of discriminating the operation of a fire detector in an area where a plurality of fire detectors are connected in parallel across the same lines, and which is also capable of detecting the change in the output produced by the detector as a result of the fire.

Claims

1. A fire alarm system having a plurality of fire detectors (D₁₁―D_1n; D_n1―D_nn) connected in parallel across a pair of lines (l₁, I; I_n, I), wherein the fire detector, actuated by fire, includes means for sending an alarm signal and an identification signal to a central control panel (Re) which, including circuits in response to the signals gives both a fire alarm and an identification of the actuated fire detector, characterized by following electronic components:

a) in each fire detector are provided:

- a fire detector circuit (1) which detects a predetermined fire detection quantity produced by a fire detector portion (2);

- first inhibit circuit (4) which inhibits the transmission of output from said fire detector circuit when a line voltage of the lines (l₁, I; l_n, I) is dropped;

- a first latch circuit (6) which stores the output sent from the first inhibit circuit (4);

- a first switching circuit (7) which works to decrease the voltage of the lines responsive to the operation of the first latch circuit (6), in order to send a fire signal to the control panel (Re);

- a first delay circuit (8) which produces an output after a predetermined period of time has passed from the operation of the first latch circuit (6);

- a second inhibit circuit (9) which inhibits the transmission of output of the first delay circuit (8) responsive to the output of a second latch circuit (14);

-a first astable multivibrator (11) which is operated by the second inhibit circuit (9);

- a second switching circuit (16) which is intermittently operated by the output of the first astable multivibrator (11), which is connected across the lines together with the first switching circuit (7), and which works to decrease the line voltage in order to send an address signal and a signal of fire detection quantity to the receivers;

- a decoder (13) which generates address signals to detect a predetermined value of a counter (12) that counts the outputs of the first non-stable multivibrator (11);

- the second latch circuit (14) stores the output of the decoder (13);

- a second delay circuit (17) which produces an output after a predetermined period of time has passed responsive to the operation of the second latch circuit (14);

-a second astable multivibrator (18) which operates responsive to the output of the second delay circuit (17);

-an analog-to-digital converter (20) which converts analog outputs into digital values, said analog outputs being produced by a flip-flop circuit (19) which is set by the second astable multivibrator (18) and which actuates the first astable multivibrator (11), and said analog outputs being further produced by the fire detection portion (2); and

- digital coincidence circuit (21) which compares the output of the converter (20) with the output of the counter (12), and stops the first astable multivibrator (11) when said outputs are in agreement;

b) and in the control panel (Re) are provided:

-a fire signal receiving circuit (25) which detects a predetermined line voltage dropped by the operation of the first switching circuit (7) in the fire detector;

- a circuit (26) for receiving addresses and fire detection quantity signals that are produced by the second switching circuit (7) in the actuated detector;

-a subsequent arranged AND circuit (28) which permits a passage of the received addresses and fire detection quantity signals;

- counter (29) which counts the pulse outputs of the AND circuit (28);

- decoders (34, 41) which detect the counter values and which indicated addresses and fire detection quantities in subsequent arranged display circuits (35, 42).

2. A fire alarm system according to claim 1, characterized in that the fire detector includes a fire detector portion (2) having at least one ion chamber (CH) or a thermistor.