Fire Alarming System

Abstract

A fire alarm system having a plurality of detectors connected to a pair of conductors, a receiver and a power supply connected to said conductors and an alarm connected to the power supply and said conductors so that an alarm is sounded upon activation of a detector, each detector upon activation producing a preselected AC signal for transmission to the receiver and the receiver includes band pass filters activated by particular frequencies and having associated indicating means so that the activated detector and therefore the location of the fire or smoke can be immediately determined.

Description

This invention relates to a fire alarm system and more particularly to an alarm system including novel and improved means for detecting the specific area in which fire has occurred.

BACKGROUND OF INVENTION

In the prior fire alarm systems a number of fire or smoke detectors are generally connected in parallel between a pair of conductors which are connected to a single receiver including a power supply and an alarm device. When any of the detectors is actuated, a closed circuit including the power supply and alarm device is completed through said detector and an alarm signal is generated by the alarm device. In such fire alarm system, however, the alarm signal is generated whenever at least one of the detectors is actuated but there is no indication of the specific detector which has produced the alarm. That is, such system can only detect the outbreak of fire but cannot detect the area in which the fire has started. Therefore, prior known fire alarming systems have required other means, such as patrols for locating the fire. However, the use of patrols is difficult especially when a large number of detectors are distributed over a wide area as in a tall building or the like.

SUMMARY OF INVENTION

In order to avoid this difficulty, certain prior systems have used detectors which are individually connected to the receiver, but such systems involve the use of bulky cables and the cost of installation is high.

Therefore, one object of this invention is to provide a fire alarm system including a number of fire or smoke detectors connected in parallel on a single communication line and having novel and improved means for detecting and indicating the detector which is excited.

According to this invention, each of the detectors is provided with an oscillator which generates an AC signal having its own characteristic frequency when excited and the receiver includes means for detecting the frequency of the received signal and indicating the detector which has generated the signal. Therefore, the system of this invention can generate an alarm signal and at the same time indicate the detector being excited.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and configurations of this invention will be clearly understood from the following description with reference to the accompanying drawings.

In the drawings:

FIG. 1 is a block diagram representing a general configuration of the fire alarm system according to this invention;

FIG. 2 is a circuit diagram representing an embodiment of the detector used in the system of this invention;

FIG. 3 is a circuit diagram representing another embodiment of the detector used in the system of this invention;

FIG. 4 is a circuit diagram representing an embodiment of the receiver used in the system of this invention;

FIG. 5 is a circuit diagram representing a modification of the detector shown in FIG. 3;

FIG. 6 is a circuit diagram representing a part of a further embodiment of the detector used in the system of this invention;

FIG. 7 is a circuit diagram representing a modification of a part of the detector shown in FIG. 2;

FIG. 8 is a circuit diagram representing a modification of the circuit shown in FIG. 5; and

FIG. 9 is a circuit diagram representing a modification of the circuit shown in FIG. 6.

Throughout the drawings, like reference numerals are used to denote like structural components.

Referring now to FIG. 1, there shown is a general configuration of the fire alarm system wherein a number of fire or smoke detectors 3-1, 3-2, 3-3, . . . 3-n are connected in parallel between a pair of conductors 1 and 2 which are in turn connected to a receiver 4. The each detector 3 includes a normally open switch circuit (not shown) which is closed when the detector senses heat or smoke, and the receiver 4 includes a power supply and an alarm device (not shown) connected in series between the conductors 1 and 2. Therefore, when the switch circuit in the detector is closed, the alarm circuit is energized to give an alarm, as in the case of prior systems.

In addition, according to this invention, each detector also includes means for generating an AC signal having a predetermined characteristic frequency, and sending it to the receiver through the conductors 1 and 2, when the detector is excited or the switch circuit is closed, and the receiver 4 also includes a number of bandpass filters corresponding to the respective characteristic frequencies of the detectors and corresponding indicators, such as lamps, which are energized respectively by the signals passing the respective filters connected thereto. Therefore, if one of the detectors senses heat or smoke, an AC signal having a characteristic frequency of said detector is sent to the receiver and this signal passes one of the filters in the receiver which has a corresponding pass-band and energizes the indicating lamp associated with said detector.

Referring to FIG. 2 representing an embodiment of this invention using a bimetallic fire detector 3, three resistors 23, 24, and 25 are connected in series between a pair of conductors 1 and 2 which are connected to the receiver 4 (FIG. 1) and to which a predetermined voltage is applied from the power supply in the receiver. A normally open switch 22 is connected in parallel with the resistor 24. The switch 22 is interlocked with a bimetallic heat sensing element 21 so that it is closed when the element 21 senses a predetermined temperature. When the element 21 senses heat, the resistor 24 is short-circuited by the switch 22 and a current which is enough to energize the alarm device in the receiver 4 is caused to flow through the conductors 1 and 2.

The junction of the resistors 24 and 25 is connected through a capacitor 53 to one end of the primary winding of a transformer 52 the other end of which is connected to the base electrode of a transistor 51. One end of the secondary winding of the transformer 52 is connected through a capacitor 54 to the second conductor 2 and also through a resistor 56 to the first conductor 1, and the other end of the transformer 52 is connected through the collector-emitter path of the transistor 51 to the ground. In this case, the second conductor 2 is also grounded as shown in the drawing.

As is evident from the drawing, the transistor 51, transformer 52 and capacitor 53 and 54 and resistors 55 and 56 which are surrounded by a dashed square 5 constitute a blocking oscillator having a characteristic frequency determined by the values of these elements. When the heat sensing element 21 senses heat and closes the switch 22, the biasing voltage of the transistor 51 is changed to drive the oscillator 5 into oscillation at its own characteristic frequency. The AC signal of this frequency is sent through the capacitor 54 and the resistor 56 to the receiver 4 and sensed in the manner to be described.

Referring next to FIG. 3 representing another embodiment of the detector 3, it comprises a well-known ionization type smoke detector portion surrounded by a dashed block 6 and an oscillator portion surrounded by a dashed block 7. The ionization smoke detector 6 includes a closed ionization chamber 61 having a pair of electrodes 611 and 612 and a radioactive source 613 and closed to the external air, an open ionization chamber 62 having a similar pair of electrodes 621 and 622 and a radioactive source 623 and opened to the external air so as to allow smoke to come in and a field effect transistor 63. The ionization chambers are connected in series between the pair of conductors 1 and 2 and the junction between the both chambers is connected to the gate electrode of the field effect transistor 63. The source-drain conduction path of the field effect transistor 63 which includes a load resistor 64 is also connected between the pair of conductors 1 and 2. The source electrode of the field effect transistor 63 is connected through a zener diode 65 to the control electrode of a silicon controlled rectifier (SCR) 66 whose conduction path is connected through a potentiometer 67 between the conductors 1 and 2.

When smoke comes in the open ionization chamber 62, the impedance of that chamber is varied and thereby changes the gate potential of the field effect transistor 63. This results in increase of the drain-to-source current of the field effect transistor and accordingly in an increase of the source potential of the transistor. When the potential exceeds the zener voltage of the zener diode 65, it is applied to the control electrode of the SCR 66 and drives it into conduction. Therefore, the conductors 1 and 2 are short-circuited through the SCR 66 to energize the alarm device in the receiver 4.

The oscillator portion 7 consists of a tuning fork oscillator circuit including a diode 71, a tuning fork 72, capacitors 73 and 74, resistors 75, 76, and 77 and a transistor 78. As shown in the drawing, one leg of the tuning fork 72 is connected through a piezoelectric element attached thereto and through a diode 71 to the movable contact of the potentiometer 67 and the other leg of the tuning form 72 is connected through another piezoelectric element attached thereto and to the base electrode of the transistor 78. The tuning fork itself is connected directly to the second conductor 2 and the base electrode of the transistor 78 is connected through a parallel connection of the capacitor 73 and the resistor 75 to the conductor 2. The base electrode also is connected through the resistor 76 to the collector electrode of the same transistor 78 and to the anode electrode of the diode 71. The emitter electrode of the transistor 78 is connected through a parallel connection of the capacitor 74 and the resistor 77 to the conductor 2. This oscillator circuit has a characteristic frequency determined by the mechanical characteristics of the tuning fork 72 and the electrical values of the other elements.

When the ionization smoke detector 6 senses smoke and the SCR 66 is driven into conduction, the biasing voltage of the oscillator circuit at the movable contact of the potentiometer 67 changes and the oscillator circuit is driven into oscillation when the biasing condition is fulfilled. This AC signal having its own characteristic frequency is amplified by a resonance circuit consisting of a capacitor 25 and the primary winding of a transformer 26 and the signal induced into the secondary winding of the transformer 26 is transmitted to the receiver 4. Capacitors 27 and 28 are inserted for blocking the DC component.

Referring to FIG. 4, there shown is an embodiment of the receiver 4 of FIG. 1 and the circuit is shown in partially block form within the dashed square 4. The receiver 4 includes an alarm device shown in a dashed block 8 and consists of an electromagnetic relay 81 having a normally open contact, a power supply 82 and a parallel connection of an indication lamp 83 and a sound generator 84 connected in series with the relay contact and the power supply. One terminal of the coil of the relay 81 is connected to the first conductor 1 and the other terminal is connected through a low-pass filter consisting of capacitors 11 and 12 and a choke coil 13, surrounded by a dashed square 10, to a voltage source 45.

The receiver 4 also includes a high-pass filter 9 consisting of capacitors 91 and 92 and a choke coil 93 and having the input connected to the conductors 1 and 2 and the output connected through an amplifier 14 to a frequency discriminating network 40. The frequency discriminating network 40 consists of a number of discriminating channels respectively corresponding to the detectors 3-1, 3-2, 3-3, . . . 3-n (FIG. 1). For purposes of simplification, only three channels are shown in the drawing. Moreover, for the purpose of explanation, it is assumed that the first, second, and third channels, respectively, correspond to the detectors 3-1, 3-2, and 3-3 and the detectors 3-1, 3-2, and 3-3 include oscillator circuits having characteristic frequencies of f.sub.1, f.sub.2, and f.sub.3, respectively. Each frequency discriminating channel consists of a bandpass filter 41, an amplifier 42, a rectifier 43 and an indicator 44. The pass-frequencies of the filters 41-1, 41-2, and 41-3 of the first, second and third channels are previously selected to be f.sub.1, f.sub.2, and f.sub.3, respectively.

For instance, if the detector 3-1 senses a fire, the DC component of the signal generated by the detector passes the low-pass filter 10 and energizes the alarm device 8 and at the same time the AC component of the signal having the characteristic frequency passes the high pass filter 9, is being amplified by the amplifier 14, and is fed to the frequency discriminating network 40. In the network, the output of the amplifier 14 only passes the bandpass filter 41-1, having the pass-frequency f.sub.1 and is amplified by the amplifier 42-1, rectified by the rectifier 43-1 and indicated by the indicator 44-1 such as an indicating lamp. Since the other bandpass filters 41-2 and 41-3 do not pass the frequency f.sub.1, the signal is only processed in the first channel and indicates that the detector 3-1 has sensed the fire.

As described in the above, according to the system of this invention, when any of the detectors senses a fire, the alarm device 8 is activated and the detector is indicated by the indicator 44 of the frequency discriminating network 40. This is also true even when a plurality of detectors are excited simultaneously.

Various circuit configurations of the oscillator in the detector can be considered. FIGS. 5 and 6 represent two examples thereof.

In FIG. 5, an AC source 30 having a characteristic frequency is connected to the primary winding of a transformer 31, the secondary winding of which is connected in series with the conduction path of the SCR 66 of the ionization type smoke detector 6 shown in FIG. 3. In this embodiment, when the detector is excited and the SCR 66 is driven into conduction a DC conduction loop including the alarm device 8 is completed and at the same time a signal from the AC source 30 is coupled through the transformer 31 to the loop and superimposed on the DC component to be sent over the conductors 1 and 2. Both AC and DC components are processed in the same manner described in conjunction with the circuit of FIG. 4.

In FIG. 6 an AC source 30 which is always in oscillatory condition as in the case of the AC source 30 in FIG. 5, is coupled through a transformer 31 to a closed circuit consisting of the secondary winding of the transformer 31, the primary winding of a transformer 32 and a pair of oppositely poled diodes 33 and 34. The secondary winding of the transformer 32 is connected through DC blocking capacitors 35 and 36 to the conductors 2 and 1, respectively. The center tap of the secondary winding of the transformer 31 is connected through a normally open switch 37 to the second conductor 2 and the center tap of the primary winding of the transformer 32 is directly connected to the first conductor 1. The normally open switch 37 corresponds to the switch 22 of FIG. 2 or the SCR 66 of FIG. 3, which forms a closed loop including the alarm device when the detector is excited. When the detector is not excited, the switch is opened and a current to be induced in the secondary winding of the transformer 31 cannot flow in the primary winding of the transformer 32 since the diodes 33 and 34 have large impedances. When the switch is closed, however, the DC component flows through the both diodes and minimizes their impedance. Therefore, the AC signal induced in the secondary winding of the transrormer 31 flows in the primary winding of the transformer 32 and is sent over the conductors 1 and 2 through the secondary winding of the transformer 32. The signal is processed in the same manner as described in connection with the receiver 4 of FIG. 4.

It is advantageous, if the each detector is provided with a sound generator for generating a sound signal when the detector is excited. FIGS. 7, 8, and 9 represent modifications of the circuits of FIGS. 2, 5, and 6 which are provided with speakers. In FIG. 7 the transformer 52 is provided with the tertiary winding 57 and the speaker 58 is arranged to be driven by the tertiary winding 57. In FIG. 8, a transformer 59 is connected in series with the conduction path of the SCR 66 and the speaker 58 is arranged to be driven by the secondary winding of the transformer. In FIG. 9, the speaker 58 is arranged to be driven by the tertiary winding of the transformer 32.

As described in the above, according to the fire detecting system of this invention, the site of a fire and area of the fire can be quickly determined at the receiver and specific fire fighting instructions can be issued immediately.

The abovementioned embodiments are given only for the purpose of explanation of this invention and various modifications and changes can be made without departing from the spirit and scope of the invention.

Claims

What is claimed is:

1. A fire alarm system comprising a plurality of fire detecting units for sensing heat or smoke, a receiving station including a direct current power supply, a pair of conductors connected at one end to said power supply, connections between each detecting unit and said conductors, each of said units including an AC generating device having a preselected frequency, heat or smoke detecting means electrically coupled with said generating means and with said conductors, and means including DC blocking means coupling said generator to said conductors whereby actuation of one of said detecting means at least partially shunts said conductors to increase the flow of current therethrough and causes an AC signal to be applied to said conductors, and said receiving means includes means responsive to an increase in current in said conductors to produce an alarm, frequency discriminating means responsive to said AC signals and a plurality of indicating means interconnected with said discriminating means, each of said indicating means being selectively activated by said discriminating means upon activation of one of said detecting units to identify the location of the detecting unit producing an alarm.