U.S. patent number 3,753,258 [Application Number 05/122,956] was granted by the patent office on 1973-08-14 for fire alarming system.
This patent grant is currently assigned to Nittan Company Limited. Invention is credited to Yukio Honda.
United States Patent |
3,753,258 |
Honda |
August 14, 1973 |
FIRE ALARMING SYSTEM
Abstract
A fire alarm system having a plurality of fire detectors
connected in parallel to a transmission line, each detector having
a band pass filter resonating at a specific individual frequency. A
receiver is connected to the transmission line and generates a
plurality of frequencies corresponding to the frequencies of the
detectors and has means for detecting specific frequencies returned
thereto when one or more of the detectors are activated by fire,
thus enabling detection and location of a fire.
Inventors: |
Honda; Yukio (Nakano-ku, Tokyo,
JA) |
Assignee: |
Nittan Company Limited (Tokyo,
JA)
|
Family
ID: |
26364683 |
Appl.
No.: |
05/122,956 |
Filed: |
March 10, 1971 |
Foreign Application Priority Data
|
|
|
|
|
Mar 31, 1970 [JA] |
|
|
45/26844 |
Mar 31, 1970 [JA] |
|
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45/26843 |
|
Current U.S.
Class: |
340/524; 340/521;
340/594; 340/533; 340/629; 340/8.1 |
Current CPC
Class: |
G08B
17/11 (20130101); G08B 25/04 (20130101) |
Current International
Class: |
G08B
17/11 (20060101); G08B 17/10 (20060101); G08B
25/04 (20060101); G08B 25/01 (20060101); G08b
025/00 () |
Field of
Search: |
;340/227,228,191,179,181,408,182,185,224,171PF,184,413,416,171,237
;310/8.1 ;343/6.5,6.5SS |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Caldwell; John W.
Assistant Examiner: Partridge; Scott F.
Claims
What is claimed is:
1. A fire alarm system comprising a plurality of fire sensing units
connected in parallel between a pair of conductors, a receiving
unit including a voltage source and an alarm device connected to
said conductors, each of said fire sensing units including a
normally open switch which is closed to short circuit said
conductors and energize said alarm device when a fire is sensed,
each fire sensing unit further including a band pass filter
connected between said conductors and having a characteristic
resonant frequency preselected peculiarly to said sensing unit,
said receiving unit further including means for generating a range
of AC signals having frequencies corresponding to said
characteristic resonant frequencies of said filters in the
respective sensing units, each of said filters being operated upon
actuation of its associated sensing unit to produce its
characteristic frequency, a conductor directly connecting the
outputs of said filters in said sensing units to said receiving
unit and means in said receiving unit and connected with the last
said conductor for discriminating the frequencies of the received
AC signals and indicating the specific detector activated by the
presence of fire whereby each detector upon activation produces
both a general alarm and an indicating signal to identify at the
receiving unit the specific detector actuated.
2. A fire alarm system according to claim 1 wherein each of said
filters is an electromechanical band pass filter and each of said
detectors includes a sounding device driven by said
electromechanical filter.
3. A fire alarm system according to claim 1 wherein said indicating
means includes a plurality of electric lamps.
4. A fire alarm system according to claim 1 wherein each of said
fire sensing units sense both ambient temperature and smoke.
Description
This invention relates to a fire alarm system and more particularly
to such a system including novel and improved means in detecting
the location of a fire.
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
excited, a closed circuit including the power supply and alarm
device is completed through said detector and an alarm signal is
generated from the alarm device. In such a fire alarm system,
however, the alarm signal is generated whenever at least one of the
detectors is excited but it cannot indicate which detector has been
excited. That is, such system can only detect a fire but cannot
detect where the fire has started. Therefore, the prior fire alarm
system has required other means, such as patrols for finding the
location of the fire. However, such a procedure is difficult
especially when large numbers of detectors are distributed over a
wide area or in a tall building.
In order to overcome this difficulty in some of the prior systems,
the detectors are individually connected to the receiver, but such
systems require a bulky bundle of cables and the cost of
installation is high. As described in a co-pending U.S. Pat.
application, Ser. No. 120,178, filed Mar. 2, 1971, this inventor
describes a novel system wherein each of the detectors includes an
oscillator which generates its own characteristic frequency when
excited and the receiver includes means for detecting the frequency
and indicating the corresponding detector. Although the system is
very effective in comparison to the prior systems, the detectors
are rather bulky and costly.
Therefore, one object of this invention is to provide an improved
low cost fire alarm system which can quickly indicate any detector
now being excited.
According to this invention, each of the detectors includes a
filter which can pass only its own characteristic frequency when
excited and the receiver includes means for generating AC signals
having at least the characteristic frequencies of the detectors and
means for detecting these frequencies and indicating the
corresponding detectors. Therefore, the system of this invention
can generate an alarm signal and at the same time indicate the
detectors being excited. In addition, the detectors of this system
can be made rather compact and at a low cost since they have few
and relatively simple structural components.
Other features and operation of this invention will be more clearly
understood from the following description and the accompanying
drawings.
In the drawings:
FIG. 1 is a diagram representing partly in block form a general
circuit configuration of a prior fire alarm system;
FIG. 2 is a diagram representing, partly in block form, a circuit
configuration of an ionization type smoke detecting system
including an embodiment of this invention;
FIG. 3(1) and 3(2) are schematic circuit diagrams explaining
operation of the embodiment of FIG. 2;
FIG. 4 is a schematic circuit diagram representing an ionization
smoke detector in accordance with another embodiment of this
invention;
FIGS. 5(1) and 5(2) are schematic circuit diagrams explaining the
operation of the embodiment of FIG. 7;
FIGS. 6(1) and 6(2) are schematic diagrams representing a sounding
device to be included in the detector of this invention;
FIG. 7 is a schematic diagram representing a circuit configuration
of a bimetal type fire detecting system and the construction of the
detector in which this invention is embodied; and
FIG. 8 is a block diagram representing a further embodiment of fire
alarm system according to this invention.
Throughout the drawings, like reference numerals are used to denote
like structural components.
Referring first to FIG. 1 representing a prior fire alarm system, a
number of fire detectors 10-1, 10-2, . . . , 10-n are connected in
parallel between a pair of conductors 1 and 2 which are
respectively connected to the both input terminals 7 and 8 of a
receiver 11. The receiver 11 includes an electromagnetic relay 12,
a power supply 13 indicated as a battery and connected in series
with the electromagnet of the relay 12 between both input terminals
7 and 8. Another power supply 14 is indicated as an AC source and
is connected in series with the normally open contact of the relay
12 and an indicating lamp 15 and a sounding device 16 such as a
bell or buzzer which is connected in parallel with the indicating
lamp 15. Although there are many types of detectors 10, most of
them can be represented by a single-pole, single-throw normally
open switch as indicated schematically in the drawing, which is
closed when the detector is excited.
When any of the detectors of the system is excited, a closed
circuit including the power supply 13 and the realy 12 is completed
to energize the relay 12 and close its contact and thus the
existance of a fire is indicated by the lamp 15, and an alarm is
sounded by the sounding device 16. As readily understood, in the
such system, the receiver can indicate the existance of a fire but
cannot indicate the site of the fire since the relay 12 is
energized similarly by any of the detectors being excited.
Referring now to FIG. 2 representing an embodiment of this
invention, a number of detectors 10-1, 10-2, . . . , are connected
in parallel between a pair of conductors 1 and 2 which are
respectively connected to input terminals 7 and 8 of a receiver 11.
The receiver 11 also has a third terminal 9 connected to a third
conductor 3 which is in turn connected to each of the third output
terminals of the respective detectors.
As shown in detail in the first detector 10-1 only, each of the
detectors consists of a fire detecting section 17 and a frequency
filtering section 18. The fire detecting section 17 of this
embodiment consists of an ionization type smoke detector including,
as well-known in the art, a closed ionization chamber 19 having a
pair of electrodes 21 and 22 and a radioactive source 23 for
ionizing the ambient air and an open ionization chamber 20 having a
similar pair of electrodes 24 and 25 and a radioactive source 26.
The electrodes are connected in series between terminals 4 and 5 of
the detector which in turn are connected to the conductors 1 and 2,
respectively. The smoke detector also includes a field effect
transistor 27 having a gate electrode connected to the junction
between the both ionization chambers 19 and 20 and a drain-source
conduction path connected through a load resistor 28 between the
both terminals 4 and 5, and a silicon controlled rectifier 30
having a conduction path connected also between the terminals 4 and
5 and a control electrode connected through a zener diode 29 to the
source electrode of the field effect transistor 27. A specific
operation voltage is always applied between the both terminals 4
and 5 by a power supply 13 included in the receiver 11.
As well-known in the art, when smoke enters the open ionization
chamber 20, it acts to raise the impedance of the chamber and
consequently the voltage at the gate electrode of the field effect
transistor 27. This action increases the drain-to-source current
and in turn increases the source voltage thereof. When the source
voltage exceeds the zener voltage of the zener diode 29, it drives
the silicon controlled rectifier 30 into conduction to form a
short-circuit between the conductors 1 and 2.
The frequency filtering section 18 consists of an electromechanical
filter consisting of a tuning fork 32, an electromagnet 31 serving
as a magnetostrictive conversion element magnetically coupled to
one leg of the tuning fork and a piezoelectric conversion element
34 attached to the other leg of the tuning fork. The electromagnet
31 has a biasing winding wound on one leg thereof and connected
between the cathode of the silicon controlled rectifier 30 and the
second terminal 5 and a driving winding wound on the other leg and
connected between the both terminals 4 and 5 through a blocking
capacitor 33. The piezoelectric element 34 is connected to the
third output terminal 6 which is connected to the third conductor
3.
As is known in the art, in the resonance condition, the
electromechanical filter of this embodiment can be represented by
an equivalent four-terminal circuit as shown in FIG. 3(1). The
circuit consists of an electrical convertor section 38 consisting
of a parallel circuit of an inductance L1 and a capacitance C1, and
a mechanical convertor section 39 consisting of a series circuit of
an inductance M1, a capacitance S1 and a resistance R which
correspond respectively to mass, stiffness and mechanical
resistance of the mechanical portion of the filter. The
electromagnetic filters of the detectors 10-1, 10-2, . . . , 10-n
of this system have their own characteristic resonance frequencies
f.sub.1, f.sub.2, . . . f.sub.n, respectively, which are
predetermined by selecting the values of the above structural
components. When an AC signal having frequency f.sub.1 is fed to
the filter 18 of the detector 10-1 through the driving winding of
the electromagnet 31, for example, it passes through the filter and
appears at the terminal 6 since the series resonance circuit 39
does not materially attenuate a signal having the same frequency as
its resonance frequency f.sub.1. When the input signal has a
frequency other than f.sub.1, however, the filter does not resonate
and the signal is greatly attenuated by the filter and will not
appear at the terminal 6. This condition can be represented by a
circuit, shown in FIG. 3(2), having an open switch 40 in place of
the series resonance circuit 39.
Referring again to FIG. 2, the receiver 11 includes a variable
frequency generator 35 connected between the terminals 7 and 8, a
rectifier 36 connected between the terminals 8 and 9 and an
indicator 37, such as a voltmeter, for indicating the level of
output of the rectifier 36. In addition, a relay 12, a DC source
13, and an AC source 14, an indication lamp 15, and a sounding
device 16 are arranged similarly to those in the receiver 11 of
FIG. 1.
When the detector 10-1 is excited by smoke coming in the open
ionization chamber 20, the silicon controlled rectifier 30 is
driven into conduction as described in the above to short-circuit
the both terminals 7 and 8 of the receiver 11. Therefore, the relay
12 is energized and an alarm signal is generated as described in
conjunction with FIG. 1. At the same time, the tuning fork
resonator 32 is activated by the biasing winding of the
electromagnet 31.
In this condition, if the variale frequency generator 35 is
operated and its frequency is varied over a wide range, and is
applied to the filter through the driving winding of the
electromagnet 31 only the frequency f.sub.1 will pass the filter
and be picked up by the piezoelectric element 34 and appear at the
output terminal 6. This signal is transmitted through the conductor
3 to the receiver 11 and rectified by the rectifier 36 and its
level is indicated by the indicator 37. Therefore, the excitation
of detector 10-1 can be determined at the receiver 11 by reading
the frequency of the variable frequency generator 35 corresponding
to the maximum swing of the indicator 37. Similarly when any of the
other detectors is excited, the excited detector can be determined
by the frequency which gives a maximum swing of the indicator
37.
FIG. 4 shows another embodiment of an ionization smoke detector
including a modification of the electromechanical filter shown in
FIG. 2. In this embodiment, the mechanical filter consists of a
driving magnet 31, a tuning fork 32 and a pick-up magnet 41. The
driving magnet 31 has a leg which includes a permanent magnet for
constantly biasing the tuning fork 32 in an activated state. The AC
signal applied from the variable frequency generator 35 to the
terminal 4 passes through the silicon controlled rectifier 30 and
the driving winding of the driving magnet 31 in superposition with
the DC current applied from the power supply 13 and is picked up by
the pick-up winding of the pick-up magnet 41 when the detector is
excited.
Since in the above mentioned embodiments the electromechanical
filter is used as a four-terminal network, the system requires at
least three conductors. However, it has been well known in the art
that such electromechanical filters having four terminals can be
changed into a two-terminal network by terminating both output
terminals with a suitable resistor. In this case, the equivalent
circuit of the filter can be represented by the circuit of FIG.
5(1) in its resonant state or by the circuit of FIG. 5(2) in its
nonresonant state. As in the case of FIG. 3, a signal having a
resonant frequency of a given detector can pass through the series
resonant circuit 39 but other signals having other frequencies can
pass through neither the series resonance circuit 39 not the
parallel resonance circuit 38 and is blocked by the filter. By
applying this principle to the system, the number of necessary
conductors can be reduced on two.
Each of the detectors may be provided with a sounding device to
produce an audible alarm upon the excitation of a detector. This
can be simply accomplished by attaching a dynamic speaker to one
leg of the tuning fork as shown in FIG. 6(1). In the drawing, a
tuning fork resonator 32 has an input piezoelectric element 60 and
an output piezoelectric element 61. A permanent magnet 62 is
attached to one leg 58 of the tuning fork and is surrounded by a
voice coil 64 of a speaker 63. This arrangement is symbolized by
the structure denoted by the numeral 71 in the equivalent circuit
diagram of FIG. 6(2). When the tuning fork is driven into resonant
condition, the permanent magnet 62 vibrates with the leg 58 at its
resonance frequency and induces an audio current in the voice coil
64. Again due to interaction between the audio current and the
permanent magnet 62, the voice coil 64 vibrates at the audio
frequency and sounds the speaker 63.
Referring next to FIG. 7 representing another embodiment of the
system of this invention, a plurality of detectors 10-1, 10-2, . .
. 10-n of which 10-1 is shown in detail in a sectional view while
the others are shown schematically in block form. All of the
detectors are connected in parallel between a pair of conductors 1
and 2 which are respectively connected to a pair of input terminals
7 and 8 of a receiver 11. The other ends of the conductors 1 and 2
are terminated with a high-pass filter 42 which blocks the DC
component of a signal but serves as a specific impedance for the AC
component thereof.
The detectors 10-1, 10-2 . . . 10-n, respectively, consist of
electromechanical filter sections 18-1, 18-2, . . . 18-n and
normally open switch sections 40-1, 40-2 . . . 40-n. The switch
sections are connected in parallel between the pair of conductors 1
and 2 but the filter sections are connected in series with the
first conductor 1. As hereinafter described, the switch sections
consist of similar normally open contact switches operated by a
bimetal element and the filter sections consist of tuning fork
resonators having their own characteristic resonant frequencies
f.sub.1.sup.. f.sub.2, . . . f.sub.n, respectively.
As shown in detail in the dashed block of the detector 10-1, each
of the detectors comprises a cylindrical housing 51 made of a
suitable material such as metal or synthetic resin, an insulating
base 52 fixed to the bottom of the housing 51 for supporting an
insulating support rod 55 and a tuning fork 32, a thermally
deformable heat sensing element 53 such as bimetal plate fixed to
the top of the housing 51 and a mesh cover 54. The support rod 55
extends upwardly through the heat sensing element 53 so as not to
interfere with its movement and supports at its upper end a pair of
normally open contacts 56 and 57. The heat sensing element 53 has
an original shape which is concave downwardly as shown by dotted
lines in the drawing and has a contact block 59 fixed to the lower
face thereof, and is so arranged that the contact block 59 contacts
with the top of the tuning fork 32 to suppress its vibration in the
original state but it is deformed thermally into a shape which is
upwardly convex as shown in the drawing and the upper face of the
element 53 pushes up the lower contact 56 into contact with the
upper contact 57. The tuning fork 32 is provided with a sounding
device, which is similar to that described in conjunction with FIG.
6 consisting of a permanent magnet 62 fixed to one leg 58 thereof,
a voice coil 64 surrounding the magnet 62 and a speaker horn 63
attached to the voice coil 64. A hole 65 is formed in the wall of
the housing 51 to emit sound generated by the speaker. The
insulating base 52 is also provided with connector pins 66, 67, 68,
69 and 70. When the detector is installed in the system, as shown
in the drawing, the contacts 56 and 57 are connected respectively
through the connector pins 66 and 67 to the conductors 1 and 2 and
the tuning fork resonator 32 is connected in series with the first
conductor 1 through the piezoelectric elements 60 and 61 and the
connector pins 69 and 70.
The equivalent circuit of the tuning fork resonator 32 of this
embodiment is shown in FIG. 5(1) in the resonant state and in FIG.
5(2) in a nonresonant state. Since it is assumed in FIG. 7 that
only the detector 10-1 is excited, the switch sections of the other
detectors are indicated as being open and the series resonant
circuits 39 (FIG. 5) are omitted from the filter sections of the
other detectors.
The receiver 11 also includes an electromagnetic relay 12, a power
supply 13, another power supply 14, an indicating lamp 15 and a
sounding device 16 which serve the same functions as those of FIG.
1. In addition, the receiver 11 includes a low-pass filter 43
consisting of a choke coil 45 and capacitors 46 and 47 and is
connected between the relay 12 and the power supply 13. A high-pass
filter 14 consisting of a choke coil 48 and capacitors 49 and 50 is
connected between the terminals 7 and 8. Between the high pass
filter 44 and the terminal 8 there are also connected a variable
frequency generator 35 and an indicator 37. The indicator 37 has a
plurality of indicating lamps which correspond respectively to the
detectors 10-1, 10-2, . . . 10-n in the system and can be
illuminated by an AC current having a level higher than a specific
value. The indicator 37 is interlocked with the variable frequency
generator 35 so that the indicating lamps respectively correspond
to the detectors 10-1 to 10-n are successively switched into the
line in correspondence with the successive change of frequency from
f.sub.1 to f.sub.n of the generator 35. The other end of the power
supply 13 and the terminal 8 are grounded as shown in the drawing.
Thus the DC component of the input signal flows through the relay
12 and the AC component flows through the indicator 37.
In operation, if a detector is not excited, all of the switch
sections 40-1 through 40-n are open and all of the filter sections
18-1 through 18-n are in the condition as shown in FIG. 5(2).
Therefore, even though the frequency of the generator 35 is varied
from f.sub.1 to f.sub.n, there is neither a DC current nor an AC
current flowing through the conductors 1 and 2 because a closed
circuit is not formed for the both DC and AC signal component.
However, when one of the detectors, for example the first detector
10-1 as shown in FIG. 7, is excited, that is, when the heat sensing
element 53 is heated to cause the bimetal to deflect upwardly as
shown by full lines in the drawing, the lower contact 56 is pushed
up into contact with the upper contact 57 to short-circuit the
conductors 1 and 2 and at the same time, the contact block 59
leaves the top of the tuning fork 32 to permit it to vibrate. In
this condition, the DC component can flow through the relay 12 to
generate an alarm signal and the AC component of frequency f.sub.1
which has been blocked only by the filter section of the detector
10-1 flows in the indicator 37 to flash the corresponding lamp.
Therefore, if the variable frequency generator 35 is continuously
varied over the full range of frequency, the activated detector is
automatically indicated on the indicator 37 at the same time an
alarm signal is given when any of the detectors is activated by
fire.
FIG. 8 represents a variation of the receiver 11. In this receiver,
the variable frequency generator 35 of the foregoing receiver is
replaced by a plurality of fixed frequency generators 35-1, 35-2,
35-3, . . . 35-n which generate frequencies f.sub.1, f.sub.2,
f.sub.3 . . . f.sub.n, respectively, and the indicating means
consists of a plurality of groups respectively corresponding to the
frequencies f.sub.1 and f.sub.n and consisting of band-pass filters
74-1 to 74-n having characteristic pass-frequencies f.sub.1 to
f.sub.n respectively, amplifiers 75-1 to 75-n, rectifiers 76-1 to
76-n and indicating lamps 77-1 to 77-n.
In operation, AC signals having frequencies f.sub.1 to f.sub.n,
respectively, are generated by the generators 35-1 to 35-n,
amplified by an amplifier 72 and applied through a chopper 73 to a
parallel connection of detectors 10-1 to 10-n and terminals 7 and
8. If one of the detectors is excited and passes its characteristic
frequency, tis frequency is fed back to the receiver 11, filtered
by a corresponding band-pass filter, amplified and rectified and
flashes one of the indicating lamps which indicates the excited
detector. It is obvious that the fire alarm device which handles
the DC component is the same as that of the foregoing embodiments,
though it is not indicated in the receiver 11 of FIG. 8.
As described in the above, according to this invention, the site of
the fire can be easily determined at the receiver and this makes it
possible to centrally control a number of fire alarm systems.
Moreover, the detectors according to this invention are rather
simple in construction and can be manufactured at low cost.
It should be noted that the abovementioned embodiments of this
invention are presented only for the purpose of illustration, and
various modifications and changes can be made without departing
from the spirit and scope of the invention. For example, though the
filter used in each detector is indicated as an electromechanical
filter and especially a tuning fork resonator, any other type of
band-pass filter having suitable narrow frequency characteristics
can be adopted. Moreover, though the detectors are illustrated as
ionization types and bimetal types, any other type of detector
having a normally open switching circuit which is closed when the
detector is excited can be used as the occasion demands.
* * * * *