U.S. patent number 3,733,596 [Application Number 05/253,868] was granted by the patent office on 1973-05-15 for alarm circuit.
This patent grant is currently assigned to Tokyo Hachiki Kabushiki Kaisha. Invention is credited to Takeo Arima.
United States Patent |
3,733,596 |
Arima |
May 15, 1973 |
ALARM CIRCUIT
Abstract
An alarm system to detect combustion products such as smoke, gas
and the like, has one or more alarm signal sending units and an
alarm signal receiving unit interconnected by wiring to the sending
units. Each alarm signal sending unit has a sensing or response
element to detect the presence of vapors or smoke and the like and
provide a signal; the sending unit also includes an amplifier
non-continuously brought to its current-carrying state for
amplifying an output signal of the response elements responding to
a change of the surrounding physical condition. The alarm signal
sending units are suitable for being connected in large numbers in
parallel with a common alarm signal receiver unit, because the
amplifier in each sending unit has a high impedance and dissipates
low power. A smoke-sensing element of the ion type and
necessitating no repeater is expediently included in the alarm
signal sending device.
Inventors: |
Arima; Takeo (Setagaya-ku,
Tokyo-to, JA) |
Assignee: |
Tokyo Hachiki Kabushiki Kaisha
(Tokyo-to, JA)
|
Family
ID: |
26372801 |
Appl.
No.: |
05/253,868 |
Filed: |
May 16, 1972 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
887485 |
Dec 23, 1969 |
|
|
|
|
Foreign Application Priority Data
|
|
|
|
|
Dec 26, 1968 [JA] |
|
|
43/95614 |
May 3, 1969 [JA] |
|
|
44/34012 |
|
Current U.S.
Class: |
340/518; 250/389;
340/629; 340/533 |
Current CPC
Class: |
G01T
7/125 (20130101); G08B 17/11 (20130101) |
Current International
Class: |
G08B
17/11 (20060101); G01T 7/12 (20060101); G08B
17/10 (20060101); G01T 7/00 (20060101); G08b
017/10 () |
Field of
Search: |
;340/237S
;250/83.6FT,43.5D,44 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Caldwell; John W.
Assistant Examiner: Myer; Daniel
Parent Case Text
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is a continuation-in-part of my prior U.S.
application Ser. No. 887,485 filed on Dec. 23, 1969, and now
abandoned.
Claims
What is claimed is:
1. An alarm system for detecting smoke, vapor and physical
conditions in an ambient region comprising in combination, an alarm
signal sending unit, an alarm signal receiving unit, connecting
means interconnecting said sending and receiving units with a power
source, said alarm signal sending unit comprising: a sensing means
featuring a changed impedance in response to a change in said
physical conditions in the ambient region of said sensing means,
said changed impedance providing an output signal; and amplifier
means connected to amplify said output signal; a pulse switching
means producing a continuous series of conducting intermittent
pulses each pulse of said series of pulses lasting for a first
interval of time which is substantially shorter than a second
interval of time between successive of said pulses; means
connecting said power source to said amplifier means through said
pulse switching means to place said amplifier means intermittently
in conductive state for short durations of time each of which
equals said first interval of time; and a power switching means
connected to receive an amplified output signal through said
amplified means and establish flow of current through said alarm
signal receiving unit to actuate an alarm, whereby the alarm system
is responsive to signals from said sensing means only during said
first intervals of time.
2. An alarm system as claimed in claim 1 wherein said pulse
switching means comprises a switching element cyclically opening
and closing.
3. An alarm system as claimed in claim 1 wherein said pulse
switching means comprises a blocking oscillator, generating a pulse
train output having a short "on" period and a comparatively long
"off" period, and wherein said power switching means comprises a
thyristor.
4. An alarm system as claimed in claim 1 wherein said pulse
switching means comprises a multivibrator, generating a pulse train
output having a short "on" period and a comparatively long "off"
period, and wherein said power switching means comprises a
thyristor.
5. An alarm system as claimed in claim 1 wherein said connecting
means interconnecting said sending and receiving units with the
power source comprises first and second lines, and wherein a
resistor is included in series with said first line and a capacitor
is connected across said first and second lines.
6. An alarm system as claimed in claim 5 which includes a Zener
diode connected in parallel with said capacitor so as to supply
said sensing means with a constant voltage.
7. An alarm system as claimed in claim 6 wherein said sensing means
comprises two ion-type smoke detectors connected in series.
8. An alarm system as claimed in claim 7, wherein said amplifier
means comprises a first transistor, and wherein a field effect
transistor is connected at the base of said first transistor so as
to be able to adjust the conductivity of said first transistor.
9. An alarm system as claimed in claim 8 wherein a source-electrode
of said field effect transistor is connected to an output terminal
of said pulse switching means and a gate electrode of said field
effect transistor is connected to a junction point between said two
ion-type smoke detectors connected in series.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an alarm system for detecting smoke,
vapor and the like, and more particularly to an alarm transmitter
provided with an amplifier for intermittently amplifying a weak
input signal given by a sensing element responsive to the presence
of smoke and the like in a surrounding ambient medium.
2. Description of the Prior Art
In general, wired alarm systems, for example, fire alarm systems
consist of one or more signal sending units a common
signal-receiving unit and suitable wiring to interconnect these
units. The receiver unit has a power source and a receiving member
of alarm signals, the latter being connected with the power source
in series. There are two kinds of signal sending units generally
used, one being a manual type which emits a signal by manual
operation and the other is an automatic type which emits a signal
automatically in response to a change of the surrounding physical
state. In the automatic type are included such signal sending units
that use a semiconductor varying its resistance in response to the
change of surrounding physical state, and those that use a sensing
element having an ionization chamber changing its resistance in
response to said change of surrounding physical state. The
semiconductor and ionization chamber devices respond sensitively to
said change, but however, their outputs are very weak. If the alarm
system is so constructed that the weak signal is transmitted
through alarm lines as it is, distinction of the weak signal from a
disturbance or a spurious signal will become difficult, and
disturbances do occur due to inductive interferences to which the
alarm lines are apt to be subjected and to any slight defect of
insulation which might possibly exist or develop in the lines. This
makes it difficult to ensure an accurate and reliable operation of
the receiver unit.
In such a case, it is expedient to amplify the weak output signal
by a suitable amplifier means. However, the amplifiers in question
have a small impedance, i.e., impedance seen from the source. If an
amplifier means having a small impedance is connected to the
transmitter, the resultant impedance of the signal sending or
transmitting unit itself will naturally reduce. As it is customary
to connect many signal transmitting units to a common receiving
unit, the resulting impedance of transmitting units seen from the
receiving unit in turn becomes very small. As a result, the current
supplied from the source in the receiver becomes large, resulting
in consumption of a large amount of power. In addition to the
above, many disadvantages are brought about by the provision of an
amplifier having a small impedance. For example, in the wired alarm
circuit, discontinuity of the circuit is a serious problem;
therefore, in order to detect the discontinuity, a resistor having
a known resistance is connected to the ends of the alarm lines and
the condition of the circuit, i.e., whether the circuit is normal
or abnormal is ascertained by reading the resistance of the
resistor by a suitable instrument upon circuit testing; however,
when many signal transmitting units having a small impedance are
connected in parallel, the detection of discontinuity becomes
difficult as it is impossible to distinguish and isolate the
impedance of the signal transmitting unit from the resistance of
resistor. Moreover, when a great number of such signal transmitting
units are connected in parallel, heavy current is drawn from the
receiver and therefore there is a fear of causing malfunction of
the alarm signal receiving means because of the heavy current.
Thus, it will be required to limit the number of transmitters to be
connected.
In order to solve these problems, the following means are
considered to be effective.
1. making the impedance of the signal transmitting unit high,
2. providing a separate power source for the amplifying means.
However, if a resistor having a high resistance is merely inserted
in series into the signal transmitting unit in order to make the
impedance of the unit high, it will result in the amplifying means
not being supplied with enough power to operate. If, however, there
is a suitable power source in the vicinity of the transmitter, the
problem can be overcome, but such a power source will not generally
be available and therefore it will be necessary to wire power
supply lines from the power source in the receiver in addition to
wiring the signal lines. This increases the cost of installation of
the lines and makes the maintenance of the system involved and
difficult.
Furthermore, it is desirable and necessary that alarm system must
not respond to any spurious signals. Response elements responding
to the change of physical state have, however, a tendency to
respond also to physical states other than that to be supervised.
Further, alarm systems, for example fire alarm systems, are
generally provided with a great number of alarm signal transmitting
units arranged in different spots, and it is therefore desired to
fit up the alarm transmitting units simply and quickly.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a novel
alarm system having an improved alarm transmitter free from the
above stated disadvantages.
Another object of the invention is to provide an alarm system which
does not respond to any spurious signal.
It is a further object of the invention to provide an alarm system
having signal transmitting units connectable to alarm lines without
the necessity of paying attention to the polarity thereof, thereby
enabling quick installation.
According to the invention, an amplifier non-continuously brought
to the current-carrying state is used as an amplifier for the alarm
transmitter. This amplifier consists of either an amplifier
cyclically rendered operable by being cyclically energized only
during a very short period of time, or an amplifier which is biased
to "off" state though it is always energized and which is brought
to an "on" state only when the response element responding to the
change of surrounding physical staTe produces an output. In either
case, there will not exist any current constantly flowing through
the amplifier, and the current will flow through the amplifier only
for a short period of time or only when the response element
produces the output. The mean value of the current dissipated by
the amplifier will therefore be rendered every small.
In fire alarm systems, the use of a smoke sensing element of the
ion type responding to combustion products such as smoke or gas
produced in the first stage of a fire makes it possible to detect
fire at an early stage thereof. However, this kind of smoke sensor
cannot be fitted readily within the ordinary alarm receiver and
requires the addition of a repeater including a source with a
voltage stabilizer because it uses an amplifier through which a
current flows constantly and because the sensitivity of the sensing
element varies according to the voltage applied across the element.
This results in increased cost for installation and troublesome
wiring work.
Accordingly, in order to obviate these disadvantages, the invention
provides an alarm transmitter having an ion type smoke sensing
element connectable directly to a signal transmitting unit without
the necessity of any repeater.
According to the invention, an alarm system having an alarm
transmitting unit, hardly responding to any spurious signal is
provided by utilizing a signal amplifier non-continuously brought
to the operable state.
Also, an alarm transmitting unit according to the invention is
connectable independent of the polarity and this is rendered
possible by the use of a diode bridge circuit.
Furthermore, according to the invention, an alarm transmitter
having an ion type smoke sensor is provided making it unnecessary
to use any repeater and this is rendered possible by utilizing an
amplifier that is brought non-continuously to the current-carrying
state and by utilizing a zener diode which limits voltage to a
predetermined value.
Other objects, features and advantages of the invention will become
apparent from the following description to be read in conjunction
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an electric circuit diagram illustrating an embodiment of
the invention;
FIG. 2 is a diagram of wave form of the output pulse of a switching
element used in the circuit of FIG. 1;
FIG. 3 is an electrical circuit diagram illustrating another
embodiment of the invention;
FIG. 4 is a circuit diagram of a diode bridge which may be used
with an a.c. power source in the circuits of FIGS. 1 and 2; and
FIG. 5 is an electric circuit diagram illustrating still another
embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to FIG. 1, a receiver unit R includes therein a
source E and an alarm signal receiving means, for example a relay
L. One end of one line l.sub.1 of a pair of lines l.sub.2 for power
supply and signal transmission is connected to one terminal of the
source E, while one end of the other line l.sub.2 is connected to
one terminal of the signal receiver means L. The other terminal of
the receiver means L is connected to the other terminal of the
source E, the other ends of lines l.sub.1 and l.sub.2 being
connected to a transmitter unit P placed remote from the receiving
unit R. The transmitter unit P comprises a switching element for
short-circuiting the pair of alarm lines l.sub.1 and l.sub.2, for
example a thyristor S, a RC circuit consisting of a resistor r and
a capacitor C, a switching element FF and an amplifier A. The
capacitor C is connected via resistor r between lines l.sub.1 and
l.sub.2 to be charged by the current from source E limited by means
of resistor r. The switching element FF has a high impedance and
consists of for example a blocking oscilator circuit, a
free-running multivibrator, or the like. The element FF will be
"on" during a period t.sub.1, as shown in FIG. 2, and will be "off"
during a period t.sub.2, the ratio t.sub.1 to t.sub.2 or the
mark-space ratio being adequately changed for the purpose
concerned. Preferably, the period t.sub.1 is chosen to 5 .times.
10.sup..sup.-5 seconds and the period t.sub.2 to 2 - 4 seconds,
t.sub.1 being much smaller than t.sub.2. The amplifier A consists
of for example a field-effect transistor amplifier, to the signal
input terminals P.sub.3 and P.sub.4 of which are connected a
response element N responding to a change of the surrounding
physical condition. The element N responds for example to the
changes of temperature, moisture, pressure, light, wind, smoke,
weight and the like and emits an output signal.
In operation, a small current constantly flows from the source in
receiver unit R through the pair of lines l.sub.1 and l.sub.2 and
resistor r to capacitor C, the current being however extremely
small in magnitude because it is limited by resistor r having a
high value of resistance. As a result, the effective impedance of
transmitter unit P seen from receiving unit R becomes very high.
The capacitor is charged by the weak current, the voltage across
the capacitor being increased gradually. When the voltage of
capacitor C reaches a predetermined level, the switching element FF
turns on impressing the voltage of the capacitor to amplifier A. As
a result, the amplifier becomes operable and, if the response
element N is emitting an output in response to the change of
surrounding physical state, it will amplify the output and produce
an output signal to turn short-circuiting element S on. Thus, the
short-circuiting element S will short circuit the pair of lines
l.sub.1 and l.sub.2, and a heavy current unrestricted by resistor r
will flow from source E through lines l.sub.1 and l.sub.2 and
receiving means L, actuating the latter to ring an alarm. The
switching element FF turns off after the expiry of period t.sub.1
to halt the discharge of capacitor C through amplifier A. The
output signal of amplifier A will therefore disappear, but the
signalling of the alarm will not be interrupted since the
short-circuiting element which in this case is thyristor S has
self-holding ability. When no signal is emitted by response element
N in response to the change of surrounding physical state,
amplifier A will not of course emit the output signal even if
switching element FF enters on-period t.sub.1, thus no alarm will
be sounded. In this case, amplifier A will merely allow capacitor C
to discharge at a rate corresponding to the conductivity of
amplifier A determined by its bias value, and capacitor C will
merely be re-charged when switching element FF enters the
off-period t.sub.2.
According to the system above described, the current constantly
supplied from the receiver unit to the transmitter unit is
restricted by resistor r; thus, all of the aforementioned
disadvantages which are caused by the otherwise constantly supplied
heavy current such as in prior art apparatus, are eliminated. In
addition, as the transmitter unit is provided with capacitor C as a
charge storing means, amplifier A is satisfactorily operable with
the help of the charge stored in that capacitor. Moreover, though
in this case amplifier A becomes operable only for the short period
of time t.sub.1 and inoperable for the long period of time t.sub.2,
the operation of amplifier A for short period of time is
satisfactory for the generation of an alarm; and the fact that the
amplifier A is in an inoperable state for a long period of time
t.sub.2 provides insensitivity of amplifier A for any spurious
signal which would arise in that period. Thus, this alarm system is
assured to be insensible to most of the spurious signals.
In FIG. 3 is shown another embodiment of the invention.
Corresponding parts in FIG. 3 are designated by same reference
numerals as in FIG. 1. The circuitry of FIG. 3 is different from
the circuitry of FIG. 1 in that the former lacks current limiting
means r and charge storing means C. The operation of the circuit of
FIG. 3 is almost similar to that of the circuit of FIG. 1. Thus,
switching element FF becomes "on" for period t.sub.1 and "off" for
period t.sub.2 as shown in FIG. 2, connecting amplifier A between
lines l.sub.1 and l.sub.2 for period t.sub.1 to bring the amplifier
to the operable state. When the response element N is not detecting
any change of the surrounding physical condition, the current
flowing for period t.sub.1 from source E through switching element
FF and amplifier A is so small in intensity that it cannot actuate
receiving means L (the current is adjusted in that manner). During
the period t.sub.2, the current from source E is directed to pass
through a portion of the components of switching element FF and
therefore is very weak in intensity. If response element N detects
a change, in the ambient condition, amplifier A will emit an output
signal when connected between lines l.sub.1 and l.sub.2 for period
t.sub.1 and as a result an alarm will be sounded in the same manner
as in FIG. 1.
A diode bridge circuit illustrated in FIG. 4 can be connected to
the power input side of transmitter unit P. In order to assure
normal functioning of unit P, it is normally necessary to take care
of the polarity of voltage applied to the pair of power input
terminals. For example, in the circuits of FIGS. 1 and 3,
transmitter unit P should be connected to lines l.sub.1 and l.sub.2
so that a positive electric potential is applied to terminal
P.sub.1 while a negative potential to terminal P.sub.2. This is a
troublesome job in actual installation work. However, if a diode
bridge circuit as in FIG. 4 is provided, it will be unnecessary to
pay attention to the polarity of the lines during installation work
because the bridge circuit always corrects the polarity so that the
positive voltage be applied to the anode of thyristor S and the
negative voltage to the cathode thereof irrespective of the
polarity of voltage applied to terminals P.sub.1 and P.sub.2.
Moreover, if the diode bridge circuit is provided, source E of the
receiver unit may be an A.C. source instead of a D.C. source.
FIG. 5 illustrates a further embodiment of the invention. In this
embodiment, an ion type smoke detector element is used as the
response element responding to the change of surrounding physical
state to emit a signal in response to the presence of smoke. The
ion type smoke sensing element comprises an ionization chamber
having a source of radiation for ionizing the surrounding air and a
pair of electrodes provided in said chamber. In the embodiment
shown, two such smoke sensing elements are used, in the outer
ionization chamber OC of one of which is housed a pair of
electrodes OC.sub.1 and OC.sub.2 and outside air can freely flow
into the chamber, while in the inner ionization chamber IC of the
other is housed a second pair of electrodes IC.sub.1 and IC.sub. 2
and the outside air cannot flow into the chamber. The two sensing
elements are connected between supply lines l.sub.1 and l.sub.2 in
series. That is, electrode OC.sub.1 is connected to line l.sub.1,
electrode OC.sub.2 to electrode IC.sub.1 and electrode IC.sub.2 to
line l.sub.2, respectively. The line l.sub.1 is connected via
resistor R.sub.3 to line l.sub.2 and by virtue of a zener diode ZD
connected between l.sub.1 and l.sub.2, the voltage across lines
l.sub.2 and l.sub.1 is limited to a fixed value determined by diode
ZD, even though the voltage between lines l.sub.1 and l.sub.2 may
be higher, thus supplying the smoke sensing element with a constant
voltage.
Between lines l.sub.1 and l.sub.2 are further connected a
transistor amplifier A, a capacitor C having same function as that
in FIGS. 1 and 3 and a free-running multivibrator FMV. The
multivibrator FMV is a switching element corresponding to FF in
FIGS. 1 and 3, one terminal P.sub.5 of output terminals P.sub.5 and
P.sub.4 of which is connected to the source electrode of a
field-effect transistor F.sub.1. The gate electrode of transistor
F.sub.1 is connected to junction T of electrode OC.sub.2 with
electrode IC.sub.1 , the drain electrode of which being connected
to an input terminal of amplifier A, i.e. to the base of
transistor.
The operation of multivibrator FMV is substantially the same as
that of a wellknown multivibrator and can be briefly explained as
follows: The FMV comprises two field-effect transistors F.sub.2 and
F.sub.3, and it is firstly assumed that F.sub.3 is "on" while
F.sub.2 is "off"; then capacitor C.sub.1 is gradually charged and
the gate of F.sub.3 will be biased to positive as the charging
considerably progresses, rendering the voltage between the gate and
the source of F.sub.3 to be lower than the cut-off valve so that
F.sub.3 turns off. As a result the gate of F.sub.2 is biased to
negative and F.sub.2 turns on. Capacitor C.sub.1 is therefore
charged at reversed polarity against the previous one, and as the
charging progresses the gate of F.sub.3 will be biased to negative
and when the voltage between the gate and the source of F.sub.3
increased above the cut-off voltage the transistor F.sub.3 will
turn on, biasing the gate of F.sub.2 to positive to turn F.sub.2
off. In the manner described above, F.sub.2 and F.sub.3 are
alternately in turn-on and turn-off stages, generating
substantially rectangular pulses at the terminals P.sub.5 and
P.sub.4. The pulses are set similar to the previous example so that
the on-period t.sub.1 is a few 10 micro-seconds while the
off-period t.sub.2 is a few seconds.
The circuitry of FIG. 5 thus constructed will function as follows:
Since the air in the ionization chamber of ion type smoke sensing
element is ionized as afore-mentioned, a weak current is normally
flowing through ionization chambers OC and IC connected in series,
and thus the junction point T has a certain voltage obtained from
dividing the voltage between lines l.sub.1 and l.sub.2 by the ratio
of impedances of two sensing elements. To the source electrode of
transistor F.sub.1 is supplied the output voltage of FMV during
period t.sub.1, but the transistor in amplifier A will remain in
its off-state as the voltage of junction T at normal condition
cannot turn F.sub.1 on and no base current is applied to the
transistor. In a normal condition, therefore, the current to ion
type smoke sensor P (which corresponds to the transmitting units in
FIGS. 1 and 3) is only a current which is limited by resistor r
having a high resistance and flows through elements ZD, C, FMV, OC
and IC, the current being very weak in intensity. Upon occurrence
of a fire, smoke or gas will flow into outer ionization chamber OC
and prevent the air in the chamber from being ionized by absorbing
air ions or energy of radiation material. As a result, the path
between the electrodes of outer ionization chamber OC will have a
higher impedance, thereby restricting the flow of current. The
potential of the junction point T therefore will drop, and
transistor F.sub.1 will turn on when period t.sub.1 is commenced.
The output voltage of FMV therefore causes the base current of
transistor of amplifier A to flow through F.sub. 1 to turn the
transistor on, and the output voltage of amplifier A turns on
thyristor SCR which short-circuits lines l.sub.1 and l.sub.2. As a
result, an alarm will be caused in the same manner as in the
circuits of FIGS. 1 and 3.
It is to be understood that this invention is not limited to the
exact construction in the embodiments shown and described, and
various changes and modifications may be made without departing
from the spirit and scope of the invention as defined in the
appended claims.
* * * * *