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Claims  |
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What is claimed is:
1. A fire sensing system, comprising:
a plurality of band-pass filters separating infrared radiation from a
source of infrared radiation into a plurality of wavelength bands;
an infrared sensor sensing an infrared radiation which has passed through
each of said band-pass filters, one of the wavelength bands comprising a
CO.sub.2 -molecular resonance radiation wavelength band;
a signal processor determining whether a disastrous fire occurs or not in
response to outputs of the infrared sensors and a change in a ratio of the
outputs of the infrared sensors; and
a chopper periodically chopping said infrared radiation from said source of
infrared radiation in order to provide said infrared radiation to said
infrared sensors.
2. A fire sensing system as recited in claim 1, further comprising an
infrared sensor for a band of 1-16 .mu.m wavelength.
3. A fire sensing system as recited in claim 1, wherein the pass band of
each of said band-pass filters excludes a 5-8 .mu.m wavelength band of
infrared radiation.
4. A fire sensing system as recited in claim 1, wherein said signal
processor detects the outputs of said infrared sensors synchronous with
two periodical signals which are synchronous with the rotation of said
chopper, said periodical signals having two 90-degree different phases and
said signal processor then produces a mean square of the resulting
synchronization-detected signals.
5. A fire sensing system, comprising:
a plurality of band-pass filters separating infrared radiation from a
source of infrared radiation into a plurality of wavelength bands;
an infrared sensor sensing an infrared radiation which has passed through
each of said band-pass filters, one of the wavelength bands comprising a
CO.sub.2 -molecular resonance radiation wavelength band;
a signal processor determining whether a disastrous fire occurs or not in
response to outputs of the infrared sensors and a change in a ratio of the
outputs of the infrared sensors, and
wherein said signal processor computes the blackbody radiation intensity of
the sensing band of one of said infrared sensors which senses a CO.sub.2
-molecular resonance radiation band in response to said one of said
infrared sensors, and said signal processor compares the computer
blackbody radiation intensity with an output of said one of said infrared
sensors in order to sense CO.sub.2 -molecular resonance radiation and
determines an occurrence of a disastrous fire when sensing the CO.sub.2
-molecular resonance radiation.
6. A fire sensing system as recited in claim 5, wherein said signal
processor comprises a filter passing a signal of a predetermined frequency
of the sensing outputs of said infrared sensors, a comparator comparing
said signal with a predetermined reference level, and a microcomputer
determining the existence of an uncontrolled fire in response to a signal
produced by the comparator.
7. A process for sensing a fire, comprising the steps of:
computing the temperature of an infrared source from a ratio of outputs of
a plurality of infrared sensors sensing at least two wavelength bands of
an infrared radiation from a monitored area;
computing the intensity of infrared radiation of one of the wavelength
bands from said computed temperature;
computing a heating area from the intensity of the infrared radiation and
an output of an infrared sensor sensing said one of the wavelength bands;
utilizing one of the infrared sensors for sensing a CO.sub.2 -molecular
resonance radiation wavelength band;
computing the blackbody radiation intensity of the infrared source in a
CO.sub.2 -molecular resonance radiation wavelength band from the
temperature and the heating area of the infrared source both computed from
an output of the other infrared sensor in accordance with said temperature
and heating area computing steps; and
comparing the computed blackbody radiation intensity with an output of said
one of said infrared sensors sensing CO.sub.2 -molecular resonance
radiation and determining an occurrence of a disastrous fire when sensing
the CO.sub.2 -molecular resonance radiation.
8. A process for sensing, a fire as recited in claim 7, wherein a selection
determining which of the outputs of said infrared sensors are computed
depends on a sensed target temperature.
9. A process for sensing a fire as recited in claim 7, further comprising
the step of driving an alarm when determining an occurrence of disastrous
fire.
10. A process for sensing a fire as recited in claim 7, further comprising
the step of displaying a computed heating area of the infrared source on a
monitor.
11. An environment monitor, comprising:
a plurality of band-pass filters separating infrared radiation from a
monitored space into a plurality of wavelength bands;
an infrared sensor sensing infrared radiation passing through each of said
band-pass filters, one of the wavelength bands comprising a CO.sub.2
-molecular resonance radiation wavelength band;
a signal processor determining the occurrence of fire and computing a
temperature of the infrared radiation from the monitored space from
outputs of the infrared sensors of the wavelength bands and a change in a
ratio of said sensing outputs; and
a chopper periodically chopping the infrared radiation from the infrared
source in order to provide the infrared radiation to said infrared
sensors.
12. An environment monitor as recited in claim 11, further comprising an
infrared sensor for a 1-16 .mu.m wavelength band of infrared radiation.
13. An environment monitor as recited in claim 11, further comprising a
contact type temperature sensor for measuring an indoor air temperature
and wherein said signal processor produces a signal controlling an air
conditioner in response to outputs of said contact type temperature sensor
and said infrared sensors.
14. An environment monitor as recited in claim 11, further comprising a
contact type temperature sensor for measuring an indoor air temperature
and wherein said signal processor produces a signal controlling a room
cooler and a room heater in response to outputs of said temperature sensor
and said infrared sensors.
15. An environment monitor as recited in claim 11, wherein the pass band of
each of said band-pass filters excludes a 5-8 .mu.m wavelength band of
infrared radiation.
16. A process for sensing a fire, which comprises the steps of:
computing the temperature of an infrared source from outputs of a plurality
of infrared sensors sensing at least two different wavelengths by
comparing the ratio of said outputs;
computing the blackbody radiation intensity of at least one of said
different wavelengths from said computed temperature;
computing a heating area of said infrared source from said blackbody
radiation intensity and output from said infrared sensor sensing said at
least one of said different wavelengths; and
determining the existence of a uncontrolled fire from changes in said
computed temperature and said computed heating area.
17. a process for sensing a fire as recited in claim 16, further comprising
the steps of:
utilizing one of said plurality of infrared sensors for sensing radiation
at a wavelength corresponding to CO.sub.2 -molecular resonance;
computing the blackbody radiation intensity of said wavelength
corresponding to CO.sub.2 -molecular resonance from said computed
temperature and said computed heating area; and
comparing computed blackbody radiation intensity of said wavelength
corresponding to CO.sub.2 -molecular resonance with an output of said
infrared sensor sensing radiation at a wavelength corresponding to
CO.sub.2 -molecular resonance to determine the existence of a flaming
infrared source.
18. A process for sensing a fire as recited in claim 16, further comprising
the step of displaying said heating area on a display monitor.
19. A fire sensing system, comprising:
a plurality of band-pass filters separating infrared radiation from a
source of infrared radiation into a plurality of wavelength bands, wherein
one of said band-pass filters passes a CO.sub.2 -molecular resonance
radiation wavelength band;
a plurality of infrared sensors sensing said separated infrared radiation
which has passed through each of said band-pass filters;
a signal processor for determining a temperature and a heating area of said
source of infrared radiation and determining the existence of an
uncontrolled fire based on changes in said temperature and said heating
area; and
a signal processor for determining the existence of a flame in said source
of infrared radiation by comparing an output of a sensor sensing said
CO.sub.2 -molecular resonance radiation wavelength with a value predicted
by said temperature and said heating area for determining the existence of
an uncontrolled flaming fire.
20. A fire sensing system, comprising:
a plurality of band-pass filters separating infrared radiation from a
source of infrared radiation into a plurality of wavelength bands;
a plurality of infrared sensors sensing said separated infrared radiation
which has passed through each of said band-pass filters;
a signal processor for determining a temperature and a heating area of said
source of infrared radiation and determining the existence of an
uncontrolled fire based on changes in said temperature and said heating
area; and
a chopper periodically chopping said infrared radiation from said source of
infrared radiation in order to provide said infrared radiation to said
infrared sensors. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fire sensing system using an infrared
sensing process and more particularly to a fire sensing system separating
an incident infrared radiation into a plurality of wavelength bands,
sensing a change in the absolute value and the ratio of an infrared
radiation of each separated wavelength band, and determining in response
to the sensed time change whether a disastrous fire occurs or not. The
present invention relates to a fire sensing system adapted for use in a
fire prevention system used in a residence, a building, a warehouse, etc.,
requiring a reliable and highly sensitive fire sensing which is free from
a false alarm caused by nondisastrous flaming sources such as an electric
heater, a gas heater or a stove.
The present invention also relates to a technology used with an environment
monitor sensing the occurrence of an indoor disastrous fire, and an indoor
environment unpleasant to a person and produces a signal controlling an
alarm or an air conditioner.
2. Description of the Related Art
A multitude of prior-art fire sensing methods and systems automatically
sensing the occurrence of disastrous fire have been provided. These
methods and systems intend to sense the occurrance of disastrous fire in a
predetermined monitored area and must operate so that a malfunction due to
a heating source providing no disastrous fire, e.g., a stove rarely occurs
while maintaining a high sensitivity to the occurrence of a disastrous
fire.
Prior-art fire sensing systems using, e.g., a phototube, bimetal or
telecamera have been provided. The phototube type fire sensing system is
subject to malfunction due to sunlight or light from an electric lamp, for
example, because the phototube is sensitive to ultraviolet wavelengths.
The bimetal type fire sensing system is insufficiently effective because
of low fire-sensitivity of the bimetal. The telecamera type fire sensing
system requires an excessive number of telecameras as well as a continuous
monitoring by a person, so that a desired performance is difficultly
obtained.
Recently, an infrared radiation sensing process for sensing an infrared
radiant from a flame has been greater noticed. In this infrared radiation
sensing process, both a simple system determining the occurrence of
disastrous fire when it senses an infrared radiation of a predetermined
level or higher and a fire sensing system (see Examined Japanese patent
application publication No. SHO 56-7196) including a method of determining
whether or not the level of an output signal from an infrared sensor tends
to increase for a predetermined period of time or more have been proposed.
In addition, in order to increase reliability, efforts have been made in
developing a technology of separately sensing two or more wavelength band
of infrared radiation from a flame and of determining whether a disastrous
fire occurs or not from sensed signal. One form of this technology is a
system including a sensor for visible or near infrared radiation and a
sensor for other infrared radiation, the system determining a
nondisastrous fire when the intensity of the visible or near infrared
radiation is stronger than that of the other infrared radiation such as
the case of a radiation from am electric lamp, etc.
Another form of this technology is a system sensing the intrinsic spectral
distribution of a flame. The spectral distribution of infrared radiation
from an infrared source absent a flame, is generally in agreement with
Planck's law of radiation as shown in solid lines A and C of FIG. 2 so
that the higher the temperature of a heating object, the more the top of
the spectral distribution shifts towards a shorter-wavelength band. On the
other hand, an infrared radiant object with flame has a different
intrinsic character. That is, it has a spectral distribution with a peak
as shown in the solid line B of FIG. 2. The peak of the spectral
distribution of the solid line B is derived from the phenomenon of
CO.sub.2 -molecular resonance radiation at about 4.3 .mu.m wavelength.
Thus, in principle, sensing a peak of about 4.3 .mu.m wavelength caused by
CO.sub.2 -molecular resonance radiation senses a flame.
In order to sense the peak of about 4.3 .mu.m wavelength, some attempts
have been proposed. For example, the art of Unexamined Japanese patent
application publication No. SHO 50-2497 senses the amount of radiation at
the 4.3 82 m wavelength and at two wavelengths before and after the 4.3
.mu.m wavelength and determines a presence of flame when each of the
amounts of radiation at the 4.3 .mu.m wavelength and at the two
wavelengths before and after the 4.3 .mu.m wavelength equals or exceeds a
predetermined value. In addition, the art of Unexamined Japanese patent
application publication No. SHO 57-96492 determines whether or not there
is a depression between two projections in the amount of radiation in
order to sense the occurrence of flame.
In accordance with a method of determining the occurrence of nondisastrous
fire when the radiation intensity of visible or near infrared radiation is
greater than the radiation intensity of the other infrared radiation as in
light from an electric lamp, the occurrence of a false alarm due to a
normal light from the electric lamp is rare. On the other hand, since this
method determines as the occurrence of disastrous fire, the presence of a
heater such as an electric heater, having no or low visible or near
infrared radiation, the method produces a false alarm, so that an
application of the method is very restricted.
In accordance with the method of sensing the amounts of radiation at the
4.3 .mu.m wavelength and two wavelengths before and after the 4.3 .mu.m
wavelength and determining the presence of flame when each of the amounts
of radiation at the 4.3 .mu.m wavelength and two wavelengths before and
after the 4.3 .mu.m wavelength equals or exceeds the predetermined value,
this method can sense the presence of flame but not determine whether the
flame is derived from a disastrous fire or a normal or flame producing
heater. That is, this method entails a drawback in that it can produce a
false alarm in response to the occurrence of a flame of a gas range, gas
stove or the like.
Various prior-art air conditioners sensing indoor conditions by means of a
temperature sensor and a humidity sensor in order to control a room cooler
and room heater or the air conditioners to thereby produce a comfortable
indoor environment have been provided.
These prior-art air conditioners control an indoor temperature in response
to a sensing signal from a contact type temperature sensor, e.g., a
thermistor, placed in or near the body of the air conditioners. That is,
the air conditioners only consider the temperature of air surrounding the
temperature sensor as an average indoor temperature and controls the room
heater and room cooler of the air conditioners.
The temperature which the body of an indoor person feels is the most
important factor for controlling an indoor environment by means of air
conditioners or room heaters and room coolers. The temperature of
radiation heat which the skin of human body receives from an infrared
radiant from interior surfaces of a room, contributes to the temperature
which the body of the person feels in addition to the temperature of air
in direct contact with the skin of the body of the person.
For example, heat radiant from a room heater, window arrangement, etc.,
produces a hot feeling on the human body, while a window arrangement and
wall of a room that absorbs heat radiant from the human body produces the
feeling of a bone-reaching chill. Thus, the prior-art method of
controlling an environment in response to a single temperature output of
the contact type temperature sensor such as the thermistor sensing air in
contact with the sensor cannot provide a truly comfortable environment to
a person.
SUMMARY OF THE INVENTION
The present invention was made in view of the above-described problems. A
primary object of the present invention is to provide a fire sensing
system which very rarely produces a false alarm in response to the normal
conditions of heaters useful for life environment, e.g., an electric
heater, a gas heater and a stove, while maintaining high-sensitivity for
sensing the occurrence of disastrous fire.
Another object of the present invention is to provide a fire sensing method
which also recognizes the progression of a fire.
A further object of the present invention is to provide an environment
monitor which senses changes in the indoor environment inclusive of the
occurrence of disastrous fire, and is able to provide an indoor
environment confortable to a person, but which very rarely produces a
false alarm in response to a normal condition of a useful heater, and has
a high sensitivity the occurrence of disastrous fire.
The typical aspects of the present invention will be described hereinafter.
A fire sensing system of a first aspect of the present invention conprises:
a plurality of band-pass filters separating an infrared radiation from an
infrared source into a plurality of wavelength bands; an infrared sensor
sensing infrared radiation which has passed through each of said band-pass
filters, one of the wavelength bands comprising a CO.sub.2 -molecular
resonance radiation wavelength band; and a signal processor determining
whether a disastrous fire occurs or not in response to outputs of the
infrared sensors and a time change in a ratio of the outputs of the
infrared sensors.
The fire sensing system of the first aspect of the present invention senses
CO.sub.2 -molecular resonance radiation when a useful flaming heater such
as a gas heater and a flaming stove provides the infrared source while
determining a flaming condition of a flaming heater as a nondisastrous
fire since the sensed outputs of the wavelength bands and a ratio of the
sensed outputs become constant. On the other hand, this fire sensing
system determines as a nondisastrous fire the heating condition of a
useful non-flaming heater such as an electric heater when the non-flaming
heater provides the infrared source since the sensed outputs of the
wavelength bands and a ratio of the sensed outputs are constant and the
fire sensing system will not sense CO.sub.2 -molecular resonance
radiation. Thus, this fire sensing system eliminates the occurrence of a
malfunction caused by the normal condition of useful heater and thereby
provides accurate fire sensing.
A method of a second aspect of the present invention comprises the steps
of: computing the temperature of an infrared source from a ratio of
outputs of a plurality of infrared sensors sensing at least two wavelength
bands of infrared radiation from a monitored area; producing the intensity
of infrared radiation of one of the wavelength bands from said computed
temperature; and computing a heating area from the intensity of the
infrared radiation and the output of an infrared sensor sensing said one
of the wavelength bands, whereby the method determined the progression of
a fire.
This method displays an increasing heating area on a monitor or the like,
thereby providing a recognition of the progression of a disastrous fire.
An environment monitor of a third aspect of the present invention
comprises: a plurality of band-pass filters separating an infrared radiant
from a monitored spacing into a plurality of wavelength bands; an infrared
sensor sensing an infrared radiation which has passed through each of said
band-pass filters, one of the wavelength bands providing a CO.sub.2
-molecular resonance radiant wavelength band; and a signal processor
determining the occurrence of disastrous fire and computing temperatures
of the infrared radiation from the monitored spacing from outputs of the
infrared sensors of the wavelength bands and from a time change in a ratio
of said sensing outputs.
The environment monitor of the third aspect of the present invention
measures and continuously monitors the common physical quantity of the
radiation temperature in order to control the radiation temperature for
environment control and on the other hand, recognizes an abnormal pattern
of the radiation in the occurrence of disastrous fire and senses CO.sub.2
-molecular resonance radiation thereby to accurately determine whether a
non-flaming electric heater, a flaming heater such as a gas heater or a
flaming stove, or the occurrence of disastrous fire causes the change in
the temperature of the overall environment. Thus, this environment monitor
provides a comfortably controlled environment to human body and a
fire-sensing free from malfunction.
The above and other objects and novel features of the present invention
will be apparent from the following description, the drawings and the
accompanying claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of the fundamental arrangement of a
fire-sensing system of one embodiment of a first aspect of the present
invention;
FIG. 2 is a graph representing a relationship between the wavelength and
amount (relative value) of an infrared radiation from an infrared source;
FIG. 3 is a graph representing a temperature change in the occurrence of
disastrous fire;
FIG. 4 is a graph representing a change in a heating area in the occurrence
of disastrous fire;
FIG. 5 is a circuit block diagram of one embodiment of a signal processor;
FIG. 6 is a graph representing a change in the output of each infrared
sensor of the fire-sensing system of FIG. 1 in the occurrence of
disastrous fire;
FIG. 7 is a perspective view of one example of a package type infrared
sensor;
FIG. 8 is an illustration of a fire-sensing system with the package type
infrared sensor of FIG. 7;
FIG. 9 is an exploded perspective view of the package type infrared sensor
of FIG. 7, representing the interior thereof;
FIG. 10 is a circuit diagram of one example of a circuit of the package
type infrared sensor of FIG. 7;
FIG. 11 is a circuit block diagram of one embodiment of a signal processor
of a fire-sensing system of a second aspect of the present invention;
FIG. 12 is a graph representing ratios of sensing outputs of infrared
sensors of a fire-sensing system of the second aspect of the present
invention;
FIG. 13 is a graph representing ratios of the theoretical values of sensing
outputs of the infrared sensors of an experimental system of the second
aspect of the present invention;
FIG. 14 is a graph representing ratios of the infrared sensors when the
experimental apparatus of the second aspect of the present invention
monitors a heating panel;
FIG. 15(A) is a graph representing a temperature change computed from the
sensing output of the infrared sensors when the experimental apparatus of
the present invention monitors the heating panel;
FIG. 15(B) is a graph representing a change in heating area computed from
the sensing output of the infrared sensors when the experimental apparatus
of the present invention monitors the heating panel;
FIG. 15(C) is a graph representing a change in CO2-ratio computed from the
sensing output of the infrared sensors when the experimental apparatus of
the present invention monitors the heating panel;
FIG. 16(A) is a graph representing a temperature change computed from the
sensing output of the infrared sensors when the experimental apparatus of
the present invention monitors a methanol flame;
FIG. 16(B) is a graph representing a change in heating area computed from
the sensing output of the infrared sensors when the experimental apparatus
of the present invention monitors the methanol flame;
FIG. 17(A) is a graph representing a temperature change computed from the
sensing output of the infrared sensors when the experimental apparatus of
the present invention monitors a setting fire to a news paper;
FIG. 17(B) is a graph representing a change computed from the sensing
output of the infrared sensors when the experimental apparatus of the
present invention monitors the setting fire to the news paper;
FIG. 17(C) is a graph representing a change in CO.sub.2 -ratio computed
from the sensing output of the infrared sensors when the experimental
apparatus of the present invention monitors the setting fire to the news
paper; and
FIG. 18 is a schematic diagram of the fundamental arrangement of one
embodiment of an environment monitor of a third aspect of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present inventors studied the phenomenal difference between a
disastrous fire and nondisastrous fire and concluded as follows:
The heating area and the temperature of a heater, except a disastrous fire,
are fixed or become constant in a few minutes. For example, the heating
area of a room heater is fixed and the temperature of the room heater
becomes constant in a few minutes. In addition, the temperatures and
heating areas of a match and cigarette lighter not only are essentially
fixed but also extinguished in a few seconds or minutes.
On the other hand, a disastrous fire is characterized in that both the
heating area and the temperature of the disastrous fire concurrently
increase at the outbreak of the disastrous fire and also tend to continue
to increase for a few minutes even after the outbreak of the disastrous
fire. FIG. 3 represents a temperature change in a progression from a
smoking condition to a disastrous fire. FIG. 4 represents a change in
heating area in the progression from the smoking condition to the
disastrous fire. In FIGS. 3 and 4 TF represents a flaming point of time.
On the other hand, a disastrous fire without a progression from a smoking
condition, e.g., an incendiary fire, produce a temperature change after
the TF point of time of FIG. 3 and a change in heating area after the TF
point of time of FIG. 4.
In a disastrous fire, when the infrared radiation from the fire is
separated into a plurality of wavelength bands between a short-wavelength
band and long-wavelength band, sensing outputs of the wavelength bands
increase with time and a time change in ratios of the sensing outputs has
a characteristic behavior. That is, the intensity of each sensing output
reflects the area and temperature of a heater and on the other hand, since
a ratio of the sensing outputs reflects the temperature of the heater, the
sensing outputs of the wavelength bands and the ratio of the sensing
outputs tend to concurrently increase in the case of a smoking disastrous
fire and then rapidly increase when the smoking fire transfers to a
flaming fire. Then, the heating area of the heater still increases while
an increase in the temperature of the heater tends to level off so that
the sensing outputs of the wavelength bands increase while, the ratio of
the sensing outputs essentially becomes constant. Then, at the point of
time when the disastrous fire has transferred to a flaming fire, CO.sub.2
-resonance radiation is significantly increased so that the intensity of
the CO.sub.2 -molecular resonance radiation is increased with an increase
in a firing area. On the other hand, a flame which has become constant
i.e., that not of a disastrous fire, does not produce such a time change.
The inventors also took the occurence of disastrous fire as an
environmental change and studied a technology of monitoring the
environment of a residential spacing and a fire-sensing technology from
the same viewpoint. This study has concluded that in order to produce an
environment which a person staying in a room feels most comfortable, the
best environment control method monitors not only the air temperature of
the interior of the room but also the radiation temperature of the
interior of the room. The inventors have conceived that since an infrared
sensor can be used to monitor radiation temperature as well as for a
method of sensing a disastrous fire by means of a radiation temperature, a
single infrared sensor can produce an output for controlling indoor
environment by means of the air conditioner or the like and for
fire-sensing.
Then, the inventors studied in more detail an environment control and a
fire-sensing performed in response to the radiation temperature. Thus, the
inventors discovered that the indoor radiation temperature was computed
from the ratios of outputs from a plurality of infrared sensors and in
addition, providing a contact type temperature sensor such as a
thermistor, monitor the temperature which a human body staying in a sensed
spacing actually feels, in order to control an environment so that the
human body feels comfortable.
Since the temperature of an indoor environment is usually about 300 K.
(i.e., 23.degree. C.), the top of a radiation wavelength is about 10
.mu.m. Thus, the infrared sensor preferably has a band-pass filter with a
10 .mu.m central pass wavelength.
On the other hand, when a monitored environment includes an non-flaming
room heater such as an electric heater, monitoring the environment by
means of a single infrared sensor with the 10 .mu.m band-pass filter
determines that the temperature of the overall environment increases even
when the electric heater increases the temperature of part of the
environment. Thus, a monitoring of the environment by means of an infrared
sensor with a band-pass filter with an about 4 .mu.m central pass
wavelength may be preferably added.
Since the intensity of a 4 .mu.m wavelength infrared radiation from an
environment without room heater is sufficiently lower than that of a 10
.mu.m wavelength infrared radiation of the infrared radiation from the
environment without room heater and, the intensities of 4 .mu.m and 10
.mu.m wavelength infrared radiations of an infrared radiation from an
environment with a non-flaming room heater such as an electric heater are
essentially equal, both increases in the intensities of the 4 .mu.m and 10
.mu.m wavelength infrared radiations of the latter case provide a
determination that the non-flaming room heater heats up and on the other
hand, a low intensity of the 4 .mu.m wavelength infrared radiation of the
latter case provides a determination that the temperature of the overall
environment increases.
Thus, the following embodiments of the present invention provide a
fire-sensing system producing essentially no false alarms (i.e., very
rarely producing a false alarm) in response to a normal operation of a
useful heater in a living environment, high sensitivity for sensing a
disastrous fire, a fire-sensing method recognizing a progression of a fire
in addition to the operations of the above fire-sensing system, and an
environment monitor providing an indoor environment which is comfortable
to a person.
FIRST EMBODIMENT
FIG. 1 is a schematic diagram of the fundamental arrangement of a
fire-sensing system of one embodiment of the first aspect of the present
invention;
An infrared radiation sensing unit D receives infrared radiation from an
infrared source S to separate the infrared radiation into a plurality of
wavelength bands and to sense the intensity of each of the wavelength
bands.
The infrared radiation sensing unit D comprises: a rotational chopper 1
periodically chopping the infrared radiation from the infrared source S;
four band-pass filters 2a, 2b, 2c and 2d each of which comprises an
optical filter with a different pass band, which is not restricted to a
particular form; and four infrared sensors 3a, 3b, 3c and 3d each sensing
passing infrared radiation through the corresponding band-pass filters 2a
to 2d. In accordance with the four-split system of the first embodiment of
the present invention, the central wavelengths of the pass bands of the
band-pass filters 2a to 2d are suitably selected so that, e.g., the
pass-band central wavelength of the band-pass filter 2a is 2-3 .mu.m, that
of the band-pass filter 2b is 3-4 .mu.m, that of the band-pass filter 2c
is 4-5.5 .mu.m and that of the band-pass filter 2d is 8-15 .mu.m and so
that the pass-band of each of the band-pass filters 2a to 2d is 0.1-1.5
.mu.m. One of the band-pass filters 2a to 2d allows the wavelength band
(i.e., 4.3 .mu.m) of CO.sub.2 -molecular resonance radiation to pass. In
the first embodiment, the band-pass filter 2c allows CO.sub.2 -molecular
resonance radiation to pass. It should be avoided that the pass-band
central wavelength of one of the band-pass filters 2a to 2d is 5.5-8
.mu.m, since steam contained in the air absorbs a very great amount of a
5.5-8 .mu.m wavelength infrared radiation. The number of split pass-bands
will not be restricted to four but may be two or more. This number is
sufficiently practically up to at least 5.
An optical filter for the band-pass filters 2a to 2d comprises a multilayer
film in which, one of ZnSe, ZnS, Ge and other dielectrics are
alternatively vacuum deposited one another on a substrate made of Si or
the like. The thickness of the multilayer film is determined in accordance
with a target pass-band.
The infrared sensors 3a to 3d may be a semiconductor infrared sensor, a
thermopile or a pyroelectric infrared sensor. The semiconductor infrared
sensor is less preferable since it requires cooling. The thermopile or
pyroelectric infrared sensor is preferable. The pyroelectric infrared
sensor is most preferable. When each of the infrared sensors 3a to 3d is
made with a thermopile, the chopper 1 may be alternatively eliminated.
Since the pyroelectric infrared sensor is a differentiation sensor
operating in response to only a temperature differential, it is optimum
for the inventive system sensing a temperature increase. The pyroelectric
infrared sensor has an arrangement in which the top surface and back
surface of a thin plate made of a pyroelectric material such as lithium
tantalate or Pb.sub.x Zr.sub.y O.sub.3 have electrodes deposited thereon
by vacuum deposition etc. A Si-photodiode may be alternatively used in
order to sense a near-infrared band with a wavelength of an about 1 .mu.m.
A pulse motor and a direct current motor (i.e., DC motor) suitably rotates
the chopper 1. The DC motor requires a rotational speed sensor such as a
photointerrupter 4 in order to sense a rotational speed of the chopper 1.
The pulse motor requires no interrupter since a driving pulse signal for
the pulse motor provides a rotational speed of the pulse motor.
A signal processor 10 receives and processes outputs of the infrared
sensors 3a to 3d and a rotational speed sensing signal of the chopper 1
from the photointerrupter 4.
The signal processor 10 operates the magnitudes of the outputs of the
infrared sensors 3a to 3d, ratios of the outputs and time changes in the
magnitudes of the outputs and the ratios of the outputs, determines
whether the monitored infrared source S is a disastrous fire or not on the
basis of the results of the operation, and producing a signal for driving
an alarm when monitored infrared source S is determined to be a disastrous
fire.
FIG. 5 represents one example of the signal processor 10. Amplifiers 11a,
11b, 11c and 11d receive outputs of the infrared sensors 3a to 3d and
amplify them to desired levels. A phase shifter 12 receives the rotational
speed sensing signal from the photointerrupter 4 and produces
synchronizing signals SIN .phi. and COS .phi., 90 degrees phase-shifting
from each other.
Synchronous detectors 13a.sub.1, 13b.sub.1, 13c.sub.1, and 13d.sub.1, and
13a.sub.2, 13b.sub.2, 13c.sub.2 and 13d.sub.2 receive and detect the
outputs of the amplifiers 11a to 11d in synchronization with the
synchronizing signals SIN .phi. and cos .phi.. Square multipliers
14a.sub.1, 14b.sub.1, 14c.sub.1, and 14d.sub.1, and 14a.sub.2, 14b.sub.2,
14c.sub.2 and 14d.sub.2 square the detection outputs of the synchronous
detectors 13a.sub.1 to 13d.sub.1 and 13a.sub.2 to 13d.sub.2. Adders 15a,
15b, 15c and 15d add outputs of the square multipliers 14a.sub.1 to
14d.sub.1 and 14a.sub.2 to 14d.sub.2 for each channel. Square root
processors 16a, 16b, 16c and 16d square root the outputs of the respective
adders 15a to 15d. Thus, an operation of respectively
synchronization-sensing 90-degree phase-shifting synchronizing signals of
each pair and then producing an average of squared synchronization
detecting outputs eliminates a phase deviation caused by misalignment,
etc. between chopper 1 and each of the infrared sensors 3a to 3d. A/D
con | | |
