JPH0378899A - Fire detector - Google Patents

Abstract

PURPOSE:To eliminate malfunction caused by a profitable heat source and to enable accurate fire detection by judging whether fire is generated or not based on the detec tion output of an infrared detector with plural wavelength bands and a change with the passage of time in the ratio of the detection output. CONSTITUTION:Band pass filters 2a-2d are provided to separate infrared rays to be radiated from an infrared source S into the plural wavelength bands, and infrared detectors 3a-3d are provided to detect the outputs of the band pass filters. Then, a chopper 1 is provided to periodically cut the infrared rays to be radiated from the infrared source S, and a signal processing circuit 10 is provided to include a CO2 molecular resonance radiaring wavelength band as one of the plural wavelength bands and to judge whether fire is generated or not based on the outputs of the infrared detectors 3a-3d and a change with the passage of time in the ratio of the detection outputs. Accordingly, in the case of the profitable heat source with fire such as por table gas cooking stove or stove, etc., it is not judged as the fire since the detection outputs of the respective wavelength bands and the ratio of the outputs are fixed in a normal state although the CO2 molecular resonance radiation is detected. Thus, the malfunction caused by the profitable heat source can be eliminated and the accu rate fire detection can be executed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a fire detection device based on an infrared detection method. The present invention also relates to a fire detection device that determines whether or not there is a fire based on temporal changes in relative ratios. The present invention eliminates false alarms caused by non-fire sources such as electric heaters, gas stoves, and stoves, enables highly reliable and highly sensitive fire detection, and can be used in fire prevention systems in general homes, buildings, warehouses, etc. The present invention relates to a suitable fire detection device.

[Prior Art] Many fire detection methods and devices for automatically detecting the occurrence of a fire have been proposed. The purpose of these devices is to detect the presence or absence of a fire within a certain monitoring range, and they are required to be able to detect fires with high sensitivity and less malfunction due to non-fire heat sources such as stoves.

Until now, for example, fire detectors have been provided that use phototubes, bimetals, and television cameras, but phototubes are sensitive to wavelengths in the ultraviolet range, so they can malfunction due to sunlight or light from electric lamps. It has the disadvantage of being easy. On the other hand, bimetallic types have too low sensitivity and lack effectiveness. In addition, the method of monitoring using television cameras makes it difficult to judge the situation, requires too many cameras, and requires constant human monitoring, making it difficult to achieve desired results.

Under these circumstances, there has recently been a great deal of interest in infrared detection methods that detect infrared rays emitted from flames. These infrared detection methods go one step further than simply determining a fire when infrared rays above a certain level are detected, and check whether the output signal level of the infrared detector has been increasing for more than a certain period of time. A fire detector incorporating an identification circuit was proposed
No. 6-7196).

Additionally, in order to improve reliability, efforts are being made to develop technology that separately detects infrared radiation from flames in two or more wavelength bands and uses that information to determine whether or not there is a fire. Ta. One is to use two types of sensors: one that detects visible or near-infrared radiation, and one that detects infrared radiation. This method determines that there is no fire if the radiation intensity in the infrared region is high.

The other method detects the spectral distribution characteristic of flames. In general, the spectral distribution of infrared rays emitted from an infrared radiation source that does not involve a flame follows Blank's law, as shown by solid lines A and C in Figure 2, and the peak value of the spectrum shifts toward shorter wavelengths as the temperature of the heat-generating object increases. .

In contrast, infrared emitting objects with flames exhibit other unique properties. That is, as shown by solid line B in FIG. 2, it has an uneven spectral distribution. This is often caused by a phenomenon known as CO2 molecular resonance radiation, which shows a high peak at a wavelength of around 4.3 μm.Therefore, in principle, the peak at a wavelength of around 4.3 μm caused by this CO2 molecular resonance radiation can be suppressed. Flame can be detected by detecting it.

Therefore, several attempts have been proposed to capture this peak wavelength of 4.3 μm.

For example, Japanese Patent Application Laid-Open No. 50-2497 detects the radiation dose at 4.3 μm and two wavelengths before and after it, and when the radiation dose at 4.3 μm and the other two wavelengths exceeds a certain value, it is determined to be a flame. are doing. Further, Japanese Patent Laid-Open No. 57-96492 proposes detecting the occurrence of flame by determining whether or not a valley exists between two convex portions.

In addition, JP-A No. 61-32195 discloses a first radiation detection means for detecting radiation with a wavelength in the near-infrared region, a second radiation detection means for detecting radiation with a wavelength in the photographic infrared region, and a second radiation detection means for detecting radiation with a wavelength in the photographic infrared region. calculation means for receiving the output signals from the first and second radiation detection means and calculating a logical combination of output signals based on the level difference and synchronization of these output signals;
A fire detection device is disclosed that includes a detection means for distinguishing between a fire signal and a noise signal based on an output signal from the calculation means. This means that flaming fire and visible light noise are at wavelength 2.
．． There is synchronization in the correlation between 3 μm and 0.9 μm infrared radiation, but smoldering fires do not show synchronization, and in flaming fires and smoldering fires, the near-infrared intensity is greater than the photographic infrared intensity, and visible light noise is This method takes advantage of the fact that the near-infrared intensity is lower than the photographic infrared intensity.

It distinguishes between fire and visible light noise, and also between flaming fire and smoldering fire.

[Problems to be Solved by the Invention] However, in a method that determines that there is no fire if the radiation intensity in the visible or near-infrared region is greater than the radiation intensity in the infrared region, such as electric light, False alarms will be reduced, but if there is a heating element other than fire, such as an electric heater, that does not emit visible or near infrared rays, or if it is weak, it will be judged as a fire and a false alarm will be issued, which limits its application. There are many.

In addition, in a method that detects the radiation dose at a wavelength of 4.3 μm and two wavelengths before and after it, and determines that it is a flame when the radiation dose at 4.3 μm and the other two wavelengths exceeds a certain value,
Although it can detect flames, it cannot detect whether the flames originate from a fire or from a useful heat source. That is, there is a drawback that a false alarm is generated by the flame of a gas range, gas stove, or the like.

Furthermore, in a method that compares the level difference and synchrony of two types of radiation with wavelengths of 2.3 μm and 0.9 μm to distinguish between fire and visible light noise, and between flaming fire and smoldering fire, it is possible to determine the type of fire. , depending on the way it burns, there is no guarantee that the synchronicity referred to here will be observed, and it lacks reliability.

The object of the present invention is to eliminate the above-mentioned drawbacks, to provide a fire detection device that can detect fires with high sensitivity and has very few false alarms based on useful heat sources in the living environment such as electric heaters, gas stoves, and stoves. It is about providing.

[Means for Solving the Problems] The present inventors conducted a study based on the phenomenological differences between fire and non-fire, and found the following differences.

That is, in the case of a heat source other than fire, the heat generating area and temperature are constant or reach a steady state within a few minutes. For example, in a heating appliance, one heat generating area is constant, and the temperature reaches a steady state in several minutes. Furthermore, in the case of a matchstick, a lighter, etc., not only the temperature and heat generation area are constant, but the heat disappears in a few seconds or minutes.

On the other hand, fires are characterized by an increase in both the heat generating area and temperature, and even after several minutes have elapsed, they show an increasing tendency. Figure 3 shows the temperature change during the process from smoldering to fire, and Figure 4 shows the change in heat generation area. Here, TF is the point of flaming. In addition, in the case of a fire that does not go through a smoldering state, for example, a fire caused by arson, the temperature change and heat generation area change after the TF point in FIGS. 3 and 4 are shown.

Furthermore, in the case of a fire, when the emitted infrared rays are divided into multiple wavelength bands ranging from short to long wavelengths, the detection output of each wavelength band increases over time, and the temporal change in the ratio of the detection output is also unique. Show behavior. In other words, the magnitude of the detection output reflects the area and temperature of the heat generating part, whereas the ratio of the detection output reflects the temperature of the heat generating part, so in the case of a smoldering fire, the detection output of each wavelength and its Both the detection output ratios tend to gradually increase, and at the time the fire progresses to flaming, the detection outputs and their ratios rapidly increase. Further, after that, the temperature increase tends to be saturated as the area of the heat generating source increases, so the detection output increases, but the ratio remains approximately constant. Then, when the fire progresses to a flaming fire, the resonance radiation of CO2 molecules increases significantly, and its intensity increases as the fire area increases. On the other hand, in the case of flames other than fires, such temporal changes are not observed after a steady state is reached.

Based on the above findings, the present invention provides a bandpass filter that separates infrared rays emitted from an infrared source into a plurality of wavelength bands, an infrared detector that detects infrared rays that have passed through each bandpass filter, and an infrared ray emitted from an infrared source. a chopper that periodically divides the infrared rays that are detected; and a chopper that includes a CO2 molecule resonance emission wavelength band as one of the plurality of wavelength bands, and a We propose a fire detection device that includes a signal processing circuit that determines whether or not there is a fire based on temporal changes.

The plurality of bandpass filters and infrared detectors may be of a package type assembled into a single unit, and it is preferable to use a microcomputer as the signal processing circuit.

[Effect] According to the above-mentioned means, in the case of a useful heat source with flame such as a gas stove or a stove, resonance radiation of CO2 molecules is detected, but the detection output of each wavelength band and the ratio thereof settles to a steady state. Therefore, it was determined that there was no fire. Furthermore, in the case of a useful heat source that does not involve a flame, such as an electric heater, not only the detection output of each wavelength band and the ratio thereof are in a steady state, but also the resonance radiation of CO□ molecules is not detected, so it is determined that there is no fire.

This eliminates malfunctions caused by beneficial heat sources and enables highly accurate fire detection.

[Example] FIG. 1 is a basic configuration diagram of an embodiment of the present invention.

Infrared rays emitted from the infrared source S enter the infrared detection section. In the infrared detection section, infrared rays are separated into a plurality of wavelength bands, and the intensity of the infrared rays in each wavelength band is detected.

The infrared detection section includes a rotary chopper 1 that periodically divides infrared rays, bandpass filters 2a, 2b, 2c, and 2d each consisting of four optical filters each having a different transmission band, although not particularly limited, and each bandpass filter. filter 2
Infrared detectors 3a, 3b, 3c, and 3d are provided for detecting the transmitted infrared rays in association with the infrared rays 8 to 2d. In the case of the four-division method shown here, the center wavelength of the transmission band of the bandpass filters 2a to 2d is 1, for example, the center wavelength of the transmission band of the bandpass filter 2a is 2 to 3.
μm, filter 2b is 3-4 μm, filter 2c is 4-4 μm
5.5 μm, the filter 2d is appropriately selected such as 8 to 15 μm, and the transmission wavelength band width is 0.1 to 1.5 μm, respectively.
It is said that Among these filters 2a to 2d, one is selected that transmits the resonance emission wavelength band (4.3 μm) of CO2 molecules. Here, the filter 2c is CO□
It is designed to transmit the resonance emission wavelength range of molecules.

Furthermore, the wavelength band of 5.5 to 8 μm should be avoided because absorption by water vapor in the air is very large. The number of divided wavelength bands is not limited to 4 as described above, but can be divided into any number of 2 or more, but in practice it is 5 to 5.
Up to 6 divisions is sufficient.

Optical filter is Zn5e or ZnS or Ge
Other dielectrics are alternately vacuum-deposited on a substrate such as Si to form a multilayer film, and the film thickness is determined depending on the target transmission wavelength band.

As the infrared detectors 38 to 3d, semiconductor infrared detectors, thermopiles, pyroelectric infrared detectors, etc. can all be used, but semiconductor infrared detectors are not suitable because they require cooling, and thermopiles or pyroelectric infrared detectors are used. Detectors are preferred, and pyroelectric detectors are particularly preferred. Furthermore, the chopper 1 can be omitted if a thermopile is used for the infrared detector.

A pyroelectric detector is a differential detector that responds only to changes in temperature, and is suitable for the device of the present invention that measures temperature increases. Pyroelectric detectors use lithium tantalate or PbxZr.
Electrodes are formed on the front and back surfaces of a thin pyroelectric plate represented by y○3 by vapor deposition or the like. Also, the wavelength is 1μ
In the case of detecting near-infrared rays around m, a Si photodiode can also be used.

A pulse motor or a DC motor is suitable for rotationally driving the chopper 1, but in the case of a DC motor, a rotation detector 4 such as a photointerrupter is required to detect the rotation speed of the chopper. When driving the chopper with a pulse motor, the rotation speed can be determined from the drive circuit, so a photointerrupter is not required.

Output signals from the infrared detectors 3a to 3d and chopper rotation detection signals are processed by a signal processing circuit 1o. The signal processing circuit 10 calculates the magnitude of the output from each infrared detector 38 to 3d, the relative ratio of those outputs, and their time change, and determines whether or not the target infrared source is a fire based on the results. If it determines that there is a fire, it outputs an alarm drive signal.

FIG. 5 shows an example of the configuration of the signal processing circuit 10.

The output signals from the infrared detectors 38 to 3d are sent to the amplifier circuit 1.
1a, llb, llc, lld and amplified to a desired level. Further, the rotation detection signal from the photointerrupter 4 is input to the phase shift circuit 12, and synchronization signals SINφ and CO3- whose phases are shifted by 90 degrees from each other are outputted. The outputs from the amplifier circuits 11a to 11lid are sent to the synchronous detection circuits 13a to 13a in synchronization with the synchronizing signals SINφ and CoSφ.
13d, , 13a, to 13d2 and detected.

Synchronous detection circuits 13a, ~13d,, 13a2
The detection output of ~13d2 is 2 East circuit 14a2~
14 d,, squared by l 4 a2~14 d,
After being added by adders 15a to 15d for each channel, square root calculations are performed by square root calculation circuits 16a to 16d. In this way, by separately performing synchronous detection using synchronous signals with a 90 degree phase shift and taking the root mean square of the detected outputs, phase deviations caused by positional deviations between the chopper and the infrared detector can be eliminated. be removed.

The outputs of the square root operators 16a to 16d are sent to the A/D converter 1.
The signals are A/D converted in steps 7a to 17d and input to the microcomputer 18 for signal processing.

In the embodiment shown in Fig. 5, the mean square is calculated by an analog computing unit, but if the synchronously detected signal is A/D converted and input to the microcomputer 5, the mean square is calculated by the microcomputer. You can also do that. In addition, the amplifier circuit 11
Synchronous detection can also be performed by the microcomputer 18 by A/D converting the output signals of a to lid.

The microcomputer 18 performs calculations every few seconds using timer interrupts or the like based on the detection signal, and accumulates data over several minutes regarding the temperature of the infrared ray source, the increase in the heating area, and the presence or absence of co2 molecule resonance radiation. Based on the data, it is checked whether the temperature and heat generating area are constantly increasing, and if they are, it is determined that there is a fire, the driver 19 is driven to turn on the relay RLY, and the alarm 20 is activated.

For example, in the case of a smoldering fire, the outputs of the infrared detectors 3a to 3d change as shown in FIG. That is, the outputs a, b, a of the infrared detectors 3a to 3d.

d becomes dtctb, a as the temperature rises and the fire spread area increases.
Increases by 1@. Then, at the time of ignition, CO2 at TF
Infrared detectors 3a-3 because the resonance radiation of molecules increases dramatically.
The output of 3c of d increases significantly. After that, since the infrared source becomes a flame, the temperature rise decreases, and the amount of infrared rays mainly increases due to the increase in area, and the output of each infrared detector 3a to 3d increases, but the ratio of the outputs is approximately becomes constant.

On the other hand, in the case of non-fire, the temperature or area of the infrared source reaches a steady state or disappears within a predetermined period of time.

For example, in the case of heating appliances, cooking appliances, etc., the heat generating area does not increase and the temperature reaches a steady state within a predetermined period of time.

Therefore, - determine the temperature of the infrared source by comparing the outputs of the infrared detectors 38 to 3d, and calculate the outputs of, for example, 3a, 3b, and 3d among the infrared detectors 3a to 3d at that temperature,
The heat generating area can be determined by comparing it with a preset value. Furthermore, from the temperature and heat generation area of the infrared source determined by the above procedure, calculate the black body radiation intensity, that is, the infrared radiation intensity in the co2 molecule resonance emission wavelength band assuming that the heat source is a black body, and calculate the value. By comparing the output of the infrared detector 3c that detects the resonance emission wavelength band of CO2 molecules, it is possible to know whether there is resonance emission of the 602 molecules.

In this way, if the temperature and heat generating area tend to increase over a certain period of time (several minutes) and no resonance emission of CO2 molecules is observed, it can be determined that the fire is a smoldering fire. Also, at some point, the temperature and heat generation increase rapidly, and the CO□
If resonance radiation of molecules is observed, it is determined that the smoldering fire has transitioned to a flaming fire, and the alarm is notified by increasing the volume or changing the pitch of the sound, for example. be able to. Further, if resonance radiation of CO2 molecules is suddenly detected from a state where infrared rays are not detected, and high-temperature heat generation is detected along with this, and the heat generation area rapidly increases, it can be determined that arson has occurred.

On the other hand, if no increase in heat generation area is observed, it can be determined that the appliance uses flame (stove, stove).

Since the present invention makes a fire determination based on extremely realistic fire phenomena, it is possible to significantly reduce false alarms, unlike the prior art.

FIGS. 7 to 9 show the structure and usage example of a pyroelectric sensor 40 each containing four bandpass filters and an infrared detector in one package, and FIG. 10 shows an example of its circuit. show. Here, the four infrared detectors that were separately provided in the previous example are assembled into a single unit. That is, as shown in FIG. 9, this package type infrared sensor 40 has pyroelectric bodies 43a, 43b,
- 43c and 43d are arranged, and in front thereof are four-division bandpass filters 42a and 42b corresponding to each of the above-mentioned pyroelectric bodies.
, 42c, 42d is arranged, and the substrate 41
and window 42 are combined by a seal can 46, and the whole is configured as a packaged sensor capable of detecting four types of infrared wavelength bands. Each of the four-division bandpass filters 42a to 42d has a transmission center wavelength of 2.6μ.
m, 3.7 μm, 4.3 μm, and 9 μm, and the transmission bandwidth is 0.1 to 1 μm. This 4-part filter is manufactured by selectively depositing a dielectric multilayer film on a single transparent glass substrate in 4 steps, or by bonding together 4 fan-shaped bandpass filters. The infrared rays that have passed through the filters 42a to 42d are transmitted to the pyroelectric bodies 43a to 43d.
43d, and as before, the signal processing circuit 10
Processed by It is desirable to provide a partition wall in the seal can 46 to partition the internal space into four sections corresponding to the filters.

The pyroelectric bodies 43a to 43d are made up of two pyroelectric elements S, S2 connected in series, each of which is polarized in the opposite direction, as shown in FIG. FET47a, 47b, 47c, 47d
The gate terminal of is connected. This FET47a~4
A positive power supply voltage V oo is applied to each drain terminal of 7d, and an output signal is taken out from each source terminal. Further, the terminal of the other pyroelectric element S2 is connected to the ground point E, and input resistors R□, R2, R ,,R4 are connected.

Although not shown, the FETs 47a to 47d are pyroelectric bodies 43a to 43. Input resistors R to R3 are respectively mounted on an insulating substrate 41 above d, and connected to each other by bonding wires or soldering to form a seal can 4.
It is enclosed in 6.

[Effects of the Invention] As explained above, the present invention includes: a bandpass filter that separates infrared rays emitted from an infrared source into a plurality of wavelength bands; an infrared detector that detects the infrared rays that have passed through each bandpass filter; A chopper that periodically divides infrared rays emitted from an infrared source, and a detection output of an infrared detector including a CO2 molecule resonance emission wavelength band as one of the plurality of wavelength bands and the detection of the plurality of wavelength bands. The fire detection device is configured with a signal processing circuit that determines whether there is a fire based on the temporal change in the ratio of outputs, so it can be used on gas stoves,
In the case of a useful heat source with flame, such as a stove, although resonance radiation of CO2 molecules is detected, the detection output of each wavelength band and the ratio thereof settles to a steady state, so it is determined that there is no fire. Furthermore, in the case of a useful heat source that does not involve flame, such as an electric heater, not only the detection output of each wavelength band and the ratio thereof are in a steady state, but also the resonance radiation of CO2 molecules is not detected, so it is determined that there is no fire. This has the effect of eliminating malfunctions due to beneficial heat sources and enabling highly accurate fire detection.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram showing an embodiment of a fire detection device according to the present invention. Figure 2 shows the wavelength and amount of infrared radiation emitted from an infrared radiation source (
Figure 3 is a diagram showing the temperature change at the time of a fire outbreak, and Figure 4 is a diagram showing the change in heat generating area at the time of a fire outbreak. FIG. 5 is a circuit diagram showing one embodiment of a signal processing circuit. Figure 6 is a diagram showing changes in the output of each detector of the fire detection system in Figure 1 when a fire occurs, Figure 7 is a perspective view of an example of a packaged infrared detector, and Figure 8 is a diagram showing how it is used. 9 is an exploded perspective view showing the internal structure of the infrared detector, and FIG. 10 is a circuit diagram showing an example of the circuit configuration of the infrared detector. 1...ChiJ collar, 2a-2d...Band pass filter, 3a-3d...Infrared detector, 4...
Rotation detector. 0 1 2 34 56 7 8910(lJ凰)波
Long Figure 3 Figure 7 Front Figure 7 Figure 8

Claims (5)

[Claims] (1) Equipped with a bandpass filter that separates infrared rays emitted from an infrared source into a plurality of wavelength bands, and an infrared detector that detects the infrared rays that have passed through each bandpass filter, and one of the plurality of wavelength bands. The wavelength band includes the resonance emission wavelength band of the CO_2 molecule, and is based on the output of an infrared detector that detects a wavelength range of 1 to 16 μm, the output of the infrared detector in each of the wavelength bands, and the temporal change in the ratio of these detection outputs. A fire detection device characterized by comprising a signal processing circuit that determines whether or not there is a fire. (2) The fire detection device according to claim 1, further comprising a chopper that periodically divides the infrared rays emitted from the infrared source so as to be incident on the infrared detector. (3) Fire detection according to claims 1 and 2, wherein the bandpass filter has a wavelength band selected so as to avoid infrared rays in a wavelength range of 5.5 to 8 μm. Device. (4) A patent characterized in that the signal processing circuit detects the output of the infrared detector in synchronization with the rotation of the chopper and in synchronization with two periodic signals having a phase difference of 90 degrees, and then calculates the root mean square of the output. A fire detection device according to claims 2 and 3. (5) Calculate the blackbody radiation intensity in the detection wavelength band of the infrared detector that detects the resonance emission wavelength band of CO_2 molecules based on the output of the infrared detector, and calculate the black body radiation intensity in the detection wavelength band of the CO_2 molecule and
A patent that detects the presence or absence of resonance emission of CO_2 molecules by comparing the output of an infrared detector that detects the resonance emission wavelength band of molecules, and determines that there is a fire when the resonance emission is detected. Claims 1, 2, and 3
Fire detection device according to paragraphs 1 and 4.