JPH05159174A - Fire sensing method - Google Patents

Abstract

PURPOSE:To definitely discriminate fire and non-fire by detecting multi-frequency infrared ray at the same time, relating to fire sensing method which senses fire by detecting infrared ray irradiated from a fire sourse. CONSTITUTION:In a fire sensing method which performs signal processing in which infrared ray irradiated from a fire is detected and whether fire exists or not is decided based upon both the detected output and the change of detected output ratio with lapse of time, four wave lengths, that are (1) 2,8mum-3,2mum, (2) 4,2mum-4,6mum, (3) 4,6mum-5,5mum, (4) 8,0mum-10.0mum, are detected for sensing a range from smoking to a fire. Condition change from low- temperature smoking to high-temperature flaming is widely monitored, and a fire is sensed with sure without affected by atmosphere sway, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fire detection method for detecting a fire by detecting infrared rays radiated from a fire source, and particularly to detect infrared rays of multiple wavelengths simultaneously to distinguish between a fire and a non-fire. Fire detection method to clarify The present invention has been specified to provide an infrared wavelength band that eliminates false alarms due to non-fire sources such as electric heaters and cooking equipment, and provides effective fire detection even in a relatively small fire condition.

[0002]

2. Description of the Related Art Conventionally, a flame detection method for detecting infrared rays emitted from a flame has been put into practical use. Most of these flame detection methods detect the characteristic spectral line emitted from the flame (4.4 μm band; CO ₂ resonance radiation band), but there are several methods to reduce malfunctions due to infrared sources other than flames. Some attempts have been proposed. For example, JP-A-50-
No. 2497 detects the radiation doses at 4.3 μm and two wavelengths before and after it, and judges it as a flame when the radiation doses at 4.3 μm and other two wavelengths exceed a certain value. Japanese Patent Application Laid-Open No. 57-96492 proposes to detect the occurrence of a flame by determining whether or not a valley exists between two convex portions.

In addition, Japanese Patent Laid-Open No. 61-32195 discloses a first radiation detecting means for detecting radiation having a wavelength in the near infrared region and a second radiation detecting means for detecting radiation having a wavelength in the photographic infrared region. Calculating means for receiving output signals from the first and second radiation detecting means and calculating a logical combination of the output signals based on a level difference and synchronism of these output signals, and a combined output signal from the calculating means Discloses a fire detection device having a detection means for discriminating between a fire signal and a noise signal. This is because the flaming fire and the visible light noise have synchronism in the correlation of infrared rays of 2.3 μm and 0.9 μm, the smoldering fire does not show the synchrony, and the flaming fire and the smoldering fire are close to each other. Taking advantage of the fact that the infrared intensity is higher than the photographic infrared intensity and the visible light noise is the near-infrared intensity is lower than the photographic infrared intensity, the above two types of radiation are compared to distinguish between fire and visible light noise, and flaming fire and smoke. It distinguishes between fires.

[0004]

However, when the radiation intensity in the visible or near-infrared region is large compared to the radiation intensity in the infrared region such as an electric lamp, the method of judging non-fire is less likely to cause false alarms due to ordinary electric lights. However, if a heating element other than a fire does not emit visible or near-infrared rays or is weak, it is determined to be a fire and a false alarm is issued. That is, an electric heater or the like gives a false alarm and its application is largely restricted. In addition, when the radiation dose at 4.3 μm and two wavelengths before and after that is detected, and the radiation dose at 4.3 μm and other two wavelengths exceeds a certain value, it is judged as a flame. However, it is not possible to detect whether the flame comes from a fire or a useful heat source. That is, there is a drawback that a false alarm is generated by a flame of a gas range, a gas stove, or the like. Furthermore, 2.3 μm and 0.
When comparing the level difference and synchronism of two kinds of radiation of 9 μm to distinguish between fire and visible light noise, and to distinguish between flaming fire and smoldering fire, depending on the type of fire and how it burns There is no compensation to say that such synchronism is seen, and it lacks reliability.

The present inventors detect infrared rays emitted from an infrared ray source in a plurality of wavelength bands in such a situation, and based on the detection output of the infrared detector and the temporal change of the ratio of the detection outputs. An object of the present invention is to provide a detection wavelength band for establishing a highly reliable fire detection method by providing a signal processing circuit for determining whether or not there is a fire.

[0006]

In order to achieve the above object, the present invention has a short-wavelength infrared wavelength band that mainly detects relatively high temperature heat generation and a long wavelength that mainly detects relatively low temperature heat generation. Infrared wavelength band of wavelength, and the method of detecting the resonance radiation band of CO ₂ for detecting the presence or absence of flame, respectively, these wavelength bands are
2.8 μm to 3.2 μm after considering the radiation spectrum of combustible materials in the smoldered state, various kinds of loss in propagating infrared rays in the atmosphere, and loss in the casing necessary for constructing a fire detector. , 4.2μm ~ 4.6μm, 4.6
Identifies four wavelength bands of μm to 5.5 μm and 8.0 μm to 10.0 μm,
I decided to detect each. First, these are two wavelength bands as a wavelength pair for detecting high temperature heat generation, two wavelength bands as a wavelength pair for detecting low temperature heat generation,
Furthermore, it is a wavelength band for detecting the presence or absence of flame.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be specifically described below. FIG. 1 shows an example of the construction of a fire detector having a detection wavelength band according to the present invention. In this example, infrared rays radiated from a fire source or a similar heat source are periodically divided by a chopper, and four pyroelectric infrared sensors each have different infrared rays.
Detect the wavelength band. These sensors have a built-in bandpass filter that transmits a predetermined wavelength band. However, even with four or less pyroelectric infrared sensors, a method of detecting the wavelength divided into four using the switching means may be used. Further, even with only four or less pyroelectric infrared sensors, a method of detecting four kinds of wavelength bands by using the switching means may be adopted. The signal detected by each sensor is amplified by an amplifier circuit and then converted into a digital signal by an A / D converter. The microprocessor performs synchronous detection and filtering on the digital signal according to the division cycle of the chopper, and returns the signal divided by the chopper to a continuous signal sequence. Further, the signal sequence obtained here is converted into a signal sequence for communication and digitally transmitted to the host computer.

In the host computer, for example, the temperature of the infrared source is calculated from the transmitted infrared intensity signal of each wavelength band based on the ratio of the infrared intensity of each wavelength band, and from this temperature, one of the above wavelengths is calculated. The fire situation is determined by calculating the infrared radiation intensity of the band and calculating the heat generation area as follows based on the infrared radiation intensity and the output of the infrared detector that detects the wavelength band.

Let .lambda.1, .lambda.2, ... .lambda.n (n = integer of 2 or more) be the detection wavelength bands, and V1, V2, ... Vn are the detection outputs of the respective wavelength bands detected by the infrared detector D. It is assumed that these detection outputs accurately reflect the infrared intensity of each wavelength band incident on the infrared detector D. By the way, according to Planck's radiation law, the radiant intensity per unit area of infrared rays radiated by a body at a certain temperature T into a half space at a wavelength λ is expressed by the following equation.

[0010]

[Equation 1]

Here, C1 and C2 are C1 = 2πhc ² ,
It is a constant determined by C2 = hc / k. However, h is Planck's constant, c is light velocity, and k is Boltzmann's constant.

In the above equation (1), two detection wavelength bands λ1,
Substituting the radiated infrared ray intensities P1 and P2 in λ2 and its wavelength band and deriving an approximate expression for obtaining the temperature T,

[Equation 2] If there is no absorption between the infrared source S and the infrared detector D for both λ1 and λ2, P1 and P2 in the above equation (2) are used.
Can be replaced by V1 and V2. That is,

[Equation 3] Becomes From the equation (3), the temperature of the infrared source can be obtained by detecting the infrared rays of two different wavelengths.

Next, the blackbody radiation intensity per unit area at λ1 or λ2 from the temperature T obtained by the above equation (3) (this is referred to as P1 'or P2') is Planck's radiation law, that is, (1) ) Equation. On the other hand, the intensity of the infrared rays incident on the infrared detector D depends on the distance L to the infrared source S,
It becomes 1 / 2πL ² . Therefore, the infrared ray intensity P1 ″ or P2 ″ to be incident on the infrared detecting section D from the infrared ray source having a certain area of the obtained temperature T (s times the unit area) is P
It is a value obtained by multiplying 1'or P2 'by 2πL ² and s. That is, P1 ″ = P1 ′ × 2πL ² × S (4) P2 ″ = P2 ′ × 2πL ² × S (5) Since it is assumed here that the output of the infrared detector accurately reflects the intensity of the incident infrared light, P1 or P2 can be found from V1 or V2 using the above equations (3) and (2).
Therefore, if the distance L is known, the ratio between the actually detected incident infrared ray intensity P1 or P2 and the calculated incident infrared ray intensity P1 ″ or P2 ″ can be found from equations (4) and (5). The area s of the infrared source S is represented by.

Further, by using the wavelength band for detecting the CO ₂ resonance radiation band, the infrared of black body radiation in the CO ₂ resonance radiation band is calculated by the formula (1) from the temperature and heat generation area of the infrared source obtained by the above means. The intensity Pco2 'is calculated, and the infrared intensity Pco which should be incident on the infrared detector is calculated in the same manner as P1 above.
2 "is calculated and the ratio of this to the actually observed Pco2 is calculated. Here, if Pco2">> Pco2, the infrared source is accompanied by a flame. In this way, the situation of the fire is grasped,
Fire alarm.

In the example of FIG. 1, a chopper (2), an infrared sensor (3), an amplifier circuit and a microcomputer (4)
Etc. are housed in the same housing (5) as shown in FIG. Further, as another example, a housing for housing the amplifier circuit and the microcomputer (4) may be separately provided. Figure 1
In, the window portion through which infrared rays are transmitted uses polyethylene. As a matter of course, infrared transmissive crystal materials such as Si or ZnSe can also be used, and these infrared transmissive crystal materials have high transmittance. However, the above infrared transparent crystal material has a problem in mechanical strength, and if it is not handled carefully, it may possibly be damaged, and it is more expensive. Polyethylene does not break even with relatively rough handling, and is extremely inexpensive, so even if the fact that its infrared transmittance is inferior to that of the above crystalline materials is subtracted, it is an optimal material for such applications. ..

The infrared wavelength band detected in the example of FIG. 1 is a wavelength band for efficiently detecting the radiation of the heating element from the low temperature region to the high temperature region as shown in FIG. That is, the center wavelength is 3 μm, the half width is 0.4 μm, the center wavelength is 4.4 μm, the half width is 0.4
μm, center wavelength 5.5 μm, half width 0.8 μm, center wavelength 8.5 μ
The half-width of m is 1.0 μm. Regarding the above wavelength band, the radiation of the heating element in the high temperature region is mainly detected, and the heating element in the high temperature region of 400 ° C. or higher is monitored in combination with the infrared intensity detected in the wavelength band. The presence or absence of flame is monitored for the wavelength band. The wavelength band is a wavelength band that efficiently detects from low temperature to high temperature, and in combination with the wavelength band, it monitors the heating element in the high temperature range.
The heating element in the low temperature range is monitored in combination with the wavelength band.
As for the wavelength band, the radiation of the low-temperature heating element below 400 ° C is efficiently detected, and the heating element in the low-temperature region below 400 ° C is monitored in combination with the wavelength band. In the process from a smoldering state to a fire, a low temperature heating element gradually increases in temperature and expands. Therefore, it is necessary to monitor the temperature of the heat source in a wide temperature range from low temperature to high temperature.

The detection wavelength band having a center wavelength of 3.0 μm and a half width of 0.4 μm needs to be detected in order to accurately monitor a high temperature heating element. When detecting infrared rays with a short wavelength, the detection wavelength band cannot be set on the side of a wavelength shorter than 2 μm in order to avoid the influence of artificial rays such as electric lights. Also, in the vicinity of 2.6 μm,
As described above, there is an absorption band due to CO ₂ and water vapor, and the wavelength band with high atmospheric transmittance is 2.8 μm to 4.1 μm, so the limitation on the short wavelength side of the above wavelength band is 2.8 μm. Furthermore, when polyethylene or the like is used for the infrared transmitting window of the housing, the absorption band exists from 3.2 μm to 4.0 μm as shown in FIG.
The long wavelength limit is 3.2 μm. Although it is possible to widen the bandwidth of the above detection wavelength band by using an infrared transmissive crystal material for the infrared transmissive window material of the housing, 3.2 μm ~
Since the absorption band of 4.0 μm is due to the bond of CH, for example, when organic gas is generated by the heat of a fire and diffuses into the atmosphere, it may be absorbed by the gas diffused into the atmosphere. It is not appropriate to add μm to 4.0 μm to the detection wavelength band.

The detection wavelength band having a central wavelength of 4.4 μm and a half value width of 0.4 μm is a wavelength band for detecting the presence or absence of flame. Here, the resonance radiation of CO ₂ due to flame combustion is in the range of 4.2 μm to 4.6 μm as shown by the curve of combustion with flame in FIG. Therefore, it is desirable to set the wavelength band for detecting the presence or absence of flame within this range. Of these, 4.2 to 4.3 μm has an absorption band of CO _{2 in} the atmosphere, but since priority is given to sensitivity, this band is also detected in this embodiment.

The detection wavelength band having a central wavelength of 5 μm and a half value width of 0.8 μm is a wavelength band for obtaining the temperature of the heating element in combination with and. Therefore, it is necessary to secure a wide bandwidth on the relatively short wavelength side in order to have a high sensitivity to a low temperature heating element and to secure a good accuracy for a high temperature heating element. Considering the absorption of the atmosphere shown in Fig. 3, 5.5-8μ
Since m has a large absorption of water vapor and CO ₂ is absorbed in the vicinity of 4.3 μm, it is appropriate to detect the wavelength band of 4.4 to 5.5 μm. However, due to CO ₂
Since very strong radiation is generated over 4.2 μm to 4.6 μm, it is necessary to avoid this radiation band to reduce the error during flaming combustion. Therefore, the short wavelength limit of this wavelength band is 4.6 μm, and the long wavelength limit is 5.5 μm.

The detection wavelength band having a central wavelength of 8.5 μm and a half value width of 1.0 μm is for monitoring a low temperature object. It is indispensable to improve the reliability of fire detection by grasping the process from the smoldering state to the burning of the flame. However, in the wavelength band of 10 μm or more, infrared rays emitted from an object such as a human body near room temperature are also detected, which causes malfunctions and the like. Therefore, it is not appropriate to select an extremely long wavelength band even for the low temperature detection wavelength band, and it is desirable that the wavelength band is 10 μm or less. Also,
As shown in FIG. 3, it is necessary to be 8 μm or more because absorption by the atmosphere is large on the shorter wavelength side than 8 μm. Therefore, it is appropriate that the long-wavelength detection band for catching low-temperature heat generation is between 8 μm and 10 μm.

FIG. 5 shows an embodiment of the structure of the infrared sensor used in the present invention. In this mode, the pyroelectric element (7) is used as the infrared detection element, and the infrared bandpass filter is used as the window material of the sensor. However, as shown in FIG. The outer bandpass filter (6) may be independent. It is also possible to use a thermocouple type element or a quantum type element for the infrared detecting element. When the quantum type element is used, the sensing element becomes expensive, but the sensitivity is improved by about two digits as compared with the pyroelectric type and the thermocouple type. Therefore, the detection bandwidth can be made narrower than that in the above embodiment, and the temperature detection accuracy can be improved. For example, specify the characteristics of each bandpass filter with a center wavelength of 3 μm
0.1 μm, center wavelength 4.5 μm, half-value width 0.1 μm, center wavelength 5.
When the InSb detection element is used for the wavelength band of, and the HgCdTe detection element is used for the wavelength band of, the temperature detection accuracy is 1 digit and the detection area is 10 times larger. The performance of is obtained.

[0022]

EXAMPLE FIG. 7 shows an example in which a test fire from smoldering of beech wood to flame combustion is detected using the fire detection method according to the present invention. The distance between the detector and the fire source is 10m. C
H ₁ , CH ₂ , CH ₃ , and CH ₄ are the same as above,
Shows the intensity in the wavelength band of. As a result, it is possible to monitor from the heat generation state of 150 ° C by detecting infrared rays in the wavelength bands of the above and, and at the time of transition to flaming combustion about 9 minutes after the start of overheating, infrared rays in the wavelength bands of the above and By detecting the temperature and heat generation area, and by detecting infrared rays in the above wavelength band, it was possible to accurately detect the presence or absence of a flame.

[0023]

As described above, according to the present invention, infrared rays radiated from a fire are detected, and whether the fire is detected or not is determined based on the detection output of the infrared detector and the temporal change of the ratio of the detection outputs. In the fire detection method, which is characterized by performing the signal processing described above, the detection wavelength band is 2.8 μm to 3.2 μm.
2 μm to 4.6 μm, 4.6 μm to 5.5 μm, 8.0 μm to 10.0 μm
By specifying the 4 wavelength bands of, it becomes possible to widely monitor the state change from the low temperature smoldering state to the high temperature flaming combustion state, and the fire can be detected reliably without being affected by atmospheric fluctuations. I can do it.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a detector according to the present invention.

FIG. 2 is a diagram showing a detection wavelength band in the present invention.

FIG. 3 is a diagram showing typical infrared spectral transmittances of air and polyethylene.

FIG. 4 is a structural diagram of a detection portion according to an embodiment of the present invention.

FIG. 5 is a diagram showing a configuration example of an infrared sensor according to the present embodiment.

FIG. 6 is a diagram showing a configuration example of an infrared sensor according to the present embodiment.

FIG. 7 is a diagram showing an experimental result according to the present embodiment.

[Explanation of symbols]

1 Infrared transmission window 2 Chopper 3 Infrared sensor 4 Substrate equipped with amplification circuit, A / D converter, microcomputer, etc. 5 Housing 6 Infrared bandpass filter 7 Pyroelectric element 8 Infrared transmission window

Claims (1)

[Claims] 1. A fire detection method for detecting a plurality of infrared rays radiated from a fire, and judging whether or not there is a fire based on a temporal change in a ratio of the detected outputs and the detected outputs. 4 wavelength bands, ie 2.8μm-3.2μm,
4.2μm ~ 4.6μm, 4.6μm ~ 5.5μm, 8.0μm ~ 10.0
A fire detection method characterized by detecting each μm and detecting a fire even after smoldering.