JP6738632B2 - Flame detector - Google Patents

Description

The present invention relates to a flame detector for notifying that a fire has occurred, and more particularly to a flame detector that widens a monitoring angle and improves flame detection accuracy.

The current flame detector used to detect a fire that occurs in a tunnel has two wavelengths, a near infrared region with a wavelength of 0.8 μm to 1.1 μm and a mid infrared region with a wavelength of 1.0 to 2.7 μm. Is being detected.

More specifically, using a photodiode as a sensor to detect the near-infrared region, using a pyroelectric element as a sensor to detect the mid-infrared region, depending on the wavelength detected by these sensors, the fire to be detected, The determination is made with respect to a light source that causes an erroneous detection (for example, refer to Patent Document 1).

FIG. 12 shows a structure of a window material of an existing flame detector for a tunnel. As shown in FIG. 12, in a current flame detector for a tunnel, a window material in which an infrared transmission filter 112 and a hard glass 113 are sequentially laminated on the front surface of a photodiode 101 for detecting a near infrared region. Is provided.

On the other hand, on the front surface of the pyroelectric element 102 for detecting the mid-infrared region, a window material in which a silicon filter (Si filter) 111, an infrared transmission filter 112, and a hard glass 113 are sequentially laminated is provided.
The hard glass 113 serves as a protective material that protects the photodiode 101 and the pyroelectric element 102.

In the existing flame detector for tunnels, the Si filter 111, the infrared transmission filter 112, and the hard glass 113 used as window materials have the following characteristics from the transmittance characteristics for each wavelength.
Si filter 111: has a function of cutting wavelengths of about 1.0 μm or less.
Infrared transmission filter 112: It has a high transmittance in the wavelength region of about 0.8 to 2.8 μm.
Hard glass 113: Has a function of cutting wavelengths of about 2.7 μm or more.

FIG. 13 is a diagram showing relative sensitivity characteristics with respect to wavelength of each of the photodiode 101 and the pyroelectric element 102 after passing through the window material having the configuration shown in FIG. 12 which is an existing tunnel flame detector. As shown in FIG. 13, by providing the window material structure shown in FIG. 12, the photodiode 101 detects a near infrared region having a wavelength of 0.8 μm to 1.1 μm, and the pyroelectric element 102 has a wavelength of 1. It can be seen that the mid-infrared region of 0 to 2.7 μm can be detected and two wavelengths can be distinguished and detected.

Further, in the conventional flame detector disclosed in Patent Document 1, the Si filter 111 provided on the front surface of the pyroelectric element 102 can inexpensively limit the output on the short wavelength side of the pyroelectric element 102. However, since the pyroelectric element 102 has a portion overlapping with the sensitivity region of the photodiode 101, it may detect the wavelengths of various light sources, and the accuracy of fire detection may decrease.

Therefore, in order to solve such a problem, there is a flame detector in which the degree of separation between the flame and various light sources existing in the tunnel is increased (for example, refer to Patent Document 2).

The conventional flame detector disclosed in Patent Document 2 includes a photodiode that detects a near-infrared region, a pyroelectric element that detects a mid-infrared region, and a window material provided in front of the photodiode and the pyroelectric element. And structure. Then, based on the comparison between the output of the photodiode and the output of the pyroelectric element for the same detection target, the flame and the light source are discriminated and then the occurrence of the flame is detected.

Here, in the conventional flame detector disclosed in Patent Document 2, as a window material structure provided on the front surface of the pyroelectric element, the pyroelectric element is formed so as to eliminate the sensitivity region overlapping with the photodiode and the pyroelectric element. The window material that can move the sensitivity region on the short wavelength side to the long wavelength side is applied. As a result, a flame detector with a high degree of separation between the flame and the various light sources present in the tunnel is realized.

JP 2001-141559 A JP, 2014-197296, A

However, the conventional techniques have the following problems.
As an infrared detection element for flame detection, a pyroelectric element has been mainly used as shown in Patent Documents 1 and 2 because of its high infrared sensitivity. However, as the infrared detection element, in addition to the pyroelectric element, there are elements of various principles such as thermopile, bolometer, and quantum type, and each has its own characteristics.

In other words, in order to respond to various field situations that require a flame detector, the infrared detection element used in the flame detector can also be used to select a detection principle that is optimal for the situation, thereby providing a more effective fire. The detection can be executed.

The pyroelectric element is superior in sensitivity as compared with other detection principles. However, from the viewpoint of vibration resistance and response characteristics, the pyroelectric element may be inferior to those of other detection principles.

The present invention has been made in order to solve the above problems, vibration resistance, when performing flame detection using a thermopile excellent in response characteristics, aimed to improve the viewing angle and detection accuracy. The purpose is to obtain a flame detector.

A flame detector according to the present invention includes a two-wavelength thermopile including a first element having a spectral sensitivity in a first wavelength region suitable for flame detection and a second element having a spectral sensitivity in another wavelength region, It is a flame detector that detects the occurrence of flame after distinguishing the flame and the light source based on the comparison of the detection results of the 1st element and the 2nd element. In the 2-wavelength thermopile, the 1st element and the 2nd element alternate. It has an array structure having three elements arranged linearly in the optical axis and has two different spectral absorptance characteristics in which the spectral sensitivity of the absorption wavelength is adjusted by the material and thickness of the absorption film. It is a thing.

According to the present invention, when a two-wavelength thermopile including a first element having a spectral sensitivity in a wavelength range suitable for flame detection and a second element having a spectral sensitivity in another wavelength range is incorporated, two types of elements are used. The flame detector is configured to have an element array structure in which three elements are alternately arranged. As a result, it is possible to obtain a flame detector with improved viewing angle and detection accuracy when flame detection is performed using a thermopile having excellent vibration resistance and response characteristics.

3 is a schematic cross-sectional view showing a device absorption film structure of a dual wavelength thermopile according to the first embodiment of the present invention. It is the figure which showed the spectral absorption factor characteristic which the 2 wavelength thermopile in Embodiment 1 of this invention has. It is a figure which shows the element structure of the dual wavelength thermopile in Embodiment 1 of this invention. It is explanatory drawing which showed an example of the external appearance of the flame detector prototyped in Embodiment 1 of this invention. It is the figure which showed the relationship between the blackbody furnace temperature and the spectral ratio of the flame detector which concerns on Embodiment 1 of this invention. It is the figure which showed the comparison result of the spectral ratio with respect to various flames of the flame detector which concerns on Embodiment 1 of this invention. It is the figure which showed the comparison result of the spectral ratio with respect to various light sources of the flame detector which concerns on Embodiment 1 of this invention. It is the figure which showed the time change of TP1 output of the flame detector which concerns on Embodiment 1 of this invention when sunlight enters. It is a figure which shows the change characteristic of the element output with respect to the monitoring angle of the flame detector which has the arrangement|sequence of the pattern 1 which concerns on Embodiment 1 of this invention. It is a figure which shows the change characteristic of the element output with respect to the monitoring angle of the flame detector which has the arrangement|sequence of the pattern 2 which concerns on Embodiment 1 of this invention. It is a figure which shows the change characteristic of the element output with respect to a monitoring angle after enlarging a visual field of the flame detector which has the arrangement|sequence of the pattern 2 which concerns on Embodiment 1 of this invention. The structure of the window material of the existing flame detector for a tunnel is shown. It is the figure which showed the relative sensitivity characteristic with respect to wavelength of each of the photodiode 101 and the pyroelectric element 102 after permeate|transmitting the window material which has the structure shown in FIG. 12 which is an existing tunnel flame detector.

Hereinafter, preferred embodiments of the flame detector of the present invention will be described with reference to the drawings.
In order to identify and detect two wavelengths, the present invention prototypes a thermopile having two different types of spectral sensitivities (hereinafter referred to as a two-wavelength thermopile), and verifies flame detection performance to obtain vibration resistance. The technical feature is the realization of a flame detector with excellent response characteristics.

Embodiment 1.
The prototyped two-wavelength thermopile has a structure in which the spectral sensitivity of the absorption wavelength can be adjusted depending on the material and thickness of the absorption film. FIG. 1 is a schematic cross-sectional view showing an element absorption film structure of a dual wavelength thermopile according to Embodiment 1 of the present invention. Further, FIG. 2 is a diagram showing a spectral absorptance characteristic of the two-wavelength thermopile according to the first embodiment of the present invention.

As shown in FIG. 1, an element TP1 which has sensitivity up to a short wavelength and serves as an element for flame detection is formed by sequentially laminating a reflection film 11, an interference film 12, an absorption film 13, and a protective film 14. There is. On the other hand, the element TP2 having sensitivity up to a long wavelength is formed by sequentially laminating the reflection film 11, the interference film 12, and the protective film 14.

That is, by providing the absorption film 13 on the element TP1, it is possible to form a two-wavelength thermopile having two different spectral absorptance characteristics in one housing, as shown in FIG. Then, the wavelength band of the absorption film 13 is selected so as to have spectral sensitivity in the wavelength region of the element TP1. It is also possible to adopt a configuration in which the absorption film 13 having an absorptivity different from that of the element TP1 is provided on the element TP2 side.

FIG. 3 is a diagram showing an element structure of a dual wavelength thermopile according to the first embodiment of the present invention. As shown in FIG. 3, the thermopile element structure (element structure of each of the elements TP1 and TP2) in the first embodiment has a structure as shown in FIG. 3 in consideration of sensitivity, response time, and vibration characteristics. There is.

The stacking order shown in FIG. 1 is merely an example, and other stacking structures can be adopted. The absorption wavelength shown in FIG. 2 is also just an example, and can be appropriately designed according to the configuration of the dual wavelength thermopile. Furthermore, the element structure shown in FIG. 3 is merely an example, and other element structures can be adopted.

In the two-wavelength thermopile according to the first embodiment, two different types of elements, that is, the element TP1 and the element TP2 shown in FIG. 1 are arranged alternately and linearly arranged at intervals of 500 μm. The three element arrays have the following two patterns.
Pattern 1: When arranged as TP2-TP1-TP2 Pattern 2: When arranged as TP1-TP2-TP1

It should be noted that in the verification result described below, data regarding two types of element arrays of patterns 1 and 2 are mixed, but the conclusion is that the adoption of pattern 2 improves the resistance to false alarms due to parallax.

FIG. 4 is an explanatory diagram showing an example of the appearance of the flame detector prototyped in the first embodiment of the present invention. The prototype has a structure in which a two-wavelength thermopile element having three element arrays is soldered to a PC board via a heat insulating material and housed in the resin casing shown in FIG. Further, double-sided polishing Ge (germanium) is adopted as the window material on the surface of the flame detector.

The prototype flame detector uses the AC component (AC output) of the element output to make a fire determination, and the AC output can be transmitted to a data collector such as a personal computer.

In addition, the electrical specifications of the prototype are as follows.
Amplifier amplification factor AC: ×49000 (max)
Frequency characteristics AC: 1-10Hz
AC conversion 12 bits (FS=3.0V)
Sampling 20msec

Next, the result of the operation confirmation using the prototype will be described in detail below.
(1) Results of verification of spectral ratio for high-temperature objects (element array of pattern 1 is used)
The AC output of the prototype flame detector and the spectral ratio (TP1/TP2) of the element TP1 and the element TP2 were measured using the black body furnace as a heat source. In the prototype, since the AC component was measured as described above, a 4 Hz chopper was installed between the flame detector and the heat source.

FIG. 5 is a diagram showing the relationship between the blackbody furnace temperature and the spectral ratio of the flame detector according to the first embodiment of the present invention. In addition, in FIG. 5, three kinds of results of −20° C., 25° C., and 60° C. are plotted as the environmental temperature.

From FIG. 5, it can be seen that the spectral ratio (TP1/TP2) is hardly affected by the environmental temperature, increases as the temperature of the blackbody furnace increases, and is constant near 800°C. ..

Therefore, by utilizing the characteristics of FIG. 5, it is possible to exclude heat sources below a certain temperature without depending on the environmental temperature by setting an appropriate threshold value of the spectral ratio.

(2) Verification results of spectral ratios for various flames (using the element array of pattern 1)
FIG. 6 is a diagram showing comparison results of spectral ratios of various flames of the flame detector according to Embodiment 1 of the present invention. From FIG. 6, it can be seen that the spectral ratios for various combustion flames are about 1.3 or more. On the other hand, it can be seen that the hydrogen flame has a lower spectral ratio than other flames.

(3) Verification result of spectral ratio for various light sources which is a cause of false alarm (using element array of pattern 1)
FIG. 7 is a diagram showing a comparison result of spectral ratios of the flame detector according to Embodiment 1 of the present invention with respect to various light sources. It can be seen from FIG. 7 that the spectral ratio for various light sources, which is considered as a cause of false alarm, is 1.2 or less, which is lower than the spectral ratio for flame.

(4) Confirmation of influence of sunlight The sun is a high temperature object of 5500K. Therefore, we confirmed the effect of sunlight. However, in this confirmation, Si was used as the window material of the prototype flame detector for measurement.

FIG. 8: is the figure which showed the time change of TP1 output of the flame detector which concerns on Embodiment 1 of this invention at the time of irradiating sunlight. Specifically, it is the result of setting the prototype in the shade and measuring it by making sunlight incident on the prototype flame detector by the diurnal motion of the sun.

From FIG. 8, the AC output rises due to the influence of the incidence of sunlight from the time when the elapsed time exceeds 6 minutes, and although not shown, the spectral ratio is about 2 to 3, which is 1.3 as with the flame. The above values are shown. Since almost no clouds existed during the measurement, it is considered that the AC output increased significantly due to atmospheric fluctuations.

Here, in order to reduce the influence of fluctuations of sunlight, it is conceivable to use Ge as the window material. This is because the absorption spectrum of water is around 1.3 μm, and the cut-on wavelength of Ge is 1.6 μm, which is longer than that of Si. Further, there is an advantage that the price of Ge is lower than that of the interference film filter. Therefore, Ge was finally adopted as the window material for the prototype flame detector.

(5) Parallax of 2-wavelength thermopile (changed from pattern 1 array to pattern 2 array)
In the prototyped two-wavelength thermopile, two types of elements are linearly arranged in the same package as in the above-described pattern 1 and pattern 2. For this reason, the incident angle of infrared rays is slightly different for each element, which affects the spectral ratio. Therefore, the results of examining the effect of parallax on the arrangements of pattern 1 and pattern 2 are shown below.

FIG. 9 is a diagram showing a change characteristic of the element output with respect to the monitoring angle of the flame detector having the arrangement of the pattern 1 according to the first embodiment of the present invention. Specifically, the element output by the monitoring angle (incident angle) when the prototype flame detector was rotated (tilted) in the same direction as the element arrangement with respect to the heat source (blackbody furnace 400°C) It shows the change.

When the monitoring angle is within ±40°, the spectral ratio is almost constant even if the element output changes. On the other hand, when the monitoring angle exceeds ±40°, the spectral ratio also changes rapidly. An increase in the spectral ratio causes a false alarm. Therefore, when the monitoring angle is around ±50°, there is a possibility that even an object having a temperature that should not normally be judged as a fire may be judged as a fire.

As the monitoring angle increases, the incident amount on the element decreases, and the element output also decreases. Further, at a certain angle, the field of view is blocked by the cap, the filter, the casing, etc., and the element output is greatly reduced.

In a two-wavelength thermopile in which three elements are arranged as pattern 1 (TP2-TP1-TP2), when the monitoring angle becomes large, one of the TP2 elements at both ends is blocked first, and the output is greatly reduced. At this time, since the infrared rays are still incident on the central TP1, the spectral ratio (TP1/TP2) increases, which causes a false alarm.

Therefore, the same measurement as in FIG. 9 was performed using a two-wavelength thermopile with pattern 2 (TP1-TP2-TP1) in which the order of the element arrangement of the three elements was reversed. FIG. 10 is a diagram showing a change characteristic of the element output with respect to the monitoring angle of the flame detector having the arrangement of the pattern 2 according to the first embodiment of the present invention.

As can be seen from the comparison between FIG. 9 and FIG. 10, in the arrangement of pattern 1, the spectral ratio increased in the range of the monitoring angles of ±40° to ±55°, but in the arrangement of pattern 2, it turned to decrease. There is.

More specifically, when the pattern 2 array is used, the sensitivity (spectral ratio) to the front surface is reduced, but the pattern 2 array is more stable than the pattern 1 array in a wider monitoring range. The effect is that the ratio can be obtained. However, since the spectral ratio greatly increases near the monitoring angle of ±60°, the possibility of false alarm cannot be ruled out. Therefore, the monitoring angle, that is, the field of view was expanded by expanding the opening on the front surface of the element while keeping the element arrangement.

FIG. 11 is a diagram showing a change characteristic of the element output with respect to the monitoring angle after the field of view of the flame detector having the arrangement of the pattern 2 according to the first embodiment of the present invention is enlarged. As a result of expanding the field of view, the monitoring angle at which the spectral ratio abnormally rises has moved to around ±70°, but the possibility of false alarms still remains.

However, it is possible to eliminate the false alarm by devising the installation location such as installing the flame detector in the corner of the room and using the monitoring range of ±70° where the spectral ratio is abnormal as the wall surface.

(6) Sensitivity confirmation by changing the element array from pattern 1 to pattern 2 By changing the element array to be used from pattern 1 to pattern 2, there are two TP1 elements that are sensitive to flame, so the absolute output The value changes. Therefore, the difference in sensitivity between pattern 1 and pattern 2 was examined.

As a result of comparing the S/N according to the arrangement of the pattern 1 and the S/N according to the arrangement of the pattern 2, it is clear that the sensitivity to the heptane flame becomes about 1.4 times by adopting the arrangement of the pattern 2. Became. From this, the monitoring distance of the pattern 2 is increased by 20% from the monitoring distance of the pattern 1 to be about 14 m.

The following is a summary of the above verification results.
-By using the flame detector with the two-wavelength thermopile that adopts the pattern 2 arrangement, it was possible to secure a monitoring distance of 14 m or more for the heptane flame.
-Furthermore, by adopting the pattern 2 arrangement, the viewing angle could be secured at a half value angle of ±55°. In addition, when the viewing angle is expanded, an abnormal increase in the spectral ratio occurs in the vicinity of ±70°, so that the installation position needs to be careful in order to prevent false alarms.
-Ge is required as a window material in order to eliminate the influence of fluctuations of sunlight.
-Because spectroscopic measurement can be performed by the thermopile itself, expensive BPF is not required, resulting in cost reduction. However, since the difference in the spectral ratio between the light source and the flame, which is a false alarm factor, is small, it is necessary to be careful in setting the threshold.

As described above, according to the first embodiment, the two-wavelength flame detector is realized by using the thermopile type heat-sensitive element. Specifically, by selecting an absorption film so that an appropriate wavelength band can be detected, flame detection is performed by distinguishing from various light sources that are false alarm factors. As a result, it is possible to obtain a flame detector that is superior in vibration resistance and response characteristics as compared with the case where a pyroelectric element is used as an infrared ray detection element for flame detection.

Furthermore, by adopting germanium having a cut-on wavelength of about 1.6 μm as the window material, it is possible to realize an inexpensive configuration that minimizes the influence of fluctuations of sunlight.

The window material can be configured as two windows, a first window material provided on the front surface of the two-wavelength thermopile itself and a second window material provided on the light receiving window of the flame detector. In this case, one window member can be made of germanium and the other window member can be made of silicon.

Further, the flame detector is configured so as to have an element array structure in which three elements TP1 and elements TP2 are alternately arranged in a straight line. As a result, it is possible to obtain a flame detector with improved viewing angle and detection accuracy when flame detection is performed using a thermopile having excellent vibration resistance and response characteristics. In particular, by adopting an element array structure in which TP1 is arranged on both sides of TP2, even in an environment where there are light sources at both ends of the monitoring range, false alarms are suppressed and the viewing angle and detection accuracy are improved. A flame detector can be realized.

In the first embodiment, the element TP1 which is sensitive to a short wavelength and serves as an element for flame detection and the element TP2 which is sensitive to a long wavelength are used. However, an appropriate spectral ratio can be obtained. Any element can be used, and the element TP2 having sensitivity to a wavelength shorter than the element TP1 may be used.

11 reflection film, 12 interference film, 13 absorption film, 14 protective film.

Claims (4)

A two-wavelength thermopile including a first element having a spectral sensitivity in a first wavelength region suitable for flame detection and a second element having a spectral sensitivity in another wavelength region is provided, and the two elements of the first element and the second element are provided. A flame detector that detects the occurrence of flame based on the comparison of the detection results, after distinguishing the flame and the light source,
The two-wavelength thermopile has an array structure having three elements in which the first element and the second element are alternately arranged linearly, and the absorption wavelength spectrum is determined by the material and thickness of the absorption film. A flame detector having two different spectral absorptivity characteristics with adjusted sensitivity . In the two-wavelength thermopile, the array structure is formed by disposing the first elements at both ends of the second element ,
The first element has a first absorption film as the absorption film, and is configured by sequentially laminating a reflection film, an interference film, the first absorption film, and a protective film,
The second element is
When the absorbing film has a second absorbing film having a different absorption rate from the first absorbing film, a reflecting film, an interference film, the second absorbing film, and a protective film are sequentially laminated. Consists of
The flame detector according to claim 1, wherein the flame detector is configured by sequentially laminating a reflection film, an interference film, and a protection film when the absorption film is not included . Further comprising a first window member provided on the front surface of the two-wavelength thermopile itself and a second window member provided on the light receiving window of the flame detector,
The flame detector according to claim 1 or 2, wherein the first window member is made of germanium, and the second window member is made of silicon. Further comprising a first window member provided on the front surface of the two-wavelength thermopile itself and a second window member provided on the light receiving window of the flame detector,
The flame detector according to claim 1, wherein the first window member is made of silicon, and the second window member is made of germanium.

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