JP2003227751A - Flame detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a flame with satisfactory accuracy even when sunlight or stray light is incident. <P>SOLUTION: A filter used to cut off light in an infrared region, a filter used to cut off the stray light, a narrow-band filter through which only light in a band of a line spectrum by a carbon dioxide resonance radiation emitted by the flame is transmitted, and a wide-band filter through which light in a band wider than the band of the line spectrum is transmitted, are installed. The light transmitted through the narrow-band filter and the light transmitted through the wide-band filter are converted into electrical signals by a plurality of light receiving elements. The flame is decided when a difference between values corresponding to strengths of the electrical signals is a prescribed value or more on condition that a transmission band of the narrow-band filter is equal to that of the wide-band filter, and when the ratio of the values corresponding to the strengths of the electrical signals is within a prescribed range. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flame detector, and more particularly to a flame detector capable of detecting a flame even in the presence of artificial light such as sunlight or a halogen lamp without being affected by the light. Regarding the flame detector.

[0002]

It is known in the prior art to detect the resonance radiation emitted by the hot carbon dioxide contained in the flame for sensing the flame. Although there are many wavelengths in the line spectrum of the resonance radiation of carbon dioxide, in order to distinguish it from general artificial lighting and sunlight, those existing in the infrared region or ultraviolet region are used for flame detection. Is preferred. The reason for this is that artificial light such as illumination has a small amount of light components belonging to the infrared region or the ultraviolet region, and the disturbance of external light when sensing a flame is small.

Conventionally, in order to detect a flame under sunlight, the generation of the flame has been detected by detecting the line spectrum of the carbon dioxide gas generated by the resonance radiation. As a method, with continuous spectrum such as sunlight or artificial light,
In order to distinguish from the flame line spectrum, a narrow band monochromatic filter that transmits only the flame line spectrum, and a plurality of narrow band monochromatic filters that transmits light of one or more wavelengths in the vicinity of the band By comparing and calculating the multiple outputs obtained by, the light was discriminated whether it was a line spectrum of flame or a continuous spectrum of sunlight.

Another method has been to detect the occurrence of a flame by utilizing the flicker of light generated by the flame.

In the conventional method using the resonance emission of carbon dioxide gas, a filter using at least three monochromatic filters is required in order to obtain a flame detector capable of reliably detecting a flame with few false alarms. Also, it has a drawback that the decision circuit for sensing becomes complicated and therefore expensive.

Further, the filter composed of two or less filters has a drawback that there are many false alarms. The one using the flicker of the flame is also cheap, but it has a drawback that there are many false alarms.

Radiation from sunlight, general artificial light or a stove is emitted not only in visible light but also in these infrared regions, but these radiations are continuous spectra. On the other hand, the resonance emission spectrum of carbon dioxide gas emitted by the flame is a line spectrum in which energy is concentrated in an extremely narrow region. Utilizing the difference between the continuous spectrum and the line spectrum for flame detection, two filters are used.
A flame detector that can detect a flame with the same degree of certainty as that using a conventional three filters has also been proposed (Japanese Patent Laid-Open No. 10-29138).
No. 326391, 2000-321132).

In this flame detector, a wide band filter including a line spectrum band of carbon dioxide resonance radiation emitted by a flame and transmitting light in a band wider than this band and a band filter of the line spectrum of carbon dioxide resonance radiation are transmitted. Two filters are used: a narrow band filter and a filter. And
The light intensity (light energy) from the flame that has passed through these two filters is divided by the bandwidth of the filter to obtain the average intensity.

When the intensity of the spectrum of the light transmitted through the filters is a linear continuous spectrum, the energy of the light transmitted through the two filters is proportional to the transmission bandwidth, so this energy is divided by the bandwidth. The average strength is the same.

However, when the transmitted light is a line spectrum of resonance radiation emitted by carbon dioxide, both of the two filters transmit this line spectrum, and although the amount of transmitted energy is almost the same, a broadband filter is used. The energy of the transmitted light is divided by the wide bandwidth to calculate the average intensity, and the energy transmitted through the narrow band filter is divided by the narrow bandwidth to calculate the average intensity.
There is a difference between the two average intensities.

Therefore, the flame can be detected by determining whether the difference between the average intensities is greater than or equal to the threshold value.

However, since the size of the flame that can be detected by the flame detector is inversely proportional to the square of the distance from the flame to the flame detector, in order to detect a near flame to a distant flame over a wide range, A wide range of dynamic range is required. This also applies to the flame detection signal and noise, and therefore the above threshold is set according to the distance from the flame detector to the main detection position, but the threshold is set according to the nearby detection position. If set, the level of the flame detection signal for distant flames becomes too low, resulting in undetectable or false detection.On the contrary, if the threshold is set according to the distant detection position, the noise level for nearby flames will be reduced. It becomes too high and false detection occurs. Therefore, there is a problem that it is difficult to accurately detect the flame over a wide range.

When light having strong energy in the infrared region such as sunlight or a halogen lamp is incident,
Due to the temperature rise of the filter in the flame detector, secondary radiation of infrared rays is generated from the filter, and this secondary radiation becomes noise and erroneous detection occurs. Further, when stray light enters the flame detector, the stray light enters from the side surface of the filter, resulting in erroneous detection.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to make an erroneous detection even when light or stray light having strong energy in the infrared region such as sunlight or a halogen lamp is incident. An object of the present invention is to provide a flame detector that eliminates the above problems.

[0015]

In order to achieve the above object, the present invention provides a first light blocking filter for blocking light in the infrared region and a light transmitting side of the first light blocking filter for blocking stray light. And a second light-shielding filter that is arranged, and a light-transmitting side of the second light-shielding filter,
A narrow band filter that transmits only light in the entire band of the line spectrum of carbon dioxide resonance radiation emitted by a flame, and a narrow band filter that is arranged on the light transmission side of the second light-shielding filter and that includes the band of the line spectrum. A wideband filter that transmits light in a wider band, and a first light receiving element that converts light that has passed through the narrowband filter into a first electric signal,
And a second light receiving element that converts light that has passed through the broadband filter into a second electric signal.

In the present invention, the first light blocking filter for blocking light in the infrared region and the second light blocking filter arranged on the light transmitting side of the first light blocking filter so as to block stray light are used. Therefore, even in a place where artificial light such as sunlight or a halogen lamp exists, the flame can be sensed without being affected by the light, and erroneous detection due to stray light is eliminated.

As the light receiving element of the present invention, lead selenide, a thermopile or a pyroelectric type light receiving element can be used.

In the present invention, in place of the narrow band filter and the wide band filter, there is a predetermined band for transmitting light, and only the light in the band of the line spectrum of carbon dioxide resonance radiation emitted by the flame is transmitted within the predetermined band. You may use the 1st filter in which the band which is not made is formed, and the 2nd filter which permeate | transmits the light of the band substantially the same as the said predetermined band, and including the band of the said line spectrum.

In the present invention, the strength of the second electric signal is calculated from the value corresponding to the strength of the first electric signal on the assumption that the transmission bands of the narrow band filter and the wide band filter are equal. The difference obtained by subtracting the value corresponding to is greater than or equal to a predetermined value, and the ratio between the value corresponding to the strength of the first electric signal and the value corresponding to the strength of the second electric signal is within a predetermined range. It is possible to further provide a judging means for judging a flame.

The value corresponding to the strength of the electric signal may be the value of the strength of the electric signal itself, and the moving average value of the strength of the electric signal in a predetermined sample section is used as a reference level, and the predetermined sample of the strength of the electric signal is used. It may be a value obtained by subtracting the reference level from the moving average value of the sample section shorter than the section.

The electric signal may be used by amplifying or not amplifying the electric signal converted by the light receiving element, but it is superimposed on the electric signal when the flame light is detected.
The flicker component of the flame in the range of Hz to 10 Hz may be extracted by filtering or the like, and the extracted flicker component may be amplified or used without amplification. That is, the moving average value may be calculated based on the flicker component of the flame light included in the electric signal.

When the intensity of the spectrum of the light transmitted through the filter is a continuous spectrum, the energy of the light transmitted through the two filters of the wide band filter and the narrow band filter is substantially proportional to the transmission bandwidth, so that the narrow band filter is used. And when it is assumed that the transmission bands of the broadband filters are equal, that is, when the values corresponding to the intensities of the electric signals are converted into the values when the transmission bands of the filters are equal, they correspond to the intensities of the first electric signals. The difference obtained by subtracting the value corresponding to the intensity of the second electric signal from the value is
It becomes less than the specified value. The cause of the difference being less than the predetermined value is the shape of the intensity distribution of the spectrum of the light passing through the filter, the distance between the band centers of the two filters, and the like.

On the other hand, when only the light of the flame is present, the spectrum of the flame is a line spectrum, so the spectrum transmitted through the wide band filter and the narrow band filter is mainly only the line spectrum and transmitted through the wide band filter. The amount of the generated energy and the amount of energy transmitted through the narrow band filter are substantially the same. Therefore, assuming that the transmission bands of the narrow band filter and the wide band filter are equal, the value corresponding to the strength of the first electric signal is larger than the value corresponding to the strength of the second electric signal.

Therefore, the difference obtained by subtracting the value corresponding to the strength of the second electric signal from the value corresponding to the strength of the first electric signal, assuming that the transmission bands of the narrow band filter and the wide band filter are equal, respectively. The flame can be detected by determining whether or not is greater than or equal to a predetermined value.

When the flame is detected using only this difference, as described above, depending on how the predetermined value is set, detection becomes impossible or erroneous detection occurs.

On the other hand, considering the ratio of the values corresponding to the intensity of the electric signal, when the intensity of the spectrum of the light passing through the filter is a continuous spectrum, it passes through two filters, a wide band filter and a narrow band filter. Since the energy of light is substantially proportional to the transmission bandwidth, it corresponds to the ratio of the value corresponding to the intensity of the second electric signal to the value corresponding to the intensity of the first electric signal, or the intensity of the second electric signal. The ratio of the value corresponding to the intensity of the first electrical signal to the value is equal to the ratio of the transmission bandwidth.

On the other hand, when only the light of the flame is present, the amount of energy transmitted through the wide band filter and the amount of energy transmitted through the narrow band filter are substantially the same as described above. The ratio between the value corresponding to the strength of the electric signal of 1 and the value corresponding to the strength of the second electric signal is approximately 1. Therefore, the ratio of the value corresponding to the strength of the first electric signal and the value corresponding to the strength of the second electric signal is within a predetermined range, for example, a value between 1 and the ratio of the transmission bandwidth. The flame can be detected by determining whether or not it has become.

Even when this ratio is used, if the value corresponding to the denominator when calculating the ratio becomes extremely small, the detection accuracy deteriorates, and in some cases calculation becomes difficult and erroneous detection occurs.

In the present invention, if it is determined whether both the difference condition and the ratio condition are satisfied, it is possible to accurately determine whether or not the flame is generated without causing the erroneous detection as described above. Can be determined.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention in which a flame is detected by utilizing infrared rays having a wavelength of 4.4 μm emitted from the flame will be described below.

As shown in FIG. 1, in the first embodiment,
A case 10 having an open upper end is provided. A filter holder 12 having a pair of element storage grooves 12A and 12B is housed in the bottom of the case 10. Light-receiving elements 14A and 14B are fixed to the bottoms of the element storage grooves 12A and 12B of the filter holder 12 by sticking or the like.

The element holding groove 1 is provided on the filter holder 12.
Narrow band filter 16A that transmits only the light in the band of the line spectrum of carbon dioxide resonance radiation emitted by the flame so as to close 2A and 12B, a wide band that includes the band of the line spectrum and that transmits light in a band wider than the band. Filter 16B
And are fixed by sticking or the like. .

On the opening side of the case 10, a first light-shielding filter 20 for shielding light in the infrared region and a second light-shielding side of the first light-shielding filter for shielding stray light are arranged. The light-shielding filter 18 and the light-shielding filter 18 are arranged at a predetermined distance and are fixed and arranged in order by sticking or the like.

The narrow band filter 16A and the wide band filter 16B can be constructed by using thin plates of silicon or germanium which are easy to process. When the narrow band filter 16A and the wide band filter 16B are configured by using a thin plate of silicon or germanium, a light transmission band is formed in a region with a wavelength of 8 μm or more, and stray light may enter through this light transmission band. , Second shading filter 1
It is preferable that a thin sapphire plate 8 is used to block light in the wavelength region of 8 μm or more.

The first light blocking filter 20 for blocking the light in the infrared region can be formed by using a thin plate of silicon or germanium, or can be formed by further coating a thin plate of silicon or germanium with an antireflection film. . The first light blocking filter 20 preferably blocks light with a wavelength of 2 μm or less.

As described above, the filters 16A and 16
B is made of a thin plate of silicon or germanium, the first light-shielding filter 20 is made of a thin plate of silicon or germanium, and the second light-shielding filter 18 is made of a thin plate of sapphire. ,lightweight,
And an inexpensive flame detector can be constructed.

The light receiving elements 14A and 14B are the flame determining device 2
2, the flame determination device 22 is connected to an alarm circuit 24 that issues an alarm when a flame is determined.

As shown in FIG. 2, the flame determination device 22 includes amplifiers 22A and 22B for amplifying electric signals output from the light receiving elements 14A and 14B, and amplifiers 22A and 22A, respectively.
It is configured by a determination circuit 22C configured by a microcomputer that determines whether or not there is a flame by calculation based on the electric signal amplified by 22B.

FIG. 3A shows the characteristics of the wide band filter 16B, and FIG. 3B shows other characteristics of the wide band filter 16B.
An example of the characteristics of the narrow band filter 16A is shown in (c). In the figure, the horizontal axis represents wavelength, the vertical axis represents transmittance, and
Indicates a transmittance of 0% and 1.0 indicates a transmittance of 100%. W2 is the transmission bandwidth of the wide band filter 16B.
Indicates the transmission bandwidth of the narrow band filter 16A. A is
The position of the line spectrum of the resonance emission of carbon dioxide is shown, and the band center of the wide band filter 16B and the band center of the narrow band filter 16A are made not to coincide with each other. As described above, by making the band centers not coincide with each other, manufacturing becomes easier as compared with the case where the band centers coincide with each other. The value of A is, for example, 4.4 μm.

As shown in FIG. 3, the broadband filter 16B includes the band W1 of the line spectrum of the carbon dioxide resonance radiation emitted by the flame centered at 4.4 μm which is the wavelength of the resonance radiation of carbon dioxide, and the band W1. It has a band W2 for transmitting light in a wider band.

The narrow band filter 16A is a filter having a center of 4.4 μm and transmitting only the band W1 of the line spectrum in which the resonance radiation of the flame is present.
It is a filter that transmits light from 3 μm to 4.5 μm.

The band center of the wide band filter 16B is provided at a position separated by a predetermined wavelength from the wavelength of 4.4 μm which is the band center of the narrow band filter 16A. The value of the ratio W2 / W1 (= n) of the transmission band is 1.5 or more and usually 5
The 10th place is chosen. Further, it is preferable to set the predetermined wavelength so as not to deviate from the sensitivity of the light receiving element.

In the above, an example in which the band center of the wide band filter 16B is provided at a position separated by a predetermined wavelength from the band center of the line spectrum has been described, but it may be provided so as to coincide with the band center of the line spectrum.

As the light receiving element, one having a good sensitivity and a short response time in the infrared wavelength range of 3 to 5 μm is preferable. The price is relatively low, and lead selenide, a thermopile formed by thin film technology, and a pyroelectric type light receiving element are suitable as the light receiving element which meets this purpose.

Next, referring to FIG. 5, the flame determination routine by the determination circuit 22C will be described. First, the infrared rays that have passed through the wide band filter 16B and the narrow band filter 16A are converted into electric signals by the light receiving elements 14A and 14B. Then, one of the obtained two electric signals passes through the amplifier 22A and the other one passes through the amplifier 22B and is input to the determination circuit 22C.

The determination circuit 22C takes in the electric signals output from the light receiving elements 14A and 14B in step 100, and converts the intensities of the respective electric signals into digital values.

In practice, the strength of the electric signal fluctuates with time due to the influence of the ambient temperature and the like. In order to reduce this effect as much as possible, a moving average process is performed in step 102, and a moving average value of a section of the electric signal strength shorter than the predetermined section is defined based on the moving average value of the predetermined section of the electric signal strength (standard). The moving average values) V1 and V2 are calculated as values corresponding to the strength of the electric signal.

For example, the intensity of the electric signal is 10 samples /
When converting to a digital value in seconds, when the moving average value of the 8192 sample sections is calculated, the average value for about 14 minutes is sequentially obtained. As a result, the influence of the ambient temperature that changes gently can be reduced by the moving average process of the predetermined section (long section). This moving average value becomes the level when the flame is not detected, that is, the reference level. On the other hand, when a flame is detected, the intensity of the electric signal changes in a few seconds to a few tens of seconds. Therefore, in order to reduce electric noise, one sample or two shorter than the above-mentioned predetermined interval is used.
Calculate a moving average value in a short section of 8 samples. The moving average value of one sample section corresponds to the intensity of the electric signal itself.

Since the standardized moving average values V1 and V2 are based on the moving average value of the long section, they can be obtained by subtracting the moving average value of the long section from the moving average value of the short section.

In the next step 104, the normalized moving average values V1 and V2 are converted into values when the transmission bands of the narrow band filter and the wide band filter are equal,
From the value (converted value) corresponding to the intensity of the first electric signal to the second value
The difference V obtained by subtracting the value (converted) value corresponding to the intensity of the electric signal is calculated.

There is a difference in the normalized moving average value between the case of a continuous spectrum such as artificial light and the case of a flame line spectrum for the following reason.

FIG. 4 shows an example of a typical continuous spectrum having a wavelength of around 4.4 μm. In the figure, 31 is a spectrum of illumination light such as an electric lamp, 32 is a black body radiation spectrum around 400 ° C., and 33 is a black body radiation spectrum at a temperature around 200 ° C. In addition, in the figure, the radiation intensity at 4.4 μm is set to 1 in each spectrum, and the intensities at other wavelengths are expressed as relative intensities.

As shown in the figure, the radiation spectrum of the black body reaches a peak at a wavelength of around 4.4 μm when the temperature is around 400 ° C. Then, the intensity decreases a little around the wavelength of 4.4 μm, and rises to the right (inclination is positive) at a temperature lower than the wavelength of 4.4 μm, 4.4.
At a temperature higher than the wavelength of μm, a continuous spectrum with a downward slope (negative slope) is obtained. In addition, most of the light from the sun, electric lamps, etc. is also a downward-sloping continuous spectrum. In the case of a continuous spectrum, since the change in relative intensity with respect to wavelength, that is, the slope is not large, the intensity of light (radiation) transmitted through the wide band filter 16B and the narrow band filter 16A is approximately proportional to the transmission bandwidth of the filter. Therefore, the normalized moving average value when the transmission bands of the narrow band filter and the wide band filter are equal, for example, the normalized moving average value V1 / W1 and the normalized moving average value V2 / W2 per unit transmission bandwidth. Is almost equal to.

However, when the change in the relative intensity with respect to the wavelength is large, the difference V in the standardized moving average value per unit transmission bandwidth depending on the interval between the band centers of the filters.
Becomes larger and Vo is a predetermined value exceeding 0, V ≧
It is Vo.

Therefore, by setting the value of Vo to the optimum value, it is possible to distinguish whether or not it is a continuous spectrum.

On the other hand, when only the light of the flame is present, the spectrum of the flame is the line spectrum, and therefore the spectrum transmitted through the wide band filter and the narrow band filter is mainly only the line spectrum of 4.4 μm. The amount of energy transmitted through the wide band filter 16B and the amount of energy transmitted through the narrow band filter 16A are substantially the same. Therefore, the normalized moving average value of the energy of the line spectrum transmitted through the wide band filter 16B per unit transmission bandwidth is the normalized moving average value of the energy of the line spectrum transmitted through the narrow band filter 16A per unit transmission bandwidth. It becomes smaller than V1 / W1> V2 /
W2 is established. The difference V between V1 / W1 and V2 / W2 can be increased as the bandwidth of the broadband filter is increased.

From the above, there is a difference in the standardized moving average value between the case of the continuous spectrum and the case of the line spectrum when the transmission bands of the narrow band filter and the wide band filter are the same. Focusing on, it is possible to distinguish between general external light having a continuous spectrum, such as sunlight and artificial light, and flame having a line spectrum.

Whether the line spectrum only exists or both the line spectrum and the continuous spectrum coexist, V ≧ Vo as long as the flame line spectrum exists.

Therefore, in the present embodiment, the standardized moving average V2 obtained by the infrared rays transmitted through the wide band filter is used as the standard, and the standardized moving average value V2 obtained by the transmission band of the narrow band filter is used. And the converted value is (W1 · V2) / W2 = V2 / n, and the difference V is calculated by the following equation.

[0060] V = V1-V2 / n (1) The difference V may be calculated by the following formula.

V = V1 / W1-V2 / W2 (2) V = n · V1-V2 (3) Equation (2) is that the normalized moving average value is transmitted through the unit transmission band. The difference is calculated by converting the value into the value obtained by the equation (3), and the normalized moving average value V1 obtained by the infrared rays transmitted through the narrow band filter is transmitted through the wide band filter by using the transmission band of the wide band filter as a reference. The difference V is obtained by converting to a standardized moving average value obtained in the band.

In the next step 106, the standardized moving average value V obtained by the infrared rays transmitted through the narrow band filter is obtained.
The ratio V2 / V1 of the standardized moving average value V2 obtained by the infrared light transmitted through the broadband filter for 1 is calculated. As described above, the ratio V2 / V1 is approximately 1 when the line spectrum of the carbon dioxide resonance radiation emitted by the flame is incident, and is equal to the ratio n of the transmission bandwidth when the continuous spectrum is incident. Therefore, it is a value within the range represented by the following formula.

1 ≦ V2 / V1 ≦ n (4) In the next step 108, the difference V is a predetermined value Vo that is set in advance (this value varies depending on the formulas used in (1) to (3)). , And the ratio V2 / V1 satisfies the above equation (4). When the determination in step 108 is affirmative, the flame is determined in step 110, and a signal for issuing an alarm is output to the alarm circuit 24.

Instead of the above equation (4), the normalized moving average value V2 obtained by the infrared ray transmitted through the wide band filter represented by the following range is normalized by the infrared ray transmitted by the narrow band filter. Average value V1
A ratio of V1 / V2 may be used.

1 ≧ V1 / V2 ≧ 1 / n (5) In the above description, an example in which a digital circuit configured by a microcomputer is used as the determination circuit has been described, but an analog circuit may be used.

FIG. 6 is a schematic configuration diagram showing a second embodiment of the present invention. In FIG. 6, 81 is a band-pass filter that evenly transmits the entire band, 82 is a filter that blocks only resonance emission of carbon dioxide and has substantially the same band as the filter 81, 83 and 84 are light receiving elements, and 86 is a filter 81. This is a calculation circuit that calculates the difference in the intensities of the spectra transmitted through the filter 82. Filter 81 and filter 82
The difference in the intensities of the spectra transmitted through corresponds to the electric signal output from the light receiving element 14A of the first embodiment.

The light receiving element 83 and the calculation circuit 86 are connected to a determination circuit 87 for performing the same determination as that of the determination circuit 22C of the first embodiment. The determination circuit 87 is connected to an alarm circuit 24 that issues an alarm when a flame is determined. Note that the description of the amplifier is omitted in this embodiment.

FIG. 7 is a diagram showing the transmission bandwidths of the filter 81 and the filter 82. FIGS. 7A and 7B show the filter 8
1 shows the transmission bandwidth, and (c) shows the transmission bandwidth of the filter 82. In the figure, W3 indicates the transmission bandwidth of the filter 81, W4 and W5 indicate the transmission bandwidth of the filter 82, and W6 indicates the transmission stop bandwidth (light-shielding bandwidth) sandwiched between the two transmission bandwidths of the filter 82. ing. The transmission bandwidth of the filter 81 is as shown in FIGS.
Any of these may be used. Each bandwidth has a relation of W3 = W4 + W5 + W6.

A represents the position of the line spectrum of the resonance radiation of carbon dioxide, and the band center of the filter 81 and the band center of the filter 82 are separated by a predetermined wavelength. In this way, by separating the band centers by a predetermined wavelength, manufacturing becomes easier than when the band centers coincide.

Also in this embodiment, the flame can be detected as in the first embodiment.

[0071]

As described above, according to the present invention, it is possible to accurately detect a flame even when light or stray light having strong energy in the infrared region such as sunlight or a halogen lamp is incident. You can get the effect.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram of a flame determination device according to the first embodiment.

FIG. 3 is a characteristic diagram of a narrow band filter and a wide band filter used in the first embodiment.

FIG. 4 is a diagram showing a representative example of spectra of various radiators that emit a continuous spectrum.

FIG. 5 is a flowchart showing a flame determination routine.

FIG. 6 is a schematic configuration diagram showing a second embodiment of the present invention.

FIG. 7 is a characteristic diagram of a filter used in the second embodiment.

[Explanation of symbols]

14A, 14B Light receiving element 16A narrow band filter 16B wide band filter 18 Second shading filter 20 First shading filter

Claims (4)

[Claims] 1. A first light blocking filter for blocking light in the infrared region, a second light blocking filter arranged on the light transmitting side of the first light blocking filter so as to block stray light, and the second light blocking filter. A narrow band filter which is arranged on the light transmission side of the filter and which transmits only light in the band of the line spectrum of carbon dioxide resonance radiation emitted by the flame, and a light transmission side of the second light shielding filter, A wideband filter including the entire band of the line spectrum and transmitting light in a band wider than the band; a first light receiving element that converts light transmitted through the narrowband filter into a first electric signal; and the wideband filter And a second light receiving element for converting light transmitted through the second electric signal into a second electric signal, and a flame detector including the second light receiving element. 2. The flame sensor according to claim 1, wherein the narrow band filter, the wide band filter, and the first light-shielding filter are made of a silicon thin plate or a germanium thin plate, and the second light-shielding filter is made of a sapphire thin plate. . 3. A first light blocking filter for blocking light in the infrared region, a second light blocking filter arranged on the light transmitting side of the first light blocking filter so as to block stray light, and for transmitting light A first filter having a predetermined band, wherein a band that does not transmit only light in a band of a carbon dioxide resonance radiation line spectrum emitted by a flame is formed in the predetermined band, and the band is substantially the same as the predetermined band and A second filter that transmits light in a band including the entire band of the line spectrum; a first light receiving element that converts the light that has passed through the first filter into a first electric signal; and the second filter A flame detector comprising: a second light receiving element for converting the transmitted light into a second electric signal. 4. The first filter, the second filter, and the first light-shielding filter are composed of a silicon thin plate or a germanium thin plate, and the second light-shielding filter is composed of a sapphire thin plate. Flame detector.