JPH10326391A - Flame sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flame sensor at a low cost and with high certainty by preparing two filters which transmit a wide band of line spectra of carbon dioxide resonance radiation and transmit only the line spectra respectively and a photodetector which transducers the transmitted light into the electric signals. SOLUTION: A filter 1 transmits the spectra of 3.4 to 5.4 μ, for example, around 4.4 μ of the wavelength of carbon dioxide resonance radiation in a wider range than a line spectrum. The transmission band width of the filter 1 is set at w1. A filter 2 transmits only a band of flame resonance radiation of 4.4 μ, e.g. the spectra of 4.3 to 4.5 μ. The transmission band width of the filter 2 is set at w2. Then, the value of w1/w2 is selected at 1.5 or more (about 5 to 10). The infrared rays that passed through both filters 1 and 2 are converted into the electric signals by a photodetector 3. These two electric signals are sent to a calculation circuit 6 through the amplifier circuits 4 and 5 respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flame detector that senses the light of a flame in a place where sunlight or artificial light exists, without being affected by the light.

[0002]

2. Description of the Related Art It has long been known that a good method for sensing a flame is to detect resonance radiation emitted by high-temperature carbon dioxide contained in the flame. There are many wavelengths in the line spectrum of carbon dioxide resonance radiation,
In order to distinguish it from general artificial lighting or sunlight, it is preferable to use those in the infrared region or the ultraviolet region for detecting a flame. This is because artificial light such as illumination has few light components belonging to both bands, and there is little disturbance of external light at the time of flame detection.

Conventionally, in order to detect a flame under sunlight, the generation of a flame is detected by detecting a line spectrum of the carbon dioxide gas generated by the flame by resonance radiation. As a method, a continuous spectrum like sunlight or artificial light,
In order to distinguish 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 transmit light of one or more wavelengths in the vicinity of the band. Were compared to calculate the output to determine whether the light was a line spectrum of fire or a continuous spectrum of sunlight.

As another method, the occurrence of a flame is detected by utilizing the flicker of light generated by the flame.

[0005]

In the conventional method using the resonance radiation of carbon dioxide gas, a method using a filter is as follows.
To obtain a flame detector that reliably detects a flame with few false alarms, at least three monochromatic filters are required, and the calculation circuit for the detection is complicated, so that it has the disadvantage of being expensive.

[0006] What is composed of two or less filters is
It had drawbacks with many misinformation. The method using the flicker of flame also had a disadvantage that it was inexpensive but had many false reports.
The present invention provides two filters that can detect a flame with the same certainty as the conventional one using three filters, or that provide a simple calculation circuit using three filters. It is intended to make it possible to obtain an inexpensive and highly reliable sensor.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a technique for detecting a flame by detecting a line spectrum of a carbon dioxide gas emitted from a flame by resonance radiation. The idea of the invention can be applied in all wavelength ranges from ultraviolet to infrared, but the basic concept is the same in any wavelength range. A case where a line spectrum of the resonance radiation of the above is used will be described as an embodiment.

Light such as sunlight, general artificial light or a stove emits not only visible light, but also in the infrared region. However, these emissions are continuous spectra. On the other hand, the spectrum of the resonance emission of the carbon dioxide gas generated by the flame is a line spectrum in which energy is concentrated in a very narrow region. The difference between such a continuous spectrum and a line spectrum is used for flame detection. In the present invention, the following means are used to detect these line spectra.

The first means includes a first filter having a wide transmission band including a band of a line spectrum of the infrared resonance radiation and transmitting a band at least twice the band, and transmitting only the line spectrum. Two of the narrow passband second filters are used. Then calculate the intensity of light from the flame that has passed through these two filters. The intensity here is the average intensity obtained by dividing the amount of energy transmitted through the filter by the bandwidth of the filter. In that case, if the spectrum of the light passing through the filter is a continuous spectrum,
Since the energy of light transmitted through the two filters is proportional to the transmission bandwidth, the average intensity obtained by dividing this energy by the bandwidth is the same.

However, if the transmitted light is a line spectrum emitted by carbon dioxide gas, the two filters both transmit this line spectrum and have the same amount of transmitted energy, but have a wide band. The energy of light transmitted through the first filter is divided by a wide bandwidth to calculate an average intensity, and the energy transmitted through the first filter having a narrow bandwidth is divided by a narrow bandwidth to calculate an average intensity. There is a difference between the two average intensities. Utilizing this property, the light of the flame is detected.

The second means comprises a first filter which includes a band of the line spectrum of the infrared resonance radiation and transmits a band which is at least 1.5 times as wide as this band. Only the line spectrum of the selected radiation uses a second filter that blocks transmission. Then, the amount of energy transmitted through these two filters is subtracted. Then, the energy amount of the portion where the transmission bandwidth overlaps between the two filters is lost by subtraction, and only the energy of the line spectrum of the infrared resonance radiation is transmitted by the first filter and blocked by the second filter. , As a result of the subtraction. Utilizing this property, the light of the flame is detected.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in accordance with an embodiment using infrared rays having a wavelength of 4.4 microns emitted by a flame.

FIG. 1 is a schematic configuration diagram showing the configuration of an embodiment of the present invention by the first means. In FIG. 1, 1 is a band-pass filter having substantially the same transmission band on both sides of the line spectrum of the resonance radiation of carbon dioxide as a center, 2 is a narrow-band transmission filter transmitting the line spectrum of the resonance radiation of carbon dioxide, 3 is Light receiving elements 4 and 5 are amplifiers; 6 is a circuit for calculating the difference between the intensity of the spectrum transmitted through the filter 1 and passed through the amplifier 4 and the intensity of the spectrum transmitted through the filter 2 and passed through the amplifier 5; 7 is a calculation circuit 6 is a circuit for issuing an alarm when the output exceeds a certain level.

In FIG. 2, (a) shows the characteristics of the filter 1 and (b) shows the characteristics of the filter 2, wherein the horizontal axis represents the wavelength and the vertical axis represents the transmittance. It represents a transmittance of 100%. w1 is the transmission bandwidth of the filter 1 and w2 is the transmission bandwidth of the filter 2. In FIG. 2, A indicates the position of the line spectrum of the resonance emission of carbon dioxide. In the embodiment described below, the value of A is 4.4 microns.

FIG. 3 shows an example of a typical continuous spectrum having a wavelength of around 4.4 microns. In FIG. 3, reference numeral 31 denotes a spectrum of illumination light such as an electric lamp, 32 denotes a radiation spectrum of a black body at about 400 ° C., and 33 denotes a spectrum of black body radiation at a temperature around 200 ° C. In FIG. 3, each spectrum is expressed with the radiation intensity at 4.4 μm as 1, and the intensity at other wavelengths is expressed as relative intensity thereto.

The details of the present invention will be described with reference to the embodiment shown in FIG. As shown in FIG. 2, the filter 1 is a band-pass filter having a transmission band of the same width on both sides around a center of 4.4 μm, which is the wavelength of the resonance radiation of carbon dioxide. This filter transmits a broader band compared to the line spectrum, for example, from 3.4 microns to 5.4 microns, with the same width being 1 micron. This transmission bandwidth is defined as w1.

The filter 2 is a filter which transmits only a certain band of the resonance radiation of the flame at 4.4 μm, for example, a filter which transmits from 4.3 μm to 4.5 μm. Let this transmission bandwidth be w
Let it be 2. The value of w1 / w2 is 1.5 or more and usually 5-1.
Elected in 0th place.

The infrared light transmitted through the two filters 1 and 2 is converted into electricity by the light receiving element 3. One of the two obtained electric outputs passes through the amplifier circuit 4, and the other one passes through the amplifier 5 and is sent to the calculation circuit 6.

The light receiving element 3 preferably has good sensitivity and short response time in the infrared wavelength range of 3 to 5 microns. As a light receiving element which is relatively inexpensive and suitable for this purpose, lead selenide, a thermopile formed by thin film technology, and a pyroelectric light receiving element are suitable.

The calculation circuit 7 performs the following calculation. A1 / w1 = a1 'and b, where a1 is the electric output transmitted through the filter 1 and b1 is the electric output transmitted through the filter 2.
1 / w2 = b1 'is calculated. This division may be performed by adjusting the amplification factor of the amplifier 4 or 5, or may be performed in the calculation circuit 6.

Next, b1'-a1 '= c1 is calculated. There is a difference between the case of a continuous spectrum such as artificial light and the case of a line spectrum of a flame for the following reasons.

As shown in FIG. 3, the emission spectrum of the black body peaks at a wavelength around 4.4 microns at temperatures around 400.degree. Although the intensity slightly decreases before and after this wavelength, it can be regarded as an almost horizontal straight line in a narrow band. At lower temperatures, the spectrum rises to the right, and at higher temperatures, a continuous spectrum descends to the right. In each case, within a narrow bandwidth of about several microns, the spectrum can be regarded as almost a straight line.

Accordingly, if the filter 1 is a filter having a transmission band of the same width on both sides centered at 4.4 microns, the average intensity of any one of the three emission spectra shown in FIG. Corresponds to an intensity at 4.4 microns. Most of the light from the sun or electric lamps as a light source is a continuous spectrum, and the spectrum can be regarded as almost a straight line within a narrow band as shown in FIG. Is approximately proportional to the transmission bandwidth of Therefore, a1 / w1
And b1 / w2 are equal. a1 ′ = b1 ′. That is, c1 = 0.

On the other hand, when only the light of the flame exists, the spectrum of the flame transmitted through the entire band-pass filter is 4.4 because the spectrum of the flame is originally a line spectrum.
Only the micron line spectrum. The amount of energy transmitted through the filter 1 and the amount of energy transmitted through the filter 2 are the same. Accordingly, the intensity obtained by dividing the energy of the line spectrum transmitted through the filter 1 by the total transmission bandwidth w1 is smaller than the energy intensity obtained by dividing the energy of the line spectrum transmitted by the filter 2 by the bandwidth w2 of the line spectrum. b1 '>a1' holds. That is, c1> 0.

In other words, comparing a1 'and b1', there is a difference between the case of a continuous spectrum and the case of a line spectrum. By paying attention to this difference, general external light such as sunlight or artificial light having a continuous spectrum can be distinguished from flame having a linear spectrum.

In the case where only the line spectrum exists, or in the case where the line spectrum and the continuous spectrum coexist, c1> 0 if the flame line spectrum exists. The value of c1 is proportional to the size of the flame. In this way, the flame detector of the present invention can detect the emission of the flame separately from sunlight and other radiation.

FIG. 4 shows an example of a flame detector using an analog calculation circuit. In FIG. 4, 41 is an input adjuster, and 42 is a differential amplifier. Since the actual filters 1 and 2 do not have the ideal characteristics as shown in FIG. 2, an input adjuster 41 is used to adjust the difference between the characteristics.

First, when light having a continuous spectrum, for example, electric light, is simultaneously supplied to the filters 1 and 2, the amplifier 41
, The output having passed through the filter 1, the light receiving element 3, and the input adjuster 4 enters one of the two input terminals of the differential amplifier 42 as an input.

On the other hand, the output passing through the filter 2, passing through the light receiving element 3, and passing through the amplifier 5 enters another input terminal of the differential amplifier 42. In this state, the output of the differential amplifier 42 has a difference between the inputs of both terminals. The input adjuster 41 is adjusted so that this output becomes zero.

As shown in FIG. 3, in a relatively narrow range of wavelengths, the spectral intensity of a continuous spectrum can be regarded as a straight line regardless of the temperature of the radiator. If the output of the differential amplifier 42 is adjusted to be zero by adjusting the amplifier 41, the output of the differential amplifier 42 becomes zero for all other continuous spectra. That is, the spectra 31, 32, 3 in FIG.
The output will be zero for any of the three types of continuous spectra. The input adjuster 41 plays the role of division in the above description.

Thus, the flame detector of the present invention is insensitive to continuous spectrum light. In other words, artificial light or sunlight does not cause false alarms. In the case of flame light, the amplifiers 4 and 5 are used as described with reference to FIG.
, The difference is detected by the operation of the differential amplifier 42, and the presence of a flame is determined.

FIG. 5 shows an embodiment of the present invention using a digital calculation circuit. 5, 51 and 52 are A / D converters,
53 is a CPU. Here, the AD converters 51 and 52 may be provided outside the CPU 53 as shown in FIG.
It may be included inside U53. Flame detection is C
This is performed by software in the PU 53. The general specifications of the software are as follows.

First, light having a continuous spectrum is simultaneously projected on the filters 1 and 2. The output of the AD converter 51 at that time is a, and the output of the AD converter 52 is b. A weight is assigned to either a or b so that the following equation is satisfied. The weighting may be performed by multiplying a by a certain number, or realized by multiplying b by a certain number. Now, assuming that a is weighted, and a constant constant of the weight is k, b−k ×
Choose k such that a = 0.

K is a specific value determined mainly by the characteristics of the filters 1 and 2 and the characteristics of the light receiving element 3 of each sensor. Once determined, the value is peculiar to the sensor and includes the ambient conditions and the like. For some, it is almost the same.

The flame detector is now ready for alert. From the output values a and b of the AD converters 51 and 52 when the flame detector enters the alert state, b−k × a = c
Is calculated.

When c = 0, the light input to the flame detector is of a continuous spectrum. If there is a line spectrum emitted by a flame, c> 0 regardless of whether light having a continuous spectrum such as sunlight coexists.

Therefore, in the case of the flame detector using the CPU 53, the value of c is always calculated, and when this value exceeds a predetermined value, the CPU 5 issues an alarm of flame generation.
You just need to make the software of No.3. In this way, it is possible to obtain a flame detector with almost no false alarms by a digital circuit.

Although the above-mentioned flame detector does not utilize the relatively low-frequency flicker emitted by the flame, the flicker is detected in the form of the flicker of the line spectrum emitted by the carbon dioxide gas so that the presence of the flame can be known. Then, a better flame detector can be obtained. FIG. 6 is an embodiment of an analog type flame sensor using flicker based on the flame sensor of FIG.

In FIG. 6, reference numeral 61 denotes an electric filter;
Is a circuit for issuing an alarm. The filter 61 is an analog low-pass filter that passes mainly signals of a frequency of 20 Hz or less contained in the flame. Differential amplifier 4
The output from 2 includes both DC and AC components, which are the components of the flickering flame light. The DC component is determined by the average size of the flame, and the AC component is generated by the flicker of the flame.

The output of the filter 61 extracts only the AC component based on the flicker and sends it to the alarm circuit 62. On the other hand, the output including both the AC component and the DC component from the differential amplifier 42 is also sent directly to the alarm circuit 62.

The alarm circuit 62 outputs a flicker component signal sent from the filter 61, a value of an AC component due to flicker of the flame directly sent from the differential amplifier 42 without passing through the filter 61, A circuit that measures the signal levels of both the DC component indicating the magnitude of the signal and the AC component due to flicker, and issues an alarm when one of them exceeds a certain level (hereinafter referred to as an OR circuit). ), Or a circuit (hereinafter referred to as an AND circuit) that issues an alarm when both exceed a certain level at the same time, so that they can be properly used.

A highly sensitive OR circuit is used in a place with little external light, such as when used for flame detection in a warehouse, and a place with a lot of external light, such as an office or a place where sunlight is present outdoors. It is recommended to use an AND circuit with less false alarm for flame detection in the above.

FIG. 7 shows another embodiment of the flame detector of the present invention utilizing flicker. In FIG. 7, reference numeral 71 denotes a digital filter. The digital filter 71 has the same function as the filter 61 in FIG. The filter 71 may be provided outside the CPU 53 as shown in FIG. 7, or may be built in the CPU 53 as software, and a component specific to the flickering of the flame light is included in the CPU 53 in the description of FIG. It is to detect whether or not it is included in the numerical value c calculated in the above.

Then, both the OR circuit and the AND circuit of the value of the AC component due to the flicker of the flame and the value including both the DC component indicating the size of the flame and the AC component due to the flicker, which are obtained by digital calculation, are connected to the CPU 53. And both of these circuits can be properly used. The proper use of these two circuits is the same as in the embodiment of FIG.

FIG. 8 is a schematic configuration diagram showing the configuration of the present invention by the second means. In FIG. 8, reference numeral 81 denotes a band-pass filter that transmits the entire band evenly; 82, a filter having substantially the same transmission band as the band-pass filter 81; and a filter that blocks only resonance emission of carbon dioxide gas; 83 and 84, light-receiving elements; 85 is a circuit for calculating the average intensity of the spectrum transmitted through the filter 81, 86 is a calculation circuit for calculating the difference between the spectra transmitted through the filter 81 and the filter 82, and 87 is the difference between the outputs of the calculation circuits 85 and 86. The circuit 88 is an alarm circuit for issuing an alarm when the output of the calculation circuit 87 exceeds a certain level.

FIG. 9 is a diagram showing the transmission bandwidths of the filters 81 and 82. FIG.
(B) shows the transmission bandwidth of the filter 82. In FIG. 9, w3 is the transmission bandwidth of the filter 81, w4 and w5.
Is the transmission bandwidth of the filter 82, w6 is the filter 8
2 shows a transmission rejection bandwidth sandwiched between two transmission bandwidths. Each bandwidth is w3 = w4 + w5 + w
It has a relationship of 6.

A indicates the position of the line spectrum of the resonance radiation of carbon dioxide. Light transmitted through the filters 81 and 82 enters the light receiving elements 83 and 84, respectively.
The output from the light receiving element 83 is processed in the calculation circuit 85 using the transmission bandwidth w3 of the filter 81, and is output from the calculation circuit 85 as the average intensity.

On the other hand, the outputs of the two light receiving elements 83 and 84 enter a circuit for calculating the difference between the two outputs, for example, a calculation circuit 86 composed of a differential amplifier or the like, and the difference is calculated. In the calculation, the output is canceled out at w4 and w5 in FIG. 9 which is a band common to the two filters 81 and 82, and a non-common band, that is, at w6 in FIG. 9 which is a band of resonance emission of carbon dioxide gas. , Only output. The average intensity obtained by processing the output with w6 is such that the radiation in the transmission band w3 of the filter 81 is a continuous spectrum and the intensity of the radiation changes linearly as in the case of an incandescent lamp. If it is, it matches the average intensity calculated by the calculation circuit 85.

Therefore, the output of the circuit 87 for calculating the difference between the outputs of the calculation circuits 85 and 86 becomes zero when the input is a continuous spectrum. However, when the spectrum in the infrared region is mostly occupied by the resonance radiation of carbon dioxide gas, such as light from a flame, the output of the calculation circuit 87 does not become zero.

The output from the filter 81 is only the line spectrum of the resonance radiation, and the calculation circuit 85 outputs the intensity of the line spectrum as the average intensity divided by the bandwidth w3 of the filter 81.
Is wider than the bandwidth w6 of the resonance radiation of the carbon dioxide gas, the intensity of the resonance radiation of the carbon dioxide gas output from the calculation circuit 85 is output as a value reduced by the wider bandwidth.

On the other hand, the output of the calculation circuit 86 is
Only the difference between 1 and the output of the filter 82, that is, the resonance radiation of carbon dioxide, is output without being reduced.
Therefore, a difference occurs between the outputs of the calculation circuits 85 and 86, and the difference is calculated by the calculation circuit 87 and output. The value of this output increases as the flame increases and as w3 / w6 increases.

In this way, external light having a continuous spectrum is distinguished from flame light having a line spectrum. For the same reason, when both the continuous spectrum and the line spectrum are mixed, only the value of the line spectrum is output from the calculation circuit 87. When the output of the calculation circuit 87 exceeds a predetermined value, the alarm circuit 88 operates.

If it is difficult to realize the characteristics of the filter 82 with one filter, the transmission band w shown in FIG.
A filter having the characteristics of the filter 82 can be realized by using two filters, a band-pass filter having a band of 4 and a band-pass filter having a band of w5, and superimposing the outputs with an adder circuit.

FIG. 10 shows a dome-shaped window provided on the light receiving surface of the flame detector. In FIG. 10, 101 is a sensor main body, 1 and 2 are filters, and 102 is a transparent dome having a rough surface.

Since the filter 1 or the filter 2 is generally flat, its sensitivity has a directional characteristic close to a sphere. Therefore, the sensitivity of the flame detector changes depending on the position where the flame is generated. Or a difference in sensitivity due to a difference in the relative position from the position where the image occurs. In order to eliminate the disadvantage, a dome-shaped window having diffuse reflection is provided.

This window is made of plastic which transmits the mid-infrared rays well. Ordinary glass is not recommended due to poor mid-infrared transmittance. A large number of irregularities are provided on the front surface or the back surface to provide irregular reflection. Due to the irregular reflection of the dome-shaped window, the difference in performance due to the difference in the direction of light arriving at the sensor main body 101 is reduced.

[0057]

According to the present invention, which takes advantage of the fact that general external light has a continuous spectrum and that flame light has a characteristic line spectrum of resonant emission of carbon dioxide gas, the present invention makes use of the present invention. Differentiating from various lights, it is possible to reliably detect only the light emitted by the flame, and obtain a flame detector with less false alarm, which is of great benefit in industrial or disaster prevention.

[Brief description of the drawings]

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

FIG. 2 is a characteristic diagram of a filter used in an embodiment of the present invention.

FIG. 3 is a diagram showing typical examples of spectra of various radiators emitting a continuous spectrum.

FIG. 4 is a diagram showing an embodiment using an analog circuit.

FIG. 5 is a diagram showing an embodiment using a digital circuit.

FIG. 6 is a diagram showing another embodiment using an analog circuit.

FIG. 7 is a diagram showing another embodiment using a digital circuit.

FIG. 8 is a diagram showing an embodiment using flicker.

FIG. 9 is a characteristic diagram of another filter used in the present invention.

FIG. 10 shows a dome-shaped window.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 filter 2 filter 3 light receiving element 4 differential amplifier 5 amplifier 6 differential amplifier 7 alarm circuit 41 input adjuster 42 differential amplifier 43 amplifier 51 A / D converter 52 A / D converter 53 CPU 61 low-pass filter 71 digital filter 81 filter 82 filter 85 calculation circuit 86 calculation circuit 87 calculation circuit 102 dome-shaped window

Claims (9)

[Claims] 1. A band-pass optical filter that includes a line spectrum of carbon dioxide resonance radiation emitted by a flame and transmits a band at least 1.5 times the band of the line spectrum, and a line spectrum of resonance radiation of the carbon dioxide gas. A flame detector comprising: a filter that transmits only light; and a light-receiving element that converts light transmitted through each of the filters into an electric signal. 2. A band-pass filter that includes a line spectrum of carbon dioxide resonance radiation emitted by a flame and transmits a band at least 1.5 times the band of the line spectrum, and has a transmission band substantially the same as the filter. A flame sensor comprising: a filter that blocks only a line spectrum of a resonance radiation of carbon dioxide gas and does not transmit the light; and a light receiving element that converts light transmitted through each of the filters into an electric signal. 3. A circuit for calculating an average intensity over the entire transmission band for each of the two signals transmitted through the filter and converted into an electric signal, and a circuit for calculating the average intensity value of the two signals. 3. The flame sensor according to claim 1, further comprising a circuit for calculating a difference. 4. The flame according to claim 3, wherein the circuit for calculating the difference between the two signals transmitted through the filter and converted into an electric signal is constituted by an analog computer including a differential amplifier. sensor. 5. The circuit according to claim 1, wherein the circuit for calculating the difference between the two signals transmitted through the filter and converted into an electric signal is a digital circuit centered on a CPU. The flame detector according to claim 1. 6. The flame detector according to claim 1, wherein a lead selenide, a thermopile, or a pyroelectric light receiving element is used as the light receiving element. 7. The presence or absence of a flame is determined by the intensity of the line spectrum of the resonance emission of the carbon dioxide obtained as a result of calculating two electric signals obtained from the two filters. The flame detector according to claim 1. 8. The flicker of flame light included in the signal of the line spectrum of the resonance radiation of carbon dioxide gas, which is obtained as a result of calculating two electric signals obtained from the two filters to determine the presence or absence of the flame. The flame detector according to any one of claims 1 to 6, wherein the determination is made based on an AC component of the flame detector. 9. The dome-shaped diffusion transparent plate is used for a light receiving window of the flame detector.
The flame detector according to any one of the above.