JPH09325068A - Flame sensor and flame detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a specific ultraviolet ray emitted from a flame with a temperature compensation included, by forming a photodetecting part of a photoconductive material selected from MgS, CaS, SrS. SOLUTION: A flame sensor 50 has a photodetecting part 8 formed of a photoconductive material selected from MgS, CaS, SrS. When the photodetecting part 8 detects a detection light, electrodes 3, 4 provided can take out a current generated at the photodetecting part 8 because of a photoconductive effect. Specifically, a thin film layer 1 of the photoconductive material having a photoconductive characteristic to ultraviolet rays is formed on a sensor substrate 2, and electrodes 3, 4 of three systems are arranged at the side of an upper part of the thin film layer 1. The electrodes 3, 4 are paired. One pair of the electrodes and the thin film layer 1 constitute a detection photoconductive element, and the other pair of electrodes, the thin film layer 1 and a metallic light-shielding film 9 covering a photodetecting part 8a constitute a temperature compensation photoconductive element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flame sensor for recognizing a specific wavelength component of radiation emitted from a flame to detect the presence or absence of a flame, and a flame detector equipped with such a sensor. More specifically, approximately 200 nm to 280 nm excluding the wavelength range of light that is a noise source such as sunlight or room light from the emission wavelength range of flames.
The present invention relates to a flame detection technology for detecting ultraviolet rays having a wavelength component of.

[0002]

2. Description of the Related Art Conventionally, as a flame sensor, a thermocouple type in which heat generated by a flame is converted into electric energy by using a thermocouple to detect the flame, and a hydrogen ion in the flame is detected by using a hydrogen flame ionization detector. There are known a hydrogen flame ionization detector type that converts electric energy into electric energy to detect a flame, and a photoelectric tube type that uses a photoelectric tube to convert light energy emitted by a flame into electric energy to detect a flame.

[0003]

Each of the above flame sensors has the following drawbacks. 1 Thermocouple type flame sensor generates a flame that is a heat source,
Since the temperature around the sensor does not rise or drop rapidly even after it disappears, it has poor transient response to changes in the flame state during ignition, extinguishing, etc., and is especially suitable for use in sealed enclosures with poor temperature changes. The usage range is limited due to problems. 2 The flame sensor of hydrogen flame ionization detector requires that the electrode part be provided inside the flame, and in order to be applicable to a wide range of flames from small flames to large flames, not only the electrode part but also the support part etc. have high heat resistance. And reliability are required. Therefore,
It is difficult to apply it to a flame whose shape or size changes greatly, and its use range is limited to use in a water heater, a small boiler, or the like. 3 The photoelectric tube type flame sensor is superior to the thermocouple type or hydrogen flame ionization detector type flame sensor in the accuracy of determining whether the flame is on or off, and can be installed at a distance from the flame. However, since the conversion efficiency of converting light energy into electric energy is low due to the structural limitation of the phototube, it should be detected as a flame sensor.
In the wavelength range of nm to 280 nm, the light receiving sensitivity is low, and it cannot be said to be sufficient to detect the weak light in the wavelength range emitted from the flame. In FIG. 5, the horizontal axis shows the wavelength, and the vertical axis shows the relative intensities of flame light, sunlight, and room light (fluorescence generated from the fluorescent tube) and the detection sensitivity of the photoelectric tube. Here, the gas light that is flame is shown by a solid line, the room light as interfering light is shown by a broken line, and the sunlight is shown by a one-dot chain line.
Further, regarding the detection sensitivity of the photoelectric tube, this is indicated by a chain double-dashed line. Therefore, to detect only the flame,
It can be seen that it is preferable to detect the wavelength range from 200 nm to 280 nm. Further, the photoelectric tube type has a problem that the structure is complicated, the life is relatively short, and the usable temperature range is limited to about 100 ° C. The present invention is to solve the above problems.

[0004]

[Means for Solving the Problems]

[Structure] A first characteristic structure of the flame sensor according to claim 1 according to the present invention for achieving the above object is MgS,
It is provided with a light receiving portion made of a photoconductive material selected from CaS and SrS, and an electrode capable of taking out a current generated in the light receiving portion by a photoconductive effect when the light receiving portion receives light.

[Operation / Effect] MgS, CaS, SrS,
The respective band gaps Eg are 4.4 eV and 4.41 e.
V, and 4.3 eV, and the long wavelength limits of these absorption spectra are 281.8 nm, 281.1 nm, 288.
It is 3 nm. These photoconductor materials absorb radiation below these wavelengths and generate an electrical current. Therefore, by providing such a material in the light receiving section and detecting the current generated by the photoconductive effect, it is possible to effectively separate the light that is a noise source that normally exists, such as sunlight and room light, and the emitted light from the flame. Separately, the emitted light from the flame can be detected to function as a flame sensor. Here, the rise of sensitivity at the long-wavelength end of the absorption spectrum of these materials becomes steep due to the photoconductive characteristics, so that there is a problem that the photoelectric tube in the prior art has (the low sensitivity part is Can be eliminated). That is,
As described above, when it is attempted to detect flames with less influence of interfering light, 200 nm to 2 nm indicated by SB in FIG.
It is preferable to selectively detect ultraviolet rays having a wavelength of about 80 nm. However, the emission spectrum of the flame in this band becomes weaker as the wavelength becomes shorter. On the other hand, the photosensitivity of the phototube has a maximum sensitivity range of 200 nm to 220 nm and a quantum efficiency (photoelectric conversion efficiency) of 20% to 3%.
0%, and 5 in the wavelength range of 240 nm to 280 nm.
% To 10%. Therefore, in particular, when the flame is small or when the distance from the flame is large, means for improving the detection sensitivity such as enlarging the light receiving area of the photoelectric tube is required, which causes a problem that the device becomes large. In such a situation, in order to satisfactorily detect ultraviolet rays in a specific band, as shown by a hatched area in FIG. 5, for example, at a long wavelength end of about 280 nm or less,
A sensor that has a sharp rise in detection sensitivity and maintains a relatively high sensitivity in a short wavelength region below this is preferable. The flame sensor having this configuration can provide such a sensor. Here, the long wavelength end of SrS is theoretically 288
Although it is nm, this can be regarded as an error range. further,
With this configuration, a relatively high sensitivity (quantum efficiency) can be obtained, and the device configuration is simple as described later. In addition, due to the characteristics of the material, relatively high temperature (500 ℃
Before and after) can also be used. Furthermore, it has a longer life than before.

[Structure] When a flame detector including the flame sensor having the above-described structure is formed, the following structure is preferable. That is, the flame detector of the present invention according to claim 2 is characterized in that it comprises a detector body having a hollow closed structure whose inside is filled with a vacuum or an inert gas.
A flame sensor having a light receiving portion made of a photoconductive material selected from S, CaS, and SrS, and an electrode capable of taking out a current generated in the light receiving portion by a photoconductive effect when the light receiving portion receives light. The detection light irradiating section in the main body of the detector to which the detection light is introduced and radiated, and the ultraviolet transmission filter in the detection light introducing section into the main body of the detector are provided.

[Operation / Effect] In this flame detector, the flame sensor provided with the photoconductor material unique to the present invention described above is disposed in the detection light irradiation section of the detector body. Radiation light from the flame is introduced and irradiated to the detection light irradiation unit from the detection light introduction unit. In this case, by providing the detection light introducing section with an ultraviolet ray transmitting filter, the arrival of light other than ultraviolet rays to the flame sensor is suppressed. Therefore, it is possible to suppress the arrival of visible light, infrared rays, etc., which cause the temperature of the flame sensor to rise, and improve the detection accuracy of the sensor. Further, in the flame detector adopting this configuration, in the long wavelength side (for example, in the wavelength range of 280 nm or more) due to the noise removal by the ultraviolet filter and the characteristics of the photoconductor material itself constituting the flame sensor. Since it has a double noise removal structure for removing the noise of the sword, the flame can be detected with high accuracy. By the way, the inside of the detector main body is maintained in vacuum or is filled with an inert gas. The above photoconductor material is generally affected by moisture and its characteristics are likely to change. Therefore, the performance can be appropriately maintained by housing the flame sensor of this configuration in the detector main body and making the surrounding atmosphere moisture-tight.

[Structure] A second characteristic structure of the flame sensor according to claim 3 for achieving the above object is that the long wavelength end is 28
It is provided with a light receiving part made of a fluorescent material having a photoconductive property, which is at 0 nm and generates a current by absorbing ultraviolet light having a wavelength shorter than this long wavelength end, and an electrode capable of taking out a current generated in the light receiving part by absorbing ultraviolet light. And to configure a flame sensor. [Operation / Effect] A fluorescent material absorbs ultraviolet rays, and when the electrons it possesses are excited to an intermediate level between the valence band and the conduction band and then transition to the valence band, fluorescence is emitted. Emit. However, the electrons in the excited state are further excited to the conduction band due to factors such as the material temperature, and the electrons can be detected as a current. Therefore, such a material is
It can be considered as having certain photoconductive properties. Now, as I have explained,
In order to surely remove the influence of noise, it is necessary that the long wavelength end be approximately 280 nm. Therefore, in the flame sensor of the present application, the fluorescent material having such characteristics is used for the light receiving portion, and the current obtained by the photoconductive characteristics is detected. As a result, it is possible to detect a specific spectral region of radiated light emitted from a flame having a long-wavelength end of 280 nm or less as electrical information via the electrodes. In such a flame sensor, a large-area light receiving element can be constructed using a relatively inexpensive material. Furthermore, a high-voltage power supply and the like are unnecessary, and the device configuration can be simplified. Furthermore, as in the case of the photoelectric tube type, 1
It can be used only at about 00 ℃,
Since it can be used at 0-300 ℃, a small cooling device is required. Furthermore, the life can be extended.

[Structure] According to claim 4, which achieves the above object.
The third characteristic configuration of the flame sensor concerned is the base material composition; activation.
When expressed in the form of agent, (Sr, Ba, Mg)_ThreeSi_Two
O₇; Pb²⁺, (Ba, Zn, Mg)_ThreeSi_TwoO₇; P
b²⁺, BaSi_TwoO_Three; Pb²⁺, Y_TwoO_ThreeEu, CsI;
Na⁺, (Ca, Zn)_Three(PO_Four)_Two; Tl⁺, CaSi
O_Three; Pb ²⁺, CaSiO_Three; Mn²⁺Fluorescence represented as
Equipped with a light receiving part made of a material selected from the materials, UV
It is possible to take out the current generated in the light receiving part by absorption
The purpose is to configure a flame sensor with electrodes. [Action and effect] Excitation spectrum of such a fluorescent material
The long wavelength end of (substantially absorption spectrum) is a problem for the present application.
It is in the vicinity of 280 nm to 290 nm. Each fluorescent material
Table 1 below shows the specific long wavelength end
You.

[0010]

[Table 1] Base material composition Activator Long wavelength edge (nm) (Sr, Ba, Mg) ₃ Si ₂ O ₇ Pb ²⁺ 270 (Ba, Zn, Mg) ₃ Si ₂ O ₇ Pb ²⁺ 280 BaSi ₂ O ₃ Pb ²⁺ 270 Y ₂ O ₃ Eu 280 CsI Na ⁺ 260 (Ca, Zn) ₃ (PO ₄ ) ₂ Tl ⁺ 280 CaSiO ₃ Pb ²⁺ 270 CaSiO ₃ Mn ²⁺ 280

Therefore, by using such a material for the light receiving portion, it is possible to detect the radiated light generated from the flame according to the same principle as described above. In such a flame sensor, as described above, it is possible to construct a large-area light receiving element by using a relatively inexpensive material. Furthermore, a high-voltage power supply and the like are unnecessary, and the device configuration can be simplified. Further, unlike the case of the photoelectric tube type, it cannot be used only at about 100 ° C., and can be used at about 200 to 300 ° C., so that the cooling device can be small. Furthermore, the life can be extended.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. The flame detector 100 of the present application is shown in FIG.
As shown in FIG. 2, a flame sensor 50 having a unique structure of the present application is used in a detector main body 51 of a hollow closed structure having a vacuum inside, and a detector main body into which the detection light introduced into the detector main body 51 is introduced and irradiated. It is configured to be provided in the detection light irradiation unit 52 inside.
Furthermore, in the detection light introducing section 56 of the detector main body 51,
An ultraviolet transmission filter 53 is provided. And
The output end of the flame sensor 50 is connected to a determination device 54 for determining the on / off state of the flame based on the output of the flame sensor 50, and a display device 55 for displaying the result of the determination device 54. . Therefore, as shown in FIG. 1, when the flame F is in front of the flame detector 100, the light emitted from the flame is detected by the detection light introducing portion 56 of the flame detector 100.
Is introduced into the main body 51 of the detector and is received by the light receiving section 8 of the flame sensor 50 provided in the detection light irradiation section 52, and a detection output can be obtained.

As shown in FIG. 2, the flame sensor 50 includes a light receiving portion 8 made of a photoconductive material selected from MgS, CaS, and SrS, and a photoconductive material when detection light is received by the light receiving portion 8. Electrodes 3 and 4 capable of taking out the current generated in the light receiving portion 8 due to the effect are configured.
Each electrode is formed in a comb shape as shown in FIG.
First of all, the schematic structure of the flame sensor 50 will be briefly described. As shown in FIG. 2, a thin film layer of a photoconductor material exhibiting photoconductive properties with respect to ultraviolet rays is formed on a sensor substrate (specifically, a sapphire substrate 2). The electrodes 3 and 4 of the three systems are provided on the upper side of this thin film layer. Further, these electrodes 3 and 4 are paired with each other as will be described later,
One pair and the thin film layer constitute a photoconductor element for detection, and the other pair and the thin film layer and the metal light-shielding film 9 covering the light receiving portion constitute a photoconductor element for temperature compensation. Therefore, in the flame sensor 50, it is possible to detect a specific ultraviolet ray emitted from the flame with temperature compensation.

Based on FIG. 2, Mg as the photoconductor material
The case where S is used will be described in more detail. In the flame sensor 50, a thin film layer of the MgS photoconductor 1 (a part of which constitutes the light receiving portion 8) is formed on the sapphire substrate 2 by a physical vapor deposition method such as laser heating. A buffer layer is provided between the metal electrode 4 and the MgS photoconductor 1 to form an ohmic contact structure. That is, the buffer lower electrode 3 is patterned under the metal electrode 4. Further, in the flame sensor 50, SiN, SiO ₂ , is provided on the MgS photoconductor 1 which is not covered with the metal electrode 4 and the metal electrode 4 which is the light receiving portion 8.
Alternatively, the insulating film 5 which transmits at least ultraviolet rays of Al ₂ O _{3 having} a wavelength of 280 nm or less is formed by a chemical vapor deposition method or the like.

Further, as shown in FIG. 2, in the peripheral portion of the photoconductor element, a connection window 7 opened to connect the metal electrode 4 and the outside is provided by a photoetching process. On the other hand, as described above, in order to construct a photoconductor element for temperature compensation, the metal electrode 4 is used.
Another metal film different from the above is vapor-deposited and formed on the insulating film 5, and the metal light-shielding film 9 is patterned by a photoetching process so as to shield one of the two light-receiving portions 8 shown in FIG. Further, a bonding pad for covering the connection window 7 is formed from the same metal film as the metal light-shielding film 9 through the same photo-etching process.

Therefore, in the structure shown in FIG. 2, three electrodes composed of the lower electrode 3 and the metal electrode 4 are formed,
One photoconductor element (for detection) is formed between the center electrode and the left electrode, and another photoconductor element (for temperature compensation) is further formed between the center electrode and the right electrode, The light receiving portion 8a is shielded from only one of the pair of photoconductor elements. By thus forming a pair of photoconductor elements on the same substrate and shielding one photoconductor element from light, it is possible to obtain good matching of the electrical characteristics of both photoconductor elements. By taking the difference in the output current or the output voltage between the two photoconductor elements, the dark current component having a severe temperature characteristic is canceled out, and the temperature can be compensated.

By adopting the above configuration, in the flame detector 100 of the present application, it is possible to detect the light from the flame on the short wavelength side of approximately 280 nm or less, thereby reducing noise such as sunlight and room light. You can do it without picking it up. More than,
1 is an embodiment of a photoconductive element that constitutes the flame sensor of the present application.

[Another Embodiment] Another embodiment of the present application will be described below. (A) In the above embodiment, a material selected from MgS, CaS, and SrS was adopted as the photoconductor material forming the light receiving portion. However, in addition to these materials, the following materials are used. It is also possible to configure the light receiving unit. That is, so-called fluorescent material, base material composition; (Sr, Ba, Mg) ₃ Si ₂ O ₇ ; P expressed in the form of activator
b ²⁺ , (Ba, Zn, Mg) ₃ Si ₂ O ₇ ; Pb ²⁺ , Ba
Si ₂ O ₃ ; Pb ²⁺ , Y ₂ O ₃ ; Eu, CsI; Na ⁺ ,
(Ca, Zn) ₃ (PO ₄ ) ₂ ; Tl ⁺ , CaSiO ₃ ; P
b ²⁺ , CaSiO ₃ ; Mn ^{2+ and the} like are used as the material forming the light receiving portion. Such a material is a fluorescent material having an absorption spectrum having a long wavelength end in the vicinity of 280 nm and emitting fluorescence by absorbing ultraviolet light having a wavelength shorter than 280 nm. Further, such a material exhibits photoconductive characteristics in a broad sense depending on its temperature state, and can be used for detecting ultraviolet rays of a specific wavelength from a flame with the same configuration and principle as above. In the above embodiment, M
The flame sensor is arranged in a vacuum atmosphere in consideration of the durability of the gS, CaS, and SrS materials against water and temperature, but this material does not necessarily have to adopt such a structure. There is no.

(B) In the above embodiment, the metal light-shielding film 9 is provided on the light-shielding side. However, instead of providing this metal light-shielding film, the light-receiving portion shielded by the metal light-shielding film 9 is provided. A configuration in which a polyimide resin film is applied on the insulating film 5 so as to cover 8a can also be adopted. According to this structure, the metal film forming process for one layer can be omitted, which is effective in simplifying the manufacturing process and reducing the cost.

(C) In the above embodiment, the inside of the detector main body 51 is in a vacuum state, but this configuration is necessary mainly for avoiding the influence of water on the solid photoconductive material. Therefore, for example, the inside of the detector main body 51 may be filled with an inert gas such as nitrogen or helium.

(D) Further, as shown in FIG.
In place of the lower electrode 3 and the metal electrode 4 of the embodiment shown in FIG. 3, the lower electrode 3 for ohmic contact is deposited on the photoconductor and patterned by a photoetching process to form the lower electrode 3 and the light receiving portion 8. On top of the photoconductor 1 not covered by the lower electrode, SiN, SiO ₂ ,
Alternatively, an insulating film 5 of Al ₂ O ₃ is formed by a chemical vapor deposition method or the like, and a contact window 6 for contacting the metal electrode 4 to be formed on the upper portion and the lower electrode 3 in a later step is formed through a photoetching step. Is also preferable. In this case, since the metal electrode 4 and the metal shielding film 9 can be patterned respectively from the same metal film deposited on the insulating film 5 through a photo-etching process, the metal electrode 4 as in the embodiment shown in FIG.
In addition, there is an advantage that two metal film forming steps are not required to form the metal light shielding film 9.

(E) Instead of the sapphire substrate shown in FIGS. 2 and 4, sapphire, hexagonal SiC, ZnO, G
A substrate made of aAs, Si, MgAl ₂ O ₄ , or NdGaO ₃ may be used. (F) In constructing the flame sensor 50 of the present application, as shown in FIGS. 2 to 4, a pair of photoconductive elements does not necessarily have to be formed. It may be.

It should be noted that although reference numerals are given in the claims for convenience of comparison with the drawings, the present invention is not limited to the configuration of the accompanying drawings by the entry.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration and a usage state of a flame detector.

FIG. 2 is a diagram showing a sectional configuration of a flame sensor.

FIG. 3 is a plan view of a flame sensor.

FIG. 4 is a cross-sectional view showing another configuration example of the flame sensor.

FIG. 5 is a diagram showing the emission spectra of flame, sunlight, and room light, and the phototube detection sensitivity.

[Explanation of symbols]

 3 electrodes 4 electrodes 8 light receiving part 50 flame sensor 51 detector main body 52 detection light irradiation part 53 ultraviolet transmission filter

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H01L 31/0264 H01L 31/08 L

Claims (4)

[Claims] 1. A light receiving part (8) made of a photoconductive material selected from MgS, CaS and SrS, and generated in the light receiving part (8) by a photoconductive effect when the light receiving part (8) receives light. (3) that can take out the electric current
(4) A flame sensor comprising: 2. A light receiving section (8) comprising a detector body (51) having a hollow closed structure whose interior is filled with vacuum or an inert gas, and which is made of a photoconductor material selected from MgS, CaS and SrS. A flame sensor (50) provided with electrodes (3) and (4) capable of taking out a current generated in the light receiving part (8) by a photoconductive effect when the light receiving part (8) receives the light. A flame detector provided in a detection light irradiation part (52) in the detector main body for introducing and irradiating with, and an ultraviolet transmission filter (53) in the detection light introduction part in the detector main body. 3. A light receiving section made of a fluorescent material having a long wavelength end at 280 nm and having a photoconductive property of generating a current by absorbing ultraviolet light having a shorter wavelength than the long wavelength end, and the light receiving section being absorbed by the ultraviolet light. A flame sensor with an electrode that can take out the current generated in the. 4. A base material composition; (Sr, Ba, Mg) ₃ Si ₂ O ₇ ; Pb ²⁺ , (B
a, Zn, Mg) ₃ Si ₂ O ₇ ; Pb ²⁺ , BaSi ₂ O ₃ ;
Pb ²⁺ , Y ₂ O ₃ ; Eu, CsI; Na ⁺ , (Ca, Z
n) ₃ (PO ₄ ) ₂ ; Tl ⁺ , CaSiO ₃ ; Pb ²⁺ , Ca
A flame sensor having a light receiving part made of a material selected from a fluorescent material expressed as SiO ₃ ; Mn ²⁺ , and having an electrode capable of taking out a current generated in the light receiving part by absorption of ultraviolet rays.