JPH0772078A - Infrared gas sensor - Google Patents

Abstract

PURPOSE:To provide an infrared gas sensor which can detect the generation and increase of a to-be-detected gas without being influenced by the generation and increase of a disturbing gas present at the same time. CONSTITUTION:A light of a first wavelength lambda1 of an absorption spectrum of a to-be-detected gas and a light of a second wavelength lambda2. different from the first wavelength are applied to a to-be-detected space 10 to measure a concentration of a disturbing gas by the use of the light of the second wavelength lambda2. An output of a sensor 7 corresponding to the light of the second wavelength lambda2 is subtracted from an output of a sensor 6 corresponding to the light of the first wavelength lambda1 by a differentiator 8 for compensation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sensor for detecting the generation and increase of a specific gas in a detected space without being affected by the generation and increase of other gases coexisting in the detected space.

[0002]

2. Description of the Related Art Conventionally, as a gas sensor, for example, a contact chemical sensor, an infrared analyzer, etc. have been known.
The contact-type chemical sensor measures thermochemical changes and electrochemical changes due to gas adsorption on the sensor material. An infrared analyzer projects infrared rays onto various cells such as a reference cell, a sample cell, and an interference cell, detects the absorption by a condenser microphone, and analyzes the gas component in the sample cell.

[0003]

However, in the case of the contact type chemical sensor, the generation or increase of the measured gas cannot be detected unless the measured gas directly contacts the sensor itself. Therefore, if the gas diffusion rate is Vd and the allowable detection time delay is Td, the distance L from the gas generation point to the sensor must be Vd × Td or less. In addition, there is a problem that gas selectivity is generally poor and that many malfunctions occur due to the generation of gases other than the gas to be measured. On the other hand, in the case of an infrared analyzer, a plurality of cell containers made of a material that transmits infrared rays (CaF ₂ , MgF _2, etc.) is used, and a suction device must be added to the sample cell, so the device configuration is It had a problem that it became large and complicated. An object of the present invention is to provide an infrared gas sensor which has a large space to be detected, is not affected by coexisting gas, and has a simple structure.

[0004]

To achieve the above object, a first infrared gas sensor according to the present invention comprises a light source,
An optical system that projects the light emitted from the light source into the detection space, a first filter that transmits only light of the first wavelength λ1 with a predetermined transmittance Tf1, the detection space and the first space. A first optical sensor for measuring the intensity of light transmitted through the filter; a second filter for transmitting only light of a second wavelength λ2 different from the first wavelength λ1 with a predetermined transmittance Tf2; A second optical sensor 2 for measuring the intensity of light transmitted through the space to be detected and the second filter.
And subtracting means for subtracting the output of the second optical sensor from the output of the first optical sensor, and the first wavelength λ in the detected space from the output signal from the subtracting means.
It is configured to include a detection unit that detects the generation and increase of the gas to be detected that absorbs one light. In the above structure, it is preferable that the light source is capable of blinking, and the detecting means phase-detects the output from the subtracting means with a drive signal for blinking the light source as a reference signal. Further, it is preferable to blink the light source that is always turned on by a mechanical chopper. The second infrared gas sensor of the present invention includes a light source, an optical system for projecting light emitted from the light source into a space to be detected, and only light having a first wavelength λ1 at a predetermined transmittance Tf1. A first filter that transmits the light;
A second filter for transmitting only light of a second wavelength λ2 different from the wavelength λ1 of the second wavelength λ1 at a predetermined transmittance Tf2;
And a switching means for alternately switching the second filter, an optical sensor for measuring the intensity of light transmitted through the detected space and the first or second filter switched to the switching means, and the switching means. And a detection means for phase-detecting the output of the photosensor using the switching signal as a reference signal to detect the generation and increase of the gas to be detected that absorbs the light of the first wavelength λ1 in the space to be detected. Is configured. In the above structure, it is preferable that the switching means is a chopping blade having first and second filters and rotating in a predetermined direction. In addition, a third infrared gas sensor of the present invention includes a first light source that can blink, a first filter that transmits only light of a first wavelength λ1 at a predetermined transmittance Tf1, and the first infrared sensor. A first optical system that projects light emitted from a light source and transmitted through the first filter into a space to be detected;
A blinkable second light source, a filter 2 for transmitting only light of a second wavelength λ2 different from the first wavelength λ1 with a predetermined transmissivity Tf2, and the second light emitted from the second light source. A second optical system that projects the light transmitted through the filter into the detection space, and the intensities of the light from the first light source and the light from the second light source that pass through the detection space. An optical sensor to be measured, and a detection gas that phase-detects the output of the optical sensor using the blinking signal of the first or second light source as a reference signal and absorbs the light of the first wavelength λ1 in the detection space. And a detection means for detecting the occurrence and increase of In the above structure, it is preferable that the first optical system and the second optical system also serve as the same optical system. The fourth infrared gas sensor of the present invention includes a light source, an optical system for projecting light emitted from the light source into a space to be detected, and only light having a first wavelength λ1 at a predetermined transmittance Tf1. A first filter that transmits the light, a first optical sensor that measures the intensity of light that has passed through the detection space and the first filter, and a first that converts the output of the first optical sensor into a logarithmic signal. Logarithmic conversion means, a second filter that transmits only light of a second wavelength λ2 different from the first wavelength λ1 with a predetermined transmittance Tf2, the detected space and the second
Second optical sensor for detecting the measurement of light transmitted through the filter, second logarithmic conversion means for converting the output of the second optical sensor into a logarithmic signal, and output intensity of the second logarithmic conversion circuit. Gain adjusting means, a subtracting means for subtracting the output of the gain adjusting means from the output of the first logarithmic converting means, and an output signal from the subtracting means for the first wavelength λ1 in the detected space. Detection means for detecting the generation and increase of the gas to be detected which absorbs the light.

[0005]

The principle of the present invention will be described below. Molecules other than symmetrical diatomic molecules such as oxygen and nitrogen and monatomic molecules such as helium and argon have absorption spectra specific to each molecule in the infrared region. Therefore, the light of the first wavelength λ1 which is one absorption wavelength of the absorption spectrum of the gas to be detected is projected into the space to be detected, and the absorptance of the light of the first wavelength λ1 is measured to detect the gas to be detected. Occurrences and increases can be detected. However, in general, the gas that absorbs light of wavelength λ1 is rarely the only gas to be detected, and other gases that are present at the same time often also absorb. For example,
The absorption spectrum of water vapor is superimposed on the 7.7 μm band, which is one of the absorption spectra of methane gas. In this case, the absorption rate of light having a wavelength of 7.7 μm is determined by the concentrations of methane gas and water vapor. Therefore, if only the absorptance at this wavelength is measured, an increase in water vapor will be erroneously detected as an increase in methane gas. Water vapor has a broad absorption spectrum in the infrared region, which may be further spread depending on the association state of water. In addition, carbon dioxide, ozone, and the like existing in the atmosphere also have a wide absorption spectrum, and molecules having an absorption spectrum at wavelengths at which these absorption spectra do not overlap at all are limited.

To detect the concentration of molecules susceptible to interfering gases, it is necessary to measure the interfering gas concentration at other wavelengths and use it to compensate. This detailed method will be described below using mathematical expressions. For the sake of simplicity, the transmissivity will be used instead of the absorptivity. The transmittance when light is projected into the atmosphere (detection space) in which the first molecule that is the molecule to be detected and the second molecule that is the interfering molecule coexist is the so-called Lambert as shown in (Equation 1) below. -It is expressed by Beeru's law. T (λ) = T1 (λ) · T2 (λ) ··· (Equation 1) where T1 (λ) = EXP (−σ1 (λ) · N1 · L) T2 (λ) = EXP (− σ2 (λ) · N2 · L) where T (λ): transmittance of the detected space for light of wavelength λ T1 (λ): transmittance of the detected space for light of wavelength λ due to absorption of the first molecule T2 (λ): Transmittance of the space to be detected with respect to light of wavelength λ due to absorption of the second molecule σ1 (λ): Absorption cross section of light of wavelength λ of the first molecule σ2 (λ): Second molecule Cross-section for light of wavelength λ of N1: number of first molecules per unit volume N2: number of second molecules per unit volume L: optical path length in the space to be detected. The above (formula 1) is established only when the concentrations of the first and second molecules are sufficiently low and the absorption cross sections do not interfere with each other, but in a general situation where a gas sensor is used, this condition is satisfied. You can think of yourself as satisfied.

The absorption wavelength (first wavelength) λ1 that is most advantageous for detecting the first molecule is determined based on its absorption cross section, the spectral radiant emittance of the light source, the spectral characteristics of the optical sensor, and the like. At this time, it is assumed that the second molecule also has an absorption spectrum at the first wavelength λ1, and the following conditional expression (equation 2
And a second wavelength λ2 that satisfies 2 ′). σ1 (λ2) = 0 ... (Equation 2) σ2 (λ1) = σ2 (λ2)> 0 (Equation 2 ′) where the difference in logarithm of the transmittance with respect to the wavelengths λ1 and λ2 is S
It is shown in (Formula 3) as l. Sl = ln (T (λ1))-ln (T (λ2)) = ln (T1 (λ1) · T2 (λ1))-ln (T1 (λ2) · T2 (λ2)) = -σ1 (λ1) · N1 · L (Equation 3) This Sl is the first regardless of the concentration N2 of the second molecule.
Is proportional to the concentration N1 of the molecule. That is, the generation and increase of the molecule to be detected can be detected without being interfered with by the coexisting molecule.

The absorption cross section σ of methane gas is about 10 ⁻²² m ² (varies depending on the pressure). Therefore, the detected concentration at 1 atm is 1 ppm = N = 2.7 × 10
^When the optical path length L of the detected space is ¹⁹ m ^-3 and 10 m, the exponent part of the above (Equation 1) is as shown in the following (Equation 4). σ · N · L = 2.7 × 10 ⁻² << 1 ... (Equation 4) When the condition of (Equation 4) is satisfied, (Equation 1) is expressed as (Equation 5) below. But it doesn't matter. T ([lambda]) = 1- [sigma] 1 ([lambda]) N1.L- [sigma] 2 ([lambda]) N2.L (Equation 5) Here, if (Equation 2) is satisfied, wavelengths λ1 and λ2 are satisfied. The transmittance difference S is expressed by (Equation 6). S = T (λ1) -T (λ2) = 1-σ1 (λ1) · N1 · L-σ2 (λ1) · N2 · L- (1-σ1 (λ2) · N1 · L-σ2 (λ2) · N2 .L) =-. Sigma.1 (.lamda.1) .N1.L ... (Equation 6) This S is proportional to the concentration N1 of the first molecule regardless of the concentration N2 of the second molecule, like S1. .

Next, since S1 and S are valid only when (Equation 2) is established, when the second equation (Equation 2 ') of (Equation 2) is not established, that is, the wavelength λ1 of the second numerator is obtained. Consider the case where the absorption cross-sections for λ2 are not equal (often there is no choice but to choose λ2 in this way from the distribution of the absorption spectrum of the second molecule). The ratio thereof is shown as B in (Equation 7). B · σ2 (λ1) = σ2 (λ2) (Equation 7) When (Equation 7) holds, the logarithm of the transmittance for the wavelength λ1 and the logarithm of the transmittance for the wavelength λ2 are 1 / B. The difference is S
It is shown in (Formula 8) as l '. Sl ′ = ln (T (λ1)) − (1 / B) · ln (T (λ2)) = − σ1 (λ1) · N1 · L−σ2 (λ1) · N1 · L + σ1 (λ2) · N1 · L / B + σ2 (λ2) · N1 · L / B = −σ1 (λ1) · N1 · L ... (Equation 8)

Similarly, when (Equation 4) and (Equation 7) are established, the difference between the transmittance for wavelength λ1 and 1 / B of the transmittance for wavelength λ2 is shown as S'in (Equation 9). S ′ = T (λ1) − (1 / B) · T (λ2) = 1−σ1 (λ1) · N1 · L−σ2 (λ1) · N1 · L − (1-σ1 (λ2) · N1 · L / B- [sigma] 2 ([lambda] 2) * N1 * L / B) =-[sigma] 1 ([lambda] 1) * N1 * L (Equation 9) These Sl 'and S'are the same as Sl and S are the second numerator. , Which is proportional to the concentration N1 of the first molecule.

Based on the principle described above, the space to be detected is irradiated with light having a second wavelength λ2 different from the first wavelength λ1 which is the absorption spectrum of the gas to be detected, and the concentration of the interfering gas is changed to the second wavelength. It measures using the light of (lambda) 2. This is used to compensate for the absorptance of light of the first wavelength λ1. As a result, the generation and increase of the specific gas in the detected space can be detected without being affected by the other gas existing at the same time.

[0012]

【Example】

<First Embodiment> First of infrared gas sensor of the present invention
The embodiment will be described with reference to FIGS. 1 and 2. It should be noted that this embodiment (the same applies to the following embodiments) will be described by taking a case where it is used as a methane gas sensor as an example. Further, the first embodiment is effective when (Equation 4) that is satisfied in many cases is satisfied. FIG. 1 is a block diagram showing the configuration of an infrared gas sensor according to the first embodiment. In FIG. 1, the infrared gas sensor includes a light source 1, a drive circuit 2 for driving the light source 1 to blink, an optical system 3 for irradiating the space 10 to be measured with light emitted from the light source 1, 1st filter 4 which transmits only the light of wavelength 1 of 1
A first optical sensor 6 for detecting the intensity of light transmitted through the measured space 10 and the first filter 4, and a second optical sensor 6.
Second filter 5 that transmits only light of wavelength λ2 of
A second optical sensor 7 for detecting the intensity of light transmitted through the measured space 10 and the second filter 5;
Difference device 8 for generating a difference signal between the output of the optical sensor 6 and the output of the second optical sensor 7, and a lock-in amplifier 9 for phase-detecting the output of the difference device 8 using the drive signal of the drive circuit 2 as a reference signal. And is provided.

The light source 1 may be a black body furnace such as SiC,
Alternatively, a blinkable lamp may be used. In this embodiment, several H
A 20 W halogen lamp capable of flashing at z was used. First
Of the wavelength λ1 = 7.65 μm, and the first filter 4 transmits only the light of wavelength λ1 = 7.65 μm (band = 0.2 μm) with the transmittance Tf1 = 0.6. Second wavelength λ2
= 5.25 μm, the second filter 5 has a wavelength λ2 =
Transmittance Tf2 for only light of 5.25 μm (band = 0.2 μm)
= 0.6 to transmit. As the first and second photosensors 6 and 7, pyroelectric photosensors having no sensitivity wavelength dependency and requiring no cooling were used. The space 10 to be detected is filled with a very standard atmosphere containing water vapor and the like. In the first embodiment, the output of the lock-in amplifier 9 corresponds to S shown in (Equation 6) above. By monitoring the output of the lock-in amplifier 9, it was possible to detect the generation of methane gas in the detection space 10 without being affected by the increase or decrease in humidity.

The first and second filters 4 shown in FIG.
And 5, first and second photosensors 6 and 7, and differencer 8
FIG. 2 shows a cross-sectional structure of an element in which the element is integrated. Figure 2
In a substrate 11 made of MgO or the like by a sputtering method or the like.
An electrode 12 such as Pt is formed. P on the electrode 12
bTiO₃, LiTaO₃, Pb_1-xLa_xTi_{1-x / 4}O
₃Pyroelectric materials such as (x = 0 to 0.25) are applied to the sputtering method, etc.
Therefore, thin films 13 and 14 oriented in the same direction are formed.
ing. On the thin films 13 and 14 of pyroelectric material, respectively,
The electrodes 15 and 16 are formed by the putter method or the like.
The material of the electrodes 15 and 16 has a good absorption rate in the infrared region.
NiCr, Sb, etc. are used. On electrodes 15 and 16
Are dielectric multilayer interference filters 17 and 18, respectively.
Is provided. Dielectric multilayer interference filter 17 and
And 18 are the first and second filters 4 and 5 shown in FIG.
Corresponding to Si, Ge, Se, Te, LiF, NaF,
CaF ₂, MgF₂The combination of thin films formed by
It is composed of In addition, the thin films 13 and 14 of the pyroelectric material
Between the electrodes 15 and 16 during the thin film formation.
Using a mask, or by etching after formation
To separate. In addition, each dielectric multilayer interference filter 17 and
And 18 have different film thicknesses of each material,
Replace and make thin films individually. Integrated type shown in FIG.
In the case of a device, the signal between electrodes 15 and 16 is
Corresponds to a signal. The reason is that the thin film 13 of pyroelectric material and
Since 14 are oriented in the same direction,
Are connected so that their polarities face each other. Servant
Therefore, the signal between the electrodes 15 and 16 receives the dielectric multilayer film.
Red separately transmitted through the filters 17 and 18
It corresponds to the difference in the strength of the outside line. Such an integrated element
Store in a container with a diameter of 2 to 6 mm and a thickness of 2 to 5 mm
It is possible to make the device smaller, simpler, cheaper and more robust.
It is valid.

In the first embodiment, the light source 1 is made to blink, but the same effect can be obtained even if the light source 1 is constantly turned on and the light from the light source 1 is chopped by a mechanical chopper or the like. To be Further, the background noise is sufficiently small, and the first and second optical sensors 6 and 7 and the difference unit 8
If the DC stability of is good, the blinking of the light source 1, the mechanical chopper, and the lock-in amplifier 9 are unnecessary. Further, in the first embodiment, the first wavelength λ1 and the second wavelength λ1
The case where the absorption cross-sections of the second molecule with respect to 2 are equal is shown, but when they are not equal, (Equation 7) and (Equation 9)
As shown in, the transmittance Tf2 of the second filter 5 may be set to 1 / B, or the sensitivity of the second optical sensor 7 or the gain of the amplifier inserted thereafter may be set to 1 / B.

<Second Embodiment> Next, a second embodiment of the infrared gas sensor of the present invention will be described with reference to FIG.
The second embodiment is also effective when (Equation 4) which is satisfied in many cases is satisfied. Further, the constituent elements denoted by the same reference numerals as those in the first embodiment shown in FIG. 1 are substantially the same, and the description thereof will be omitted. In FIG. 3, the light source 1 is emitted by the power source 19 at a constant intensity. A chopping blade 20 is provided so as to face the optical system 3 with the measured space 10 interposed therebetween. The chopping blade 20 is
It has at least one set of filters having the same characteristics as the first and second filters 4 and 5 in the first embodiment shown in FIG. This chopping blade 20 is rotated by a controller 21, and a selector (switching) for switching between a first filter 20a that transmits only light of a first wavelength λ1 and a second filter 20b that transmits only light of a second wavelength λ2. Function). The light passing through the first filter 20a and the light passing through the second filter 20b alternately reach the optical sensor 6. Further, the reference signal is supplied from the controller 21 to the lock-in amplifier 9. The lock-in amplifier 9 is an optical sensor 6
The phase detection is performed on the output from the reference signal based on the reference signal. The output of the lock-in amplifier 9 indicates the generation and increase of methane gas. The second embodiment is effective when using a light source such as a black body furnace that has a large light emission intensity but a large heat capacity and cannot blink, or when using background light such as sunlight. Further, since only one optical sensor is used in the second embodiment, it is not affected by the variation in the sensitivity of the optical sensor unlike the first embodiment.

<Third Embodiment> Next, a third embodiment of the infrared gas sensor of the present invention will be described with reference to FIG.
The third embodiment is also effective when (Equation 4) which is satisfied in many cases is satisfied. Further, the constituent elements denoted by the same reference numerals as those in the first embodiment shown in FIG. 1 are substantially the same, and the description thereof will be omitted. In FIG. 4, the first and second light sources 22 and 23 are capable of blinking, and are alternately turned on by the drive circuit 24. The drive signal of the drive circuit 24 is supplied to the lock-in amplifier 9 as a reference signal. The optical system 25 projects the light emitted from the first and second light sources 22 and 23 onto the space 10 to be detected,
The diameter is sufficiently larger than the distance between the first light source 22 and the second light source 23, and the light from the first and second light sources 22 and 23 is equivalently projected onto the detected space 10. The light emitted from the first light source 22 and transmitted through the detected space 10 and the first filter 20a is transmitted to the optical sensor 6 and the second light source 2
3 to be detected and the detection space 10 and the second filter 2
The light transmitted through 0b arrives alternately. The output of the optical sensor 6 is phase-detected by the lock-in amplifier 9. The output of the lock-in amplifier 9 indicates the generation and increase of methane gas.

The third embodiment can effectively function even when the accuracy of the transmittances Tf1 and Tf2 of the first and second filters 20a and 20b is insufficient. The reason will be described below. Generally, a dielectric multilayer interference filter is used as the first and second filters 20a and 20b, and the transmission wavelength and the transmittance thereof are controlled by the film thickness of each thin film and the refractive index of the material. However, since it is impossible to control the transmission wavelength and the transmittance independently, the first and second
It is not always easy to fabricate filters such as the filters 20a and 20b, which have different transmission wavelengths and have mutually set transmittance ratios.
On the other hand, in the case of the present invention, since extremely high accuracy is required for the transmission wavelength, the manufacturing accuracy of the transmittance may be sacrificed to some extent. Even in the case where the transmissivity is somewhat insufficient as described above, the transmissivities of the first and second filters 20a and 20b are controlled by controlling the emission intensity of the first and second light sources 22 and 23. It is possible to compensate for the error in Tf1 and Tf2. Since only one optical sensor is used in the third embodiment, the sensitivity of the optical sensor is not affected by variations, as in the case of the second embodiment.

<Fourth Embodiment> Next, a fourth embodiment of the infrared gas sensor of the present invention will be described with reference to FIG.
The fourth embodiment is effective even when (Equation 4) is not always satisfied. Further, the constituent elements denoted by the same reference numerals as those in the first embodiment shown in FIG. 1 are substantially the same, and thus the description thereof will be omitted. In FIG. 5, first and second logarithmic conversion circuits 26 and 27 are connected to the first and second photosensors 6 and 7, respectively, and the outputs of the first and second photosensors 6 and 7 are Converted to logarithm. The gain adjustment circuit 28 is connected to the second logarithmic conversion circuit 27,
The output intensity of the second logarithmic conversion circuit 7 is controlled. Differentiator 8
Generates a difference signal between the output of the first logarithmic conversion circuit 26 and the output of the gain adjustment circuit 28. The lock-in amplifier 9 detects the phase of the output of the difference unit 8. The output of the lock-in amplifier 9 indicates the generation and increase of the detected gas.

The gain of the gain adjusting circuit 28 is set to 1 when (Equation 2) is satisfied, and is set to 1 / B according to (Equation 7) and (Equation 8) when (Equation 2) is not satisfied. Just do it. Further, by appropriately adjusting the gain of the gain adjusting circuit 28, it is possible to compensate for variations in the sensitivity of the first and second optical sensors 6 and 7, and errors in the transmittance of the first and second filters 4 and 5. be able to. When the background noise is sufficiently small and the DC stability of the first and second photosensors 6 and 7, the difference unit 8 and the gain adjusting circuit 28 is sufficiently good, the light source 1 blinks, the mechanical chopper, and the lock. The in-amplifier 9 becomes unnecessary.

[0021]

As described above, according to the present invention, the first wavelength λ which is the absorption spectrum of the gas to be detected is detected in the space to be detected.
1 and a different second wavelength λ2 light, the concentration of the interfering gas is measured using the second wavelength λ2 light, and the sensor corresponding to the measured first wavelength λ1 light Since the output of the sensor corresponding to the light of the second wavelength λ2 is subtracted from the output of the sensor to compensate for it, the generation and increase of the specific gas in the detection space can be detected without being affected by other gases that are present at the same time. It has the effect of being able to.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a first embodiment of an infrared gas sensor of the present invention.

FIG. 2 is a cross-sectional view showing the configuration of an element in which the first and second filters, the first and second photosensors, and the difference device according to the first embodiment of the present invention are integrated.

FIG. 3 is a block diagram showing the configuration of a second embodiment of the infrared gas sensor of the present invention.

FIG. 4 is a block diagram showing the configuration of a third embodiment of the infrared gas sensor of the present invention.

FIG. 5 is a block diagram showing the configuration of a fourth embodiment of the infrared gas sensor of the present invention.

[Explanation of Codes] 1: Light source 2: Driving circuit 3: Optical system 4: First filter 5: Second filter 6: First optical sensor 7: Second optical sensor 8: Difference device 9: Lock-in Amplifier 10: Detected space 11: Substrate 12: Electrode 13: Pyroelectric material thin film 14: Pyroelectric material thin film 15: Electrode 16: Electrode 17: Filter 18: Filter 19: Power supply 20: Chopping blade 21: Controller 22 : First light source 23: second light source 24: drive circuit 25: optical system 26: first logarithmic conversion circuit 27: second logarithmic conversion circuit 28: gain adjustment circuit

Claims (8)

[Claims] 1. A light source, an optical system for projecting light emitted from the light source into a space to be detected, and a first filter for transmitting only light having a first wavelength λ1 at a predetermined transmittance Tf1.
A first optical sensor that measures the intensity of light that has passed through the space to be detected and the first filter, and only light having a second wavelength λ2 different from the first wavelength λ1 has a predetermined transmittance Tf2. A second filter that transmits light, a second optical sensor 2 that measures the intensity of light that has passed through the detection space and the second filter, and the second optical sensor based on the output of the first optical sensor. Infrared comprising subtraction means for subtracting the output of the detection means and detection means for detecting the generation and increase of the detected gas that absorbs the light of the first wavelength λ1 in the detected space from the output signal from the subtracting means. Gas sensor. 2. The infrared type according to claim 1, wherein the light source is capable of blinking, and the detecting means phase-detects the output from the subtracting means with a drive signal for driving the light source blinking as a reference signal. Gas sensor. 3. The infrared type gas sensor according to claim 2, wherein the light source which is constantly turned on is made to blink by a mechanical chopper. 4. A light source, an optical system for projecting light emitted from the light source into a space to be detected, and a first filter for transmitting only light having a first wavelength λ1 at a predetermined transmittance Tf1.
A second filter that transmits only light of a second wavelength λ2 different from the first wavelength λ1 with a predetermined transmittance Tf2;
Switching means for alternately switching the first and second filters, an optical sensor for measuring the intensity of light transmitted through the detected space and the first or second filter switched to the switching means, A detection unit that phase-detects the output of the optical sensor using the switching signal of the switching unit as a reference signal and detects the generation and increase of the detected gas that absorbs the light of the first wavelength λ1 in the detected space. Infrared gas sensor equipped. 5. The infrared gas sensor according to claim 4, wherein the switching means is a chopping blade having first and second filters and rotating in a predetermined direction. 6. A blinkable first light source and a first wavelength λ.
A first filter that transmits only one light with a predetermined transmittance Tf1; and a first optical system that projects the light emitted from the first light source and transmitted through the first filter into a space to be detected, Only the second light source capable of blinking and the light having the second wavelength λ2 different from the first wavelength λ1 have a predetermined transmittance Tf2.
A second optical system that projects light emitted from the second light source and transmitted through the second filter into the detection space; and the first optical system that transmits through the detection space. An optical sensor for measuring the intensity of each of the light from the light source and the light from the second light source, and phase detection of the output of the optical sensor using the blinking signal of the first or second light source as a reference signal, The first in the detected space
Infrared gas sensor, comprising: a detection means for detecting the generation and increase of the gas to be detected which absorbs the light of wavelength λ1. 7. The first optical system and the second optical system both use the same optical system.
Infrared gas sensor described. 8. A light source, an optical system for projecting light emitted from the light source into a space to be detected, and a first filter for transmitting only light having a first wavelength λ1 at a predetermined transmittance Tf1.
A first optical sensor for measuring the intensity of light transmitted through the detected space and the first filter; first logarithmic conversion means for converting an output of the first optical sensor into a logarithmic signal; A second filter that transmits only light having a second wavelength λ2 different from the first wavelength λ1 with a predetermined transmittance Tf2; and detecting a measurement of light that has passed through the detection space and the second filter. Second photosensor, second logarithmic conversion means for converting the output of the second photosensor into a logarithmic signal, gain adjusting means for adjusting the output intensity of the second logarithmic conversion circuit, and the first Subtracting means for subtracting the output of the gain adjusting means from the output of the logarithmic converting means, and generation and increase of the detected gas that absorbs the light of the first wavelength λ1 in the detected space from the output signal from the subtracting means. Detecting means for detecting Infrared gas sensor having a.