JPH07151685A - Non-dispersion type infrared gas analyzer - Google Patents

Abstract

PURPOSE:To make possible the measuring of a high-density gas component in a small curve of output characteristics with a single sample cell long enough to obtain the quantity of a signal allowing stable measurement for a low density gas component in a multi-component infrared gas analyzer which analyzes the low density gas component and the high density gas component simultaneously. CONSTITUTION:An infrared-ray source section 2 which has a gas 10 to be measured of a component with a high density rang as measuring area sealed in at a specified partial pressure is arranged with an infrared transmission window 9 on the incoming side of a measuring cell 1 and a detection block 5 which has a detection unit 7 made up of an infrared sensor 7A and an optical band pass filter 7B in a pair assembled into a sensor mounting block 6, on the outgoing side. A transmission wavelength band of the optical band pass filter provided on the detection unit 7 of the gas to be measured with the high density range as measuring area is so set to cover almost the whole of one absorption band of the gas 10 to be measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-dispersive infrared gas analyzer for continuously measuring the concentrations of a plurality of components of interest in a multi-component gas contained in a sample gas.

[0002]

2. Description of the Related Art An infrared gas analyzer selectively detects the absorption amount of infrared rays by a gas component of interest in a sample gas composed of a plurality of components and continuously determines the concentration of the gas component in real time. It is a device that measures the target. Infrared gas analyzers are widely used for gas analysis purposes in various fields because they generally have good selectivity and high measurement sensitivity.

Next, the structure of a conventional non-dispersive infrared gas analyzer and its operating principle will be described with reference to FIG.
In FIG. 2, 1 is a measuring cell for flowing a sample gas, 2 is an infrared light source unit, 3 is a rotating sector which intermittently guides the infrared light flux emitted from the infrared light source unit 2 to the measuring cell 1, and 4 drives a rotating sector 3. The motors 5 are detection blocks arranged on the infrared ray emission side of the measurement cell 1. The detection block 5 includes an optical bandpass filter 7B such as a multi-layer thin film interference filter whose transmission wavelength band corresponds to the absorption wavelength band of the gas component of interest in the sample gas, and a spectral sensitivity characteristic that is flat in this wavelength band. The detection unit 7 in which a pair of infrared sensors 7A such as a pyroelectric type sensor and a semiconductor sensor having the above are combined and combined, the number corresponding to the measurement target component gas (in the illustrated example, 3 represented by # 1 to # 3). These are collected and arranged and housed in the sensor mounting block 6.

In the infrared gas analyzer configured as described above, the infrared light emitted from the infrared light source unit 2 becomes an optically modulated infrared light flux 8 which is intermittent at the opening / closing cycle of the rotating sector 3 and becomes a measuring cell. In the process of entering the sample cell 1 and passing through the measurement cell 1, infrared rays in a wavelength band peculiar to each gas component constituting the sample gas are absorbed according to the concentration of the gas component and reach the detection block 5. . Then, in the detection block 5, for each of the detection units 7 arranged and housed in the detection block 5, the detection unit 7
Infrared of the transmission wavelength band of the optical bandpass filter 7B provided in is converted into an electric signal by the infrared sensor 7A,
The signal is output as a signal representing the concentration of the gas component having the absorption wavelength band in the transmission wavelength band of the optical bandpass filter 7B.

The absorption of infrared rays by the sample gas described above means that when the gas component constituting the sample gas contains a gas component composed of molecules having an electric dipole moment sensitive to an electric field, The vibration of molecules and the rotational movement associated with the vibration occur when excited by an oscillating electric field of infrared rays. The wavelength band of infrared rays to be absorbed and the strength of absorption are the structures of molecules constituting the gas component. Peculiar to the gas component determined by The infrared wavelength λ and the frequency ν have an inverse relationship λ = C / ν with the speed C of light as an intermediary, and if one value is given, the other value is obtained. Therefore, in the following description, Both will be used equally.

FIG. 4 schematically shows an infrared absorption spectrum observed with gas samples having different concentrations (C1 to C4) of specific components at atmospheric pressure. In the infrared absorption spectrum of the gas sample, it corresponds to the change in the rotational state of the molecule caused by the excitation of the vibration around the wavelength λb corresponding to the frequency of the molecular vibration of the gas component molecule showing the infrared absorption. Infrared absorption is observed as an adjacent continuous spectrum as illustrated in FIG.

It is known that the Lambert-Beer law represented by the following equation (1) holds between the intensity of infrared absorption by the sample gas and the gas concentration.

[0008]

## EQU1 ## I = I ₀ exp (-kcL) ----------- (1) where, I ₀ ; incident light amount of infrared ray I; transmitted light amount of infrared ray c; of measured gas component Concentration k; Extinction coefficient L; Infrared transmission thickness The value of the extinction coefficient k in the equation (1) is a numerical value indicating the degree of ease of absorption of infrared rays, and thus the infrared absorption spectrum illustrated in FIG. It is considered to represent the value of the extinction coefficient k. As shown in the figure, the value of this extinction coefficient k becomes a large value for infrared rays near the absorption center of the wavelength λb corresponding to the frequency of molecular vibration, and this absorption center wavelength λb
Although it will show a small wavelength dependence in the region away from, the absorption of infrared rays as described above, the molecular vibration of the gas component constituent molecules and the rotational state of the molecule caused by the excitation of vibration. Since it occurs in response to changes, it is unique to the gas component, which is determined by the structure of molecules constituting the gas component.

In the above infrared gas analyzer, an optical bandpass filter 7B is used to detect light having a wavelength spread corresponding to the infrared absorption wavelength range of the component molecule to be measured.
Since it is led to 7A, the signal value S output from the sensor as the change amount ΔI of the transmitted light amount and the concentration c of the component to be measured have a relationship represented by the following expression (2) in a strict sense.

[0010]

[Equation 2]

S: signal of infrared gas analyzer S ₀ ; signal span k (λ, c); function of extinction coefficient, wavelength and concentration λ; wavelengths of infrared rays λ ₁ , λ ₂ ; integration range c; gas component to be measured However, the value of the extinction coefficient corresponding to the change in the amount of transmitted light obtained by the integral of equation (2) is regarded as the value of the average extinction coefficient of the molecule to be measured in the optical bandpass filter transmission wavelength range, If this is taken as the equivalent extinction coefficient, this integration range λ
_For incident light and transmitted light in the wavelength range from ₁ to λ ₂ ,
Since the relationship of equation (1) is established at a practical level, the following description will be premised on the relationship of equation (1).

As described above, since the relationship of the formula (1) is established between the incident light and the transmitted light in the infrared gas analyzer, the infrared sensor 7A has the following formula (1). Difference ΔI between the amount I of transmitted infrared light and the amount I ₀ of incident light
Is detected as the concentration analysis signal S. That is, the concentration analysis signal S of the infrared gas analyzer is expressed by the following equation (3).

[0013]

## EQU3 ## S∽ΔI = I ₀ −I = I ₀ {1-exp (−kcL)} ------ (3) On the other hand, dividing both sides of equation (1) by I ₀ Taking the logarithm,
Applying the logarithmic expansion formula, if the value of the difference ΔI between the incident light amount I _{0 of} infrared light and the transmitted light amount I is small, the terms of ΔI / I ₀ squared or more are usually sufficiently small values, and therefore the approximation is omitted. Equation (4) is derived by doing.

[0014]

## EQU00004 ## log I / I ₀ = log (1−ΔI / I ₀ ) ≈−ΔI / I ₀ = log exp {−kcL} = − kcL That is, ΔI / I ₀ = S / I ₀ = kcL-- --------- (4) This formula (4) shows that when the change ΔI in the amount of light incident and transmitted by infrared rays is not so large and the omission approximation of the terms of ΔI / I ₀ squared or more is possible, It shows that the sensitivity of the infrared gas analyzer is proportional to the cell length L.

By the way, in an infrared gas analyzer for simultaneously measuring a low-concentration gas component and a high-concentration gas component, a sample cell having a long cell length is usually used so that a sufficient signal amount can be obtained even in the measurement of the low-concentration gas component. To be selected. When a high-concentration gas component is measured with a sample cell having a long cell length, the difference ΔI between the incident light amount I _{0 of} infrared rays and the transmitted light amount becomes large, and the approximation for deriving equation (4) cannot be established. The detected electric signal S and the concentration c of the component gas to be measured are expressed by the formula
It has a non-linear relationship expressed by (3).

In the above equation (3), the electric signal S has a constant value I ₀ with respect to the value of kcL which is the product of the extinction coefficient k, the length L of the sample cell and the concentration c of the gas component to be measured. It shows that it fluctuates on the curve. Therefore, when a high-concentration sample gas component is measured in a sample cell having a long cell length in comparison with the value of the extinction coefficient k, the signal output with respect to the concentration change is saturated near the full scale of the measured gas concentration, and Becomes smaller and the signal resolution decreases. In such a case, even if a linearization circuit that electrically corrects the non-linear relationship between the input and output is applied, the linearization circuit will not work in the region where the change in the signal output with respect to the density change is small as described above. It cannot function.

Therefore, a detection unit (7A ', 7B') for measuring the high-concentration gas component is provided near the light source, and the cell length L for the high-concentration gas component is shortened to reduce the value of kcL to reduce the high concentration. Avoiding a decrease in the change in signal output in the region
However, this method has a drawback that the structure is complicated. Also, as an alternative,
The transmission wavelength range of the optical bandpass filter may be set to a narrow range of the absorption band of the gas to be measured having a small extinction coefficient k to reduce the value of kcL. In the figure showing an example of the absorption spectrum characteristic, an example of the transmission wavelength range of the optical bandpass filter selected and set as a narrow range of the area where the absorption coefficient k is small is shown as an area (a).

The region (a) selected as described above is a region adjacent to the region exhibiting strong absorption and the value of the extinction coefficient k largely changes with wavelength. Therefore, the relationship between the electric signal S detected by the infrared sensor 7A and the concentration c of the component gas to be measured changes greatly due to a slight difference in the center wavelength of the transmission wavelength band of the optical bandpass filter and the band width.

On the other hand, in the optical bandpass filter of the multilayer thin film interference filter system in which the transmission wavelength range is determined by the thickness of the thin film, the thickness of the thin film is controlled with high accuracy so that the above fluctuations are not noticeable, and it is repeatedly manufactured. Is extremely difficult. Therefore, the transmission wavelength range of the optical bandpass filter is
It is difficult to repeat the infrared gas analysis with a small variation in characteristics by a method in which the absorption band k of the gas to be measured is limited to a narrow region where the absorption coefficient k is small.

[0020]

SUMMARY OF THE INVENTION It is an object of the present invention to prevent the output signal from being saturated when the concentration of a high concentration gas component is measured by a sample cell having a long cell length capable of stably measuring the low concentration gas component. The linearity between the concentration and the output signal is kept small within the range of change, and a reproducible method is devised to reduce the concentration of the same sample gas in one device equipped with a single sample cell. An object of the present invention is to provide a non-dispersion type infrared gas analyzer capable of simultaneously and continuously measuring a gas component and a high-concentration gas component.

[0021]

In order to achieve the above object, in the non-dispersion type infrared gas analyzer according to the present invention, the infrared light source has a sealed structure provided with an infrared transmitting window, The light source part has the same molecular structure as the measured gas component or the measured gas over the high concentration range of the measurement range, and is different from the measured gas that shows the infrared absorption equivalent to one infrared absorption by the measured gas. The component gas is enclosed at a partial pressure sufficient to completely absorb infrared rays in the absorption center wavelength region having a large absorption coefficient k in the infrared absorption band of the gas. Then, the transmission wavelength band of the optical bandpass filter provided in the detection unit for detecting the gas of the component sealed in the infrared light source unit is set to a range corresponding to the entire one infrared absorption band of the gas, The infrared sensor provided in this detection unit has a flat spectral sensitivity in the transmission wavelength band of the optical bandpass filter.

Further, in the non-dispersive infrared gas analyzer according to the present invention for simultaneously analyzing a plurality of components, a detection unit composed of a plurality of non-selective infrared sensors and an optical bandpass filter is provided, and an infrared light source is provided. The infrared light source part has a sealed structure with an infrared transmission window, and the infrared light source part has a molecular structure part that is the same as the measured gas component or the measured gas over a high concentration range. A gas having a component different from that of the gas to be measured that exhibits an infrared absorption equivalent to two infrared absorptions is sufficient to completely absorb infrared rays in the absorption center wavelength region having a large absorption coefficient k in the infrared absorption band of the gas. It shall be sealed by pressure. And
A single measurement cell common to a plurality of components is provided, and the transmission wavelength band of the optical bandpass filter provided in the detection unit for detecting the gas of the component enclosed in the infrared light source part is one infrared absorption band of the gas. The infrared sensor provided in this detection unit has a flat characteristic in the transmission wavelength band of the above optical bandpass filter.

[0023]

With the above structure, the infrared light source section in which the gas to be measured is enclosed emits the infrared light flux from which the infrared rays in the absorption center wavelength region of the gas to be measured are removed, and enters the measurement cell through the infrared transmitting window. Then, the light passes through the measurement cell and is received by the detection unit. Then, in the measurement cell, infrared rays in the wavelength region having a small value of the absorption coefficient k, which has not been absorbed by the measured gas enclosed in the light source, are absorbed by the measured gas.

On the other hand, in the wavelength range of infrared light detected by the detection unit, the incident wavelength range is limited by the optical bandpass filter, and the infrared light source section detects infrared rays in the absorption center wavelength range of the gas to be measured. Since it is excluded, the value of the extinction coefficient k of the measured gas is small and the wavelength range is relatively narrow. As described above, only the wavelength region in which the value of the absorption coefficient k of the gas to be measured is small becomes the effective detection wavelength region, so even when a high-concentration gas component to be measured is introduced into the measurement cell,
Absorption does not saturate, and a relatively large signal change is output from the infrared sensor.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A block configuration of an embodiment of a non-dispersive infrared gas analyzer according to the present invention is shown in FIG. 1, and the present invention will be described with reference to this drawing. In FIG. 1, 1 is a measuring cell for flowing a sample gas, and 2 is an infrared light source unit. This infrared light source unit 2
Is a hermetically sealed structure provided with an infrared transmission window 9, and the gas to be measured is a component whose measurement range is up to a high concentration range.
10 is enclosed at a predetermined partial pressure sufficient to completely absorb infrared rays in the central absorption wavelength region. Therefore, the infrared light source section 2 lacks the infrared component in the wavelength region near the absorption center wavelength of the enclosed gas.
Infrared rays having a wavelength distribution as illustrated in FIG.

By the way, the absorption of infrared rays by the gas occurs in response to the molecular vibration of the gas component constituent molecules and the change in the rotational state of the molecule caused by the excitation of the vibration, and the structure of the molecules constituting the gas component. Therefore, even if different molecules have the same structural part in the structure of the molecule, they show the same absorption in the wavelength range corresponding to this structural part. Therefore, when the measurement target gas is an active and unstable gas, it may be possible to substitute the gas sealed in the infrared light source unit 2 with another stable gas having the same structural portion as the measurement target gas. For example,
Nitrosyl chloride (molecular formula NOCl), which is one of the starting materials for synthetic fibers, is an unstable and highly reactive gas, so nitrosyl chloride gas is enclosed in the infrared light source 2 of the infrared gas meter that contains a high concentration of nitrosyl chloride in the analysis range. Doing so is not preferable from the viewpoint of ensuring long-term stability. Therefore, the molecular structure has the same nitrogen-oxygen bond (N-O) as nitrosyl chloride.
Since nitrosyl chloride is contained in the infrared light source section 2 when chemically stable nitrous oxide (N ₂ O) having an absorption wavelength range overlapping with the infrared absorption wavelength range of nitrosyl chloride is enclosed, the nitrosyl chloride gas is said to be enclosed. It functions similarly, but does not cause a problem such as corrosion of the infrared light source section 2.

Next, 3 is a rotating sector for connecting and disconnecting the infrared light flux emitted from the infrared light source section 2, 4 is a motor for driving the rotating sector 3, and 5 is a detection block provided on the emitting side of the measuring cell 1, for detection. The block 5 includes a plurality of infrared sensors 7A (three represented by # 1 to # 3 in the illustrated example) corresponding to each measurement component gas contained in the sample gas in the sensor mounting block 6, and a multilayer film interference filter, for example. The detection unit 7 formed by pairing the optical bandpass filter 7B is arranged in parallel. An optical bandpass filter provided in the detection unit 7 for measuring the high concentration gas component
Even if there is some error in the boundary wavelength of the transmission band when the filter makes the boundary wavelength of the 7B transmission band, the region where the absorption coefficient of the component to be measured greatly changes with wavelength does not overlap with this boundary wavelength. The wavelength outside the absorption band of the gas to be measured is designed to fall within the range of λ1 to λ2 in the spectrum of FIG. On the other hand, the optical bandpass filter 7B mounted on the detection unit 7 for measuring low-concentration gas components is set in a range overlapping the absorption center of the measurement target gas.

The infrared sensor 7A, which is another component of the detection unit 7, has a characteristic that the spectral sensitivity is flat in the transmission wavelength band of the optical bandpass filter 7B, for example, a pyroelectric sensor or a semiconductor. A sensor or the like is appropriately selected. With such a configuration, as to the components of the gas to be measured whose concentration is high, as described above, the infrared light source unit 2 has a predetermined amount sufficient to absorb the infrared rays in the absorption center wavelength region. Since the infrared rays in the absorption center wavelength range are absorbed inside the infrared light source section 2 because they are sealed by partial pressure, the infrared rays in this wavelength range do not substantially enter the measuring cell 1. In, only absorption of infrared rays in a wavelength region adjacent to the absorption center wavelength region and having a small absorption coefficient value occurs.

FIG. 5 is a diagram schematically showing the state of absorption in the measuring cell 1. The wavelength distribution of infrared light incident on the infrared sensor 7A of the detection unit 7 for analyzing high-concentration gas components will be described below with reference to this diagram. explain. In FIG. 5, λ
1 and λ2 represent the boundary wavelengths of the transmission band of the optical bandpass filter 7B, and the infrared sensor 7A includes λ1 and λ2.
Infrared rays with wavelengths outside are not incident. Also, λc and λd
Indicates the absorption center wavelength region of the high-concentration gas component, and the gas component enclosed in the infrared light source unit 2 completely absorbs infrared rays in this wavelength region, so the infrared sensor 7A has this wavelength region. Infrared rays do not enter. After all, the infrared rays substantially incident on the infrared sensor 7A of the detection unit 7 for analyzing the high-concentration gas component are λ1 to λc and λ in which the wavelength region of λc to λd shown by hatching in FIG. 5 is missing.
Infrared rays in the wavelength range from 2 to λd.

In general, neither the transmission band of the optical bandpass filter nor the absorption center wavelength band of infrared absorption by the gas component has a sharp and clear boundary as schematically shown in FIG. However, if the attention is paid only to the relationship between the relative intensity of the light incident on the measurement cell 1 and the light transmitted through the measurement cell 1 and detected by the infrared sensor 7A, the essence of the phenomenon is bent and interpreted by the above modelization. There is no.

As described above, the infrared sensor 7A of the detection unit 7 for analyzing the high-concentration gas component has the small absorption coefficient k of the gas component to be measured, that is, λ1 to λc and λ2 to λ.
Since infrared rays in the wavelength range of d are detected, even if a measurement cell having a long cell length is used, the absorption of the gas component having a high concentration is not saturated, and the relationship between the output signal S and the concentration c of the gas component to be measured is: Equation (4) can be approximated and a linear relationship is established.

FIG. 6 is a diagram for explaining the relationship between the output signal S of the detection unit 7 and the product cL of the concentration c of the gas component to be measured and the cell length L of the measuring cell 1. In FIG. 6, k
= 1.0 is the curve according to the prior art illustrated in FIG. 2 in which the transmission band of the optical bandpass filter of the detection unit 7 for analyzing the high concentration gas component is set to the absorption center wavelength region of infrared absorption by the high concentration gas component. It is an example of analysis characteristics of high-concentration gas components of an infrared gas meter for simultaneous analysis of low-concentration and high-concentration components of the constitution. As you can see in this curve,
When the value of k is large and the density cell length product exceeds 2% m, the output signal is saturated and the change in the output signal when the density increases becomes small.

On the other hand, the curve of k = 0.1 shows that the value of the extinction coefficient for the gas component to be measured is the absorption center wavelength as a result of restricting the detection wavelength region of the detection unit 7 for analyzing the high concentration gas component by the method of the present invention. It illustrates the relationship of the cell length concentration product cL of the gas component to be measured with respect to the output signal S of the detection unit 7 when it becomes 1/10 of the value in the range. In this case, the value of the output signal at the maximum concentration cell length product of 5% m is reduced to about 40% when the value of the extinction coefficient is 1, so that the output signal value at the maximum concentration cell length product is k = 1.0, the analytical characteristics when amplified to the same value are shown as the normalized output in the figure.

As described above, in the infrared absorption due to the gas component, since the region showing the weak absorption is distributed adjacent to the absorption central wavelength region showing the strong absorption, the infrared light source unit 2
By changing and adjusting the partial pressure of the gas component 10 to be measured, which has a measurement range up to the high-concentration range to be sealed in, the absorption infrared wavelength range emitted from the infrared light source unit 2 is cut off, and the remaining infrared intensity wavelength distribution is obtained. Can be changed.

When a multilayer thin film interference filter is applied as the optical bandpass filter 7B provided in the detection unit 7 for measuring high concentration gas components, the boundary wavelength of its transmission band is basically determined by the structural design of the thin film layer. , In addition,
The distribution reflects the changes in the conditions during production. Therefore, by adjusting the partial pressure of the gas 10 enclosed in the infrared light source unit 2 and selecting the optical bandpass filter 7B included in the detection unit 7, the intensity of the infrared light incident on the infrared sensor 7A, which is a component of the detection unit 7, is adjusted. The wavelength distribution of can be changed to some extent.

When the wavelength distribution of the infrared intensity used for analysis is changed by the above means, the value of the equivalent extinction coefficient of the component to be measured in the wavelength range of interest, which is determined by the principle of equation (2), is also changed to some extent according to this change. It can be changed, and as a result, the linearity as an analysis characteristic also changes. When the maximum value of the product cL of the concentration c of the gas component to be measured and the cell length L of the measurement cell is 5% m, the value of the equivalent extinction coefficient of the gas component to be measured is adjusted by the above method. Then, the value of the concentration analysis signal S represented by the equation (3) detected by the infrared sensor 7A in the concentration cell length product cL is obtained, and the value of the concentration analysis signal at the maximum value 5% m of the concentration cell length product is obtained. Table 1 shows FS and the linearity of the concentration analysis signal S obtained with the value of the concentration cell length product being zero and the value at the maximum value of 5% m as the both ends reference. The value of the concentration analysis signal S normalized by the value FS of the concentration analysis signal at the highest value of the concentration cell length product is shown in FIG.

[0037]

[Table 1]

As shown in Table 1 and FIG. 7, in the infrared analyzer in which the detection wavelength range of the detection unit 7 for high-concentration gas component analysis is restricted by the method of the present invention, the absolute value of the output signal S of the detection unit 7 is reduced. The value is slightly reduced, but the linearity is greatly improved. As described above, if the cut function for removing infrared rays in the wavelength range that is inconvenient for the measurement of high-concentration components is imparted by the gas itself of the measurement target component that exhibits strong absorption in the wavelength range, the cut wavelength range is the molecule of the gas. Since it depends on the structure itself, the cut region can be defined extremely accurately as compared with a thin film interference type optical bandpass filter that artificially controls the thickness of the thin film to determine the transmission wavelength range.

Further, the boundary wavelength of the transmission band of the optical bandpass filter 7B provided in the high-concentration gas component measuring detection unit is a region where the absorption coefficient of the component to be measured largely changes depending on the wavelength even if there is some manufacturing error. Since the component to be measured is designed outside the region showing absorption, the absorption in the wavelength region adjacent to the absorption center wavelength region in the measurement cell is the range of the transmission band of the optical bandpass filter 7B. Fits inside. Therefore, the output signal of the infrared sensor 7A of the high-concentration gas component measuring detection unit 7 has the same magnitude for the same concentration change even if there is some manufacturing error in the transmission band of the optical bandpass filter 7B. , The transmission wavelength range of the optical bandpass filter 7B as in the infrared gas analyzer according to the prior art in which the transmission wavelength range of the optical bandpass filter 7B is set to a narrow range of the region where the absorption coefficient k is small in the absorption band of the gas to be measured. The relationship between the electric signal S detected by the infrared sensor 7A and the concentration c of the component gas to be measured does not change significantly due to a slight difference in the center wavelength of the band or the band width.

Further, in an infrared gas analyzer for analyzing a plurality of components for simultaneously and continuously measuring a low concentration gas component and a high concentration gas component in the same sample gas, a detection unit for measuring the low concentration gas component is used. The boundary wavelength of the transmission band of the optical bandpass filter 7B mounted on the No. 7 is set to a range overlapping with the absorption center of the gas component to be measured, and the length of the sample cell can stably measure the low concentration gas component. Set to a long value.

On the other hand, for the high-concentration gas component, the infrared light source section 2 formed in a sealed structure absorbs the gas to be measured 10 of the component whose measurement range is up to the high-concentration region or the absorption wavelength region of the measurement target component. An alternative gas having a wavelength range is enclosed at a partial pressure sufficient to completely absorb infrared rays in the absorption center wavelength range of the gas, and the boundary wavelength of the transmission band of the optical bandpass filter 7B provided in the detection unit 7 is measured. The wavelength is set just outside the absorption band of the target gas component, and the sample cell has a configuration in which the cell length is set so as to be suitable for the measurement of low-concentration gas components.

When the non-dispersion type infrared gas analyzer for low and high concentration multi-component analysis is constructed as described above according to the present invention, the low concentration gas component has a large absorption coefficient and the gas to be measured has a large absorption coefficient. While the light in the absorption center wavelength range of is captured with high sensitivity and stability, for high-concentration gas components, the light in the wavelength range where the value of the absorption coefficient outside the absorption center wavelength range of the gas is small is detected. Since the measurement is performed, even if a sample cell with a long cell length set to be suitable for measuring low-concentration gas components is used in common, the output is not saturated and the measurement is performed linearly up to the high-concentration range. .

[0043]

When the infrared gas analyzer for simultaneously analyzing low-concentration gas components and high-concentration gas components is constructed as described above, as described above, the components of the measured gas having high concentrations are , In the measurement cell, since the absorption of infrared rays in the wavelength range where the value of the absorption coefficient adjacent to the absorption center wavelength range is small occurs, even if a measurement cell with a long cell length suitable for the analysis of low-concentration gas components is commonly used, Absorption due to high-concentration gas components is no longer saturated. As a result, the reference linearity at both ends was about 54% when measured by an apparatus having a conventional structure in which the gas to be measured 10 was not enclosed in the infrared light source section 2, which made it practically impossible to analyze in the high concentration range. According to the present invention, the measured object has a partial pressure and light of the gas to be measured enclosed in the infrared light source section 2 so that the value of the equivalent absorption coefficient is about 40% to 50% of the value in the conventional apparatus. Under the condition that the maximum value FS of the concentration analysis signal is slightly reduced to 95% by selecting the transmission band of the bandpass filter,
The results show that the linearity at both ends can be measured while being reduced to 35%, which can withstand practical use. That is, according to the present invention, by using a single infrared gas meter of a multi-component gas, which has a simple structure and has a simple structure and is inexpensive, both the low-concentration gas component and the high-concentration gas component are It is possible to obtain the effect that the linearity can be maintained and the measurement can be performed accurately.

Since the light source is filled with a gas component having a high-concentration region as a measurement range and is provided with a cutting function for removing infrared rays in a wavelength region which is inconvenient for measuring the high-concentration component, detection of the high-concentration gas component is performed. Even if an optical bandpass filter with a wide transmission wavelength range is selected so that the sensitive wavelength band of the unit corresponds to almost the entire absorption band of one gas to be measured, the effective transmission range will not change in concentration. In contrast, a relatively narrow range where sufficient change can be obtained, the concentration vs. output characteristics are stable, and non-linearity tests and adjustments by electrical circuits are not required each time the analyzer is manufactured. The effect that can be obtained is also obtained.

Further, in order to prolong the life of the infrared light source, an inert gas may be filled in the light source section. In the present invention, this filled gas is, for example, a CO ₂ gas to be measured. In this case, the gas to be measured can be used as a substitute, and in this case, it is not necessary to separately install an optical filter, and an effect that an infrared gas analyzer can be economically constructed can be obtained.

Not only the infrared gas meter for multi-component analysis but also an optical band pass filter having a transmission band in the absorption center wavelength region of the gas component to be measured is used, the cell length of the measurement cell is set to a gas inlet / outlet. If the method of the present invention is applied to an infrared gas analyzer for the purpose of measuring a gas component having a large extinction coefficient over a high concentration that must be shortened so that it is difficult to measure, it is possible to measure the introduction and replacement of the sample gas reasonably. The effect that the cell length of the cell can be set is also obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of the essential parts of an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a main part configuration of an infrared gas analyzer according to a conventional technique.

FIG. 3 is a sectional view showing the configuration of the main part of an infrared gas analyzer according to another conventional technique.

FIG. 4 is an explanatory diagram for explaining properties of an infrared absorption spectrum and a transmission wavelength range of an optical bandpass filter.

FIG. 5 is an explanatory view for explaining a wavelength range of infrared rays detected by a detection unit for analyzing a high concentration gas component of an infrared gas analyzer according to the present invention.

FIG. 6 is an explanatory diagram for explaining the influence of the value of the extinction coefficient on the relationship between the cell length concentration product and the output signal in the infrared gas analyzer.

FIG. 7 is an explanatory diagram illustrating the relationship between the value of the extinction coefficient and the normalized concentration analysis signal S.

[Explanation of symbols]

 1 Measuring Cell 2 Infrared Light Source Section 3 Rotating Sector 5 Detection Block 6 Sensor Mounting Block 7 Detection Unit 7A Infrared Sensor 7B Optical Bandpass Filter 8 Infrared Luminous Beam 9 Infrared Transmission Window 10 Measured Gas

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kozo Akao No. 1 Tanabe Shinden, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. No. 1 inside Fuji Electric Co., Ltd.

Claims (6)

[Claims] 1. A non-selective infrared sensor, an optical bandpass filter placed in front of the infrared sensor, an infrared light source section having an infrared transmitting window, and an airtightly configured infrared light source section. A non-dispersive infrared gas analyzer, comprising: a gas to be measured sealed at a partial pressure of. 2. A gas to be measured enclosed in an airtight infrared light source section having the same molecular structure as that of the gas to be measured and exhibiting an infrared absorption equivalent to one infrared absorption by the gas to be measured. The non-dispersive infrared gas analyzer according to claim 1, wherein the gas has a component different from that of the gas, and the gas is sealed at a predetermined partial pressure. 3. The transmission wavelength band of the optical bandpass filter corresponds to the entire absorption band of one gas to be measured, and the spectral sensitivity of the non-selective infrared sensor is flat in the transmission wavelength band of the optical bandpass filter. The non-dispersive infrared gas analyzer according to claim 1 or 2, which has characteristics. 4. An infrared gas analyzer for simultaneous analysis of a plurality of components, comprising: a plurality of pairs of a non-selective infrared sensor and an optical bandpass filter; And a gas of a specific component of the gas components to be measured enclosed in the infrared light source unit at a predetermined partial pressure, and a single measurement cell common to the plurality of components. Dispersive infrared gas analyzer. 5. The gas enclosed in the hermetically-sealed infrared light source section has the same molecular structure as the gas of a specific component among the gas components to be measured, and one infrared absorption by the gas to be measured. The non-dispersive infrared gas analyzer according to claim 4, wherein the gas has a component different from that of the gas to be measured that exhibits the same infrared absorption, and the gas is sealed at a predetermined partial pressure. 6. A characteristic in which the transmission wavelength band of the optical bandpass filter corresponds to the entire one absorption band of the gas to be measured, and the spectral sensitivity of the non-selective infrared sensor is flat in the transmission wavelength band of the optical bandpass filter. The non-dispersive infrared gas analyzer according to claim 5 or 6, characterized in that