JPH0135292B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a multi-component infrared gas analyzer that can be miniaturized by substantially eliminating an interference cancellation cell.

[Prior art]

Infrared gas analyzers, which measure the content and concentration of gases by utilizing the fact that each component contained in the gas absorbs infrared rays in a certain wavelength range, have a wide measurement concentration range and are capable of measuring multiple components. It has many advantages, such as being able to detect one component in the gas and being highly selective, being able to continuously and quickly analyze each component, and almost all gases absorb infrared rays, so it can be used for various process control and has a wide range of applications. It has excellent characteristics. This type of infrared gas analyzer generally irradiates a sample cell (sample cell) containing a gas to be measured in the form of a mixed gas such as CO, CO ₂ , CH ₄ , etc. with infrared rays, and then detects the transmitted light that has passed through the cell. The detected values of each gas component are compared and measured by passing it through a special filter installed on a rotor that rotates at a constant rotational speed, and then electrically detecting it with a photoelectric conversion element such as a semiconductor element (photocell). is configured to do so.

By the way, in such an infrared gas analyzer, when performing quantitative analysis of a gas mixture of two or more components, an optical filter is usually installed that passes only infrared rays in a specific wavelength range in order to eliminate interference from gas components other than the gas to be measured. are using. However, if a gas component having an absorption wavelength in the passage region of this filter exists on the optical path, interference will occur due to this gas component. Therefore, as a means for removing this interference, it is common practice to dispose an interference removal cell filled with an interference component gas on the optical path.

Here, a conventional infrared analyzer using an interference removal cell will be briefly explained based on FIG.
3 is a rotor that rotates at high speed, and 4 is a reference chamber that is filled with the same gas as the measurement gas (CO ₂ ) at _a high concentration. A cell 5 is an inert gas-filled cell filled with a gas (usually _N2 gas) that is inert to infrared rays (does not absorb infrared rays); 6 is an inert gas-filled cell that absorbs in the infrared overwavelength region that passes through the reference cell 4; Interference removal cell filled with a high concentration of gas with a wavelength as an interference component gas,
7 is a condenser, 8 is a detector, and the reference cell 4 and the inert gas-filled cell 5 are arranged on the rotor 3. Further, both cells 4 and 5 are each equipped with a narrowband transmission type interference filter 9 that allows only the vicinity of the absorption wavelength band (4.3 μm) to be measured to pass through and blocks the passage of other wavelength bands.
Therefore, when the sample cell 4 filled with CO ₂ gas is irradiated with infrared rays from the light source 1, its transmission characteristics change to the center wavelength as shown in FIG.
Infrared rays in the wavelength range of 4.3 μm and a half width of 0.2 μm or less are transmitted.

When measuring CO ₂ gas, first
When the gas to be measured 10 inside is ignored, the infrared rays emitted from the light source 1 pass through the reference cell 4 and the inert gas-filled cell 5, which alternately cross the optical path 11 as the rotor 3 rotates, and further eliminate interference. After passing through the cell 6, the light is collected by a condenser 7 and sent to a detector 8.
Detected in The variation in the amount of light at this time is shown in FIG. 3, where a is the amount of infrared light that has passed through the inert gas filled cell 5, and b is the amount of infrared light that has passed through the reference cell 4. The black vertical line in Figure b is the amount of light absorbed by CO ₂ , which is
This is because absorption of CO ₂ does not occur at all wavelengths around 4.3 μm, but only at certain specific (plural) wavelengths around 4.3 μm. The amount of light (shaded area) in figure a is converted into an electrical signal by the detector 8, which is amplified by the amplifier and becomes a measurement signal (voltage), and the amount of light shown in b (shaded area) is also detected. The signal is converted into an electrical signal by the converter 8 and becomes a reference voltage.

Next, if CO ₂ is present in sample cell 2,
Since infrared rays having a wavelength of around 4.3 μm are absorbed by CO ₂ (absorption as shown in FIG. 3b also occurs in this case), the amount of measurement light transmitted through the inert gas-filled cell 5 decreases. Similarly, the amount of reference light transmitted through the reference cell 4 also decreases due to absorption by CO ₂ in the sample cell 2, but the proportion of this decrease has already been absorbed by the CO ₂ in the sample cell 2.
This is smaller than the decrease in the amount of light in the inert gas filled cell 5. The arithmetic circuit is usually constructed so that the output becomes positive when [reduction rate of measurement light>reduction rate of reference light].

If the relationship between the concentration of CO ₂ gas and the output is measured in advance, the concentration of the actual gas can be measured.

By the way, if a gas having an absorption wavelength in the transmission wavelength region of the narrowband transmission type interference filter 9 (for example, CO as opposed to CO ₂ ) exists in the sample cell 2, interference will occur. In this case _, whether the output shifts to positive or negative depends on the difference in absorption wavelength between the interference component gas and the gas to be measured (CO ₂ ). (b) When the absorption wavelength of the interfering component gas does not overlap with the absorption wavelength of CO ₂ ; and (c) When the absorption wavelength of the interfering component gas partially overlaps with the absorption wavelength of CO ₂ but not others. There is.

In the case of (a), if the interference gas has an absorption wavelength at the absorption wavelength λa of CO ₂ as shown in Figure 4 a and b, then [reduction rate of measurement light > reduction rate of reference light], and the interference gas The output shifts positively. On the other hand, in case (b), as shown in c and d of the same figure, if the interference gas has an absorption wavelength at a wavelength λb other than the absorption wavelength of CO ₃ , [reduction rate of measurement light < reduction rate of reference light]. , the output shifts negatively. For example, if the measurement light 10 is decreased by 1 and the reference light 5 is also decreased by 1, these correspond to 10% and 20%, respectively, and the above-mentioned unreasonable expression < holds true. In the case of (c), if the interfering gas has an absorption wavelength in the part λa that overlaps with CO ₂ and the part λb that does not overlap with CO 2, as shown in e and f in the same figure, the absorption ratio between λa and λb will be Due to the difference in the rate of decrease of the measurement light > the rate of decrease of the reference light, three cases occur: 〃 〃 < 〃 〃 〃 〃 = 〃 〃, and the shift due to the interference gas is positive, negative, or 0 (nothing).

If a gas component having an absorption wavelength in the passage area of the narrowband transmission interference filter 9 exists on the optical path 11, it will cause interference.To prevent this, conventional interference removal cells filled with interference component gas have been used. 6 is disposed on the optical path 11, but in such a configuration, the length in the optical axis direction becomes long,
The analysis department, in other words, the analyzer itself, will become longer.
Moreover, there was the problem that one cell was added as a component.

Therefore, as a solution to this inconvenience, for example, an additional filter point may be provided in a reference cell in which each measurement gas component is individually sealed.
There is a multi-component infrared spectrometer (Japanese Patent Publication No. 34814/1983) in which an interference removal cell is substantially eliminated by enclosing an interfering gas component therein. but,
Even in such a device, it is necessary to fill each reference cell with an interfering gas component in a saturated state at the same concentration, which is troublesome.

[Summary of the invention]

The present invention has been made in view of the above-mentioned points, and includes a plurality of reference cells individually filled with each measurement gas component, the same number of inert gas filled cells as these reference cells, and a measurement target. A sample cell to which a gas is supplied, and an interference gas is supplied to either the reference cell or the corresponding inert gas filled cell so that the attenuation ratio due to the interference gas is approximately the same for both cells. The purpose of the present invention is to provide a multicomponent infrared gas analyzer which can simplify the effort required to enclose interference gas by encapsulating the interfering gas.

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

〔Example〕

FIG. 5 is a sectional view showing one embodiment of the present invention, and FIG.
The figure is a front view of the rotor. In these figures, 20 is a motor that rotates the rotor 3 at a constant speed, 21 is an amplifier, and 22 is a reference cell 4 and an inert gas-filled cell 5 formed on the rotor 3 together with a narrowband transmission type interference filter 9. An infrared transparent window (eg calcium fluoride (CaF ₂ )).

As the reference cell 4, the rotor 3
Two pieces are formed on the same circumferential surface centered on the rotation center at appropriate intervals in the circumferential direction, and one of the four
For example, CO ₂ as a measurement gas component is sealed in 4b at a high concentration, and 4b is filled with other measurement gas components.
Contains a high concentration of CO. Similarly, two inert gas filled cells 5 are provided on the rotor 3 on the same circumference as the reference cell 4, corresponding to each reference cell 4a, 4b,
Each of them is filled with N ₂ and O ₂ gases (usually N ₂ gas) that are inert to infrared rays.

Here, when measuring by continuously supplying a mixed gas containing CO ₂ and CO, which have absorption spectra at 4.3 μm and 4.7 μm, respectively, as the measurement target gas 10 to the sample cell 2, one of the measurement targets Since the gas (CO) to be measured, which is the other gas (for example, CO ₂ ), has an absorption wavelength in the transmission wavelength region of the same narrow band transmission interference filter 9, it acts as an interference gas. Similarly, CO ₂ acts as an interfering gas when measuring CO. Therefore, the gas to be measured, CO ₂
The one reference cell 4a is enclosed with
(or the inert gas filled cell 5a corresponding to the reference cell 4a) is further filled with CO as an interference gas. The concentration of CO is determined by the measurement light transmitted through the sample cell 2 and inert gas-filled cell 5a and detected by the detector 8, and the reference light transmitted through the sample cell 2 and reference cell 4a and detected. The reduction rate is set to be approximately the same. Similarly, the other reference cell 4b (or the inert gas filled cell 5b corresponding to the reference cell 4b) filled with the measurement target gas CO is also filled with CO ₂ as an interference gas, and its concentration is as follows. Set so that the reduction rate of the measurement light transmitted through the sample cell 2 and the inert gas filled cell 5b and the reference light transmitted through the sample cell 2 and the reference cell 4b is approximately the same. has been done.

When enclosing an interfering gas (CO, CO ₂ ), as mentioned above, due to the difference in absorption wavelength between the interfering gas and the gas to be measured, (a) if the absorption wavelength of the interfering component gas overlaps with the absorption wavelength of CO ₂ , (b) There are three cases: (a) no overlap and (c) a partial overlap.In the case of (b), interference gas is filled in the inert gas filled cells 5a and 5b, respectively, and the measurement target is Reduce the rate of decrease and eliminate interference (at a certain concentration of interfering gas, interference becomes 0). On the other hand, in the case of (b) when there is no overlap, interference gases (CO, CO 2 ) are filled in the reference cells 4a and 4b together with the gas to be measured (CO ₂ , _CO ) to reduce the rate of decrease in the reference light. , reduce the interference (at a certain concentration of the interfering gas the interference becomes 0). And (c)
If some of them are heavy and others do not overlap, then by knowing whether the output shift direction is positive or negative depending on the reduction ratio of the measurement light and reference light, if it is positive, use the above (a), and if it is negative, use the above (b) is adopted to reduce interference (interference becomes 0 at a certain concentration of interfering gas).

Note that when each of the interference gases (CO, CO ₂ ) is sealed in the inert gas filled cells 5a, 5b, these cells 5a, 5b substantially constitute an interference removal cell, so the inert gas N ₂ does not require inclusion.

Further, in FIG. 5, the same components as those in FIG. 1 are designated by the same reference numerals, and their explanations will be omitted.

According to the infrared gas analyzer having such a configuration, the interference gas (CO, CO ₂ ) is sealed in either the reference cells 4a, 4b or the inert gas filled cells 5a, 5b. , the interference cancellation cell 6 shown in FIG. 1 can be removed, and therefore the optical path 11 can be shortened by the length of the interference cancellation cell 6.

In addition, the concentration of the interference gas (CO, CO ₂ ) is changed so that the rate of decrease in the measurement light and the rate of decrease in the reference light are approximately the same, and the interference gases (CO, CO 2 ) are used in the reference cells 4a and 4b.
Alternatively, it is sufficient to fill either one of the inert gas filled cells 5a, 5b, respectively, so the work of filling the interfering gas is easier than filling both of them, and moreover, the interfering gas is filled in the inert gas filled cells 5a, 5b. In this case, it is not necessary to fill in the inert gas itself, which is economical.

Furthermore, conventionally, interference gas must be sealed at a high concentration, and in particular, the reference cells 4a and 4b must also be filled with a gas to be measured at a high concentration due to their properties. For this reason, the reference cells 4a, 4b
As the internal pressure of the infrared ray transmitting window 22 increases, it is necessary to increase the adhesive strength of the infrared transmitting window 22. Therefore, there is a method of increasing the cell length in order to lower the internal pressure, but this method has the disadvantage of increasing the size of the structure.

On the other hand, the present invention can solve the above-mentioned problem because it is sufficient that the concentration is such that the reduction rate of the measurement light and the reference light are almost equal.

If the concentration of the interfering gas in the sample cell 2 changes during the process of continuous measurement, a multicomponent error will occur, but this will not cause any practical problems in process measurement.

Note that the above example uses two component gases (CO ₂ and CO).
Although the present invention is not limited to this, it is also possible to measure three components such as CO ₂ , CH ₄ , and CO, and in that case, three reference cells and three inert gases are required. Encapsulated cells are used.

〔Effect of the invention〕

As explained above, the multi-component infrared gas analyzer according to the present invention has an interference gas in either the reference cells individually filled with the gases to be measured or the corresponding inert gas filled cells. Since the interference gas is filled in so that the reduction rate of the measurement light and the reference light is almost the same in both cells, there is less effort to fill in the interference gas, and when it is filled in an inert gas filled cell, it is possible to fill in an inert gas. Since there is no need to fill in gas, and the reference cell or inert gas filled cell also serves as an interference removal cell, the interference removal cell that was previously required can be removed, shortening the optical path, or in other words, making it easier for the analyzer to Enables downsizing. Further, by removing the interference cancellation cell, the number of cells is reduced by one, and an inexpensive analyzer can be provided.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing an example of a conventional infrared gas analyzer, Figure 2 is an absorption spectrum showing the transmission characteristics of CO ₂ , and Figures 3 a and b are transmission through an inert gas-filled cell and a reference cell, respectively. Figures 4a to 4f are diagrams showing the relationship between the amount of infrared rays and the wavelength;
The figure is a sectional view showing an embodiment of the multi-component infrared gas analyzer according to the present invention, and FIG. 6 is a front view of the rotor. 1...Light source, 2...Sample cell, 3...Rotor, 4, 4a, 4b...Reference cell,
5, 5a, 5b...Inert gas filled cell, 8...
Detector, 9...Narrowband transmission type interference filter, 10
...Gas to be measured, 11...Optical path.

Claims (1)

[Claims] 1. A plurality of reference cells individually filled with two or more measurement gas components and a plurality of inert gas filled cells corresponding to these reference cells are mounted on a rotor rotating at high speed from the rotation center of the rotor. The sample cells are arranged circumferentially at equal distances apart in the radial direction, and the light transmitted through each reference cell is compared with the light transmitted through the corresponding inert gas-filled cell, and the gas inside the sample cell is always on the optical axis. In a multi-component infrared gas analyzer that detects the respective concentrations of a plurality of gas components, either the reference cell or the corresponding inert gas-filled cell has an attenuation ratio due to an interference gas in both of them. A multi-component infrared gas analyzer characterized by filling an interference gas so that the cells are almost the same.