WO2019172584A1 - Gas analyzer using hitran data and multi-filter, and gas analyzing method - Google Patents

Abstract

The present invention relates to a gas analyzer for analyzing the concentration of a gas to be measured, on the basis of high resolution transmission (HITRAN) data, the gas analyzer comprising: an analyzer body for providing a space in which a gas to be measured is received and measured; a light emitting member installed in the analyzer body to irradiate an infrared ray to the gas to be measured; a transmission unit installed at a part of the analyzer body to transmit a gas in a specific wavelength band; a detector installed at a part of the analyzer body to detect a gas having passed through the transmission unit; and a controller connected to the light emitting member, the transmission unit and the detector to control operations of the light emitting member, the transmission unit and the detector, wherein the transmission unit includes one or more elements, and the elements are arranged in series with each other.

Description

Gas analyzer and gas analysis method using heatlan data and multi filter

The present invention relates to a gas analyzer and a gas analysis method, and more particularly, to a heat analyzer data and a gas analyzer using a multi filter and a gas analyzer and a gas analysis method using a heat filter and a multi filter.

Increasing energy consumption due to industrialization has caused pollutants to be released into the atmosphere, which has led to serious social problems. In particular, in order to prevent pollutants emitted into the atmosphere in a gaseous state, it is essential to understand the components and concentrations of the gases emitted from factories.

In general, gas containing complex harmful substances is emitted from the chimneys of workplaces such as thermal power plants, general boiler facilities, incineration plants, chemical manufacturing facilities, cement plants, steel mills, semiconductor manufacturing facilities, and oil refining facilities. . Therefore, the development of monitoring and measurement equipment has been steadily maintained in order to manage the concentration of the emission gas generated from the air source in real time.

NDIR (Non-Dispersive Infrared Absorption) analysis is widely used as a method of measuring the components contained in the gas. NDIR analysis uses the phenomenon that each component contained in the gas absorbs energy of a specific wavelength of infrared light passing through the gas, and then investigates the energy level of each wavelength of infrared light passing through the gas to identify the components contained in the gas. .

The conventional NDIR measurement method has a limitation in correcting errors caused by interference gases, and recently, it is widely used to compensate for the effect of concentration interference between gases by mounting a gas filter correlation (GFC). Plants such as thermal power plants, incinerators, and chemical process facilities emit various types of gases, including carbon monoxide (CO), carbon dioxide (CO2), sulfur dioxide (SO2), nitrogen monoxide (NO), nitrogen dioxide (NO2), and ammonia ( NH3), hydrogen chloride (HCl), hydrogen fluoride (HF), methane (CH4), water vapor (H20), etc. can be seen as the main components. These emissions have their own unique IR absorption wavelengths, some of which are very close to the IR absorption wavelengths and can interfere with IR absorption. For example, carbon monoxide (CO) has an absorption wavelength of 4.6 µm and carbon dioxide (CO2) has an absorption wavelength of 4.3 µm, and water vapor (H2O) has absorption wavelengths ranging from 2 to 10 µm. Therefore, when these components coexist, the exact concentration cannot be determined due to the interference effect. In order to overcome this disadvantage, GFC is being used as part of the compensation between the interference gases.

However, even in the case of GFC-applied NDIR devices, the measurement is not performed properly when the concentration of the interference gas rises above a certain level. In other words, if the component to be analyzed (eg CO) is within the range of the NDIR device's analytical concentration, if the concentration of other interfering gases (eg CO2) is high, an error occurs in the measured value of the NDIR device even if GFC is used. Done. Therefore, there is a limit to accurately measure the concentration of exhaust gas by using only NDIR with GFC. In addition, GFC fills a certain concentration of gas in the gas filter. This method also has a problem of gas leakage when used for a long time, so a correction method for measurement error is necessary.

Accordingly, the present invention has been made to solve the above problems, the problem to be solved of the present invention is to minimize the error of the concentration range of the gas to be measured, the heat column data with a function capable of measuring the precise concentration wavelength band And to provide a gas analyzer and a gas analysis method using a multi-filter.

However, the technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned above are clearly apparent to those skilled in the art from the following description. It can be understood.

The present invention was created to improve the problems of the prior art as described above, a gas analyzer for analyzing the concentration of the gas to be measured based on heatlan data, the gas to be measured is provided to provide a space for gas measurement Analytical primitives; A light emitting member installed inside the analysis main body to irradiate infrared rays to the measurement target gas; A transmission unit installed at a portion of the analysis base member to transmit gas of a specific wavelength band; A detector installed at a portion of the analysis base unit to detect gas passing through the transmission unit; And a controller connected to the light emitting member, the transmission unit, and the detector to control the operation of the light emitting member, the transmission unit, and the detector. It includes, the transmission unit, made of at least one configuration and each configuration may be arranged in series with each other.

The transmission unit may include: a first filter configured to transmit a gas having a predetermined wavelength in a region of the gas introduced into the analysis body without attenuation; And a second filter corresponding to the first filter to transmit, without attenuation, a wavelength of a specific region other than a predetermined region of the gas transmitted through the first filter. It may include.

In addition, the first and second filters may be positioned to be attached or separated from each other.

The first and second filters may further include a band pass filter that passes only signals within a specific frequency band without attenuation and attenuates the remaining frequency signals; Can be.

In addition, the first and second filters may cross each other so that an error range overlaps for precise measurement of the measurement target gas to form an interference-free zone.

The transmission unit may further include a third filter in addition to the first and second filters.

The transmission unit may further include a fourth filter in addition to the third filter.

In addition, the water removal device for reducing the relative humidity by evaporating the water inside the analysis main body under the control of the controller; It may further include.

A gas analysis method for analyzing the measurement target gas using a gas analyzer that analyzes the concentration of the measurement target gas based on the above-described heat column data. The measurement target gas for selecting the measurement target gas based on the heater column data. Selection step; An infrared irradiation step of irradiating infrared rays to the measurement target gas selected in the measurement target gas selection step by using a light emitting member provided in the gas analyzer; A gas permeation step of transmitting a gas of a specific wavelength band using a transmission unit which is a band pass filter provided in the gas analyzer to the gas that has passed through the infrared irradiation step: and confirms a concentration wavelength band error range of the gas that has passed the gas transmission step An error range checking step; It may be made, including.

In addition, the gas permeation step may be arranged in series with at least one band pass filters.

The gas permeation step may include a first permeation step of permeating a gas having a wavelength in a predetermined region using the band pass filter without attenuation among the gases introduced into the gas analyzer; And a second transmission step of transmitting a wavelength of a specific area band other than a predetermined area band of the gas transmitted in the first transmission step without attenuation using the band pass filter in correspondence with the first transmission step. It may be made, including.

In addition, an interference-free zone forming step of forming an interference-free zone by crossing each of the error ranges identified through the error range checking step to overlap the measurement target gas for precise measurement; It may be made to include more.

In addition, the gas analyzer is provided with a water removal device to reduce the relative humidity by evaporating the water inside the gas analyzer.

According to an embodiment of the present invention, the first and second band pass filters corresponding to the two bands are arranged in series by using heat experiment data, so that the error ranges of the band pass filters are intersected, thereby providing a more precise band pass filter. Can be implemented.

In addition, according to an embodiment of the present invention, even without the use of expensive GFC using the dual band pass filter as described above it is possible to analyze the concentration with little interference between gases and cost is reduced.

However, effects obtained in the present invention are not limited to the above-mentioned effects, and other effects not mentioned above will be clearly understood by those skilled in the art from the following description. Could be.

The following drawings, which are attached in this specification, illustrate preferred embodiments of the present invention, and together with the detailed description of the present invention, serve to further understand the technical spirit of the present invention. It should not be construed as limited to.

1 is a conceptual diagram schematically illustrating a gas analyzer using heatlan data and a multi-filter according to an embodiment of the present invention.

2 is a control block diagram of the controller.

3 is a block diagram of the transmission unit.

FIG. 4 is a first flowchart of a gas analysis method using hit-ran data and a multi-filter according to an embodiment of the present invention.

5 is a detailed flowchart of the gas permeation step.

6 is a second flowchart of the gas analysis method.

7 is a graph showing HITRAN spectra of various gases.

8 is a graph showing the spectra of two commercial BPFs for NO gas in accordance with one embodiment of the present invention.

9 is a graph showing the calibration curve of the NO gas (NO concentrations vary from 10, 50, 100, 200 ppm).

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. However, since the description of the present invention is only an embodiment for structural or functional description, the scope of the present invention should not be construed as being limited by the embodiments described in the text. That is, the embodiments may be variously modified and may have various forms, and thus, the scope of the present invention should be understood to include equivalents for realizing the technical idea. In addition, the objects or effects presented in the present invention does not mean that a specific embodiment should include all or only such effects, the scope of the present invention should not be understood as being limited thereby.

The meaning of the terms described in the present invention will be understood as follows.

Terms such as "first" and "second" are intended to distinguish one component from another component, and the scope of rights should not be limited by these terms. For example, the first component may be named a second component, and similarly, the second component may also be named a first component. When a component is referred to as being "connected" to another component, it should be understood that there may be other components in between, although it may be directly connected to the other component. On the other hand, when a component is said to be "directly connected" to another component, it should be understood that there is no other component in between. On the other hand, other expressions describing the relationship between the components, such as "between" and "immediately between" or "neighboring to" and "directly neighboring to", should be interpreted as well.

Singular expressions should be understood to include plural expressions unless the context clearly indicates otherwise, and terms such as "include" or "have" refer to features, numbers, steps, operations, components, parts, or parts thereof described. It is to be understood that the combination is intended to be present and does not exclude in advance the possibility of the presence or addition of one or more other features or numbers, steps, operations, components, parts or combinations thereof.

All terms used herein have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise defined. Generally, the terms defined in the dictionary used are to be interpreted as being consistent with the meanings in the context of the related art, and should not be interpreted as having ideal or excessively formal meanings unless clearly defined in the present invention.

1 is a conceptual diagram schematically showing a gas analyzer using heatlan data and a multi-filter according to an embodiment of the present invention, FIG. 2 is a control block diagram of the controller, and FIG. 3 is a block diagram of the transmission unit. 4 is a first flowchart of a gas analysis method using heatlan data and a multi-filter according to an embodiment of the present invention, FIG. 5 is a detailed flowchart of the gas permeation step, and FIG. FIG. 7 is a graph showing HITRAN spectra of various gases, FIG. 8 is a graph showing spectra of two commercial BPFs for NO gas according to an embodiment of the present invention, and FIG. A graph showing the calibration curve (NO concentrations vary from 10, 50, 100, 200 ppm).

As shown in Figures 1 to 3, as a gas analyzer for analyzing the concentration of the gas to be measured on the basis of the heat column data, the present invention is the analysis base 100, the light emitting member 200, the transmission unit 300, The detector 400 and the controller 500 may be included.

Heatlans are the world standard for calculating or simulating the transport and radiation of molecules in the atmosphere from microwaves through the ultraviolet region of the spectrum. The current version contains 49 molecular species with the most important isotopes. This data is stored as numerous high resolution line transitions containing many of the spectral parameters required for high resolution simulations.

The analysis main body 100 may accommodate a gas to be measured to provide a space for gas measurement.

The light emitting member 200 may be installed inside the analysis main body 100 to irradiate infrared rays to the measurement target gas.

The transmission unit 300 may be installed at a portion of the analysis base 100 to transmit gas of a specific wavelength band. The transmission unit 300 is composed of at least one configuration and each configuration may be arranged in series with each other.

The transmission unit 300 may include a first filter 310 and a second filter 320.

The first filter 310 may transmit a gas having a predetermined wavelength in the region of the gas introduced into the analysis body 100 without attenuation.

The second filter 320 may transmit the wavelength of a specific region other than the predetermined region band of the gas transmitted through the first filter 310 without attenuation in correspondence with the first filter 310. The first and second filters 310 and 320 may be attached to or separated from each other.

The first and second filters 310 and 320 may pass through only a signal within a specific frequency band without attenuation and attenuate the remaining frequency signals.

A band pass filter or a band pass filter is a filter that attenuates a frequency of a band. The band pass filter or a band pass filter is a filter that passes only signals within a specific frequency band without attenuation, and attenuates the remaining frequency signals.

Specifically, the joint of the low pass filter (LPF) and the high frequency filter (HPF) may be referred to as a band pass filter, where the low pass filter (LPF) removes high frequency components or noise. It is used in digital image processing to produce a smooth image. Low pass filters are usually based on a moving average or median approach. The median of the two is considered to be superior because the derived image constitutes the original image value, unlike the moving average filter.

A high pass filter (HPF) is used to remove or suppress low frequency components. Usually high frequency filters are used in combination with homogeneous low frequency filters. For example, an image may be softened using a low frequency filter, and a high frequency filter may be applied when sharpening the image. This preserves the fineness of boundaries.

The first and second filters 310 and 320 may cross each other so that an error range overlaps for precise measurement of the gas to be measured, thereby forming an interference free zone. In other words, the interference-free zone where two band pass filters overlap is low because there is no signal, so the precise analysis of the gas is possible.

The transmission unit 300 may further include a third filter 330 in addition to the first and second filters 310 and 320. The transmission unit 300 may further include a fourth filter 340 in addition to the third filter.

The detector 400 may be installed at a portion of the analysis main body 100 to detect gas that has passed through the permeation unit 300.

The controller 500 may be connected to the light emitting member 200, the transmission unit 300, and the detector 400 to control the operation of the light emitting member 200, the transmission unit 300, and the detector 400.

The gas analyzer 10 of the present invention may further include a water removing device 510, a wireless communication module 520, and a display 530.

The water removal device 510 may reduce relative humidity by evaporating water inside the analysis base 100 under the control of the controller 500.

The wireless communication module 520 may be connected to the controller 500 and may be controlled by wireless transmission and reception of information with an external wireless terminal. That is, the controller 500 is connected to an external smartphone or tablet computer through the wireless communication module 520, the light emitting member 200, the transmission unit 300, the detector 400, the water removal device 510 from the outside ), The display 530 may be operated or controlled wirelessly. The wireless communication module 520 can be used in conjunction with any one of the Wi-Fi communication module, Bluetooth communication module and Zigbee communication module.

The display 530 is installed at a portion of the analysis base 100 and may output information about the gas detected by the detector 400 under the control of the controller 500.

As shown in Figure 4 to 6, the gas analysis method for analyzing the measurement target gas using a gas analyzer for analyzing the concentration of the measurement target gas based on the heat column data, the present invention is a gas selection step S100, an infrared irradiation step S200, a gas transmission step S300, and an error range checking step S400 may be performed.

The measurement target gas selecting step (S100) is a step of selecting a measurement target gas based on data of a heater.

Infrared irradiation step (S200) is a step of irradiating infrared rays to the measurement target gas selected in the measurement target gas selection step (S100) using the light emitting member 200 provided in the gas analyzer 10.

Gas permeation step (S300) is a step of transmitting the gas of a specific wavelength band using the transmission unit 300 which is a band pass filter provided in the gas analyzer 10 to the gas passed through the infrared irradiation step (S200).

In the gas permeation step S300, at least one band pass filter may be arranged in series.

The gas permeation step S300 may include a first permeation step S310 and a second permeation step S320.

The first transmission step S310 is a step of transmitting a gas having a wavelength in a predetermined range without attenuation by using a band pass filter among the gas introduced into the gas analyzer 10.

The second transmission step (S320) The wavelength of a specific region other than the predetermined region band of the gas transmitted in the first transmission step (S310) corresponding to the first transmission step (S310), without attenuation using the band pass filter It is the step of transmitting.

Error range check step (S400) is a step of confirming the concentration wavelength band error range of the gas passing through the gas permeation step (S300).

Gas analysis method of the present invention may further comprise a non-interference zone forming step (S500).

Interference-free zone forming step (S500) In order to precisely measure the gas to be measured, cross-intersect each error range identified through the error range checking step (S400) to form an interference-free zone.

In addition, the gas analyzer 10 may include a moisture removal device 510 to reduce relative humidity by evaporating moisture inside the gas analyzer 10.

7 to 9 are graphs and tables showing embodiments of analyzing the NO gas through the gas analyzer and the gas analysis method using the same.

Hereinafter, the graphs and tables will be described.

Gas filter correlation (GFC) has been widely used to compensate for interference effects on NDIR analysis techniques. GFC has a very good function in a particular range of interfering gases. However, a disadvantage of GFC is gas leakage, and it is also difficult to make GFC.

Using a particular gas in the Hitran spectrum (FIG. 7) can find some wavelength ranges free of obstructing gases. The non-interfering wavelengths of the various gases are shown in Table 1 below.

 Non-interfering wavelengths of different gases obtained from the HITRAN spectrum

Compound	Wavelength (mm)	Full band width (nm)
CO 2	4.20 ?? 4.41	210
NO 2	6.44 ?? 6.45	10
NO	5.19 ?? 5.33	140
CO	4.46 ?? 4.54	80

As shown in Table 1, the overall bandwidth of the non-interfering wavelength is small. In contrast, commercial bandpass filters (BPFs) typically have a half-bandwidth of 100 to 200 nm (Figures 8 and 9) and a total bandwidth of several hundred nm (e.g. Table 1 shows a NO band at half-wavelength at 5.1 mm). Pass filter, band width = 100 nm, full band width = 724 nm). Thus, the selected wavelength of commercial BPF is in the range of low interference, but there is considerable interference due to the wide bandwidth. Narrow BPF can be used. However, the price of such a filter is very expensive and has a wavelength limitation. To overcome this problem, the dual attenuated wavelength BPF is used to reduce the bandwidth, and due to the attenuated wavelength, the two BPFs are newly narrowed by the interference wavelength. It becomes BPF. For example, NO BPF was used at 5.1 (100 nm) and 5.3 mm (180 nm) (FIG. 9). The total bandwidth is 290 nm and half wavelength band is 40 nm. The relationship between different NO concentrations and infrared absorption is shown in FIG. 9. The effects of CO2, NO2 and SO2 are shown in Table 2. The absorbance values of these gases were nearly 1.0. This means that there is no significant influence of these gases on NO gas detection. In terms of humidity, double BPF showed less impact up to 50% of relative humidity. The correction equation for the gas to be measured is represented by function (1).

y = f (C) (1)

When y is proportional to Io / I, f (C) is the quadratic equation of the gas concentration to be measured, Io is the detector signal associated with the zero gas, and I is the detector signal associated with the gas being measured.

The ratio of IR absorption of some interfering gases to NO (Io / I) (Note: Lambert-Beer equation: Io / I = Exp (-A), A = ECL: A = absorbance, E = absorption coefficient, C = gas Concentration, L = light path length)

NO 2 (ppm)
	N 2	10	100	200
	4.14	4.33	4.23	4.32
	4.31	4.23	4.29	4.19
	4.23	4.20	4.26	4.19
Mean (V)	4.23	4.25	4.26	4.23
SD	0.09	0.07	0.03	0.08
RSD (%)	2.01	1.60	0.70	1.77
Absorption ratio		0.99373	0.992175	0.998425
CO 2 (%)
	N 2	One	10	20
	3.82	3.74	3.71	3.88
	3.80	3.88	3.89	3.83
	3.85	3.86	3.91	3.79
Mean (V)	3.82	3.83	3.84	3.83
SD	0.03	0.08	0.11	0.05
RSD (%)	0.66	1.98	2.87	1.18
Absorption ratio		0.999129	0.996525	0.997391
Humidity (RH% at 24 ° C)
	N 2	20	50
	4.14	4.05	4.00
	3.92	3.99	3.97
	4.15	4.16	4.18
Mean (V)	4.07	4.07	4.05
SD	0.13	0.09	0.11
RSD (%)	3.19	2.12	2.80
Absorption ratio		1.00082	1.004938
SO 2
	N 2	SO 2 _1%
	4.14	4.24
	4.31	4.25
	4.23	4.19
Mean (V)	4.23	4.23
SD	0.09	0.03
RSD (%)	2.01	0.76
Absorption ratio		1.00

The detailed description of the preferred embodiments of the invention disclosed as described above is provided to enable those skilled in the art to implement and practice the invention. Although the above has been described with reference to preferred embodiments of the present invention, those skilled in the art will understand that various modifications and changes can be made without departing from the scope of the present invention. For example, those skilled in the art can use each of the components described in the above-described embodiments in combination with each other. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. The present invention does not depart from the spirit and essential features thereof. It may be embodied in other specific forms in the range. Accordingly, the above detailed description should not be interpreted as limiting in all aspects and should be considered as illustrative. The scope of the invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent scope of the invention are included in the scope of the invention. The present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. In addition, the claims may be combined to form an embodiment by combining claims that do not have an explicitly cited relationship in the claims, or may be included as new claims by post-application correction.

Claims (13)

1. Heat analyzer is a gas analyzer that analyzes the concentration of the gas to be measured based on the data.

   An analysis basic body accommodating the measurement target gas to provide a space for gas measurement;

   A light emitting member installed inside the analysis main body to irradiate infrared rays to the measurement target gas;

   A transmission unit installed at a portion of the analysis base member to transmit gas of a specific wavelength band;

   A detector installed at a portion of the analysis base unit to detect gas passing through the transmission unit; And

   And a controller connected to the light emitting member, the transmission unit, and the detector to control the operation of the light emitting member, the transmission unit, and the detector.

   The transmission unit,

   Gas analyzer using a heat filter and a multi-filter, characterized in that composed of at least one configuration, each configuration is arranged in series with each other.
2. The method of claim 1,

   The transmission unit,

   A first filter which transmits a gas having a predetermined wavelength in a region of the gas introduced into the analysis body without attenuation; And

   A second filter that transmits wavelengths of a specific region other than a predetermined region of the gas transmitted to the first filter without attenuation corresponding to the first filter without attenuation; Gas analyzer.
3. The method of claim 2,

   The first and second filters,

   Gas analyzer using heat filter data and multi-filter, characterized in that to position each other attached or separated.
4. The method of claim 2,

   The first and second filters,

   A band pass filter which passes only signals within a specific frequency band without attenuation and attenuates the remaining frequency signals; and a gas analyzer using Hitlan data and a multi-filter.
5. The method of claim 2,

   The first and second filters,

   Gas analyzer using a heat filter and a multi filter, characterized in that the interference range is overlapped so as to overlap each error range for precise measurement of the gas to be measured.
6. The method of claim 4, wherein

   The transmission unit,

   And a third filter in addition to the first and second filters.
7. The method of claim 6,

   The transmission unit,

   And a fourth filter in addition to the third filter. Heat analyzer data and a gas analyzer using the multi-filter.
8. The method of claim 1,

   And a water removal device configured to reduce relative humidity by evaporating water inside the analysis basic body by the control of the controller.
9. A gas analysis method of analyzing a gas to be measured using a gas analyzer that analyzes a concentration of a gas to be measured based on heat data.

   A measurement target gas selection step of selecting the measurement target gas based on the heater data;

   An infrared irradiation step of irradiating infrared rays to the measurement target gas selected in the measurement target gas selection step by using a light emitting member provided in the gas analyzer;

   Gas permeation step of transmitting a gas of a specific wavelength band using the transmission unit which is a band pass filter provided in the gas analyzer to the gas passed through the infrared irradiation step: And

   An error range checking step of checking a concentration wavelength error range of the gas that has passed through the gas permeation step; and a heat analyzer data and a gas analyzer using a multi-filter.
10. The method of claim 9,

    The gas permeation step,

    At least one of the band pass filters in series, wherein the analysis method using a gas analyzer using a heat filter and a multi-filter.
11. The method of claim 10,

    The gas permeation step,

    A first transmission step of transmitting, without attenuation, a gas having a wavelength in a predetermined region using the band pass filter among the gas introduced into the gas analyzer; And

    And a second transmission step of transmitting a wavelength of a specific area band other than the predetermined area band of the gas transmitted in the first transmission step without attenuation using the band pass filter in correspondence with the first transmission step. Heat analysis method characterized in that the gas analyzer using a heat filter and a multi-filter.
12. The method of claim 11,

    Heat interference characterized in that it further comprises; a non-interference zone forming step of forming an interference-free zone by crossing each of the error ranges identified through the error range check step to overlap the measurement target gas for precise measurement Gas analysis method using data and multi filter.
13. The method of claim 9,

    The gas analyzer is equipped with a water removal device to reduce the relative humidity by evaporating the water inside the gas analyzer, characterized in that the heat analysis using a multi-filter and gas analysis method.

Images