GB2057680A - Electro-optical flue gas analyzer - Google Patents
Electro-optical flue gas analyzer Download PDFInfo
- Publication number
- GB2057680A GB2057680A GB8027792A GB8027792A GB2057680A GB 2057680 A GB2057680 A GB 2057680A GB 8027792 A GB8027792 A GB 8027792A GB 8027792 A GB8027792 A GB 8027792A GB 2057680 A GB2057680 A GB 2057680A
- Authority
- GB
- United Kingdom
- Prior art keywords
- optical path
- visible light
- flue
- energy
- sample chamber
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/47—Scattering, i.e. diffuse reflection
- G01N21/49—Scattering, i.e. diffuse reflection within a body or fluid
- G01N21/53—Scattering, i.e. diffuse reflection within a body or fluid within a flowing fluid, e.g. smoke
- G01N21/534—Scattering, i.e. diffuse reflection within a body or fluid within a flowing fluid, e.g. smoke by measuring transmission alone, i.e. determining opacity
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- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Or Analysing Materials By Optical Means (AREA)
Abstract
Apparatus for the simultaneous measurement of opacity, carbon monoxide content and hydrocarbon content of flue gases along a single measurement path across a flue, comprises a sample chamber (2) extending transversely of the flue (4) and through which the flue gases may flow; means defining a single axis optical path (14) extending through the sample chamber and including focusing means (12) and an optically retro-reflective member (10) adjacent opposite sides of the flue; means including a source (16), for directing visible light along the path (14) toward the member (10); means including a source (50) independent of the visible light source (16), for directing infrared energy in predetermined spectral bands between 3 microns and 5 microns along the path (14) toward the member (10); and means (46) and (58) for sensing the respective levels of visible light and infrared energy which have made the return journey via the focusing means (12) and the common optical path (14). <IMAGE>
Description
SPECIFICATION
Electro-optical flue gas analyzer
This invention relates to apparatus for the simultaneous measurement of opacity, carbon monoxide content and hydrocarbon content of flue gases. Such measurements are used to control the air-to-fuel ratio of the fuel and air mixture being fed to the furnace, with the object being to minimize wastage of fuel due to the heating and subsequent discharge to the atmosphere of heated excess air.
Modern combustion control practice involves the simultanteous measurement and control of a number of properties of exhaust gases from furnaces utilizing fossil fuels. In the usual case the carbon monoxide level of the gases is measured and controlled to a predetermined level or target.
At high air-to-fuel ratios the carbon monoxide level is usually at a low level of about one hundred parts per million. As the oxygen abundance just falls below the level necessary to completely oxidize all of the carbon and hydrogen in the fuel, the carbon monoxide level begins to rise rapidly. It is at the beginning of this rise in carbon monoxide level that the carbon monoxide control point is generally set.
Under certain conditions, other limitations to reduction of the air-to-fuel ratios are reached before the carbon monoxide level begins its rapid rise. In some cases elemental carbon will precipitate before burning, causing higher smokestack opacity. In other cases, poor burner adjustment or burner tip fouling can lead to undesirably higher levels of hydrocarbons.
Accordingly, in order to control the operation of the furnace in a most desirable manner it is important to measure simultaneously the levels of carbon monoxide and hydrocarbons and the degree of opacity of the gases being exhausted up the flue.
There are a number of well known methods of measuring the levels of carbon monoxide and hydrocarbons in combustion gases. The preferred method is by infrared absorption spectrometry. In this method infrared light energy at selected wavelengths is transmitted through a sample of the gas to be analyzed. The level of the infrared energy passing through the gases is then compared with the infrared energy level in the absence of such gases. The resulting measurements of the absorption of the energy at these wavelengths provides a qualitative and quantitative measurement of the gas constituent levels, in this case carbon monoxide and hydrocarbons.
There are also well known methods for measuring the opacity of the combustion gases. A preferred and well known method is to transmit a source of photopic light energy (equivalent in wavelength distribtuion to the response of the human eye) through the gases to be analyzed and then to measure the amount of light transmitted, the opacity being defined as unity minus the transmission.
Measurement of the combustion gas composition is best done directly in the flue or smokestack to eliminate effects of stratification of the gas constituents. To protect the measuring instrument from the hot, corrosive combustion gases, special windows isolate the device from the gases. Over a period of time, dirt tends to build up on the windows and to cause errors in the flue gas analysis. Also, changes in the source output and detector sensitivity can cause errors. One way of reducing such errors is by the provision of a sample chamber extending across the flue and which can periodically be purged with clean air for purposes of calibrating the apparatus.
It is particularly desirable to measure the levels of carbon monoxide and hydrocarbons and the opacity of the flue gases simultaneously, and preferably in a single sampling volume passing through the sample chamber. Thus, while two separate beams of energy, one infrared and one visible, could be transmitted through a single sample chamber, the resultant size of the sample chamber would tend to be so large for the two beams that the sample chamber itself could cause undesirable turbulence which could interfere with the periodic purging thereof. Heretofore, it has thus been impractical to integrate these control and measuring devices with a desirable sample chamber.
According to the present invention there is provided apparatus for the simultaneous measurement of opacity, carbon monoxide content and hydrocarbon content of flue gases along a single measurement path across a flue, comprising
a sample chamber extending transversely of the flue from one side of the flue to the other side and through which the flue gases may flow;
means defining a single axis optical path extending longitudinally through the sample chamber, the optical path defining means including focusing means adjacent one side of the flue and an optically reflective member adjacent the other side of the flue, so that the optically reflective member may reflect a beam of radiant energy from the focusing means back along the optical path through the focusing means;;
a source for producing visible light energy and for directing the visible light energy along the optical path toward the reflective member;
a source for producing infrared energy independent of the visible light energy source and for providing the infrared energy in predetermined spectral bands between 3 microns and 5 microns and for directing the infrared energy along the optical path toward the reflective member;
means for sensing the level of the visible light energy which has traversed the sample chamber along the optical path through the focusing means to the reflective member and back through the focusing means; and
means for sensing the level of the infrared energy which has traversed the sample chamber along the optical path through the focusing means to the reflective member and back through the focusing means, so that the levels of both the visible energy and the infrared energy traversing the sample chamber may be measured along a single optical path through the chamber.
The invention will now be described with reference to the accompanying drawings, in which:
Figure 1 is an exploded view of the general components of the optical flue gas analyzer apparatus of this invention, and
Figure 2 is a side elevation, partially in section, of the apparatus of this invention as installed in a flue.
In the exploded view of Figure 1 and the schematic side elevation, partially in section, of
Figure 2 is illustrated a particularly preferred embodiment of the apparatus of this invention.
This apparatus includes a sample chamber assembly 2 extending transversely of the flue 4 from one side of the flue to the other side. When this sample chamber is in the position illustrated in Figure 1, the gases of combustion, indicated generally by the large arrow 6, may flow through the sample chamber. This sample chamber 2 suitably is of the type illustrated in pending United States
Patent Application No. 19,640 filed 12th March 1979, by Howard A. Powers and entitled "Sample
Chamber for Gas Analyzer". Since this sample chamber apparatus is disclosed in great detail in that co-pending patent application, which is assigned to the assignee of this application and, whose complete disclosure is incorporated by reference herein, only a portion of one end of that sample chamber assembly is illustrated in Figure 1.
At one end of the sample chamber 2 is provided a window 8 (shown in phantom) of a suitable material transparent to both visible and infrared energy, forming a-window through the side of the flue 4. Outside and directly adjacent that side of the flue is mounted a corner cube retro-reflector, which comprises an optically reflective member reflective of both visible and infrared energy.
A second window 8', likewise transparent to both infrared and visible energy, is also provided through the side of the flue opposite window 8.
Adjacent that second window 8' is provided a suitable focusing means, illustrated schematically in Figure 1 by a lens 12. If desired, the lens 12 may be used in place of the window 8'. Suitably the windows 8 and 8' and the focusing means 12 may be formed of calcium fluoride or other material transmissive to both infrared and visible light The optical axis of the focusing means 1 2 and the retroreflector 10, extending longitudinally through the sample chamber 2, define an optical path for energy to traverse the sample chamber from the focusing means 12 to the retro-reflector 10 and back through the chamber 2 to the focusing means 12. This single axis optical path is conveniently denoted by reference number 14.
Preferably aligned with optical path 14, as shown in Figure 1, is an incandescent lamp or other suitable source of visible light energy having at least a substantial portion of its energy in the spectral band between 500 and 600 nanometres.
This light energy source 1 6 directs its visible light energy out to and along the optical path 14, as shown in Figure 1. The portion of the energy of this visible light source which is directed along the optical path 14 is directed along a path extending through chopper and filter wheel 1 8. This chopper and filter wheel 18 is mounted in a conventional manner for rotation, driven by conventional means, at a predetermined rate. This chopper and filter wheel 18 has, radially and circumferentially spaced about its centre of rotation a plurality of neutral density filters 22, 24, 26 and 28 positioned to intersect the optical path aligned with optical path 14.The chopper wheel 1 8 is also provided with a plurality of timing apertures cooperating with light emitting diode 30 and phototransistor 32 in a conventional manner to provide timing signals to indicate when each filter and each space between filters is aligned with the optical path from the light source 1 6 to the optical path 14. Similarly, one additional hole is provided in the chopper wheel co-operating with light emitting diode assembly 34 and phototransistor assembly 36 to provide an index signal to identify which of the filters or spaces between filters is aligned with the optical path.
Between the chopper wheel 18 and the focusing means 12 is then inserted a visible light beam splitter 38, suitable of the type commonly referred to as a dielectric beam splitter, which permits approximately half of the visible light energy from the source 16 to pass therethrough towards the focusing means 12. Similarly aligned with the optical path 14 and between the beam splitter 38 and the focusing means 12 is then positioned a beam combiner/separator, which suitably is formed of glass with a light metallic coating on the side facing focusing means 12. This beam combiner/separator 40 permits most of the visible light energy to pass directly therethrough, thence to be focused by the focusing means 12 and directed along the optical path 14 to the retro-reflector 10 and back through the focusing means 12 and the beam combiner/separator 40 to the beam splitter 38.
The beam splitter 38 is angled such that approximately half of the visible light energy received back from the retro-reflector and through the beam combiner/separator is then reflected off the axis of optical path 14 through a suitable focusing lens 42 and a photopic filter which is selected such that about 90% of the energy passing therethrough will be in the 500 to 600 nanometre spectral range. From that photopic filter 44 the visible light energy is then directed to a conventional silicon detector which serves as a means for sensing the level of visible light energy which has traversed the sample chamber along the optical path 14 and returned.
The beam combiner/separator 40 with its light metallic coating on the side towards the focusing means 12 is highly reflective of infrared energy.
This beam combiner/separator 40 is also angled with respect to optical axis 14 such that infrared energy received by it from the focusing means 12 along the optical axis 14 will be directed off at an angle along another optical axis 48. Aligned with this optical axis 48 is a suitable source 50 of infrared energy covering at least the three to five micron spectral range. Between this infrared source 50 and the beam combiner/separator 40 is mounted for rotation in a suitable manner and by conventional means a rotating filter wheel 52.
This filter wheel, which is illustrated containing five filters, desirably contains at least three suitable interference filters radially and circumferentially spaced about the centre of rotation which will selectively transmit energy in the carbon monoxide spectral band, in the hydrocarbon band and in a reference band in the region between 3.5 and 4.1 microns. The reference band is chosen to avoid absorption by any gas component in the flue; it allows a correction to be made for output changes that are unrelated to carbon monoxide and hydrocarbon concentrations in the flue.Suitably the filter wheel 52 may also have coding holes co-operating with suitable light emitting diodes/phototransistor pairs for purposes of indicating when each filter and each space between filters is in position before the infrared source 50 for purposes of identifying samples in the manner described above with respect to chopper wheel 1 8.
Between the rotating filter wheel 52 and the beam combiner/separator 40 is interposed the infrared beam splitter 54, comprising an uncoated germanium window. This infrared beam splitter 54 permits approximately half of the energy from source 50 to pass therethrough and to be reflected by beam combiner/separator 40 along optical path 14 through the sample chamber 2 to retroreflector 10 and back to beam combiner/separator 40. There the energy is reflected down to the infrared beam splitter 54 where about half of that energy received back from beam combiner/separator 40 is then reflected through infrared focusing lens 56 and onto infrared detector assembly 58. This infrared detector assembly 58 may suitably comprise a lead selenide detector which is cooled by a thermo-electric device or other suitable means.
From the foregoing description of the apparatus it may be seen that chopped pulses of visible light may be directed along the optical path 14 through the sample chamber 2 and back to the detector 46 where the level of the visible light energy in the 500 to 600 nanometre spectral range may be measured by that detector and by suitable and conventional signal processing. When the sample chamber is in the configuration illustrated in
Figure 1 the flue gases, indicated by the large arrow 6, pass therethrough and the visible light signal will be attenuated by any carbon or soot content in those gases. When the sample chamber outer housing is rotated 900, in the manner described in detail in United States Patent
Application No.19,640, the sample chamber will be purged of the exhuast gases with only relatively clean air inside.During this purging condition the visible light source and detector system may be
calibrated and standardized in order to provide absolute measurements of the opacity when flue gases are again permitted to flow through the sample chamber. Similarly, the absorption of the
infrared energy from the source 50 in the different spectral bands selected by the various filters of the filter wheel 52 may be determined by measuring the level of infrared energy received by detector
58 both with the flue gases flowing through the sample chamber and during the purged condition for standardization and calibration.
The particular structure of this invention is
uniquely advantageous in that both the visible
light attenuation and the infrared absorption are measured along a single axis optical path and are measured simultaneously through the same position in the flue. This is advantageous not only for purposes of standardizing and controlling the sampling conditions but also for permitting the use of a relatively small diameter sample chamber which causes substantially less disturbance to the flow of gases through the flue. While certain spectral bands of the various filters have been noted above, it is of course understood that numerous other combinations of spectral bands for the infrared filters and density levels for the neutral density filters used with the visible light source may be incorporated. Various combinations of such filters will be used in order to meet the necessary control guidelines specified by the Environmental Protection Agency as provided, for example, in 40 C.F.R. Parts 60 through 99 relating to protection of the environment. For different types of furnaces and different fuels, different combinations will be required. It is also to be understood that the signals generated by the visible light detector 46 and the infrared detector 58 may be processed in any suitable manner, preferably digitally, to obtain the desired data in the desired format.
While the foregoing describes a particularly preferred embodiment of the apparatus of this invention, it is to be understood that it is illustrative only of the principles of the invention and is not limitative thereof.
Claims (9)
1. Apparatus for the simultaneous measurement of opacity, carbon monoxide content and hydrocarbon content of flue gases along a single measurement path across a flue, comprising
a sample chamber extending transversely of the flue from one side of the flue to the -other side and through which the flue gases may flow;
means defining a single axis optical path extending longitudinally through the sample chamber, the optical path defining means including focusing means adjacent one side of the flue and an optically reflective member adjacent the other side of the flue, so that the optically reflective member may reflect a beam of radiant energy from the focusing means back along the optical path through the focusing means;
a source for producing visible light energy and for directing the visible light energy along the optical path toward the reflective member;;
a source for producing infrared energy independent of the visible light energy source and for providing the infrared energy in predetermined spectral bands between 3 microns and 5 microns and for directing the infrared energy along the optical path toward the reflective member;
means for sensing the level of the visible light energy which has traversed the sample chamber along the optical path through the focusing means to the reflective member and back through the focusing means; and
means for sensing the level of the infrared energy which has traversed the sample chamber along the optical path through the focusing means to the reflective member and back through the focusing means, so that the levels of both the visible energy and the infrared energy traversing the sample chamber may be measured along a single optical path through the chamber.
2. Apparatus as claimed in Claim 1, further comprising unitary means for both dividing the visible light energy into pulses of predetermined duration and spacing and for periodically applying neutral density filters of predetermined density to the visible light energy produced by the source and directed along the optical path.
3. Apparatus as claimed in Claim 2 in which the unitary means comprises a rotating chopper wheel having neutral density filters radially and circumferentially spaced about its axis of rotation.
4. Apparatus as claimed in any preceding claim further comprising means for dividing the infrared energy into pulses of predetermined duration, spacing and wavelength.
5. Apparatus as claimed in Claim 4 in which the infrared energy dividing means comprises a rotating member having a plurality of filters radially and circumferentially spaced about the axis of rotation.
6. Apparatus as claimed in any preceding claim further comprising beam splitting means for passing the visible light energy from the visible light source to the sample chamber along the single axis optical path and for reflecting off the single axis optical path to the visible light level sensing means visible light energy received back from the sample chamber.
7. Apparatus as claimed in any preceding claim in which the infrared energy source is displaced from the single axis optical path and the apparatus includes beam combiner/separator means intersecting the single axis optical path for transmitting the visible light energy therethrough and for reflecting the infrared energy from the infrared source onto the single axis optical path.
8. Apparatus as claimed in Claim 7 further comprising beam splitting means interposed between the infrared energy source and the beam combiner/separator means for passing the infrared energy from the source to the beam combinerrseparator and for reflecting to the infrared level sensing means the infrared energy received back from the sample chamber.
9. Apparatus for the simultaneous measurement of opacity, carbon monoxide content and hydrocarbon content of flue gases along a single measurement path across a flue substantially as herein described with reference to the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US7074479A | 1979-08-29 | 1979-08-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB2057680A true GB2057680A (en) | 1981-04-01 |
Family
ID=22097122
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8027792A Withdrawn GB2057680A (en) | 1979-08-29 | 1980-08-28 | Electro-optical flue gas analyzer |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS5653447A (en) |
| DE (1) | DE3032641A1 (en) |
| FR (1) | FR2464470A1 (en) |
| GB (1) | GB2057680A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2245058A (en) * | 1990-05-18 | 1991-12-18 | Sieger Ltd | A gas detector |
| GB2299402A (en) * | 1995-03-15 | 1996-10-02 | Perkin Elmer Ltd | Microscope for Infrared Spectroscopy |
| WO2001033200A1 (en) * | 1999-11-04 | 2001-05-10 | L'air Liquide, Societe Anonyme À Directoire Et Conseil De Surveillance Pour L'etude Et L'exploitation Des Procedes Georges Claude | Method for continuously monitoring chemical species and temperature in hot process gases |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS60238746A (en) * | 1984-05-14 | 1985-11-27 | Meito Sci Kk | Device for detecting concentration of gaseous hydrocarbon |
| JPS60244838A (en) * | 1984-05-21 | 1985-12-04 | Meito Sci Kk | Detector for degree of contamination of waste gas in continuous heat treating device for fabric |
| JPS60257347A (en) * | 1984-06-05 | 1985-12-19 | Ngk Insulators Ltd | Normal incidence type non-dispersive infrared gas analyzer |
| AT409039B (en) * | 1999-11-26 | 2002-05-27 | Avl List Gmbh | METHOD FOR MEASURING OPACITY IN GASES |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3541336A (en) * | 1967-11-08 | 1970-11-17 | Harry Einstein | Photoelectric gas monitor having either reflective or absorbing plate at one end of sample tube |
| DE2130331C3 (en) * | 1971-06-18 | 1978-06-29 | Erwin Sick Gmbh Optik-Elektronik, 7808 Waldkirch | Method and device for determining the concentrations of the components of a mixture consisting of two gases and smoke |
| US3796887A (en) * | 1972-05-17 | 1974-03-12 | Itt | Photometric analyzer |
| DE2521934C3 (en) * | 1975-05-16 | 1978-11-02 | Erwin Sick Gmbh Optik-Elektronik, 7808 Waldkirch | Device for determining the concentrations of components in an exhaust gas mixture |
| DE2557268A1 (en) * | 1975-12-19 | 1977-06-30 | Licentia Gmbh | Smoke density determination apparatus - uses extinction of light beam compared with reference beam |
-
1980
- 1980-08-28 GB GB8027792A patent/GB2057680A/en not_active Withdrawn
- 1980-08-28 FR FR8018702A patent/FR2464470A1/en not_active Withdrawn
- 1980-08-29 DE DE19803032641 patent/DE3032641A1/en not_active Ceased
- 1980-08-29 JP JP11967680A patent/JPS5653447A/en active Pending
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2245058A (en) * | 1990-05-18 | 1991-12-18 | Sieger Ltd | A gas detector |
| GB2299402A (en) * | 1995-03-15 | 1996-10-02 | Perkin Elmer Ltd | Microscope for Infrared Spectroscopy |
| GB2299402B (en) * | 1995-03-15 | 1999-07-21 | Perkin Elmer Ltd | Method for simultaneously viewing samples and making IR measurements |
| WO2001033200A1 (en) * | 1999-11-04 | 2001-05-10 | L'air Liquide, Societe Anonyme À Directoire Et Conseil De Surveillance Pour L'etude Et L'exploitation Des Procedes Georges Claude | Method for continuously monitoring chemical species and temperature in hot process gases |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5653447A (en) | 1981-05-13 |
| FR2464470A1 (en) | 1981-03-06 |
| DE3032641A1 (en) | 1981-03-12 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |