DE2918084A1 - Optical determn. of concn. of mixed gases - involves processing absorptions at different frequencies by computer - Google Patents

Abstract

Measurements of the absortion of the gas or transparent fluid are taken at different frequencies and the results input to a computer. The computer draws upon a store which contains data on the cross-sensitivity of the gas components to be measured. The computer automatically adjusts the proportions of the sensitivity data taken from its store until a null balance is obtained with the measurements and is then able to output its estimate of the relative gs concentrations.

Description

The invention relates to a method for determining the transverse

sensitivity coefficients of several (n), especially three total extinctions (Ai) measured at one wavelength in each case with the additive Combination of the particularly linear total absorbance (Ai) determination of the concentration a corresponding number n of components (gases and possibly dust) in a gaseous medium or in transparent liquids or solids, in particular two gases, preferably SO2 and NO2 and dust in a mixture of these components or these two gases and the dust component. In addition, the invention wants a Device for carrying out this process with a computer, which is provided by an optical Measuring device on the test object or a test object at n wavelengths determined n Total absorbances as n electrical input signals and the cross-sensitivity coefficients the additive combinations are supplied from a read-only memory and from it n supplies proportional output values to the concentrations of the individual components, create.

Methods and equipment for determining the concentrations of the components a mixture consisting of two gases and smoke are known (DE-PS 21 30 331, DE-PS 25 21 934).

A problem with the known methods and devices for determining concentration consists in precisely determining the so-called cross-sensitivity coefficients. A trivial solution, the wavelength dependence of the extinctions of each To determine and take into account components would consist of the so-called Measure cross-sensitivity and then the new constants of the linear combination to calculate. As is well known, cross-sensitivity is understood to mean influencing an absorbance measurement through several gases. For example, if it is present of two gas components, in particular S02 and N02 as well as dust in a flue gas determine the extinctions at the three measurement wavelengths in a test fireplace in which only one gas component or only smoke or dust is present. This measurement method would however, do not lead to success because the dust density or gas concentration fluctuates and therefore the values cannot be measured with sufficient accuracy. In particular, a simultaneous measurement would be used to determine the coefficients all three measurement wavelengths required.

The aim of the invention is thus to provide a method and a To create device of the type mentioned, in which on extremely simple Assign the cross-sensitivity coefficients to the total absorbances measured the different wavelengths can be determined. In particular, it should be possible be, these coefficients by systematic variation of as few variables as possible can be determined quickly and reliably.

To solve this problem, the invention provides that at predetermined Concentrations of (n-1) components give the specific extinction coefficients the remaining component can be varied until the concentration is determined of the (n-1) components the predetermined concentrations due to the additive combination results. For this purpose, the device according to the invention is used to carry out the method provided that a processor can be connected to the computer, the input of which the changeable specific extinction coefficients supplied as electrical signals are and which from this the corresponding coefficients are calculated and sent to the computer gives away.

The invention is based on the knowledge that due to this procedure when there are n components (e.g. two gas components, one dust component) only n-1 specific extinction coefficients of the remaining component must be varied systematically. This means that e.g. when two gas components and dust or

Smoke to determine the cross-sensitivity coefficient only the two specific smoke extinction coefficients E13, E23 varied as long need to be until the additive combination of the measured at each wavelength Total absorbances those given by other methods Concentrations of the two gas components results.

It when the remaining component of the other components are examined separately and the variation of the specific Extinction coefficients (E13, E23) continue until the concentration is determined of the n-1 components the predetermined concentrations due to the additive combination results. In other words, only one of the components has to be isolated, which, for example, can be achieved in the case of a gas mixture in that one of the gases is examined in pure form in a test chamber. The other gas components have then the concentration is zero.

The method according to the invention can have reasonable margins of error can be used for media with up to a maximum of five components.

If in the process the components are two gases, in particular S02, N02 and dust, the invention preferably provides that in a chamber in of the two gases in a predetermined concentration, preferably the concentration Zero are present, during each of the three concentration determinations at least one, Preferably two of the specific dust extinction coefficients varied as long be until the concentration determination, the predetermined gas concentrations, in particular Zero, results. The invention is further based on the assumption that the dependency the extinction of the smoke from the wavelength is not negligible. The consideration the wavelength dependence of the specific smoke or dust absorbance increases the measurement accuracy is essential. Due to the application of the method according to the invention In particular, it is avoided that fluctuations in dust density lead to a reduction in the Accuracy of the cross-sensitivity coefficient.

According to the invention it is further assumed that the in a certain actual chimney existing dust even over a long period of time a constant one Has wavelength dependence.

For the ongoing determination of the concentration in such a chimney the invention therefore preferably provides that a dust sample is taken from the chimney and in a test chamber in which the two gas components are in predetermined concentrations present or preferably absent, being whirled around, the dust extinction coefficients can be varied and the coefficients determined in the process when determining the concentration used in the actual fireplace.

There is an advantageous further development of the device according to the invention in that there is a connection between the processor and the read-only memory, via which the coefficients determined to be applicable in the read-only memory are inscribable. The processor can be connected to the computer via detachable plug connections and the read-only memory connected, so that a certain, for the practical Use a certain device first by measuring the wavelength dependency the smoke absorbance in a test chamber to certain cross-sensitivity coefficients can be calibrated.

These cross-sensitivity coefficients measured before the device was delivered are then held in the read-only memory for all time. By reconnecting of the processor, however, a correction can be made at any time.

But it is also possible that according to a further advantageous embodiment the processor is an integral part of the Qptischen measuring device, so that at all times a readjustment of the cross-sensitivity coefficients is possible.

An embodiment particularly suitable for practice provides that the changeable specific extinction coefficients by hand, preferably are adjustable with a potentiometer. The operator needs the Potentiometer just twist it until the concentration display devices of the n-1 components the previously known concentrations, in particular the concentration Show zero.

Finally it is also possible that the changeable extinction coefficients can be set automatically by a closed control loop. In this case for example, the potentiometers are automatically adjusted by servomotors as long as until the concentration display devices determined the previously known, according to other methods Display concentration values of the n-1 components. Preferably the control loop should work digitally.

The invention provides for the determination of two gases and dust or smoke suggest that the processor has two potentiometers for varying the specific dust extinction coefficient are provided and the processor the six cross-sensitivity coefficients as output variables supplies.

It is useful if between the potentiometers and the Computing circuit analog-to-digital converter are switched on.

As already mentioned, the preferred application of the invention is when determining the concentration of two or more gas components and one dust component in a fireplace.

The preferred method according to the invention now provides that a Dust sample is taken from the measuring chimney and swirled around in a test chimney, in which the two gases in a predetermined concentration, preferably the concentration Zero present that during each of the three concentration determinations at least one of the smoke extinction coefficients is varied until the concentration is determined the given gas concentrations and that the determined cross-sensitivity coefficients can be used to determine the concentration in the measuring chimney. The essence of the invention consists so that not the cross-sensitivity coefficients of the linear combination, but the specific smoke extinction coefficients during the measurement on the test chimney can be varied. Although this requires a somewhat larger circuitry effort, which, however, is justified by the fact that only this detour is an unambiguous one Adjustment of the cross-sensitivity coefficient is possible. It is just as important that a zero adjustment should preferably be carried out. Under DJullabgleich is here understood a comparison in which the display of the (n-1) components when correct Adjustment, at the end of the adjustment process, due to fluctuations & or intentional Changes) the concentration of the n-th component is no longer influenced and regardless of whether the concentrations of the (n-1) components are zero or finite are.

According to the invention, therefore, the fluctuations in dust density interfere on the test track no longer. The output signal can be electronically averaged for any length of time, which practically completely eliminates the errors caused by statistical fluctuations will.

Since the smoke (solid component in combustion processes) in one certain actual measuring chimney has the same composition over a longer period of time and shows the same wave dependency, it is enough if before installing one Concentration measuring device on the chimney, a smoke sample (dust sample) was taken from it and the wavelength dependency according to the method according to the invention in FIG Circuit arrangement is examined. The coefficients then immediately determined kn can be written into the read-only memory and are then available during the ongoing actual measurement.

The invention is illustrated below, for example, with reference to the drawing described, the single figure is a schematic block-like representation of a shows the circuit arrangement according to the invention with the associated optical measuring device.

According to the drawing, an optical measuring device 12 is attached to a chimney 13 arranged, which through two diametrically opposite openings of the chimney 13 sends a parallel light beam 18 that passes through one on the other side The retroreflector 14 arranged in the chimney is reflected back to the measuring device 12 is where a suitably filtered photoreceiver receives the received signal at three different Detects wavelengths. If S02, N02 and smoke are to be measured, lie these wavelengths at 313, 436 and 546 nm. In detail, the structure of the optical Measuring device with the subsequent electronic evaluation stages in DE-PS 25 21 934.

The optical measuring device 12 supplies a computer 11 with the three Total extinction signals A1, A2 and A3 determined for measurement wavelengths. This calculates from the three total extinction values and six supplied by a read-only memory 15 Constants k1, k2, k3, k4, k5 and 6 three for the concentrations of S02, N02 and Rauch characteristic output signals E (S02), E (N02) and E (R). these can brought for example on numerical display instruments 19, 20 and 21 for display will.

For the sake of simplicity, the three are calculated for the Concentrations with characteristic initial values under the following conditions: 1. The dependence of the extinctions E (NO2) and E (R) on the NO2 or smoke concentration is linear.

2. Only the exhaust gas components absorb at wavelengths 313, 43 and 546 nm S02, N02 and smoke.

For the sake of simplicity, the output instruments show 19, 20 and 21 does not directly indicate the concentrations C1 (SO2), C2 (N02) or C3 (smoke) but functions that are defined as follows: E (S02) = E11. 1 . C1 (1) This is the absorbance caused by SO2 only on the 313 nm line.

E (N02) = E22. 1 . C2 (2) This is the absorbance given by N02 is caused on the line 436 nm.

E (R) = E33. 1 . C3 (3) This is the one through the smoke on the line 546 nm caused absorbance.

However, these extinctions are practical because of the linear relationship with C1, C2 and C3 and the constant factors a measure of the three concentrations. The three display devices 19, 20, 21 are expediently calibrated directly in concentrations.

C. means the concentration of the gas or smoke. 1 is from Total length of the measuring path covered by the light beam.

E .. is the specific extinction coefficient of the gas or

1J smoke j at wavelength i.

It can be shown that the three of the measuring instruments 19, 20, 21 initial values displayed with the total absorbances A. at the three wavelengths are related as follows: E (S02) = A1 + k1.A2 + k2. A3 (4) E (N02) = k3.A2 + k4. A3 (5) E (R) = k5.A2 + k6.A3 (6).

The coefficients ki of the measured three total extinctions A1 to A3 are called cross-sensitivity coefficients and are functions the specific smoke extinction coefficients E13 and E23. The specific gas extinction coefficients must be known and used as constant quantities.

For the example described, the following relationships result for the constants k1 to k6: -1 k5 = E22 - E23 (11) According to the drawing, the specific smoke extinction coefficients E13, E23 are each set to a potentiometer 22 or

23 adjustable. The set voltages are each via a Analog-to-digital converters 24, 25 are fed to processor 16. The processor 16 calculates from equations (7) to (11) the constants k1 to k6, with the crossbar to express that the six coefficients by adjusting the potentiometer 22, 23 are variable.

In the computer 11 the coefficients k1 to k6 with the total extinctions A1, A2 and A3 combined according to equations (4), (5) and (6), so that on the measuring instruments 19, 20 and 21 the output values E (SO2), E (N02) or E (R) appear.

Now the optical measuring device 12 is installed on a test chimney, in which a smoke sample filtered out of the smoke of the actual measuring chimney 13 (Dust sample) is whirled around. The gases S02 and N02 are not in the test chimney available, so that if the constants k1 to k6 are chosen correctly, the instruments 19, 20 should show zero.

In fact, however, the instruments 19, 20 show because of the cross-sensitivity a certain rash, because the extinction of the smoke depends on the wavelength. In particular, the experiment shows that the spectral course of the extinction in smoke samples of different fireplaces is different.

Now the potentiometers 22, 23 adjusted until the measuring instruments 19, 20 show the value zero. the Coefficients k1 to k6 now have the correct value and can be accessed via the Line 17 can be written into read-only memory 15. The read-only memory 15 is with the computer 11 and the optical measuring device 12 on the actual measuring chimney 13 installed, the constants determined once in the preliminary test as k1 up to k6 are always available. The processor 16 can after releasing the connections with the read-only memory 15 and the computer 11 for the calibration of another measuring device be used.

If in the actual measuring chimney with fluctuations in the wavelength dependency of the smoke must be expected, the test measurement can be repeated from time to time be collected by, for example, dust from the smoke and repeatedly according to the method according to the invention is used to correct the ki values.

You could also create a closed balancing control loop, in which the analog output voltage of the analyzer is used as the actual value. Likewise, a purely digital control loop could be set up analogously, by using the digital output variables of the analyzer as the actual value.

In principle, the method according to the invention can also be used in the Use concentration measurement of more than two gases and smoke.

The procedure can also be applied to non-linear systems of equations, provided the cross-sensitivity coefficients of the measured at a wavelength Total absorbances are clear.

The method according to the invention can also be used alone on the measuring chimney be when the concentration of smoke and gases of interest by others Method can be determined with sufficient accuracy. The unknown Extinction coefficients Eij are then also changed here until the known Absorbances or concentrations are displayed.

Furthermore, the method according to the invention can also be used for the Adjustment of the coefficients in analyzers to determine the concentration of liquid or solid substances are used. The test section is in this case no chimney, but e.g. a cuvette.

The ones shown in the drawing are also used for the coefficient adjustment required functional units 16, 22, 23, 24, 25 or the corresponding functional units in closed balancing control loops can be permanently arranged in the optical measuring device in particular, the computer 11 and the processor 16 can be in one functional unit be summarized.

Instead of the coefficients EiX, ratios of Eij of one and the same material component can also be varied. The equation coefficients k. are calculated accordingly in the above example with three material components as follows: It should be noted that often only the ratios of the extinction coefficients Eij of a material component are determined as pure numbers, not their absolute values with a physical dimension. It is therefore advisable to set an extinction coefficient for each substance component equal to 1.

When using multipliers, the range of values for the extinction coefficients Eij can be adapted to the ratios of the two measured substance components.

Claims (14)

Method and device for determining the cross-sensitivity coefficients when determining the concentration in gaseous media or transparent substances Claims: 1. Method for determining the cross-sensitivity coefficient of several (n), in particular three, total absorbances measured at one wavelength each (Ai) in the case of the additive combination of the, in particular, linear total extinctions (Ai) taking place concentration determination of a corresponding number n of components (Gases and possibly dust) in a gaseous medium or in transparent Liquids or solids, in particular two gases, preferably S02 and N02 and dust in a mixture of these components or these two gases and the dust component, by g e k e n n n z e i c h -n e t that at predetermined concentrations (C1, C2 or E (SO2) E (N02)) of (n-l) components are the specific extinction coefficients (Eij or E13, E23) of the remaining component can be varied until the Determination of the concentration of the (n-l) components based on the additive combination gives the predetermined concentrations. 2. The method according to claim 1, characterized in that g e k e n n z e i c h -n e t that the remaining component or the remaining substance of the remaining components or substances are examined separately and the variation of the specific extinction coefficients (Eij or E13, E23) takes place until the concentration of the n-l components is determined due to the additive combination, the concentration results in zero. 3. The method according to claim 1 or 2, characterized in that g e k e n n -z e i c It does not mean that it is used for media with a maximum of five components. 4. The method according to any one of the preceding claims, wherein the Components are two gases, in particular S02, N02 and dust, which means that they are not possible z e i c h n e t that in a chamber (13) in which the two gases in a predetermined Concentration, preferably zero concentration, are present during each of the three concentration determinations at least one, preferably two of the specific ones Dust extinction coefficients are varied until the concentration is determined gives the specified gas concentrations. 5. The method according to claim 4 for the ongoing concentration determination in a chimney or the like, thereby g e k e n n -z e i c h n e t that a Dust sample taken from the chimney (13) and placed in a test chamber in which the two Gas components are present or preferably absent in a predetermined concentration, is whirled around that the specific dust extinction coefficient in the specified Way can be varied and the cross-sensitivity coefficients determined in the process (ki) can be used to determine the concentration in the chimney (13). 6. Device for carrying out the method according to one of the preceding Claims with a computer, the one from an optical measuring device on the measurement object or a test object at n wavelengths determined n total extinctions as n electrical input signals and the cross-sensitivity coefficients of the additive Combinations are supplied from a read-only memory and from it n the concentrations of Individual components supplies proportional output values, thus g e k e n n -z e i c h n e t that a processor (16) can be connected to the computer (11), whose Input the changeable specific extinction coefficients (Eij or E13, E23) are supplied as electrical signals and from which the corresponding coefficients (ki) is calculated and sent to the computer (11). 7. Apparatus according to claim 6, characterized in that g e k e n n z e i c h n e t there is a connection (17) between the processor (16) and the read-only memory (15), via which the coefficients (ki) determined to be applicable in the read-only memory (15) are inscribable. 8. Apparatus according to claim 6 or 7, characterized in that g e k e n n z e i c h -n e t that the processor (16) via detachable plug connections with the computer (16) and the read-only memory (15) is connected. 9. Apparatus according to claim 6 or 7, characterized in that g e k e n n z e i c h -n e t that the processor (16) is an integral part of the optical measuring device. 10. Device according to one of claims 6 to 9, characterized in that g e k e n n -z e i c h n e t that the changeable specific extinction coefficients (Eij or E13, E23) from tape, preferably adjustable with a potentiometer (22, 23) are. 11. Device according to one of claims 6 to 9, characterized in that g e k e n n -z e i c h e t that the changeable extinction coefficients (Eij or E13, E23) can be set automatically by a closed control loop. 12. Apparatus according to claim 11, characterized in that g e k e n n z e i c h n e t the control loop is a digital control loop 13. Device after a of claims 6 to 12 for determining the concentration of two gas components, in particular 502 and N02, and dust with a cross-sensitivity coefficient determination part, by noting that at least on the processor (16) / two potentiometers (22, 23) for the variation of the specific dust extinction coefficient (E. 13, E23) are provided and the processor (16) the six cross-sensitivity coefficients as output variables (ki) returns. 14. Apparatus according to claim 13, characterized in that between the potentiometer (22, 23) and the arithmetic circuit analog-to-digital converter (24, 25) are switched.