WO2022002407A1

WO2022002407A1 - Measuring an no concentration in a gas mixture containing at least one interfering gas component

Info

Publication number: WO2022002407A1
Application number: PCT/EP2020/068681
Authority: WO
Inventors: Gerhard Wiegleb; Sebastian WIEGLEB
Original assignee: Wi.Tec-Sensorik GmbH
Priority date: 2020-07-02
Filing date: 2020-07-02
Publication date: 2022-01-06

Abstract

The invention relates to a device (8) for measuring an NO concentration (c_NO) in a gas mixture containing at least one interfering gas component, the device having at least one measuring chamber (9), which accommodates the gas mixture, and at least one optoelectronic measuring assembly (15) for measuring the NO concentration (c_NO), the measuring assembly (15) being designed, in order to measure the NO concentration (c_NO), to transilluminate the measuring chamber (9) with UV radiation suitable for this and to detect the UV radiation exiting the measuring chamber (9), the measuring assembly (15) having at least one UV light-emitting diode (34, 35, 36, 37) for generating the UV radiation. In order to reduce cross-sensitivities when measuring an NO concentration (c_NO) in a gas mixture containing SO₂ and/or NO₂, the device (8) has at least one reference measuring unit (28), which is arranged downstream of the measuring chamber (9) with respect to a radiation direction of the UV radiation transilluminating the measuring chamber (9), the reference measuring unit (28) having: at least one beam splitter (27), which is arranged such that the UV radiation exiting the measuring chamber (9) can be incident upon it; at least one gas cell (30) which is filled with NO and is arranged such that it can be transilluminated with some of the UV radiation exiting the beam splitter (27); and at least one reference detector (33), which is arranged such that the UV radiation exiting the gas cell (30) can be incident upon it.

Description

Measuring a NO concentration in a gas mixture containing at least one interfering gas component

Technical area

The invention relates to a device for measuring an NO concentration in a gas mixture containing at least one interfering gas component, having at least one measuring chamber receiving the gas mixture and at least one optoelectronic measuring arrangement for measuring the NO concentration, the measuring arrangement being set up, the measuring chamber To measure the NO concentration with a suitable UV radiation and to detect the UV radiation emerging from the measuring chamber, and wherein the measuring arrangement for generating the UV radiation has at least one UV light emitting diode.

The invention also relates to a method for measuring an NO concentration in a gas mixture containing at least one interfering gas component, the gas mixture being introduced into a measuring chamber, the measuring chamber filled with the gas mixture for measuring the NO concentration with UV radiation suitable for this purpose is transilluminated and the UV radiation emerging from the measuring chamber is detected.

State of the art

Combustion exhaust gases are generated during combustion processes in systems and machines, which as a rule, due to legal requirements, are not allowed to get into the vicinity of a system or machine untreated. In order to be able to monitor whether pollutant emissions from such a system or machine meet legal requirements, its combustion exhaust gases can be analyzed, whereby a concentration of at least one specific gaseous pollutant in the combustion exhaust gases can be determined. The gaseous pollutant can be, for example, sulfur dioxide (SO ₂ ), nitrogen dioxide (NO ₂ ), nitrogen monoxide (NO) or nitrogen oxide (NO + NO ₂ = NO _X ).

Typically, the concentration is measured by nondispersive radiation absorption in the infrared (NDIR) or ultraviolet spectral range (NDUV). Especially for lower gas concentrations in the presence of moisture (FhO vapor), the NDUV gas analysis has proven itself as a standard method for many years. A special electrodeless gas discharge lamp (EDL) is used as the radiation source for this application. A lamp body of the EDL is filled with an oxygen-nitrogen mixture and is ignited by an inductive high-frequency excitation and then emits selective radiation that is absorbed by NO. This radiation is in resonance with the spectral absorption of the NO. In this context, one speaks of UV resonance absorption.

Disadvantages of such an EDL are a limited service life of approx. 10,000 hours in continuous operation, a high power consumption (4 watts) as well as a large construction volume and high weight. Device integration in particular is made more difficult and mobile applications are only possible to a limited extent.

The use of UV light-emitting diodes has also been discussed for some time as an alternative to gas discharge lamps. The first test set-ups are available. UV light-emitting diodes are very suitable for use in measuring SO ₂ and NO ₂ , since the bandwidth of the emission of a UV light-emitting diode is smaller than the bandwidth of the absorption band of SO ₂ or NO ₂ . This results in a large measuring effect due to the total absorption of radiation.

In the case of NO concentration measurement, however, it is the other way around. The absorption band of NO around A = 226nm is much narrower than the bandwidth of the UV radiation of the UV light-emitting diode used to measure the NO concentration. In addition, there is an overlap with the absorption spectra of SO ₂ and NO ₂ , which leads to great cross-sensitivities of the _{NO concentration measurement to SO 2} and NO ₂ . The interfering gas components SO ₂ and NO ₂ absorb both in the center of the NO band and in the edge areas of the UV radiation of the UV light-emitting diode used to measure the NO concentration. Measuring the NO concentration with a UV light emitting diode is also problematic because the absorption lines and emission lines of NO are not congruent. Much of the radiation from the UV light-emitting diode is not absorbed by the NO band, which leads to a lower measurement effect.

Disclosure of the invention One object of the invention is to reduce cross-sensitivities of a measurement of an NO concentration in a gas mixture containing at least one interfering gas component.

This problem is solved by the independent patent claims. Advantageous configurations are given in the dependent claims, the following description and the figures, these configurations each taken individually or in various combinations of at least two of these configurations with one another being able to represent a further or advantageous aspect of the invention. Advantageous configurations of the device can correspond to advantageous configurations of the method, and vice versa, even if this is not explicitly referred to in the following.

A device according to the invention for measuring an NO concentration in a gas mixture containing at least one interfering gas component has at least one measuring chamber receiving the gas mixture and at least one optoelectronic measuring arrangement for measuring the NO concentration, the measuring arrangement being set up, the measuring chamber To measure the NO concentration with UV radiation suitable for this purpose and to detect the UV radiation emerging from the measuring chamber, the measuring arrangement having at least one UV light emitting diode for generating the UV radiation. In addition, the device according to the invention has at least one reference measuring unit which is arranged downstream of the measuring chamber with regard to a radiation direction of the UV radiation illuminating the measuring chamber is arranged to be acted upon, at least one gas cell filled with NO, which is arranged to be transilluminated with a part of the UV radiation emanating from the beam splitter, and at least one reference detector, which is arranged to be acted upon by a UV radiation emerging from the gas cell.

According to the invention, a UV light-emitting diode is used to measure the NO concentration in the gas mixture and gas-specific filtering is carried out using the NO-filled gas cell in order to improve the sensitivity of the measurement and at the same time reduce the cross-sensitivity of the measurement to the at least one interfering gas component . In the context of the invention, an interfering gas component is understood to be a gas component of the gas mixture which interferes with the measurement of the NO concentration in the gas mixture. This interference is caused by an overlap of the absorption spectrum of NO with the absorption spectrum of the at least one interfering component, which leads to an interfering cross-sensitivity of the NO concentration measurement to the interfering component.

The gas mixture can, for example, be an exhaust gas from an internal combustion engine of a motor vehicle, in particular a motor vehicle. A number of different interfering gas components are usually present in such an exhaust gas, such as, for example, SO ₂ , NO ₂ , unburned hydrocarbons, which interfere with an NO concentration _{measurement in a similar way to SO 2} and NO ₂ , and the like.

When the UV radiation emanating from the beam splitter passes through the gas cell filled with NO, all of the UV radiation within the NO band is absorbed. Only the wavelength edge areas of the UV radiation from the UV light-emitting diode are let through by the gas cell filled with NO and hit the reference detector, which detects this transmitted UV radiation as reference radiation. These wavelength edge regions of the UV radiation are absorbed by the at least one interfering gas component present in the measurement gas that is present in the measurement chamber, which leads to a weakening of the UV radiation at the reference detector. This weakening of the UV radiation also occurs in the same way on a measuring detector of the measuring arrangement on which a further part of the UV radiation emanating from the beam splitter impinges, so that this influencing effect (weakening) when a difference is formed and a subsequent one Quotient formation can be eliminated in evaluation electronics or in software executed with it. Overall, this reduces the cross-sensitivities of the measurement of the NO concentration in a gas mixture containing the at least one interfering gas component.

The measuring arrangement can be designed as a photometer or have one. The measuring chamber can be designed as a gas cuvette or measuring cuvette which can be transilluminated in the longitudinal direction with electromagnetic radiation in the form of UV radiation by means of at least one radiation source of the measuring arrangement.

The device can have at least one gas supply device connected to the measuring chamber, which is set up to supply the measuring chamber with the gas mixture. The gas supply device can communicate with at least one Have gas supply line connected to the measuring chamber and at least one gas discharge line communicating with the measuring chamber. Closing valves can be arranged on these lines, which can be closed after the measuring chamber has been flushed out with the gas mixture in order to have and measure static gas component concentration values, in particular a static NO concentration value, in the measuring chamber. Alternatively, the closing valves can be open or not present, so that the gas mixture flows continuously and evenly through the measuring chamber during the measurement of the respective gas component concentration, in particular NO concentration, whereby dynamic gas component concentration values, in particular a dynamic NO concentration value , exist and can be measured.

The UV light-emitting diode of the measuring arrangement can, for example, generate UV radiation with a maximum at A = 226 nm. The UV light emitting diode can be designed as an SMD module or as a microchip. The UV light-emitting diode is preferably arranged in the area of the optical axis of the measuring arrangement, as a result of which the optical imaging is simplified or more efficient.

Reference values, in particular reference voltage values U _Ref. , Can be generated by means of the reference measuring unit. By means of the measuring detector of the measuring arrangement, on which the further part of the UV radiation emanating from the beam splitter impinges, measured values, in particular measured voltage values U _Mess. , be generated. These detectors each record an integral value of the radiation power P of the UV light-emitting diode. The detectors can output the reference values or measured values via a preamplifier, which can also be part of the device. The voltage _{values U Ref.} And U _Mess. can be in a range around 1 volt.

The beam splitter of the reference measuring unit can have a splitting ratio of 50:50, so that 50% of the UV radiation emerging from the measuring chamber reaches the gas cell filled with NO and 50% of this UV radiation reaches the measuring detector of the measuring arrangement.

The gas cell of the reference measuring unit filled with NO can be designed as a gas cuvette or measuring cuvette which can be transilluminated with the part of the UV radiation emerging from the measuring chamber from the beam splitter. The measuring arrangement can additionally have at least one reference measuring device upstream of the measuring chamber, which has at least one beam splitter and at least one reference detector to which UV radiation emanating from the beam splitter can be applied in order to carry out a reference measurement. The beam splitter of the reference measuring device can be designed and arranged in such a way that it decouples 10% of the UV radiation incident on it and uses it to act on the reference detector of the reference measuring device. In order to detect lower gas component concentrations, in particular NO concentrations, it is necessary to obtain a very good signal stability at the zero point. By using the upstream reference measurement device and a comparison of the measurement signals from the upstream reference measurement device with measurement signals from the measurement detector of the measurement arrangement downstream of the measurement chamber, additional information is obtained about the contamination status of the interior of the measurement chamber. These changes in the measuring chamber can lead to an undesirable zero point drift, which must be prevented. The use of the upstream reference measuring device thus creates an improvement in the zero point stability of the gas component concentration measurement, in particular also of the NO concentration measurement.

The device according to the invention can be used, for example, to analyze a combustion exhaust gas from a system or machine or in pollutant emission measurement technology. In particular, the device according to the invention can be used for measuring an NO concentration in an exhaust gas of an internal combustion engine of a motor vehicle, in particular a motor vehicle.

According to an advantageous embodiment, the device has at least one evaluation electronics connected to the measuring arrangement, which are set up, when a zero gas is present in the measuring chamber, measured values of the reference detector and measured values of a measuring detector of the measuring arrangement, which is connected to a further part extending from the beam splitter the UV radiation is arranged to be acted upon, to detect and store, to record measured values of the reference detector and measured values of a measuring detector when the gas mixture is present in the measuring chamber, normalized measured values each as a quotient of a currently recorded measured value of the measuring detector and the stored measured value of the measurement detector, to determine normalized reference values in each case as a quotient of a currently detected measurement value of the reference detector and the stored measurement value of the reference detector, modulation values in each case by Dividing a difference between the respective normalized reference value of the reference detector and the respective normalized measured value of the measuring detector by the respective normalized reference value of the reference detector to determine a modulation function that depends on the NO concentration from the modulation values, an NO con- to determine the centering function by inversion of the modulation function, to approximate a polynomial of degree ≥ 2 to the NO concentration function, to store the coefficients of the polynomial and to determine the NO concentration in the gas mixture using the coefficients of the polynomial.

To record the measurement signals from the detectors, the zero gas is first introduced into the measurement chamber and x-rayed. The zero gas can be nitrogen or room air, for example. The zero gas does not cause any weakening of the UV radiation of the UV light-emitting diode in the measuring channel by NO and the at least one interfering gas component. In this state of the device, the reference measuring unit can be used to generate _{a reference voltage value U Ref} _. can be generated. After these voltage values have stabilized, they can be accepted and _{stored as values U * Ref} or U * _Mess , for example in a microcontroller of the device. Then the measurement signals or voltage values recorded in the following are divided by the assigned stored voltage value U * so that a normalized measured value or normalized reference value of “1” is available immediately after this zeroing. The following applies to the standardized values:

These values are included in the calculation of modulation values as follows:

This value is equal to 0 after zeroing. If the value U _{Mess changes.} as a result of an increasing NO concentration, the modulation value increases. The modulation value is always between 0 and 1 and satisfies a modulation function Mod (c) of the NO concentration c in the gas mixture. The NO concentration c can then be calculated from this modulation function by forming the inverse function of Mod (c). This function is then given by a higher degree polynomial

approximated, whose coefficients a-1, ..., a _n are stored and are available for the NO concentration calculation using this polynomial. The calculated concentration c (Mod) will thus also be equal to 0 after zeroing, since the modulation Mod (c) is then equal to 0.

According to a further advantageous embodiment, the UV light-emitting diode is arranged on a metal core circuit board. This allows the thermal power loss of the UV light emitting diode to be dissipated better and faster by the UV light emitting diode, which extends the service life of the UV light emitting diode and enables the radiation characteristics of the UV light emitting diode to be affected as little as possible by temperature fluctuations in the UV light emitting diode. is pregnant.

According to a further advantageous embodiment, at least one Peltier element is arranged on the metal core circuit board. The Peltier element can be arranged, for example, on one side of the metal core circuit board which is opposite that side of the metal core circuit board on which the UV light-emitting diode is arranged. The UV light-emitting diode can be kept at a constant temperature by means of the Peltier element.

According to a further advantageous embodiment, the device has at least one temperature sensor which is arranged to measure a temperature of the UV light-emitting diode. The temperature sensor, for example a platinum temperature sensor, which has a nominal resistance of 100 ohms at a temperature of 0 ° C., can also be arranged on the metal core circuit board. The temperature sensor is preferably arranged in the immediate vicinity of the UV light-emitting diode. The Peltier element can be controlled by means of the temperature information from the temperature sensor in order to keep the UV light-emitting diode at a constant temperature. According to a further advantageous embodiment, the measuring arrangement has at least one further UV light-emitting diode for generating UV radiation with which the measuring chamber can be transilluminated and which has a measuring wavelength that corresponds to a wavelength of a maximum of an absorption band specific for the interfering gas component. The measuring arrangement can also have two further UV light emitting diodes, for example a UV light emitting diode for measuring an SO ₂ concentration and a UV light emitting diode for measuring the NO ₂ concentration in the gas mixture. A measuring detector of the measuring arrangement can be set up to detect the various UV rays. Alternatively, the measuring arrangement can have its own measuring detector for each UV radiation. The at least one further UV light-emitting diode can be designed as an SMD module or as a microchip. The UV light-emitting diodes are preferably arranged as close to one another as possible, preferably in the area of the optical axis of the measuring arrangement. This simplifies or makes the optical imaging more efficient. For measuring the concentration of the at least one interfering gas component, the above-mentioned reference measurement using the reference measuring device upstream of the measuring chamber is advantageous, in particular to be able to compensate for contamination of the measuring chamber when determining the concentration of the interfering gas component in the gas mixture.

According to a further advantageous embodiment, all UV light-emitting diodes are arranged on the metal core circuit board.

According to a method according to the invention for measuring an NO concentration in a gas mixture containing at least one interfering gas component, the gas mixture is introduced into a measuring chamber which illuminates the measuring chamber filled with the gas mixture for measuring the NO concentration with a suitable UV radiation which UV radiation emerging from the measuring chamber is detected, a gas cell filled with NO is illuminated with part of the UV radiation emerging from the measuring chamber and the UV radiation emerging from the gas cell is detected by means of a reference detector.

The advantages mentioned above with reference to the device are correspondingly associated with the method. In particular, the device according to one of the above-mentioned configurations or a combination of at least two of these configurations with one another can be used to carry out the method. According to an advantageous embodiment, when a zero gas is present in the measuring chamber, measuring signals from the reference detector and measuring signals from a measuring detector that can be acted upon by a further part of the UV radiation emerging from the measuring chamber are electronically recorded and stored; when the gas mixture is present in the measuring chamber, measured values from the reference detector and measured values are recorded of a measuring detector, normalized measured values are determined as a quotient of a currently recorded measured value of the measuring detector and the stored measured value of the measuring detector, normalized reference values are each determined as the quotient of a currently recorded measured value of the reference detector and the stored measured value of the reference - Detector determined, modulation values are each divided by dividing a difference between the respective normalized reference value of the reference detector and the respective normalized measured value of the measuring detector by the respective Determined from the standardized reference value of the reference detector, a modulation function dependent on the NO concentration is determined electronically from the modulation values, if an NO concentration function is determined electronically by inversion of the modulation function, a polynomial of the degree ≥ 2 is attached to the NO concentration function electronically approximated, the coefficients of the polynomial are electronically stored and the NO concentration in the gas mixture is determined electronically using the coefficients of the polynomial. The advantages mentioned above with reference to the corresponding embodiment of the device are correspondingly associated with this embodiment.

In the following, the invention is explained by way of example with reference to the attached figures using preferred exemplary embodiments, the features explained below being able to represent a further-developing or advantageous aspect of the invention both individually and in different combinations with one another.

Brief description of the figures

It shows:

1 shows a spectrum of absorption spectra of sulfur dioxide, nitrogen monoxide and nitrogen dioxide recorded in transmission;

FIG. 2 shows an enlargement of the spectral range from FIG. 1 in the region of the absorption band of nitrogen monoxide; FIG. 3 shows a schematic representation of an exemplary embodiment for a device according to the invention;

FIG. 4 shows a schematic representation of a detail of the device shown in FIG. 3;

5 shows an exemplary spectral distribution of a UV radiation emitted by a UV light-emitting diode which can be used for measuring the NO concentration;

6 shows three different spectral distributions of the UV radiation on the measuring detector and on the reference detector, caused by different gases in the measuring chamber; and

7 shows diagrams of an exemplary embodiment for a modulation function Mod (c) and an NO concentration function c (M).

Detailed description of the figures

Identical or functionally identical components are provided with the same reference symbols in the figures. A repeated description of such components can be omitted in the following.

1 shows a spectrum of absorption spectra of SO ₂ (graph 1), NO (graph 2) and NO ₂ (graph 3) recorded in transmission. The radiation intensity T, measured in transmission, of an electromagnetic radiation guided through a gas mixture is plotted in% against the wavelength l of the electromagnetic radiation in nm, the gas mixture containing the interfering gas components SO ₂ and NO ₂ .

From graphs 1, 2 and 3 it can be seen that the interfering gas component SO _{2 has} _{an absorption band with a maximum at λ 3} = 285 nm, the gas component NO has an absorption band with a maximum at λ ₁ = 226 nm and the Interfering gas component NO _{2 has} an absorption band with a maximum at λ ₄ = 405 nm.

The diagram from FIG. 1 also shows the radiation spectra 4, 5 and 6 of UV light-emitting diodes, the maxima of which are also at the wavelengths λ ₁ , λ ₃ and λ ₄ . Furthermore, a reference radiation spectrum 7 of a further UV light-emitting diode is shown, the maximum of which is at a wavelength λ ₂ = 240 nm. 1 shows that the bandwidth of the UV radiation of the UV light-emitting diodes for the radiation spectra 5 and 6 is in each case smaller than the bandwidth of the respective absorption band of SO ₂ or NO ₂ . This results in a large measuring effect due to the total absorption of radiation. In contrast, the absorption band of NO is much narrower by λ = 226 nm than the bandwidth of the UV radiation of the UV light-emitting diode to the radiation spectrum 4. In addition, there is an overlap of the absorption spectrum of NO with the absorption spectra of SO ₂ and NO ₂ , which leads to large cross-sensitivities when measuring the NO concentration.

FIG. 2 shows an enlargement of the spectral range from FIG. 1 in the region of the absorption band of NO at λ = 226 nm. From FIG -LED to the radiation spectrum 4 is. In addition, the overlapping of the absorption spectrum of NO with the absorption spectra of SO ₂ and NO _{2 can be seen} more clearly.

3 shows a schematic representation of an exemplary embodiment for a device 8 according to the invention for measuring an NO concentration in a gas mixture containing _{the interfering gas components SO 2} and NO _2.

The device 8 has a measuring chamber 9 that receives the gas mixture and has a gas inlet 10 and a gas outlet 11. The measuring chamber 9 is designed as a measuring cuvette with a hollow cylindrical jacket 12 and radiation-permeable end windows 13 and 14.

In addition, the device 8 has an optoelectronic measuring arrangement 15 for measuring the NO concentration. The measuring arrangement 15 is set up to illuminate the measuring chamber 9 for measuring the NO concentration with UV radiation suitable for this purpose and to detect the UV radiation emerging from the measuring chamber 9.

For this purpose, the measuring arrangement 15 has a UV light-emitting diode, not shown in FIG. 3, for generating the UV radiation corresponding to the radiation spectrum 4 from FIGS. 1 and 2, a UV light-emitting diode, not shown in FIG. 3, for generating the UV radiation corresponding to the radiation spectrum 5 from FIGS. 1 and 2 and a UV light-emitting diode, not shown in FIG. 3, for generating the UV radiation corresponding to the radiation spectrum 6 from FIGS. 1 and 2 on. These UV light-emitting diodes are arranged on a front side of a metal core printed circuit board 16, on the rear side of which a Peltier element 17 is arranged, on which in turn a cooling rib structure 18 is arranged. A temperature sensor 19 for measuring the temperature of the UV light-emitting diodes is also arranged on the front side of the metal core circuit board 16. The UV light-emitting diodes and their arrangement on the metal circuit board 16 is shown in FIG. 4.

The device 8 has evaluation electronics, not shown, connected to the measuring arrangement 15, which are connected to the temperature sensor 19 and the Peltier element 17 in order to be able to keep the temperature of the UV light-emitting diodes constant by dissipating heat.

In addition, the evaluation electronics are connected to the UV light-emitting diodes in order to be able to control them in phase opposition or to activate and deactivate them, as is indicated by the two control signal curves 20 and 21. The UV light-emitting diodes are activated sequentially. After a first control cycle [1 -2-3-4] there is a dark phase [0] in order to be able to detect a zero point of a detector / amplifier unit.

The measuring arrangement 15 also has a collecting lens 22 which collects the UV radiation emanating from the UV light-emitting diodes and directs it onto a beam splitter 23 of the measuring arrangement 15. Part of the UV radiation impinging on the beam splitter 23 is decoupled by means of the beam splitter 23 and directed onto a reference detector 25 of the measuring arrangement 15 by means of a further converging lens 24 of the measuring arrangement 15. The other part of the UV radiation striking the beam splitter 23 passes through the measuring chamber 9.

After exiting the measuring chamber 9, the UV radiation is directed onto a beam splitter 27 of a reference measuring unit 28 of the device 8 by means of a further collecting lens 26 of the measuring arrangement 15. The reference measuring unit 28 is arranged downstream of the measuring chamber 9 with regard to a direction of radiation of the UV radiation transilluminating the measuring chamber 9.

Part of the UV radiation striking the beam splitter 27 is directed onto a measuring detector 29 of the measuring arrangement 15. The other part of the UV radiation impinging on the beam splitter 27 is decoupled by means of the beam splitter 27 and directed onto a gas cell 30 of the reference measuring unit 28 filled with NO. The gas cell 30 is permeable to radiation and arranged to be transilluminatable with the part of the UV radiation proceeding from the beam splitter 27. To this end, the gas cell 30 has radiation-permeable windows 31 and 31 at the end

32 on. The reference measuring unit 28 also has a reference detector 33, which is arranged so that it can be acted upon by UV radiation emerging from the gas cell 30.

The evaluation electronics are set up to record and store measurement signals from reference detector 33 and measurement signals from measurement detector 29 of measurement arrangement 15 when a zero gas is present in measurement chamber 9. Furthermore, the evaluation electronics are set up to record measured values from the reference detector 33 and measured values from a measurement detector 29 when the gas mixture is present in the measuring chamber 9. In addition, the evaluation electronics are set up to determine normalized measured values as the quotient of a currently recorded measured value of the measurement detector 29 and the stored measured value of the measurement detector 29 and normalized reference values as a quotient of a currently recorded measured value of the reference detector 33 and the stored measured value of the reference detector 33 to be determined. Furthermore, the evaluation electronics are set up, modulation values in each case by dividing a difference between the respective normalized reference value of the reference detector 33 and the respective normalized measured value of the measuring detector 29 by the respective normalized reference value of the reference detector

33 to be determined. In addition, the evaluation electronics are set up to determine a modulation function dependent on the NO concentration from the modulation values, to determine an NO concentration function by inversion of the modulation function, to approximate a polynomial of degree> 2 to the NO concentration function, the coefficients of the poly - To store noms and to determine the NO concentration in the gas mixture using the coefficients of the polynomial.

FIG. 4 shows a schematic representation of a detail of the device 8 shown in FIG. 3. The front side of the metal core circuit board 16 is shown, on which four UV light-emitting diodes

34 to 37 and the temperature sensor 19 are arranged. The UV light-emitting diodes 34 to 37 are arranged close to one another and in the area of the optical axis of the measuring arrangement (not shown). The UV light-emitting diodes 34 to 37 each generate UV radiation, as shown in FIGS. 1 and 2 are shown, which is indicated by the wavelengths li, l2, fo and l4. The UV light-emitting diode 34 is used to generate UV radiation with which the measuring chamber shown in FIG. 3 can be transilluminated and which has a measuring wavelength li which corresponds to a wavelength of a maximum of an absorption band specific for NO. The UV light-emitting diode 35 is used to generate UV radiation with which the measuring chamber shown in FIG. 3 can be transilluminated and which has a measuring wavelength λ ₃ which corresponds to a wavelength of a maximum of an absorption band specific _{for SO 2.} The UV light emitting diode 36 is used to generate a UV reference radiation with which the measuring chamber shown in FIG. 3 can be transilluminated and which has a measuring wavelength λ ₂ . The UV light emitting diode 37 is used to generate UV radiation with which the measuring chamber shown in FIG. 3 can be transilluminated and which has a measuring wavelength λ ₄ which corresponds to a wavelength of a maximum of an absorption band specific _{for NO 2.}

5 shows an exemplary spectral distribution of a UV radiation emitted by a UV light-emitting diode which can be used for measuring the NO concentration. The optical radiation power P (λ) in mW is plotted against the wavelength l in nm. The optical radiation power P (λ) is identical to the radiation flux Φ.

The detectors of the device not shown in FIG The absorption of radiation in the measuring chamber by NO ₂ , SO ₂ and NO, the intensity Io of the UV radiation of the UV light-emitting diodes is weakened according to the Lambert-Beer law:

Here, 1 (c) is an intensity (W / m ² ) impinging on the detector surface of the respective detector, α (λ) is a wavelength-dependent absorption coefficient of the respective gas component in the measuring chamber, c is a concentration of the respective gas component in the measuring chamber and L is the length of the distance covered by the UV radiation through the gas mixture in the measuring chamber.

With the measuring detector of the measuring arrangement of the device, the following integral radiation powers or radiation intensities E _Mess. recorded: In the spectral range of the UV radiation of the UV light-emitting diode used for NO measurement around λ ₁ .

In the spectral range of the UV radiation of the UV light-emitting diode used for the reference measurement around λ ₂ ^:

In the spectra of the UV radiation of the UV light-emitting diode used _{for SO 2} _{measurement around λ 3:}

In the spectral range of the UV radiation of the UV light-emitting diode used _{for NO 2} _{measurement around λ 4:}

Here, α _1.1 , α _1.2 , α _1.3 and α _{1.4 are} the absorption coefficients of NO ₂ at the wavelength λ ₁ , λ ₂ , λ ₃ and λ ₄ , α _2.1 , α _2.2 and α _{2.3 are} the absorption coefficients of SO ₂ at the wavelength λ ₁ , λ ₂ and λ _3, respectively. α _NO is the absorption coefficient of NO at wavelength λ ₁ , O _{NO (2)} is the absorption coefficient of NO at wavelength λ ₂ , Ci is the concentration of NO ₂ , C ₂ is the concentration of SO ₂ , C _NO is the The concentration of NO and L is the length of the distance covered by the UV radiation through the gas mixture in the measuring chamber.

_{The irradiance E Ref which} can be detected with the reference detector of the reference measuring device from FIG. 3 connected upstream of the measuring chamber.

_{The irradiance E Ref} .5 which can be detected with the reference detector of the reference measuring unit from FIG. 3 connected downstream of the measuring chamber during the NO measurement corresponds to

where LG is the length of the distance covered by the UV radiation through the NO gas in the gas cell 30. Since there is a very high NO concentration CNO.G in the gas cell, for example 100%, this integral radiation output changes only slightly due to the significantly lower NO concentration in the measuring chamber, so that the factor

versus the factor

can be neglected.

In the evaluation electronics of the device from FIGS. 3 and 4, the measured irradiance E of the different detectors can be normalized and offset by forming a quotient. This measure compensates for the signal change in the NO gas concentration CNO to be measured in the presence of NO ₂ and SO _2.

The following then applies to the NO modulation values:

6 shows different spectral distributions A, B and C of the UV radiation on the measuring detector and on the reference detector, caused by different gases in the measuring chamber. The UV radiation is used to measure the NO concentration and has a maximum at λ ₁ = 226 nm.

The spectral distributions A result when there is a zero gas, for example nitrogen or room air, in the measuring chamber. There is no weakening of the UV radiation in the measuring channel MK. In the reference channel, which has the gas cell filled with NO, there is a weakening of the UV radiation at λ ₀ . This results in a difference D = RK-MK.

The spectral distributions B result when a gas mixture with a certain NO concentration, but without SO ₂ and without NO _2, is in the measuring chamber. There is now a weakening of the UV radiation in the measuring channel MK. The change in the radiation absorption responsible for this weakening is proportional (Lambert-Beer’s law) to the NO concentration in the measuring chamber.

The spectral distributions C result when there is a gas mixture with NO, NO ₂ and SO ₂ in the measuring chamber. This results in radiation absorption in the reference channel RK and in the measurement channel MK both at lo by NO, NO ₂ and SO ₂ and radiation absorption in flanks of the UV radiation by NO ₂ and SO ₂ .

7 shows diagrams of an exemplary embodiment for a modulation function Mod (c) and an exemplary embodiment for an NO concentration function c (Mod), which result when the device from FIGS. 3 and 4 can result. The modulation function Mod (c) results from the modulation advertising calculation described above. The modulation function Mod (c) is inverted to obtain the NO concentration function c (Mod). List of reference symbols

1 graph (SO ₂ )

2 graph (NO)

3 graph (N0 ₂ )

4 radiation spectrum (NO-UV light-emitting diode)

5 radiation spectrum (S0 ₂ UV light-emitting diode)

6 radiation spectrum (N0 ₂ UV light-emitting diode)

7 Reference radiation spectrum (UV light-emitting diode)

8 device

9 measuring chamber

10 gas inlet from 9

11 gas outlet from 9

12 coat of 9

13 windows from 9

14 windows from 9

15 Measurement setup

16 metal core circuit board

17 Peltier element

18 cooling fin structure

19 temperature sensor

20 Control waveform

21 Control signal curve

22 converging lens from 15

23 beamsplitters from 15

24 converging lens from 15

25 reference detector from 15

26 converging lens from 15

27 beamsplitters from 28

28 Reference measuring unit

29 measuring detector from 15

30 gas cell from 28

31 windows from 30 32 windows from 30

33 reference detector from 28

34 UV light emitting diode (NO)

35 UV light emitting diode (SO ₂ )

36 UV light emitting diode (reference)

37 UV light emitting diode (N0 ₂ )

38 Control waveform

39 Control signal curve c concentration

C ₁ NO ₂ concentration c ₂ SO ₂ concentration C _NO NO concentration D Difference RK-MK M Modulation Mod Modulation MK Measurement channel P Radiated power RK reference channel

T radiation intensity in transmission l wavelength lo wavelength (maximum NO absorption) li wavelength (NO) l ₂ wavelength (reference) h wavelength (SO ₂ ) l4 wavelength (NO ₂ )

Claims

1. Device (8) for measuring an NO concentration (CNO) in a gas mixture containing at least one interfering gas component, having at least one measuring chamber (9) receiving the gas mixture and at least one optoelectronic measuring arrangement (15) for measuring the NO Concentration (CNO), the measuring arrangement (15) being set up to illuminate the measuring chamber (9) for measuring the NO concentration (CNO) with UV radiation suitable for this purpose and the UV radiation emitted from the measuring chamber (9). To detect radiation, the measuring arrangement (15) for generating the UV radiation having at least one UV light-emitting diode (34, 35, 36, 37), characterized by at least one reference measuring unit (28) which, with regard to a radiation direction, of the the measuring chamber (9) transilluminating UV radiation is arranged downstream of the measuring chamber (9), the reference measuring unit (28) having at least one beam splitter (27) which beau with the UV radiation emerging from the measuring chamber (9) at least one gas cell (30) filled with NO, which is arranged to be transilluminated with part of the UV radiation emanating from the beam splitter (27), and at least one reference detector (33) which is connected to a UV radiation emerging from the gas cell (30) is arranged to be acted upon.

2. Device (8) according to claim 1, characterized by at least one evaluation electronics connected to the measuring arrangement (15), which are set up, in the presence of a zero gas in the measuring chamber (9), measured values of the reference detector (33) and measured values of a measuring detector ( 29) of the measuring arrangement (15), which can be acted upon by a further part of the UV radiation emanating from the beam splitter (27), to acquire and store, if the gas mixture is present in the measuring chamber (9), measured values of the reference detector ( 33) and measured values of a measuring detector (29) to determine normalized measured values in each case as a quotient of a currently recorded measured value of the measuring detector (29) and the stored measured value of the measuring detector (29), normalized reference values in each case as a quotient to determine a respective momentarily recorded measured value of the reference detector (33) and the stored measured value of the reference detector (33), modulation values each because by dividing a difference between the respective normalized reference value of the reference detector (33) and the respective normalized measured value of the measuring detector (29) by the respective normalized reference value of the reference detector (33) to determine one of the NO concentration (C _NO ) dependent To determine the modulation function from the modulation values, to determine an NO concentration function by inversion of the modulation function, to approximate a polynomial of degree> 2 to the NO concentration function, to store the coefficients of the polynomial and to store the NO concentration in the gas mixture using the To determine the coefficients of the polynomial.

3. Device (8) according to claim 1 or 2, characterized in that the UV light emitting diode (34, 35, 36, 37) is arranged on a metal core circuit board (16).

4. Device (8) according to claim 3, characterized in that at least one Peltier element (17) is arranged on the metal core printed circuit board (16).

5. Device (8) according to claim 4, characterized by at least one temperature sensor (19) which is arranged to measure a temperature of the UV light-emitting diode (34, 35, 36, 37).

6. Device (8) according to one of claims 1 to 5, characterized in that the measuring arrangement (15) has at least one further UV light emitting diode (35) for generating UV radiation with which the measuring chamber (9) can be transilluminated and which has a measurement wavelength which corresponds to a wavelength of a maximum of an absorption band specific for the interfering gas component.

7. Device (8) according to claim 6, characterized in that all UV light-emitting diodes (34, 35, 36, 37) are arranged on the metal core circuit board (16).

8. A method for measuring an NO concentration (CNO) in a gas mixture containing at least one interfering gas component, the gas mixture being introduced into a measuring chamber (9) and the measuring chamber (9) filled with the gas mixture for measuring the NO concentration ( CNO) is transilluminated with a suitable UV radiation, whereby the UV radiation emerging from the measuring chamber (9) is detected, characterized in that a gas cell (30) filled with NO is connected to part of the gas cell (30) from the measuring chamber (9) ) exiting UV radiation is transilluminated and the UV radiation emerging from the gas cell (30) is detected by means of a reference detector (33).

9. The method according to claim 8, characterized in that when a zero gas is present in the measuring chamber (9), measurement signals from the reference detector (33) and measurement signals a measuring detector (29) which can be acted upon by a further part of the UV radiation emerging from the measuring chamber (9) can be electronically recorded and stored Measuring detector (29) are recorded, normalized measured values are determined as the quotient of a currently recorded measured value of the measuring detector (29) and the stored measured value of the measuring detector (29), normalized reference values are each determined as the quotient of a currently recorded measured value of the reference - Detector (33) and the stored measured value of the reference detector (33) are determined, modulation values in each case by dividing a difference between the respective normalized reference value of the reference detector (33) and the respective normalized measured value of the measuring detector (29) by the respective normalized reference value of the reference detector (33) can be determined, one of the NO-Ko The modulation function dependent on the concentration (CNO) is determined electronically from the modulation values, an NO concentration function is determined electronically by inversion of the modulation function, a polynomial of the degree> 2 is electronically approximated to the NO concentration function, the coefficients of the

Polynomial are stored electronically and the NO concentration in the gas mixture is determined electronically using the coefficients of the polynomial.