Radiation absorption gas analyzer, and method for analyzing gas

Abstract

The invention relates to a gas analyzer having a first gas inlet (28), a second gas inlet (30), a first measuring cuvette (12) and a second measuring cuvette (14), the first measuring cuvette (12) being provided with a first radiation source (16) and a first radiation detector (20) such that radiation emitted by the first radiation source (16) passes through the first measuring cuvette (12) and is recorded by the first radiation detector (20) and the second measuring cuvette (14) being provided with a second radiation source (18) and a second radiation detector (22) such that radiation emitted by the second radiation source (18) passes through the second measuring cuvette and is recorded by the second radiation detector (22), characterized in that the first radiation detector (20) and the second radiation detector (22) differ from one another such that the first radiation detector (20) can conduct an absorption measurement of the radiation passing through the first measuring cuvette while the second radiation detector (22) simultaneously records radiation which passes through the second measuring cuvette (14), and in that the first gas inlet (28) and the second gas inlet (30) are each connected to the first measuring cuvette (12) and the second measuring cuvette (14) such that first measurement gas from the first gas inlet (28) and second measurement gas from the second gas inlet (30) are alternately supplied to the two measuring cuvettes (12, 14) such that first measurement gas is analyzed in one of the two measuring cuvettes (12) while second measurement gas is simultaneously analyzed in the other of the two measuring cuvettes (14).

Description

[0001] Radiation absorption gas analyzer and method for gas analysis

[0002] The invention relates to a gas analyzer for gas analysis based on the optical radiation absorption principle, which is used particularly in sniffer leak detection for gas detection. A typical radiation source used in this case is infrared radiation. However, radiation absorption measurement is also conceivable using other types of optical or electromagnetic radiation.

[0003] In radiation absorption analysis, a sample cuvette is filled with a sample gas. A radiation source and a radiation detector are positioned on opposite sides of the cuvette such that the optical radiation emitted by the radiation source penetrates the sample cuvette and the sample gas contained therein and is then detected by the gas detector. Based on the change in intensity of one or more selected absorption lines or bands of the radiation detected by the radiation detector, conclusions can be drawn about the gas, its composition, or the amount of gas within the cuvette.It is also known, for example from EP 1 161 675 B1, to use a second gas inlet as a reference gas inlet in optical radiation absorption measurements for gas analysis. The reference gas from this second gas inlet is fed to another reference cuvette, different from the measuring cuvette. One or more radiation sources transmit infrared light through the measuring gas in the measuring cuvette and through the reference gas in the reference cuvette. A common radiation detector records the radiation from the measuring cuvette and the radiation from the reference cuvette. The reference cuvette is connected exclusively to the reference gas inlet, and the measuring cuvette is connected exclusively to the measuring gas inlet.

[0004] The shared radiation detector can analyze either only the radiation from the measuring cuvette or the radiation from the reference cuvette, resulting in alternating analysis of the test gas and the reference gas. Therefore, a leak can only be detected during half the measurement time, because a reference measurement is performed during the other half. As a result, the test gas measurement is slowed down because the sniffer probe must remain on the test object even during the reference gas measurement, without being able to analyze the test gas during that time. Because the reference measurement is not performed simultaneously with the actual measurement, background fluctuations can cause interference.

[0005] Against this background, the invention is based on the object of enabling a faster, improved and more reliable radiation absorption analysis of a test gas and a reference gas.

[0006] The gas analyzer according to the invention has a first gas inlet, a second gas inlet, a first measuring cuvette, and a second measuring cuvette. The first measuring cuvette is provided with a first radiation source and a first radiation detector such that radiation emitted by the first radiation source penetrates the first measuring cuvette and is picked up by the first radiation detector, thus performing a radiation absorption measurement of the gas contained in the first measuring cuvette. Correspondingly, the second measuring cuvette is provided with a second radiation source and a second radiation detector such that radiation emitted by the second radiation source penetrates the second measuring cuvette and is picked up by the second radiation detector, thus performing a radiation absorption measurement of the gas contained in the second measuring cuvette.The first gas inlet can be a test gas inlet, through which a test gas to be tested is drawn, while the second gas inlet is a reference gas inlet, through which a reference gas is drawn for a comparison measurement. Alternatively, the test gas can be supplied via the second gas inlet, while the reference gas is supplied via the first gas inlet. It is crucial that only one of the test gas and the reference gas is supplied via each of the two gas inlets, while the other of the test gas and the reference gas is supplied via the other gas inlet.

[0007] In the present disclosure, the gas admitted through the first gas inlet is referred to as the first measurement gas, regardless of whether the test gas or the reference gas is supplied through the first gas inlet. Similarly, the gas admitted through the second gas inlet is referred to as the second measurement gas, regardless of whether the second measurement gas is the reference gas or the test gas. If the first measurement gas is the test gas to be analyzed, the second measurement gas is therefore the reference gas for the comparison measurement, and vice versa. This is intended to express that either test gas or reference gas can be supplied to the first gas inlet, while the other gas is supplied to the second gas inlet.

[0008] According to the invention, each of the two measuring cuvettes is alternately supplied with the first measuring gas from the first gas inlet and the second measuring gas from the second gas inlet, i.e. test gas and reference gas are alternately supplied depending on the assignment of test gas and reference gas to the two gas inlets. It is important that the first measuring gas is supplied to one measuring cuvette, while the other measuring gas is supplied to the other measuring cuvette at the same time. This makes it possible to alternately measure test gas and reference gas in each of the two cuvettes without changing the gas at the respective gas inlets, and yet still measure the reference gas and test gas simultaneously. Both cuvettes therefore alternately measure the first and second measuring gas. Different measuring cuvettes are always supplied with different measuring gases.

[0009] The switching valves according to the invention and their control system are designed such that both gas inlets are never connected to the same measuring cuvette. This allows test gas to be supplied to one measuring cuvette from one gas inlet at the same time as reference gas is supplied to the other measuring cuvette from the other gas inlet. By simultaneously switching the switching valves, test gas and reference gas are alternately supplied to the two measuring cuvettes, while the two measuring cuvettes always contain different measuring gases.

[0010] In the present disclosure, the radiation source whose radiation penetrates the first measuring cuvette is referred to as the first radiation source, while the radiation source whose radiation penetrates the second measuring cuvette is referred to as the second radiation source. The first radiation source and the second radiation source do not necessarily have to be different radiation sources. Rather, the first radiation source and the second radiation source can be the same radiation source, whose radiation then penetrates both measuring cuvettes. Alternatively, the first and second radiation sources can be different radiation sources.

[0011] In the present disclosure, the radiation detector that detects the radiation that has passed through the first measuring cuvette is referred to as the first radiation detector, while the radiation detector that detects the radiation that has passed through the second measuring cuvette is referred to as the second radiation detector.

[0012] According to the invention, the first radiation detector and the second radiation detector are different from each other, so that the first radiation detector can perform an absorption measurement of the radiation penetrating the first measuring cuvette, while the second radiation detector simultaneously detects radiation penetrating the second measuring cuvette. This allows the first measuring gas in one measuring cuvette and the second measuring gas in the other measuring cuvette to be analyzed simultaneously.For this purpose, the first gas inlet and the second gas inlet are each connected to both the first measuring cuvette and the second measuring cuvette in such a way that the first measuring gas from the first gas inlet can be admitted exclusively into the first measuring cuvette, while the second measuring gas from the second gas inlet can be admitted exclusively into the second measuring cuvette, in order to thereby measure the second measuring gas independently of the first measuring gas and simultaneously with the measurement of the first measuring gas and without mixing the two gases.

[0013] The radiation absorption measurement of the first sample gas can therefore be carried out independently of the radiation absorption measurement of the second sample gas and simultaneously. For example, the first sample gas can be a test gas to be analyzed and the second sample gas a reference gas for a comparison measurement. Thus, while the test gas is being analyzed in one measuring cuvette, the reference gas can be analyzed independently and simultaneously in the other measuring cuvette. The reference gas serves as a comparison to the test gas in order to compensate for interference in the test gas signal. For this purpose, the difference in the measurement signal recorded with a respective radiation detector between the reference gas and the test gas can be observed. The procedure for evaluating the respective measurement signals is described in EP 1 342 070 B1.

[0014] According to the invention, a first measuring line having the first gas inlet can be connected via a first switching valve to a first input line connected to the first measuring cuvette and a second input line connected to the second measuring cuvette. Using the first switching valve, the first gas inlet can be alternately and selectively connected to the first input line or the second input line.

[0015] Accordingly, a second measuring line having the second gas inlet can be connected via a second switching valve to the first input line connected to the first measuring cuvette and to the second input line connected to the second measuring cuvette. The second switching valve can thus selectively and alternately connect the second gas inlet to the first input line or the second input line.

[0016] According to a preferred embodiment, the two switching valves are designed such that the first gas inlet can be connected to the first measuring cuvette and not to the second measuring cuvette, while the second gas inlet is connected to the second measuring cuvette and not to the first measuring cuvette and / or vice versa. This means that the two switching valves can also be designed such that the second gas inlet can be connected to the first measuring cuvette and not to the second measuring cuvette, while the first gas inlet is connected to the second measuring cuvette and not to the first measuring cuvette. This can be achieved, for example, by an appropriately designed or configured electronic control device that is connected to the two switching valves and controls their switching states.

[0017] This makes it possible to supply the first measuring gas exclusively to one of the two measuring cuvettes, while the second measuring gas is supplied exclusively to the other measuring cuvette. By synchronously switching the two switching valves, the two measuring gases can be supplied to the respective measuring cuvettes alternately to one measuring cuvette and then to the other, in order to analyze both measuring gases one after the other with both measuring cuvettes. For example, while in a first switching cycle of the switching valves the first measuring cuvette carries out the test gas and the second measuring cuvette a reference measurement with reference gas, in the subsequent second switching cycle the first measuring cuvette can carry out the reference measurement while the second measuring cuvette carries out the analysis of the test gas. The switching back and forth can take place as often as required.

[0018] Alternatively, the first gas inlet can be connected to both the first switching valve and the second switching valve, namely to a first port of the first switching valve and a first port of the second switching valve, while the second gas inlet is also connected to both switching valves, but to different gas inlets of the switching valves. In this case, the first measuring cuvette is connected to a third port of the first switching valve that is different from the first two ports, while the second measuring cuvette is connected to a third port that is different from the first two ports of the second switching valve. In this way, the effect described above can also be achieved.

[0019] The first radiation source and the second radiation source can each be designed to modulate the radiation penetrating the first measuring cuvette and the second measuring cuvette.

[0020] As an alternative to radiation modulation using a modulated radiation source, gas exchange can also be used as modulation ("gas modulation") by switching the switching valves in each of the two measuring cuvettes. This principle is described, for example, in EP 1 342 070 B1.

[0021] Preferably, the first measuring cuvette has a first outlet for the measuring gas and the second measuring cuvette has a second outlet for the measuring gas, wherein the first measuring cuvette outlet and the second measuring cuvette outlet are connected to a vacuum pump which evacuates the measuring cuvette, the two inlet lines, the two measuring lines and / or the two gas inlets.

[0022] The changeover valves can, for example, be three-way gas valves.

[0023] In the method according to the invention for gas analysis based on the principle of optical radiation absorption with a gas analyzer of the type described above, the following steps are carried out one after the other in the following order: a) feeding the first measurement gas taken in with the first gas inlet into one of the two measuring cuvettes, e.g. the first measuring cuvette, while the second measurement gas taken in with the second gas inlet is fed to the other measuring cuvette, e.g. the second measuring cuvette, b) carrying out a radiation absorption analysis of the radiation penetrating the first measuring cuvette with the aid of the first detector, while a radiation absorption analysis of the radiation penetrating the second measuring cuvette is carried out with the aid of the second detector, c) feeding the first measurement gas taken in with the first gas inlet into the other, e.g. second measuring cuvette, while the second measurement gas taken in with the second gas inlet is fed to one, e.g.first measuring cuvette, d) repeating step b).

[0024] In the context of the invention, "first sample gas" refers to the gas supplied via the first gas inlet. Depending on the assignment, this can be either test gas or reference gas. "Second sample gas" refers to the gas supplied via the second gas inlet. This is the other gas in each case. This means that if the first sample gas is test gas, the second sample gas is automatically the reference gas, and vice versa.

[0025] In the method according to the invention, initially only the first measuring gas is supplied to one measuring cuvette, while at the same time only the other measuring gas is supplied to the other measuring cuvette in order to analyze the first measuring gas in the first measuring cuvette, while the other measuring gas is analyzed in the other measuring cuvette, wherein the measuring gas in the two measuring cuvettes is then changed by switching the two gas inlets to a different measuring cuvette. Changing the assignment of test gas and reference gas at the two gas inlets is therefore not necessary. In this way, each measuring cuvette alternately analyzes first one and then the other measuring gas, while at the same time the other measuring cuvette analyzes first the other and then the one measuring gas. After the measurement in each measuring cuvette, the respective gas is evacuated using the vacuum pump.These steps can be repeated as often as required, offering the advantage of reducing measurement offset errors. Switching the allocation of the two sample gases to the two sample cuvettes can be achieved by switching the two switching valves accordingly.

[0026] In the following, exemplary embodiments of the invention are explained in more detail with reference to the figures. They show:

[0027] Figure 1 is a schematic representation of a first embodiment and

[0028] Figure 2 is a schematic representation of a second embodiment.

[0029] Both figures show a first measuring cuvette 12 and a second measuring cuvette 14. Both cuvettes 12, 14 are each cylindrical in shape. A first radiation source 16 is arranged on one end of the first measuring cuvette 12. Correspondingly, a second radiation source 18 is arranged on one end of the second measuring cuvette 14. A first radiation detector 20 is arranged at the end of the first measuring cuvette 12 opposite the first radiation source 16 such that optical radiation emitted by the first radiation source 16, typically in the form of infrared radiation, penetrates the first measuring cuvette 12 lengthwise and is picked up by the first radiation detector 20 at the opposite end.

[0030] Similarly, the second measuring cuvette 14 is provided with a second radiation source 18 on one end face and with a second radiation detector 22 on its end face opposite the second radiation source 18. The second radiation detector 22 correspondingly detects radiation emitted by the second radiation source 18 and penetrating the second measuring cuvette 14 in the longitudinal direction.

[0031] Alternatively, it is conceivable that the first radiation source 16 and the second radiation source 18 are the same radiation source, with the radiation source transmitting radiation through both measuring cuvettes 12, 14, which is received by the two radiation detectors 20, 22. For the sake of simplicity, the radiation sources 16, 18 and the radiation detectors 20, 22 are not shown in Fig. 2, but are nevertheless present.

[0032] In Fig. 1, the first measuring cuvette 12 is provided with a first measuring cuvette inlet 24. Similarly, the second measuring cuvette 14 is provided with a second measuring cuvette inlet 26. The first measuring cuvette inlet 24 is connected to a first switching valve 36 in a gas-conducting manner, while the second measuring cuvette inlet 26 is connected to a second switching valve 38 in a gas-conducting manner. The first switching valve 36 is connected to the first measuring gas line 32 and thereby opens into the first gas inlet 28. The second switching valve 38 is connected to the second measuring gas line 34 and thereby opens into the second gas inlet 30. The two switching valves 36, 38 are also connected to one another by a connecting line 41 such that each switching valve 36, 38 can optionally connect each of the two gas inlets 28, 30 to the first or the second measuring cuvette 12, 14.

[0033] The first sample gas line 32 is thus connected to the first switching valve 36 in the form of a 3-way valve, while the second sample gas line 34 is connected to the second switching valve 38 in the form of a 3-way valve. The first sample gas line 32 is connected to a first port 36a of the first switching valve 36, while the second sample gas line 34 is connected to a first port 38a of the second switching valve 38. A third port 36c of the first switching valve 36 is gas-conductingly connected to a second port 38b of the second switching valve 38 via the connecting line 41. The connecting line 41 opens into a common second sample cell line 42 connected to the second sample gas inlet 26.

[0034] The second port 36b of the first switching valve 36 and the third port 38c of the second switching valve 38 are also connected to one another and open into a common first measuring cuvette line 40 connected to the first measuring gas inlet 24. It is possible to connect the first port 36a, 38a of each of the two switching valves 36, 38 optionally to the respective second port 38b, 36b or the third port 38c, 36c. In Fig. 1, the first port 36a of the first switching valve 36 is connected to its second port 36b, so that first measuring gas from the first gas inlet 28 passes through the first measuring cuvette line 40 into the first measuring cuvette 12. In a corresponding manner, the first connection of the second switching valve 38 is connected to its second connection, so that second measuring gas from the second gas inlet 30 passes into the second measuring cuvette 14 via the second measuring cuvette line 42.In each of the two valves 36, 38, the connection from the first port 36a, 38a to the third port 36c, 38c of the respective valve is blocked.

[0035] As a result, no gas can pass from the first gas inlet 28 into the second measuring cuvette line 42 and the second measuring cuvette 14, and likewise, no second measuring gas can pass from the second gas inlet 30 into the first measuring cuvette line 40 and the first measuring cuvette 12. This switching state corresponds to process steps a) and b). By synchronously switching the two switching valves, the switching state corresponding to process steps c) and d) is then established in order to supply the second measuring gas to the first measuring cuvette 12 and the first measuring gas to the second measuring cuvette 14.

[0036] According to the invention, the absorption analysis of the radiation recorded by the two detectors 20, 22 can take place simultaneously during a respective switching state of the two switching valves 36, 38. The absorption analysis of the radiation recorded by the first radiation detector 20 takes place independently of the analysis of the radiation recorded by the second radiation detector 22. It is conceivable that the first radiation detector 20 and the second radiation detector 22 are connected to a common evaluation unit (not shown in the figure), in which the respectively recorded measurement signals are evaluated with regard to the absorbed radiation components in order to determine the gas or the gas composition within the first measuring cuvette 12 and within the second measuring cuvette 14 based on the absorption spectrum.Alternatively, it is conceivable that the first radiation detector 20 is connected to a separate evaluation unit, which is different from the evaluation unit to which the second radiation detector 22 is connected. According to the invention, an absorption analysis of the recorded radiation spectra is enabled simultaneously and independently of each other by the first radiation detector 20 and the second radiation detector 22.

[0037] By synchronously switching the two switching valves 36, 38, it is possible to alternately analyze the first measuring gas and the second measuring gas with each of the two measuring cuvettes 12, 14. The first measuring gas can be a test gas to be analyzed, which is to be tested for possible leaks, while the second measuring gas can be a reference gas for a reference measurement. By switching the two switching valves 36, 38, the test gas measurement can be carried out alternately with one (e.g. first) cuvette and the reference measurement with the other (e.g. second) cuvette, while the reference measurement is then carried out with the other (e.g. second) measuring cuvette and the test gas measurement with one (e.g. first) measuring cuvette. This allows offset errors between the two measuring cuvettes 12, 14 to be compensated.

[0038] The first measuring cuvette 12 and the second measuring cuvette 14 are each provided with a corresponding outlet 48, 50 in a region opposite their respective inlets 24, 26, wherein a first measuring cuvette outlet 48 is assigned to the first measuring cuvette 12, while a second measuring cuvette outlet 50 is assigned to the second measuring cuvette 14. The first measuring cuvette outlet 48 and the second measuring cuvette outlet 50 open into a common outlet line 52, which is evacuated by a vacuum pump 54.

[0039] The embodiment according to Fig. 2 differs from that in Fig. 1 in that the first gas inlet 28 is connected to both the first port 36a of the first switching valve 36 and to the first port 38a of the second switching valve 38, while the second gas inlet 30 is connected to both the third port 36c of the first switching valve 36 and to the third port 38c of the second switching valve 38. The first port 36a is connected to the first gas inlet 28 via the first measuring gas line 32, while the first port 38a is connected to the second gas inlet 30 via the second measuring gas line 34, the third port 36c being connected to the second measuring gas line 34 and the first port 38a being connected to the first measuring gas line 34.The second connection 36b of the first switching valve 36 is then connected exclusively to the first measuring cuvette 12, namely via the first measuring cuvette line 40, while the second connection 38b of the second switching valve 38 is connected exclusively to the second measuring cuvette 14 via the second measuring cuvette line 42.

[0040] By synchronously switching the two switching valves 36, 38, in this embodiment, one gas inlet can also be assigned alternately to one switching valve and the other gas inlet to the other switching valve in order to supply each of the two measuring cuvettes 12, 14 alternately one after the other with the first measuring gas and the second measuring gas.

[0041] The first gas inlet 28 and the second gas inlet 30 can be arranged in a manner known per se, for example as described in EP 1 161 675 B1, on or in a hand-held sniffer probe.

Claims

Claims 1. A gas analyzer having a first gas inlet (28), a second gas inlet (30), a first measuring cuvette (12), and a second measuring cuvette (14), wherein the first measuring cuvette (12) is provided with a first radiation source (16) and a first radiation detector (20) such that radiation emitted by the first radiation source (16) penetrates the first measuring cuvette (12) and is picked up by the first radiation detector (20), and wherein the second measuring cuvette (14) is provided with a second radiation source (18) and a second radiation detector (22) such that radiation emitted by the second radiation source (18) penetrates the second measuring cuvette and is picked up by the second radiation detector (22), characterized in that the first radiation detector (20) and the second radiation detector (22) are different from one another,such that the first radiation detector (20) can perform an absorption measurement of the radiation penetrating the first measuring cuvette, while the second radiation detector (22) simultaneously records radiation penetrating the second measuring cuvette (14), and that the first gas inlet (28) and the second gas inlet (30) are each connected to the first measuring cuvette (12) and the second measuring cuvette (14) in such a way that first measuring gas from the first gas inlet (28) and second measuring gas from the second gas inlet (30) are alternately supplied to the two measuring cuvettes (12, 14) in such a way that first measuring gas is analyzed in one of the two measuring cuvettes (12), while simultaneously second measuring gas is analyzed in the other of the two measuring cuvettes (14).

2. Gas analyzer according to claim 1, characterized in that the first radiation source (16) and the second radiation source (18) are different radiation sources or the same radiation source.

3. Gas analyzer according to claim 1 or 2, characterized in that a first measuring line (32) having the first gas inlet (28) is connected via a first changeover valve (36) to a first inlet line (40) connected to the first measuring cuvette (12) and to a second inlet line (42) connected to the second measuring cuvette (14).

4. Gas analyzer according to one of claims 1 - 3, characterized in that a second measuring line (34) having the second gas inlet (30) is connected via a second changeover valve (38) to a first inlet line (40) connected to the first measuring cuvette (12) and to a second inlet line (42) connected to the second measuring cuvette (14).

5. Gas analyzer according to claim 1 or 2, characterized in that the first gas inlet (28) is connected to a first connection (36a) of the first switching valve (36) and to a first connection (38a) of the second switching valve (38), while the second gas inlet (30) is connected to a third connection (36c) of the first switching valve (36) and a third connection (38c) of the second switching valve (38), wherein a second connection (36b) of the first switching valve is connected to the first measuring cuvette (12) and a second connection (38b) of the second switching valve (38) is connected to the second measuring cuvette (14).

6. Gas analyzer according to one of claims 3 to 5, characterized in that the two switching valves (36, 38) are designed such that the first gas inlet (28) can be connected to the first measuring cuvette (12) and not to the second measuring cuvette (14), while the second gas inlet (30) is connected to the second measuring cuvette (14) and not to the first measuring cuvette (12) and vice versa.

7. Gas analyzer according to one of the preceding claims, characterized in that the second radiation detector (22) and the first radiation detector (20) are connected to an evaluation device which is designed to evaluate the measurement signals transmitted by the first radiation detector (20) and by the second radiation detector (22) according to the principle of radiation absorption analysis.

8. Gas analyzer according to one of the preceding claims, characterized in that the first radiation source (16) and the second radiation source (18) are each designed for gas modulation of the radiation penetrating the first measuring cuvette (12) and the second measuring cuvette (14).

9. Gas analyzer according to one of the preceding claims, characterized in that the first measuring cuvette (12) has a first measuring cuvette outlet (48) for the measuring gas and the second measuring cuvette (14) has a second measuring cuvette outlet (50) for the measuring gas, wherein the first measuring cuvette outlet (48) and the second measuring cuvette outlet (50) are connected to a vacuum pump (54).

10. A method for gas analysis according to the principle of optical radiation absorption with a gas analyzer according to one of the preceding claims, characterized by the steps in the following order: a) feeding the first measurement gas taken in through the first gas inlet (28) into one of the two measurement cuvettes (12), while the second measurement gas taken in through the second gas inlet (30) is fed to the other measurement cuvette (14), b) carrying out a radiation absorption analysis of the radiation penetrating the first measurement cuvette (12) using the first detector (20), while a radiation absorption analysis of the radiation penetrating the second measurement cuvette (14) is carried out using the second detector (22), c) feeding the first measuring gas taken in through the first gas inlet (28) into the other measuring cuvette (14), while the second measuring gas taken in through the second gas inlet (30) is fed to the one measuring cuvette (12), d) repeating step b).

11. Method according to the preceding claim, characterized in that in steps a) and b) only first measuring gas from the first gas inlet (28) is analyzed in one measuring cuvette (12) without second measuring gas from the second gas inlet (30) being introduced into one measuring cuvette (12), while only second measuring gas from the second gas inlet (30) is analyzed in the other measuring cuvette (14) without first measuring gas from the first gas inlet (28) being introduced into the other measuring cuvette (14).

12. Method according to one of the preceding claims, characterized in that in steps c) and d) only second measuring gas from the second gas inlet (30) is analyzed in one measuring cuvette (12) without first measuring gas from the first gas inlet (28) being introduced into one measuring cuvette (12), while only first measuring gas from the first gas inlet (28) is analyzed in the other measuring cuvette (14) without second measuring gas from the second gas inlet (30) being introduced into the other measuring cuvette (14).

13. Method according to one of the preceding claims, characterized in that steps a) - d) are repeated at least once.

14. Method according to one of the preceding claims, characterized in that the two switching valves (36, 38) are switched after step a) and before step c) and are switched after step c) and before a repeated step a).

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