Gas detection device with two measuring chambers and two detectors

Abstract

Gas detection device (1) for detecting at least one target gas in at least one gas mixture, wherein the gas detection device (1) comprises a radiation source (50) configured to emit electromagnetic radiation, a first measuring chamber (6) and a second measuring chamber (6'), as well as a first measuring detector (7) and a second measuring detector (7'), wherein the second measuring chamber (6') is spatially separated from the first measuring chamber (6), wherein the gas detection device (1) is configured such that a first gas mixture flows through the first measuring chamber (6) and a second gas mixture flows through the second measuring chamber (6'), wherein the gas detection device (1) is configured such that electromagnetic radiation emitted by the radiation source (50) first penetrates the first measuring chamber (6) and then the second measuring chamber (6'), wherein the first measuring detector (7) is configured toto measure a measure of a physical effect in the first measuring chamber (6), wherein this physical effect is caused by electromagnetic radiation penetrating the first measuring chamber (6) and correlates with the presence of target gas in the first measuring chamber (6), and to generate a first signal correlated with the physical effect in the first measuring chamber (6), and wherein the second measuring detector (7') is configured to measure a measure of a physical effect in the second measuring chamber (6'), wherein this physical effect is caused by electromagnetic radiation penetrating the second measuring chamber (6') and correlates with the presence of target gas in the second measuring chamber (6'), and to generate a second signal correlated with the physical effect in the second measuring chamber (6'), characterized in that the gas detection device (1) comprises a reflector (76) for electromagnetic radiation,wherein the radiation source (50) and the reflector (76) are arranged such that the electromagnetic radiation emitted by the radiation source (50) first passes through both measuring chambers (6, 6'), is reflected by the reflector (76) and passes through both measuring chambers (6, 6') a second time.

Description

The invention relates to a gas detection device for detecting a target gas in a gas mixture. The gas detection device comprises a radiation source configured to emit electromagnetic radiation, a measuring chamber, and a measuring detector, wherein the gas mixture flows through the measuring chamber and the measuring detector is configured to measure a physical effect in the measuring chamber, wherein this physical effect is caused by electromagnetic radiation penetrating the measuring chamber and correlates with the presence of the target gas in the measuring chamber, and to generate a signal correlated with the physical effect in the measuring chamber. A gas detection device comprises a measuring chamber and a measuring detector, particularly a photoionization detector, for detecting a gas in gas mixtures. Such gas detection devices are used in both stationary and, especially, portable applications. The gas mixture is introduced into the measuring chamber by means of a pump or other driving unit and is exposed to electromagnetic radiation emitted into the chamber by a suitable radiation source (usually a lamp, particularly a UV lamp). An advantage of photoionization detectors as measuring detectors is their compact size and robustness, making them suitable for use in portable gas detection devices. One such gas detection device is marketed, for example, by Dräger (Lübeck, Germany) under the name X-PID. CN 110596232 A and EP 1 262 770 A2 each disclose a gas detection device comprising a radiation source designed to emit electromagnetic radiation, a measuring chamber and a measuring detector, wherein the gas mixture or at least a part of the gas mixture flows through the measuring chamber and wherein openings are arranged transversely to the direction of the emitted radiation in opposing wall sections of the wall, through which the gas flowing through the gas measuring path enters and exits the measuring chamber. From EP 1 243 921 A2 a gas detection device is known which uses a common radiation source to irradiate several electrodes arranged in series, which are arranged in a common measuring chamber of a photoionization detector. German patent DE 197 32 470 A1 describes an infrared gas analyzer capable of detecting various components in the exhaust gases of an internal combustion engine. Radiation from a radiation source 1 passes through a first measuring cuvette 4, then two chambers 18 and 19 of an opto-pneumatic detector 5, and then a second measuring cuvette 6. Two further detectors 7 and 8 are arranged downstream of the second measuring cuvette 6. Detector 5 detects the proportions of carbon dioxide or carbon monoxide in the exhaust gas 9. Detectors 7 and 8 detect the proportions of hydrocarbons and nitrogen oxides, respectively, in the exhaust gas 9. Two optional additional detectors 10 and 11 detect further substances, such as nitrogen monoxide and nitrogen dioxide. The device of DE 199 57 364 A1 comprises a transmitter, a first chamber that receives the measuring gas, an acoustic detector, and a second chamber that receives a reference gas. Electromagnetic radiation from the transmitter penetrates a window 1, then the first chamber, then a window 2, and then the second chamber. The acoustic detector measures an acoustic effect. The gas analyzer of EP 0 427 037 A2 comprises an infrared emitter S, an aperture wheel P, a cuvette M containing a gas sample to be analyzed for CO, CO2 and / or CH4, a cuvette V containing a reference gas arranged parallel to the cuvette M, a first pneumatic radiation receiver E1 with a diaphragm condenser C1, and behind it a second pneumatic radiation receiver E2 with a diaphragm condenser C2. The infrared rays penetrate the cuvettes M and V and the two radiation receivers E1 and E2. US 4 376 892 A discloses that photons from a transmitter 15 first pass through a window 14, then a first chamber 10, then a window 12, and then a second chamber containing a counter 11. The noble gas in the closed chamber 10 converts the photons into UV radiation. The counter 11 measures the concentration of a gas in the second chamber. The invention is based on the objective of improving a gas detection device in such a way as to detect the target gas or at least one target gas with greater reliability. The solution according to the invention lies in a gas detection device according to the features of the independent claim. The problem is solved by a gas detection device for detecting at least one target gas in at least one gas mixture, wherein the gas detection device comprises a radiation source configured to emit electromagnetic radiation, a first measuring chamber and a second measuring chamber, as well as a first measuring detector and a second measuring detector, wherein the second measuring chamber is spatially separated from the first measuring chamber, wherein the gas detection device is configured such that a first gas mixture flows through the first measuring chamber and a second gas mixture flows through the second measuring chamber, wherein the gas detection device is configured such that electromagnetic radiation emitted by the radiation source first penetrates the first measuring chamber and then the second measuring chamber, wherein the first measuring detector is configured to measure a measure of a physical effect in the first measuring chamber.wherein this physical effect is caused by electromagnetic radiation penetrating the first measuring chamber and correlates with the presence of target gas in the first measuring chamber, and to generate a first signal correlated with the physical effect in the first measuring chamber, and wherein the second measuring detector is configured to measure a measure of a physical effect in the second measuring chamber, wherein this physical effect is caused by electromagnetic radiation penetrating the second measuring chamber and correlates with the presence of target gas in the second measuring chamber, and to generate a second signal correlated with the physical effect in the second measuring chamber. First, some terms used should be explained: Electromagnetic radiation can be light, especially UV light or visible light, but also high-frequency or X-ray radiation, especially soft X-rays (photon energy at most 5 keV). A "measuring chamber separator" is understood to be a structure impermeable to fluids, especially gases, and to radiation, especially on or in a wall of the measuring chamber. The same applies here to the designation "measuring chamber window", with the proviso that this is permeable to electromagnetic radiation. The first gas mixture flowing through the first measuring chamber can differ from the second gas mixture flowing through the second measuring chamber. This allows for independent measurements. However, the gas mixtures do not necessarily have to be different; they can also be at least partially identical in terms of their components, the same, or even the same gas mixture. This offers advantages for comparative or reference measurements. The “induced physical effect” could be, for example, a weakening of electromagnetic radiation, an ionization of molecules, an acoustic effect, or a physically measurable chemical effect. Each measuring detector interacts with a measuring chamber in the manner described below. It measures a physical effect in the associated measuring chamber, whereby this physical effect is caused by electromagnetic radiation penetrating this measuring chamber and correlates with the presence of target gas in the measuring chamber, and generates a signal from this that correlates with the measured physical effect. The invention is based on the idea of ​​increasing the reliability of the measurement by providing, in addition to the first measuring chamber, a second measuring chamber with its own associated second measuring detector, and by illuminating both measuring chambers with electromagnetic radiation from the same radiation source, such that the electromagnetic radiation emitted by the radiation source first penetrates the first measuring chamber and then the second measuring chamber. By having a second measuring chamber in the gas detection device, an additional measuring point is created that is spatially separate from the first measuring chamber and can be irradiated with a different gas mixture than, or with the same or the same gas mixture as, the first measuring chamber, thereby enabling two independent measurements to be taken at two measuring points in separate measuring chambers.According to the invention, the measuring chambers are penetrated by electromagnetic radiation emitted from the same radiation source. This eliminates the need for a second, additional radiation source for the second measuring chamber. Furthermore, in many cases, this ensures that, due to the shared radiation source, the radiation penetrating each measuring chamber is identical, or at least, in the absence of target gas, the radiation from the second measuring chamber is inherently coupled to the radiation from the first measuring chamber. Thus, signals generated by the respective measuring detectors can be compared, since the radiation parameters (intensity, wavelength, etc.) in both measuring chambers are determined by the same radiation source and are therefore coupled.Changes in radiation, for example due to aging of the radiation source and / or the influence of environmental conditions, affect both measuring chambers synchronously. This means that, particularly in comparative measurements, such changes can cancel each other out to a certain extent, thus reducing the distortion of the measurement result. This represents a significant practical advantage, especially in relative or differential measurements or for compensating for age-related changes in the emitted radiation. Furthermore, this approach can achieve higher reliability of the measurement result, particularly when the same gas mixture is supplied to both measuring chambers. In some cases, the measurement errors of the two detectors may be opposite and thus attenuate each other, and it also creates desirable redundancy should one of the detectors or one of the measuring chambers fail. Advantageously, the gas detection device is further configured such that a radiation direction in which electromagnetic radiation penetrates the first measuring chamber is perpendicular or oblique to a flow direction in which the first gas mixture flows through the first measuring chamber, and / or a radiation direction in which electromagnetic radiation penetrates the second measuring chamber is perpendicular or oblique to a flow direction in which the second gas mixture flows through the second measuring chamber. With this arrangement, the direction of the radiation is essentially perpendicular to the flow directions of the two gas mixtures. This results in a cross-flow principle for at least one measuring chamber, preferably for both measuring chambers, which creates favorable flow conditions. The cross-flow principle particularly facilitates the formation of a laminar flow of the gas mixture, which is advantageous for precise measurement. This enables safe and reliable measurements even with relatively low flow rates of the respective gas mixture. Furthermore, the perpendicular or oblique transmission to the flow direction has the advantage that the points where the radiation enters and exits the measuring chamber are located at different points, especially on different sides, than the connections for supplying and discharging the gas mixture. This reduces the risk of mutual interference, which could lead to inaccuracies and reduced measurement quality. Advantageously, the gas detection device comprises a measuring chamber separator that gas-tightly separates the first measuring chamber from the second measuring chamber and forms part of a wall of both the first and second measuring chambers. The measuring chamber separator incorporates at least one measuring chamber window transparent to electromagnetic radiation, and the gas detection device is configured such that electromagnetic radiation emitted by the radiation source passes through the first measuring chamber, then through the measuring chamber window (or at least one), and then through the second measuring chamber. The measuring chamber separator thus enables a particularly compact and small gas detection device, especially since the two measuring chambers form a single component. The radiation emitted by the radiation source can therefore travel a relatively short distance from one measuring chamber to the other.This allows for a particularly compact design. Furthermore, with regard to radiation, this ensures a particularly close coupling of the two measuring chambers, so that the radiation entering the second measuring chamber is coupled to the radiation leaving the first measuring chamber. Furthermore, it can be advantageous to provide the measuring chamber window with an optical filter designed to attenuate electromagnetic radiation in at least one wavelength range. This can be achieved by arranging the optical filter as a separate element on the measuring chamber window or by integrating the optical filter into the measuring chamber window (e.g., in the case of optical radiation, by tinting the measuring chamber window). In this way, the second measuring chamber receives the radiation with a reduced spectrum.It is particularly preferred if the gas detection device comprises a first optical filter and a second optical filter, wherein the first optical filter is located between the radiation source and the first measuring chamber and the second optical filter is located between the first optical filter and the second measuring chamber, so that the electromagnetic radiation first passes through the first optical filter and then through the second optical filter, and wherein the second optical filter preferably has a narrower passband than the first optical filter.In this way, broadband measurements (with a full or wider spectrum) can be performed in the first measurement chamber, and selective measurements (with a reduced, i.e., narrower, spectrum) in the second measurement chamber. The selective measurement in the second chamber is coupled to the measurement in the first measurement chamber (broadband measurement) by means of the shared radiation source, for example, with respect to the intensity of the radiation. For example, the radiation source emits radiation with such a broad spectrum that the spectrum of the radiation contains at least two different spectral lines (for example, spectral lines at 10.0 eV and 10.6 eV in the case of a krypton radiation source).In the first measurement chamber, located closer to the radiation source, detection with the full spectrum and the maximum ionization energy of 10.6 eV is advantageously performed. The optical filter at the boundary with the second measurement chamber has a narrower transmission band than the first optical filter, so that the 10.6 eV spectral line is removed by filtering (e.g., using calcium fluoride, CaF₂), and the second measurement chamber is then irradiated with a 10.0 eV spectral line. This allows for the advantageous combination of different investigation objectives, for example, by using the higher-energy 10.6 eV spectral line for a better detection limit and the 10.0 eV spectral line to utilize its superior selectivity. It should be noted that the measuring chamber separator and the optical filters can be constructed in one piece or in multiple pieces, i.e., the gas-tight separation function and the filter function are combined in one element, or separate elements are provided for the gas-tight separation function and spectrum-dependent different transmission properties (optical filters). Advantageously, the first and second measuring chambers are designed to each have separate inlet and outlet openings for their respective gas mixtures, allowing them to be traversed independently. This enables different gas mixtures to flow through the two chambers simultaneously: one mixture through the first chamber and a different mixture through the second. This can be used, for example, to designate a reference gas with a known composition as the target gas for the first chamber and a sample gas, the composition of which is to be analyzed, as the target gas for the second chamber. Alternatively, a fluid connection can link the first measuring chamber to the second, so that both chambers are filled with the same gas mixture. In this configuration, the gas mixture flows first through one chamber, then through the fluid connection, and then through the other chamber. This creates a series connection of the measuring chambers. It is also possible for a portion of the gas mixture to flow through both chambers, while another portion is diverted through the fluid connection, for example, for analysis outside the chambers. It can also be provided that the two measuring chambers are arranged parallel to each other and that the two gas mixtures are identical. The gas mixture is split upstream of the two measuring chambers, so that a first part of the gas mixture flows through the first measuring chamber and a second part of the gas mixture flows through the second measuring chamber. The same gas mixture then flows through both measuring chambers. This allows for a higher throughput and a faster response to changes in the gas mixture, e.g., changing concentrations, compared to a gas detection device with only one measuring chamber. It is also possible that two different gas mixtures flow through the two parallel measuring chambers. One gas mixture flows only through one measuring chamber, the other gas mixture only through the other measuring chamber. According to the invention, the gas detection device comprises a reflector for electromagnetic radiation, wherein the radiation source and the reflector are arranged such that the electromagnetic radiation emitted by the radiation source first penetrates both measuring chambers, is reflected by the reflector, and then penetrates both measuring chambers a second time. The radiation is thus reflected back through the measuring chambers by means of the reflector, thereby increasing the optical path length and thus the resulting physical effect. In this way, the usable radiation in the measuring chambers can be increased with minimal effort. This, in turn, allows for a further increase in measurement sensitivity with minimal effort. In an advantageous embodiment, the gas detection device is configured such that both measuring chambers are supplied with the same or even identical gas mixture. The first measuring detector is configured to detect at least one predetermined target gas in the supplied gas mixture in the first measuring chamber and to generate a signal correlating with the presence or absence of the target gas in the gas mixture as the first signal. The second measuring detector is configured to analyze the gas mixture in the second measuring chamber and to generate a signal correlating with the composition of the gas mixture as the second signal. Thus, the first measuring chamber can be used to search for the presence of a specific gas (the target gas). The second measuring chamber can then be used to analyze the gas mixture for its components.In this sense, the first measuring chamber can function as a searcher for the target gas, and the second measuring chamber as an analysis unit. The same radiation source is used for both measuring chambers. This allows for a particularly compact and cost-effective design. This saves effort and, thanks to the two measuring chambers and shared radiation source, increases measurement quality. In a further development of this embodiment, a separation column is connected upstream of the second measuring chamber. A separation column typically comprises a tube or capillary with a defined inner diameter through which a gas mixture containing substances to be analyzed is passed; such a separation column constitutes the core component of a gas chromatograph, and its structure and operation are well known to those skilled in the art. Frequently, several separation columns and / or a plurality of capillaries are provided for the separation column, particularly for multi-parameter measurements. Thus, it is possible to connect different separation columns or different capillaries of a separation column to the measuring chambers of the gas detection device according to the invention. Such a differentiated configuration ensures that a separate measuring chamber can be provided for each separation column and / or each capillary of the separation column. Advantageously, the gas detection device is further provided with a calibration unit designed to calibrate the sensitivity of the separation column using the second measuring detector. This allows for relatively simple calibration of the upstream separation column using the second measuring chamber. Thus, rapid and largely self-sufficient calibration can be achieved, which is a valuable advantage, especially for portable gas detection devices used in the field, as no central test station is required. It is unnecessary to transport the portable gas detection device to such a central test station for calibration. The calibration unit can also be configured to perform the calibration by coupling the two measuring chambers with their respective measuring detectors.The calibration device can also be configured to perform a sensitivity calibration of the second measurement chamber and its second measurement detector using the first measurement chamber and its second measurement detector. This allows fluctuations or changes in the radiation characteristics of the radiation source (for example, due to aging) to be detected and, to a certain extent, computationally compensated. The gas detection device preferably comprises, in addition to the two measuring chambers, at least one further measuring chamber and, for each of the two further measuring chambers, a further measuring detector, wherein the first measuring chamber, the second measuring chamber and each further measuring chamber are arranged in a stack, wherein the gas detection device is configured such that electromagnetic radiation emitted by the radiation source penetrates each measuring chamber at least once, and wherein each further measuring detector is configured to measure a measure of a physical effect in the associated further measuring chamber, wherein this physical effect is caused by electromagnetic radiation penetrating the associated further measuring chamber and correlates with the presence of target gas, and to generate a further signal that correlates with the physical effect in the associated further measuring chamber.In this design, the flow direction through the measuring chambers is preferably perpendicular or oblique to the stacking direction. This allows for the combination of additional measuring chambers to create further independent measuring points while sharing the radiation source. By essentially "stacking" the additional measuring chambers onto the first and second chambers, this stacking design results in a relatively compact arrangement. This not only allows for efficient sharing of the radiation source but is also compact and therefore particularly suitable for a portable gas detection device. Furthermore, this design enables a clear and space-saving connection of fluid lines to the measuring chambers. In one embodiment, the first measuring detector is a first ionization detector or comprises one, and the second measuring detector is a second ionization detector or comprises one, wherein the first ionization detector is configured to measure the ionization of a target gas in the first measuring chamber and to generate a first signal that correlates with the ionization in the first measuring chamber, and wherein the second ionization detector is configured to measure the ionization of a target gas in the second measuring chamber and to generate a second signal that correlates with the ionization in the second measuring chamber. Preferably, the first and second measuring detectors are each implemented as a photoionization detector. Photoionization detectors are robust and fast-responding, thus enabling a compact gas detection device that can be portable. Advantageously, the first and / or second measuring detector each comprises a pair of electrodes, the two electrodes of the electrode pair being arranged in the associated measuring chamber such that the gas mixture flows between the two electrodes as it passes through the measuring chamber. This places the gas mixture in the effective area between the two electrodes, thereby increasing the measurement signal and thus the sensitivity. It can also be provided that the first measuring detector is or comprises a first absorption detector, and the second measuring detector is or comprises a second absorption detector, wherein the first measuring detector is configured to measure the absorption of electromagnetic radiation in the first measuring chamber as a measure of the physical effect and to generate a first signal correlated with the absorption in the first measuring chamber, and the second measuring detector is configured to measure the absorption of electromagnetic radiation in the second measuring chamber as a measure of the physical effect and to generate a second signal correlated with the absorption in the second measuring chamber. This configuration is preferably combined with at least one optical filter.Some target gases absorb a significant proportion of electromagnetic radiation only in certain wavelength ranges. Furthermore, it can also be provided that the first measuring detector is a first photoacoustic detector or includes one, and the second measuring detector is a second photoacoustic detector or includes one. In a photoacoustic detector, the gas mixture is introduced into a measuring chamber and excited by pulsed electromagnetic radiation. The wavelength of the electromagnetic radiation used is selected such that at least one excitation specific to the target gas to be detected can be generated, because the target gas absorbs electromagnetic radiation. The energy absorbed in this process excites the molecules of the target gas, which then relax, forming a pressure wave. This results in acoustic waves.The intensity of the acoustic waves, which can be recorded with a sound transducer (microphone) or other suitable sensor, correlates with the strength of absorption and is therefore a measure of the concentration of the target gas. As a measure of the physical effect, the first measuring detector is designed to measure a photoacoustic effect in the first measuring chamber, and the second measuring detector is capable of measuring a photoacoustic effect in the second measuring chamber. The invention can therefore be applied to different sensor concepts. Advantageously, the measuring chambers each comprise a wall, an inlet opening, and an outlet opening, wherein the respective gas mixture flows into the measuring chamber through the inlet opening and out of the measuring chamber through the outlet opening. The inlet opening and the outlet opening of a measuring chamber are arranged on two opposing wall sections of the measuring chamber and are preferably aligned with each other on a single axis. This allows for a particularly rapid and reliable formation of laminar flow, which ensures a fast response time and improved measurement sensitivity of the gas detection device. Furthermore, thanks to the laminar flow, no mixing of different gases entering sequentially occurs, thus making better use of the gas mixture flow. It is advantageous for at least one measuring chamber to have a wall with an oval cross-sectional area, with two electrodes of the measuring detector positioned on the two less curved sections of the wall. Positioning them on the less curved sides allows for a relatively homogeneous field between the electrodes, resulting in more favorable measurement characteristics (e.g., linearity). Furthermore, this arrangement utilizes the longer sides of the oval for electrode placement, enabling the use of relatively large electrode areas and thus increasing measurement sensitivity. This design can be used particularly in conjunction with an ionization detector. Preferably, the gas detection device comprises a fluid feeder, in particular a pump, wherein the fluid feeder causes the gas mixture(s) to flow through the gas detection device. In one embodiment, the fluid feeder causes the gas mixture to be divided, so that at least a portion of the gas mixture flows through the first measuring chamber and at least another portion flows through the second measuring chamber. It is also possible for the fluid feeder to feed two different gas mixtures. Alternatively, two different fluid feeders can be used for two different gas mixtures. The fluid feeder ensures a reliable and reproducible supply of the gas mixture to the two measuring chambers. Furthermore, the respective gas mixture(s) reach the measuring chambers more quickly than if the gas mixture were to diffuse into the measuring chambers. Advantageously, the gas detection device includes an additional radiation source, with both the first and second measuring chambers located between the radiation source and the additional radiation source. The two measuring chambers are thus exposed to electromagnetic radiation from opposite sides. This increases the total radiation acting on both measuring chambers, thereby generating a stronger measurement signal and advantageously increasing the measurement sensitivity of the gas detection device. It is particularly beneficial if the two electromagnetic radiations emitted by the two radiation sources differ in at least one wavelength range. This allows for a broadening of the measuring range. The gas detection device is advantageously designed as a portable unit. The benefits of its compact design are particularly evident in this configuration. It is especially preferred that the gas detection device be designed as a handheld device. The user can carry the portable gas detection device with them and will be alerted if a target gas is present in their vicinity. Advantageously, the gas detection device includes its own power supply unit. This is preferably implemented as a set of rechargeable batteries. This further facilitates the portable use of the gas detection device. The invention is explained in more detail below with reference to the accompanying drawings and exemplary embodiments. The drawings show: Fig. 1 a perspective view of a handheld gas detection device; Fig. 2 a schematic top view of a gas detection device comprising a measuring unit with an upstream gas chromatography separation column; Fig. 3a, b a top view in the direction of radiation showing the interior of a single measuring chamber and a side view of the gas detection device according to the invention with a radiation source and two measuring chambers; Fig. 4 a side view of a first embodiment of the gas detection device with a fluid connection for parallel connection of the measuring chambers; Fig. 5 a side view of a second embodiment of the gas detection device with stacked measuring chambers and a fluid connection for series connection; Fig.6 an alternative embodiment to the first embodiment with a different arrangement of the sensor electrode; and Fig. 7a , b detailed views of the radiation-remote end of the gas detection device with an attached reflector or a second radiation source. A gas detection device according to a first embodiment of the invention is designated in its entirety by reference numeral 1, cf. Fig. 1. It has an approximately cuboid housing 10, on one end face 11 of which an inlet 12 for supplying at least one gas mixture to be analyzed is arranged. Inside the housing 10, a measuring device 2 and a power supply unit 13, which functions as an energy storage device for operating the gas detection device, are arranged. Furthermore, an evaluation and control circuit 18 is provided, which is connected, inter alia, to the measuring device 2. The measuring device 2 comprises two measuring chambers 6 and 6' and two measuring detectors 7 and 7' (one for each measuring chamber 6, 6') as well as a separation column 3, both of which are arranged on a connection block 20, see Fig. 2; furthermore, a further connection block 21 is provided, to which the separation column 3 is connected at its beginning. Optional fluid lines for supplying and removing at least one gas mixture, as well as power supply lines and measuring or signal lines, are not shown. The gas mixture to be analyzed is guided from the inlet 12 via fluid lines (not shown) to the measuring device 2, through it, and from there via a pump 4, designed as a blower unit in this embodiment, to an outlet (not shown) from the housing 10. The measuring device 2 is explained in more detail below with reference to Fig. 3. The measuring device 2 is designed as a photoionization detector (PID) and comprises a radiation source 50, designed as a UV lamp, at one end. The radiation source 50 emits electromagnetic radiation, in particular UV light, along a radiation direction 51, via a spectrum sufficient for the analysis of the gas mixture, but at least two spectral lines. A flow direction in which the gas mixture(s) flow through the measuring chambers 6, 6' lies in the planes of Fig. 3a) and Fig. 3b). The radiation direction 51 is perpendicular to the plane of Fig. 3a) and lies in the plane of Fig. 3b). The description refers by way of example to an orientation of the gas detection device 1 in which the radiation source 50 is arranged at the bottom and the measuring chambers 6, 6' are stacked vertically above the radiation source 50. The radiation source 50 is arranged directly below the first measuring chamber 6, which has an interior space 60 enclosed by a wall 61. Fig. 3a) shows the first measuring chamber 6. A second measuring chamber 6' is preferably constructed in the same way as the first measuring chamber 6. Between two opposing sections 62, 63 of the wall 61, an opening 64 for the gas mixture to flow in and an opening 65 for the gas mixture to flow out of the interior 60 of the first measuring chamber 6 of the gas detection device 1 are arranged. The flow directions through the openings 64, 65 are positioned on the same axis. Thus, these openings 64, 65 define a direction for the flow of the gas mixture through the interior 60 of the measuring chamber 6. Furthermore, two electrodes 71, 72 of the measuring detector 7 are arranged on the wall 61, specifically on opposing wall sections 62, 63 and to the left and right, respectively, of the direction of gas flow. Almost the entire interior 60 lies between them, so that the electrodes 71, 72 can cover a large area and thus achieve high measurement sensitivity. A measuring chamber separator 66 is arranged between the radiation source 50 and the first measuring chamber 6, forming a base element of the wall 61. The measuring chamber separator 66 includes a measuring chamber window 68 with an optical filter 69, which is transmissive to electromagnetic radiation but gas-tight, located in or on the measuring chamber separator 66. Magnesium fluoride, for example, can be used as the material for the measuring chamber window 68 with the optical filter 69; however, other materials transparent to electromagnetic radiation, especially UV light, such as lithium fluoride or calcium fluoride, can also be used. The wall 61 of the measuring chamber 6 outside the measuring chamber window 68 consists of a non-ionizing material, which is preferably also non-transmissive to electromagnetic radiation. Examples of such materials are Teflon or plastic materials, particularly polyethylene or polypropylene.Advantageously, this material is electrically insulating in order to reduce the risk of negative interference with the electromagnetic field detected by the measuring detector 7 in the interior 60 of the first measuring chamber 6. As can be clearly seen in Fig. 3a), the first measuring chamber 6 has an oval shape in its cross-sectional view in the direction of radiation 51. The openings 64, 65 for the inlet and outlet of the gas mixture are located at the apex of the more strongly curved (transverse) sides, and the electrodes 71, 72 are arranged on the less curved (longitudinal) sides, preferably centrally. This results in a laminar flow of the gas mixture through the measuring chamber 6 parallel to the measuring chamber divider 66. The laminar flow allows for better utilization of the gas mixture flow for the measurement. Furthermore, mixing of different gases entering sequentially does not occur, thus improving gas flow utilization. The effort required for purging, and in particular the flow required for purging, can be reduced in this way.This simplifies fluid transport, reduces the energy consumption required, and thus enables greater reliability. The design-related flow direction of the gas mixture is therefore orthogonal to the radiation direction 51. This results in a high utilization rate of the radiation emitted by the radiation source 50. The electrodes 71, 72 are arranged such that they do not contact the measuring chamber separator 66 and, in particular, are positioned spatially spaced away from the measuring chamber separator 66. Since the material typically used for the optical filters 69 of the measuring chamber separator 66 has a high dielectric constant (preferably in the range of 4 to 5, for example for magnesium fluoride, or in the range of 6 to 7 for calcium fluoride), the arrangement of the electrodes 71, 72 spaced away from the measuring chamber separator 66 has the advantage that the influence of the often unavoidable parasitic capacitance is reduced in many cases.A second measuring chamber 6' is mounted on top of the first measuring chamber 6, with a further measuring chamber divider 66' between them. This further measuring chamber divider 66' also has a measuring chamber window 68' with an optical filter 69', through which radiation from the first measuring chamber 6 enters the second measuring chamber 6' along the radiation direction 51. On the side of the measuring chamber 6' opposite the measuring chamber divider 66, either another measuring chamber divider 66' or a cover element 67 is arranged. The description above for the first measuring chamber 6 applies accordingly to the second measuring chamber 6'; in particular, it has a structural design corresponding to the first measuring chamber 6, including the arrangement of the electrodes 71, 72 as shown in Fig. 3a). Identical or similar elements are designated with the same reference numerals.In this way, the radiation emitted by the radiation source 50 into the first measuring chamber 6 is guided along the radiation direction 51, through the measuring chamber separator 66' between the first measuring chamber 6 and the second measuring chamber 6' into the said second measuring chamber 6', so that a second measurement independent of the measurement in the first measuring chamber 6 is carried out there. The measuring chambers 6, 6' can be supplied with gas mixtures independently of one another, even with different gas mixtures. This is illustrated by way of example in Fig. 3, where different connecting lines 14, 14' are arranged for supplying different gas mixtures to the inlet openings 64, 64' of the two measuring chambers 6, 6'. Similarly, different connecting lines 15, 15' can be connected to the outlet openings 65, 65'. A parallel connection of the measuring chambers 6, 6' (see Fig. 4) or a series connection of the measuring chambers 6, 6' (see Fig. 5) can also be provided by means of fluid connections 16. Since the same radiation source 50 is always used, a coupling with respect to the radiation is achieved, which facilitates calibration. In one embodiment, the gas detection device 1 comprises a calibration unit 17 (see Fig. 1), which performs a calibration using the radiation coupling of the measuring chambers 6, 6' and / or calibrates an upstream separation column 3 by means of the measuring detector 7' in the second measuring chamber 6'. In a second embodiment, on the side of the second measuring chamber 6' furthest from the radiation source, a further measuring chamber 6" is arranged directly on top of the second measuring chamber 6', comprising a further measuring chamber divider 66", a further measuring chamber window 68", a further optical filter 69", and a further measuring detector 7"; optionally, several further measuring chambers are successively arranged. This is illustrated in Fig. 5; in the following explanation, the same reference numerals are used for elements identical or similar to those of the first embodiment. Each of the second and subsequent measuring chambers 6', 6" is equipped, like the first measuring chamber 6, with openings 64', 64'' and 65', 65'' for the inflow and outflow of the gas mixture to be analyzed. Fluid connections 16 can be provided between the measuring chambers 6, 6', 6"; for illustrative purposes, one fluid connection 16 between the first and second measuring chamber 6, 6' is shown in Fig. 5, as well as another fluid connection 16' between the second and third measuring chamber 6', 6". In this way, the measuring chambers 6, 6', 6" can be connected in series in the direction of flow, and the gas mixture to be analyzed can thus be directed from one measuring chamber 6 to the next measuring chamber 6', 6". This allows several measurement series to be carried out with the same gas mixture to be analyzed, overlapping over time. Fig. 5 shows a series connection of three measuring chambers 6, 6', 6''. It is also possible that at least three measuring chambers 6, 6', 6'' are connected in parallel. A particular advantage lies in the fact that at least some of the optical filters 69, 69', 69" can be designed such that their transmission properties differ from one another. "Differentiated" here means, in particular, that the second optical filter 69' has a narrower transmission range than the optical filter 69 between the radiation source 51 and the first measuring chamber 6. An exemplary embodiment is such that, when the radiation source emits two spectral lines in the range of 10.0 and 10.6 eV (electron volts), both are directed through the first optical filter 69 and the first measuring chamber divider 66 into the first measuring chamber 6, but the second optical filter 69' has a narrower transmission range to the second measuring chamber 6', so that only the spectral line with 10.0 eV can pass through.This allows at least two target gases to be detected and distinguished from each other in the gas mixture to be analyzed by evaluating their different absorption coefficients at the various spectral lines. Furthermore, the advantages of using specific spectral lines can be combined, for example, if a better detection limit can be achieved with the 10.6 eV spectral line, which is particularly advantageous for a search detector in a search path, and / or if better selectivity can be achieved with the 10.0 eV spectral line, which is particularly advantageous for a separation path. Thanks to this multi-chamber arrangement, broadband measurements on the one hand and selective measurements on the other can be performed simultaneously with the same measuring device 2. Furthermore, it is possible to connect the inlet openings 64, 64', 64" of the various measuring chambers 6, 6', 6'' to connecting lines 14 and / or a capillary of the separation column 3 (see Fig. 2) in different ways, thus enabling not only one but also several separation columns 3, or, in the case of multi-capillary separation columns, the individual capillaries, to be connected and measured individually in a cost-effective and compact manner. This allows different gas mixtures to be supplied to the measuring chambers 6, 6', 6" for analysis; however, it is also possible to connect at least some of the measuring chambers in series (as shown with the fluid connection 16 in Fig. 5), so that the same gas mixture to be analyzed flows through the different measuring chambers sequentially and can thus be measured, for example, using different spectral lines, as explained above.Pump 4 can, in particular, act as a driving force for the required flow of the gas. Alternative designs for the cover element 67, located furthest from the radiation source 50 in the direction of radiation 51, are shown in Figs. 7a and 7b. For example, a reflector 76 can be mounted on this cover element 67 of the last measuring chamber 6' or 6'' in the direction of radiation. This reflects the radiation back through the various measuring chambers 6", 6', 6 against the original direction of radiation 51, thus efficiently increasing the total radiation. Together with the previously described arrangement of the electrodes 71 and 72, this has the further advantage that the cover element 67 can remain free of the electrodes 71 and 72. This makes it possible to arrange a large-area reflector 76 on the cover element 67, thereby increasing the usable radiation in the respective interior space 60 of the two measuring chambers 6 and 6' with minimal effort. Alternatively, a second radiation source 50' can be attached to the cover element 67, which emits electromagnetic radiation into the measuring chambers 6", 6', 6 from the opposite side and preferably with a different spectrum, i.e., a spectrum differing from that of the radiation source 50, thus opening up additional measurement possibilities. In particular, the radiation can be amplified, thereby achieving higher measurement sensitivity, or additional measurement variants can be developed by using radiation with a different spectrum or spectral lines. The two radiation sources 50, 50' can also emit radiation with the same spectrum. An example of a suitable combination of six measuring chambers I to VI with different measuring chamber dividers 66 or optical filters 69', 69 (here exemplarily implemented from magnesium fluoride or calcium fluoride) for different spectral lines is given in the following table. This configuration includes a search path to which measuring chambers I and VI are connected, and a measuring path comprising several capillaries (OP-1 or DB-624) of the separation column of a gas chromatograph (GC), to which the remaining measuring chambers are connected. Here, measuring chambers I and IV, II and V, and III and VI are each connected in series in the direction of flow by means of fluid connections 16. Lamp UV source 10.6 UV window [MgF2] measuring chamber separator Rehearsal room of measuring chamber IGC with OP-110, 6 UV window [MgF2] measuring chamber separator Rehearsal room of measuring chamber IIGC with DB-62410, 6 UV window [MgF2] measuring chamber separator Rehearsal room of measuring chamber III, seeker 10, 6 UV window [CaF2] measuring chamber separator with optical filter Rehearsal room of measuring chamber IVGC with OP-110, 0 UV window [MgF2] measuring chamber separator Rehearsal room of measuring chamber VGC with DB-62410, 0 UV window [MgF2] measuring chamber separator Rehearsal room of measuring chamber VISucher10, 0 UV reflector reflection In an alternative embodiment, shown in Fig. 6, the electrode 71 is arranged on the measuring chamber separator 66 and the electrode 72 on the cover element 67. This allows for spatially extended electrodes 71, 72. They should be made of a material transparent to radiation or not be completely covered so that the radiation emitted by the radiation source 50 can enter the measuring chambers 6, 6'.

Claims

Gas detection device (1) for detecting at least one target gas in at least one gas mixture, wherein the gas detection device (1) comprises a radiation source (50) configured to emit electromagnetic radiation, a first measuring chamber (6) and a second measuring chamber (6'), as well as a first measuring detector (7) and a second measuring detector (7'), wherein the second measuring chamber (6') is spatially separated from the first measuring chamber (6), wherein the gas detection device (1) is configured such that a first gas mixture flows through the first measuring chamber (6) and a second gas mixture flows through the second measuring chamber (6'), wherein the gas detection device (1) is configured such that electromagnetic radiation emitted by the radiation source (50) first penetrates the first measuring chamber (6) and then the second measuring chamber (6'), wherein the first measuring detector (7) is configured toto measure a measure of a physical effect in the first measuring chamber (6), wherein this physical effect is caused by electromagnetic radiation penetrating the first measuring chamber (6) and correlates with the presence of target gas in the first measuring chamber (6), and to generate a first signal correlated with the physical effect in the first measuring chamber (6), and wherein the second measuring detector (7') is configured to measure a measure of a physical effect in the second measuring chamber (6'), wherein this physical effect is caused by electromagnetic radiation penetrating the second measuring chamber (6') and correlates with the presence of target gas in the second measuring chamber (6'), and to generate a second signal correlated with the physical effect in the second measuring chamber (6'), characterized in that the gas detection device (1) comprises a reflector (76) for electromagnetic radiation,wherein the radiation source (50) and the reflector (76) are arranged such that the electromagnetic radiation emitted by the radiation source (50) first passes through both measuring chambers (6, 6'), is reflected by the reflector (76) and passes through both measuring chambers (6, 6') a second time. Gas detection device (1) according to claim 1, characterized in that the gas detection device (1) is designed such that a radiation direction (51) in which electromagnetic radiation penetrates the first measuring chamber (6) is perpendicular or oblique to a flow direction in which the first gas mixture flows through the first measuring chamber (6), and / or a radiation direction (51) in which electromagnetic radiation penetrates the second measuring chamber (6') is perpendicular or oblique to a flow direction in which the second gas mixture flows through the second measuring chamber (6'). Gas detection device (1) according to one of the preceding claims, characterized in that the gas detection device (1) comprises a measuring chamber separator (66) which separates the first measuring chamber (6) from the second measuring chamber (6') in a gas-tight manner and forms both a part of a wall of the first measuring chamber (6) and a part of a wall of the second measuring chamber (6'), wherein a measuring chamber window (68) transparent to electromagnetic radiation is provided in the measuring chamber separator (66) and wherein the gas detection device (1) is configured such that electromagnetic radiation emitted by the radiation source (50) penetrates the first measuring chamber (6), then the measuring chamber window (68) and then the second measuring chamber (6'). Gas detection device (1) according to claim 3, characterized in that the measuring chamber window (68) is provided with an optical filter (69) and the optical filter (69) is designed to attenuate electromagnetic radiation in at least one wavelength range. Gas detection device (1) according to one of the preceding claims, characterized in that the gas detection device (1) comprises a first optical filter (69) and a second optical filter (69'), wherein the first optical filter (69) is located between the radiation source (50) and the first measuring chamber (6) and the second optical filter (69') is located between the first optical filter (69) and the second measuring chamber (6') and wherein the second optical filter (69') preferably has a narrower passband than the first optical filter (69). Gas detection device (1) according to one of the preceding claims, characterized in that a fluid connection (16) connects the first measuring chamber (6) with the second measuring chamber (6') such that the first and the second gas mixture are the same gas mixture, and the gas mixture first flows through one measuring chamber (6), then through the fluid connection (16) and then through the other measuring chamber (6'). Gas detection device (1) according to claim 6, characterized in that the gas detection device (1) is designed such that the gas mixture first flows through the first measuring chamber (6), then through the fluid connection (16) and then through the second measuring chamber (6'). Gas detection device (1) according to one of the preceding claims, characterized in that the two measuring chambers (6, 6') are arranged parallel to each other, the first and the second gas mixture are the same gas mixture, and the gas detection device (1) is designed such that a first part of the gas mixture flows through the first measuring chamber (6) and a second part of the gas mixture flows through the second measuring chamber (6'). Gas detection device (1) according to one of the preceding claims, characterized in that the first measuring detector (7) is configured to detect at least one predetermined target gas in the first measuring chamber (6) and to generate as a first signal a signal correlating with the presence or absence of the target gas, and the second measuring detector (7') is configured to analyze the gas mixture in the second measuring chamber (6') and to generate as a second signal a signal correlating with a composition of the gas mixture. Gas detection device (1) according to claim 9, characterized in that a separation column (3) is arranged in front of the second measuring chamber (6') when viewed in a flow direction of the gas mixture. Gas detection device (1) according to claim 10, characterized in that the gas detection device (1) comprises a calibration device (17) which is designed to calibrate the sensitivity of the separation column (3) using the second measuring detector (7'). Gas detection device (1) according to one of the preceding claims, characterized in that the gas detection device (1) comprises at least one further measuring chamber (6'') and for each of the or at least one further measuring chamber (6'') a further measuring detector (7''), wherein the first measuring chamber (6), the second measuring chamber (6') and the or each further measuring chamber (6'') are arranged in a stack, wherein the gas detection device (1) is configured such that electromagnetic radiation emitted by the radiation source (50) penetrates each measuring chamber (6, 6', 6'') at least once, and wherein the or each further measuring detector (7'') is configured to measure a measure of a physical effect in the associated further measuring chamber (6''), wherein this physical effect is caused by electromagnetic radiation penetrating the associated further measuring chamber (6'') and correlates with the presence of target gas.and to generate a further signal that correlates with the physical effect in the associated additional measuring chamber (6''). Gas detection device (1) according to one of the preceding claims, characterized in that the first measuring detector (7) comprises a first ionization detector, and the second measuring detector (7') comprises a second ionization detector, wherein the first ionization detector (7) is configured to measure a measure of the ionization of target gas in the first measuring chamber (6) and to generate a first signal correlated with the ionization in the first measuring chamber (6), and wherein the second ionization detector (7') is configured to measure a measure of the ionization of target gas in the second measuring chamber (6') and to generate a second signal correlated with the ionization in the second measuring chamber (6'). Gas detection device (1) according to one of the preceding claims, characterized in that the first measuring detector (7) comprises a first absorption detector and the second measuring detector (7') comprises a second absorption detector, wherein the first absorption detector (7) is configured to measure an absorption of electromagnetic radiation in the first measuring chamber (6) as a measure of the physical effect and to generate a first signal correlated with the absorption in the first measuring chamber (6), and the second absorption detector (7') is configured to measure an absorption of electromagnetic radiation in the second measuring chamber (6') as a measure of the physical effect and to generate a second signal correlated with the absorption in the second measuring chamber (6').

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