FR2756928A1 - Analysing gas mixtures and miniturised apparatus therefor - Google Patents

Abstract

A volume of gas mixture is divided into at least two fractions, one of which is subdivided into equal samples which are directed into at least two respective cells (4) each able to detect a different constituent of the mixture, while another is fed through a separating column (31) from which different constituents emerge sequentially, and successive portions of this fraction are then directed through cells (4), the two series of measurements obtained from cells (4) being processed to obtain indications of the nature and proportions of the constituents. Also claimed is apparatus wherein all the components required to analyse gas in this manner are incorporated in a single integrated solid state module comprising at least two superposed plates.

Description

Integrated method and device for analyzing several contained components
in a gas mixture.

 The present invention relates to an integrated method and device for analyzing several components contained in a gas mixture.

 The technical sector of the invention is the field of the production of measurement systems and sensors for the analysis of the composition of gases.

 The main application of the invention is to be able to produce a sensor which can be described as multigas to monitor and control the ambient air in which we live, in order to detect, in particular any possible overshooting of admissible thresholds for various components determined such as for ozone, carbon dioxide, sulfur oxide, nitrogen oxide, etc ...

It is known indeed that more and more legislation is enacted by different countries in the world for air monitoring: we can cite in particular the French law of August 2, 1961, (Law 61 842 supplemented by decrees of May 13, 1974 N074 415 and of April 18, 1996 N096 335) which organizes the repression of emissions of dangerous gases, in particular toxic, corrosive, odorous, radioactive, etc ...; the decree of May 23, 1974 defines pollutants, their level and their measurement conditions, such as: sulfur dioxide
S02 for which the arithmetic mean of the daily average rate values recorded during the year must be a maximum of 40 to 60 micrograms per m3 with a 24-hour average value of 100 to 150 micrograms per m3 maximum; for nitrogen dioxide NO2, the average value per hour or per period less than 1 hour taken throughout the year, must be less than 200 micrograms per m3 for a 98 percentile: this 98 percentile is determined in the decree of May 13, 1974 cited above as the value of the measurement taken from among all the measurements recorded during the year and classified in ascending order, such that the number of measurement values lower than this value of the percentile is equal to 98 % of the total number of measurements recorded. With regard to lead particles, the maximum average of the daily average values recorded during the year, 3 must be less than 80 micrograms per m with a maximum average value recorded for 24 hours of 100 to 150 micrograms per m
Similarly, there is a European directive 70 220 of the
Council of Europe of 20 March 1970, which concerns the approximation of the laws of the member states relating to the measures to be taken against air pollution by gases from the engines fitted to vehicles and supplemented by various directives which have followed; a common European position N05 96, also adopted by the Council of Europe on 30 November 1995, concerns the assessment and management of ambient air quality, with particular regard to the formation of ozone (see also European Directive 92/72 / EEC of 21 September 1992 on air pollution by ozone) and various atmospheric pollutants such as sulfur dioxide, nitrogen dioxide, fine particles such as soot, suspended particles, lead, benzene, hydrocarbons, carbon monoxide, cadmium, arsenic, nickel, mercury, etc ...

However, no current equipment is able to satisfy these various regulations and / or directives, even if many sensors and instruments exist for specific detection measures, in particular for certain pollution risks, which correspond to the same main application of the present invention for the monitoring of the environment, one can note for example the patent application NOFR 2,572,951 published on May 16, 1986, and entitled Method of semi-dry capture of pollutants contained in fumes; or that described in application NO EP 486.596 published on May 27, 1992 and entitled Self-supporting thin film filament sensor, its manufacturing process and its applications in gas detection and gas chromatography to determine a static or dynamic characteristic of a surrounding environment; or the various patent applications filed by the German companies BOSCH GmbH and BROWN BOVERI such as those respectively FR 2,499,720 describing a polarographic measurement probe for determining the oxygen content of the gases, or
FR 2,489,521 on a device comprising an oxygen detector.

 These various instruments, like many other sensors existing to date for measuring the concentration of certain components of gas mixtures, certainly make it possible to obtain the reading and measurement of such a component that one wants to monitor and control. , but they are all quite large, require protected electronic boxes, regulated in temperature, and cannot, in certain cases anyway, detect small amounts of concentration such as those decreed above in the regulations, which require by example of value measurements of the order of 10.6 parts per billion approximately, except being able to take large volumes of ambient air, which makes the measurement and control station even more cumbersome.

In addition, for a few years and in order to be able to measure precisely and in particular such low concentrations, miniaturized sensors and analysis systems have been developed using the semiconductor technique: there are in particular various publications and patent applications such that that FR 2.615.287 entitled Microsensor with integrated technology for detecting the presence of certain gases using a silicon support frame or that
EP 665 428 describing a device for measuring the quantities of gases, using at least one detector of the semiconductor type; there are also various publications that appeared in the reference document
ISBN 3-8007-2 200-3 edited by Herbert REICHL, Anton HEUBERGER,
VDE Verlag GmbH at the fifth international conference on microsystem technologies, which took place in Potsdam in September 1996, such as in particular, pages 181 et seq., The description of a miniaturized air analyzer using components made of machined silicone including a gas sensor with a chemical filtering element for calibration, two cut-off and pumping micro-organs, the assembly being integrated on a common support also made of silicone and in which communication channels are dug between the various previous elements; in this same publication, it is described on pages 217 and following, methods of manufacturing such components, and on page 787, membrane micro-pumps, which can be used in such miniature sensors.

 This new sensor manufacturing technology is indeed very interesting since it makes it possible to miniaturize these but if we then want to control and measure several possible components in a gas mixture, it is necessary to stack and connect together several of these instruments with compatibility problems that it can generate; moreover, when certain sought-after gaseous components have very similar characteristics, which is often the case, it is then difficult to differentiate them, especially when looking for very low concentration values of the order of 10'6 micrograms / m3 .

 The problem posed is therefore to produce a measurement system making it possible to control at the same time the presence or not of several given components in any gaseous mixture such as ambient air, to measure the possible concentration, even very low, and provide an exploitable result, practically in real time and continuously, and this with good reliability, even for low concentrations like those mentioned above and in a small footprint with low energy consumption, and allowing to realize easily implantable systems in miniaturized and discreet structures that we want to be able to have in the environment, in large numbers, and therefore at a reduced cost.

One solution to the problem posed is a method of analyzing several components contained in a gas mixture, from which a sample of a given volume is taken, according to which
- dividing said sample into at least two samples,
- similar subsamples of one of these samples are sent to at least two measurement cells, each of at least one given characteristic linked to the concentration of at least one of said components that may be present in the gas mixture and that we want to analyze,
- the other sample is sent through at least one separation column for said components, then at the output of this column, this fractionated sample is directed into at least two measurement cells, each of at least one given characteristic related to the concentration at least one of said components to be analyzed,
the results of the two series of measurements carried out on each of the samples by said cells are noted and, by calculation and comparison with known references, the nature and the concentration of at least two of said sought components and possibly present in the gas mixture.

 The objective of the present invention is achieved with an analysis device according to the above method such that all of the means necessary for implementing it are integrated into a single sensor of modular design, using the semiconductor properties. materials in which these means are made, and comprising at least two plates integrating said means, and assembled in layers superposed one against the other.

 These different plates can be according to the invention, specific to each functionality of the device as described below, namely one for the measuring cells, another for the piping such as the connections between cells and the means of sampling, another for the connection cut-off and pumping devices, and at least one other for the electronic signal processing control part, such a design and arrangement allows modularity of the multi-sensor, therefore consisting of predefined base plates , which are then adaptable according to the evolution of the sensors and the components, with then reservations of connection of modules to come, which ensure an opening and an adaptability of the system, as are the electronic circuit boards of the microcomputers .

 The result is new integrated methods and devices for simultaneous and real-time analysis of several components contained in a gas mixture, responding to the problem posed and using the known semiconductor type manufacturing technology, as mentioned above, but unlike the devices envisaged to date in this field, making it possible to produce a true multigas sensor.

 Indeed, by separating the samples of gas mixture into at least two similar samples which are then analyzed, one globally and the other after separation, we can by cross-checking the measurements, remove any doubt about the presence or not of a component whose measurement of characteristics can interfere with that of another and therefore distort the measurement of their concentration, when these two gaseous components are simultaneously present in an analysis cell; thanks to the separation column which makes it possible to separate and isolate each of said components before sending them to an analysis cell, it is thus possible on the one hand to remove the doubt existing after the overall gross analysis carried out on the other part of the sample, and on the other hand refine the result of the measurement by precisely cross-checking between the various measurements carried out, making it possible to detect with more certainty and reliability, very low concentration values.

 By thus multiplying the various analysis cells which can be of the physico-chemical or photometric or mass spectrometric type, by choosing the most effective for a given component, a measurement of the concentration thereof is obtained at a value of l 'order of 106 particles per billion and having ruled out any risk of interference with other components.

 In addition, thanks to the miniaturization of such a multi-gas sensor, its operating energy consumption is very low and also allows greater calculation speed, which makes it possible to have a measurement result practically in real time and in continued.

 Such multi-gas sensors according to the invention can thus be integrated into very small measurement stations, which can be installed in a network in an urban environment for example, and connected to a control center from which managers can be informed, in order to take any possible action to reduce or stop any anomaly by acting on its cause and possibly alert the populations, as is now required by the regulations of many countries, such as in France following the decree of April 18 1996 NO 96 335.

 We could cite other advantages of the present invention, but those mentioned above already show enough to prove its novelty and interest.

 The description and the figures below represent an exemplary embodiment of the invention, but are in no way limiting: other embodiments are possible, within the scope and scope of this invention, in particular by adapting it to any gas mixture.

 Figure 1 is a schematic view of a device according to the invention.

 Figure 2 is an exploded perspective view of an embodiment of a device according to the invention.

 According to FIG. 1, thanks to any pump 15, a sample of a given volume 1 is taken from the ambient air or from any gas mixture for which the analysis is to be carried out.

 Said sample 1 is divided into at least two samples 21, 22 in a distribution unit 2 which can simply be a network of connecting micro-channels comprising different closing or opening valves.

 One of these so-called samples 2i is divided into similar sub-samples and sent to at least two measurement cells 4, arranged in parallel, and each capable of measuring at least one given characteristic linked to the concentration of at least one of said components that one searches in the gas mixture where it can possibly be present, each of said cells 4 being a priori dedicated to a different component.

These different measurement cells 4 can be physicochemical or photometric cells reacting in particular for example to a characteristic of carbon monoxide CO, sulfur dioxide S02, nitrogen dioxide NO2, BTX (Benzene, Tolluene ,
Xylene), hydrocarbon gas (CHC) compounds, ozone 03, etc.

 A raw measurement of the possible concentration of such gases is thus obtained, knowing however that some of these can interfere with each other and therefore cause a raw measurement which is not representative of their actual concentration.

 The other sample 22 is sent simultaneously through at least one separation column 31, such as a gas chromatography column which retains all of said components which are thus adsorbed then selectively desorbed according to a given order and known thanks to a suction pump 19 located at the outlet of said column 31: sub-samples are thus obtained containing different components sequentially separated as a function of their desorption time.

 At the outlet of this separation column 31, said sub-samples thus obtained and separated are sent, in at least two measurement cells 4, of the same type as those indicated above; one can then either send each of the sub-samples thus fractionated from the sample 22 in all the cells 4 available, or sequentially address each of them in one of the said cells 4 or a group of at least one of the said measurement cells , corresponding at least to a given characteristic linked to the concentration of the component corresponding to the separation sequence given by said column 3l.

 Indeed, depending on the characteristics of the separation column 31, we know in which chronological order said components are extracted from it and we can then open in the distribution unit 2, the circuit corresponding to the measurement cell 4 of the component sought , only at the predetermined time of the potential extraction of this component from the separation column 3l.

 The management of these sequential openings of circuits to the cells 4 can be carried out, either by a clock, or by sending a part of each of the sub-samples thus separated at the output of the separation column 3l, in a presence detection sensor 5, such as a plasma detector which makes it possible to determine on the one hand if said sought-after component is present or not, and on the other hand to have a relative measurement of concentration.

 The results of the two series of measurements thus carried out, on the one hand on the first raw sample 21 in all of the cells 4, and on the other hand on the sub-samples fractionated from the sample 22 by the cells 4, allow to calculate, according to a method such as that explained below, at least the nature and the concentration of at least two sought components, insofar as there are at least two analysis cells 4; in FIG. 1, five analysis cells are shown making it possible to know the nature and the concentration of five given components, insofar as these are of course present in the initial sample 1 at a rate measurable by said cells 4 , otherwise, the concentration is considered to be zero.

 These results thus obtained can also be compared with known references of the components sought for validation of the measurement.

An example of calculating the concentrations [Cj] of the different gaseous components that are sought in a given gas mixture as a function of the values Vj originating from the different analysis cells, is such that
[Cs] - f (Vj)
where f is for example a polynomial with several variables Vj, whose weighting coefficients of each term can be predetermined, as a function of said analysis cells 4 and of the gaseous components sought, by the known method called AIM (this method is described by example in the publication Sensors and
Actuators B 28 (1995) 217-222, entitled Neural networks and abductive networks for chemical sensor signals: a case comparison, by Messrs SOMMER, TOBIAS and al).

 i is from 1 to n, n being the number of values from the different analysis cells 4 for a given gas component, each analysis cell 4 can be the source of several V values for different gas components, such as as for example the chromatography columns (separation column 3, followed by a plasma detector 5).

 Each concentration coefficient Cj defined by a function f cannot therefore be obtained by a single measurement Vj. The more measurement values Vn there are, the more the calculation of this concentration is refined over the same cycle and allows the required precision to be obtained.

Thus, according to the invention, one can have for example
- raw measurements V1 to VL on sample 2, by electrochemical and photometric cells 4,
- VL +, to V2L measurements on sample 22 by gas chromatography after the separation column 31,
- measurements V2L + I to V3L by a mass spectrograph on a third sample 23 as explained below,
- V3L +, to V4L measurements from the second sample 22 after the separation column 32 by the same electrochemical and photometric cells 4.

 When it is desired to be able to detect and analyze the concentration of components of heavy gases which cannot be treated by physicochemical or photometric cells, we divide said sample 1 of gas mixture to be analyzed, into at least three samples, of which the previous two 2 , and 22, and the third 23 of which is sent through a second sampling system 32 which can be like the previous one, a separation column such as gas chromatography, and also comprising a pump 192 for suction and desorption at the outlet; the sub-samples thus fractionated by this second separation column 32 are then sent, either simultaneously or sequentially as after the first separation column 31 for the sample 22, in measurement cells 6 each of the latter measuring at at least one given characteristic linked to the concentration of at least one of said components that is sought and which, for components whose molecules are heavy, may be mass spectrometers.

 As for the previous separation column 3 l, this second separation column 32 may include a bypass at its outlet to send part of each separated sub-sample to a presence detection sensor 52 of a desired component such as a plasma detector.

 The entire distribution network by connecting conduit between the various components of the device, is firstly connected to a reference air source 8 to ventilate and calibrate the device, and secondly to a purge outlet 7.

 Depending on the type of gaseous component sought, if there is no specific sensor 4 for analyzing it and measuring its concentration, it is possible to react chemically such as by oxidation-reduction, ie the entire sample, at the inlet of the device, or at least one of the subsampling of the gaseous mixture with a known reagent, for example before the corresponding analysis cell, in order to obtain a resulting component which can then be more easily analyzed.

 As shown in FIG. 1, the same measurement cells 4 are preferably used for the analysis on the raw sample 2 "as for the analysis on the fractional sub-samples of the sample 22 after the separation column 31 .

According to FIG. 2, the analysis device according to the invention comprises four plates integrating the different means necessary for implementing the method of the invention, which plates are assembled in layers superposed against each other, and constitute said multilayer sensor
one of these plates 12 supports all the measurement cells 4, 6 and of analysis,
- Another 13, immediately superimposed on the previous 12, supports all the sampling means 3 including at least the separation columns and all the connections 18 in which the gas mixture and its samples 21, 22, 23 circulate as a whole of the device and in the cells 4, 6 for measuring and analyzing the plate 12,
- Another 14, immediately superimposed on the previous 13, includes all the cut-off and opening 11 and pumping members 15, 19 authorizing said circulation of the samples of the gaseous mixture in the various connections 18 and the sampling means 3 ,
- At least a fourth plate 9, 10 placed above or below the previous sandwich assemblies in the above order, includes all the electronic means for controlling the switching devices 11 and pumping 15, 19 for collecting signals recorded by measurement cells 4, 6 and of communication with the outside of the device.

 The various sub-components of said sensor, as described above, are produced in micro-technology on the basis of silicon, pyrex, metal, thick layer and thin layer, metallic or polymer, doped or not with metallic, magnetic or non-magnetic oxide, polarized or non-polarized, according to any known technique.

 According to the representation of FIG. 2, five plates are in fact represented, the fourth plate 9, 10 described above being in fact separated into two superimposed plates, one of which 9 comprises the electronic means for collecting the signals, and the electronic control means connected respectively by a single common conductor bus 16 to the plate 12 of the measuring cells 4, 6 and by another single common conductor or bus 17 to the plate 14 of all the cut-off and opening members 11 and pumping 15, 19; the known definition of a Bus designates a conductor common to several circuits making it possible to distribute information or supply currents.

 The second plate 10 represented in FIG. 2 may be that comprising the communication unit with one or more standard link interfaces for establishing one or more communications with any acquisition network belonging to more global monitoring equipment for addressing the result of the measurements and / or with any calculation unit making it possible to send or receive any information and / or instruction for configuration or programming for said electronic means of the multisensor.

 It is also possible to use the electronic means of said multisensor to process any information received by any other measurement equipment or other sensor such as meteorological, measurement of particle rate, etc. which can be connected by a bus. parallel to that 16 of the multisensor described above, which other external sensor can be another additional plate which can be added to the previous ones or be a separate component.

Claims (10)

 1. Method for analyzing several components contained in a gas mixture, a sample of which is taken from a given volume (1), characterized in that  - dividing said sample (1) into at least two samples (2 "22),  - similar subsamples of one of these said samples (2i) are sent in at least two measurement cells (4), each of at least one given characteristic linked to the concentration of at least one of said components which may be present in the gas mixture and that we want to analyze,  - the other sample (22) is sent through at least one separation column (3i) of said components, then at the output of this column (31), this sample (22) fractionated is directed into at least two cells (4) measurement, each of at least one given characteristic linked to the concentration of at least one of said components to be analyzed,  - the results of the two series of measurements carried out on each of the samples (21 22) by the cells (4) are noted and, by calculation and comparison with known references, the nature and the concentration of at least two of said said are deduced therefrom sought after components and possibly present in the gas mixture.  2. Analysis method according to claim 1, characterized in that, at the outlet of the separation column (31), each of the fractional sub-samples of the sample (22) is sequentially distributed, in at least one of said cells (4) for measuring at least one given characteristic linked to the concentration of the component corresponding to the separation sequence given by said column (3i).  3. Analysis method according to any one of claims 1 or 2, characterized in that the said sample (1) is divided into at least three samples (2l, 22, 23) of which the third (23) is sent to through a second sampling system (32) and then at the output thereof in at least two analysis cells (6), each of at least one given characteristic linked to the concentration of at least one of said sought components .  4. Analysis method according to any one of claims 1 to 3, characterized in that at the outlet of each separation column (3), a part of each subsample thus separated is sent to a detection sensor presence (5) of at least one sought-after component.  5. Analysis method according to any one of claims 1 to 4, characterized in that chemically reacts at least one of the sub-samples of the gas mixture with a known reagent, before analyzing it.  6. Analysis method according to any one of claims 1 to 5, characterized in that the same measuring cells (4) are preferably used for analysis on the raw sample (2,), as for analysis on the fractional sub-samples of the sample (22) after the separation column (3l).  7. Device for analyzing several components contained in a gas mixture according to the method of any one of claims 1 to 6, characterized in that all the means necessary for the implementation of the method are integrated in one and the same sensor. modular design, using the semiconductor properties of the materials in which these means are made, and comprising at least two plates integrating said means and assembled in layers superposed one against the other.  8. Analysis device according to claim 7, characterized in that it comprises at least four plates, of which  - one (12) supports all the measurement and analysis cells (4, 6),  - Another (13), immediately superimposed on the previous one (12), supports all the sampling means (3) including at least the separation columns and all the connections (18) in which the gas mixture and its samples circulate ( 21, 22, 23) throughout the device and in the cells (4, 6) for measuring and analyzing the plate (12),  - Another (14), immediately superimposed on the previous one (13), includes all the cut-off and opening (11) and pumping (15, 19) members authorizing said circulation of the samples of the gaseous mixture in the various connections (18) and the sampling means (3),  - at least a fourth plate (9, 10) placed above or below the previous ones, assembled in sandwiches in the above order, includes all the electronic means for controlling the cut-off (11) and pumping (15, 19 ), for collecting the signals picked up by the measuring cells (4, 6) and for communicating with the outside of the device.  9. Device according to claim 8, characterized in that it comprises a single common conductor Bus (16) between the plate (12) of the cells (4, 6) for measurement and analysis, and that (9, 10) electronic means for collecting signals from said cells, and another single common conductor Bus (17) between the plate (14) of the cut-off (11) and pumping (15, 19) members and that of the electronic control means (9, 10).  10. Device according to any one of claims 8 or 9, characterized in that it comprises at least one standard connection interface on a support plate (9, 10) of the electronic means, for establishing communication with any unit of external calculation, send the measurement results to it and receive all information and instructions for setting and programming for said electronic means.