FR2520115A1 - Analysing gas/air mixtures for seal monitoring system - using intensity variations caused by infrared or ultraviolet absorption - Google Patents

Abstract

The mixture to be analysed is input to an operating chamber where it is subjected to infrared or ultraviolet radiation which becomes modulated by the absorption band of the gas. The contents are evaluated from the intensity variation. The gas-air mixture is fed into the chamber until the pressure exceeds atmospheric. The pressure is held constant during three or more radiation cycles. The effect of the radiation commences immediately the pressure exceeds the atmospheric pressure. Before the mixture is fed in, a gas which does not absorb the infrared or ultraviolet radiation is passed through the chamber which is then evacuated to a pressure below atmospheric so as to increase the gas conc. in the mixture. The method for analysing gas-air mixtures is applicable to monitoring the sealing of many different objects in widely different areas of application, e.g. in the aircraft and motor vehicle industries.

Description

 The present invention relates to the technique of measurements, relates to the control of the tightness of the enclosures and closed systems and in particular relates to a method of analysis of gas-air mixtures as well as a device for its implementation.

 The invention can be applied in the construction of cars, airplanes, tractors as well as in the chemical, oil and gas industries and in many other branches including in the construction of residential and industrial buildings, especially for checking tightness.

 Mass spectrometry, halogen, thermocatalytic, ultrasonic and other types of leak detectors are known today. All of these leak detectors are for special use. The mass spec leak detector is mainly intended for the vacuum industry, halogen detectors, for the refrigeration industry, the other types of leak vectors are used in various areas of the industry to detect gross faults. due to piercings.

 The main requirements to be met by the indicated leak detectors consist in ensuring the continuous continuous control of the seal with the necessary precision as well as in using a test gas ensuring uniform filling with a gas mixture. air test of the entire volume of the objective to be checked.

 However, these leak detectors do not sufficiently meet the requirements mentioned.

For example, a halogen leak detector cannot operate in continuous operation due to the accumulation of refrigerant in the sensitive element, which requires blowing for the ventilation of the latter. In addition, the use of such a refrigerating agent does not allow uniform filling of the volume of the device to be tested, which significantly reduces the precision of control, in particular when testing loudspeakers of large volumes.

 The latter drawback is also inherent in mass spectrometry leak detectors.

 The problem of uniform filling of the volume to be controlled by a gas-air working mixture is partially solved by creating a method for the analysis of gas-air mixtures (see, for example, ltURSS author's certificate NO 298876, cl. GOl H 21/34, of 16.03.71) using, as test gas, nitrous oxide. In this process the gas-air mixture to be analyzed is sent into the working chamber and this mixture is acted on with ultraviolet or infrared radiation modulated according to the absorption bands of the test gas; according to the variation in the intensity of the radiation, the presence of the test gas in the gas-air mixture is determined. The method described can also be used either for the analysis of gas-air mixtures, or for detecting leaks from closed containers.

 A device for analyzing gas-air mixtures is known (see, for example, the author's certificate of URUS NO 428242, cl. GO1 m 3/04 dated 15.05.74) comprising a working chamber whose entrance is connected to a gas-air mixture sampling device and the outlet of which is connected to a vacuum pump; a source of infrared or ultraviolet radiation is placed in a determined position relative to an entrance window of the working chamber; between the source and the between are placed one after the other on the path of said radiation a radiation switch and a modulator which form the optical working and reference channels, and on the path of radiation having passed through the chamber containing the gas-air mixture is placed an infrared or ultraviolet radiation receiver, electrically connected to the corresponding inputs of a comparator circuit whose output is connected to an indicator block.

 In the indicated device which is a leak detector - gas analyzer, implementing the method according to the USSR author's certificate NO 298876, the analysis of the gas-air mixture is carried out in the dynamics of its current, because the gas-air mixture is sent to the working chamber without interruption. In this case, during the analysis there is a variation of the pressure, the speed, and the temperature of the gas-air mixture. In addition, variations in atmospheric pressure also influence the result of the analysis.

 The instability of the main parameters of the mixture analyzed also reduces the sensitivity and precision of the control and limits, moreover, the threshold sensitivity of the device, which in turn leads to the reduction of the field of application of the device.

The drawbacks indicated are explained by the fact that the threshold sensitivity of the device described in the concentration of dressai gas, for example nitrous oxide, in the gas-air mixture is determined by the simplified formula
Qmin = Cmin P # p = const. ' (1) where Qmin is the minimum flux in ls-1 of gas-air mixture ana-
lysed reliably detected, flowing through a
leakage of the piercing type.

Cmin is the minimum concentration in% vol of ES gas
sai recorded by the device
Z is the volume flow rate in / s of the gas-air mixture
analyzed through the working chamber
p is the atmospheric pressure in Pa.

 The above formula shows that the higher the volume flow rate of the analyzed gas-air mixture passing through the working chamber of the device, the lower the sensitivity with respect to the minimum gas-air mixture current. The volume flow in turn depends on the pressure and the speed of the gas-air mixture in the working chamber.

 In all gas leak detectors, the volume flow of the analyzed gas-air mixture passing through the working chamber, due to the variation of the pressure and the speed of passage of the analyzed gas-air mixture, is a variable quantity, this which is the main cause limiting the sensitivity and measurement accuracy of the test gas content of the analyzed gas-air mixture.

An apparatus is also known for detecting high concentrations of flammable vapors and gases caused by leaks ("Plant Engineering" 1979, vol. 33
N 19, p-129-131); an infrared analyzer for detecting heavy water leaks in nuclear reactors ("Canadian chemical processing", 1978, vol.62, N05, p.26-28); the infrared gas analyzer used as a leak detector, in the US manual for non-destructive methods of quality control "(" Metall handbook, 1976, chapter "Leak tightness control", p.260-270) ; infrared leak detectors (see, for example, Great Britain patent N 1442195, cl. GOlA, US patent N03771350, cl. 73-405 R); leak detection technology in underground pipes and systems described in the "Journal of Optics; 1980, vol. 11, Nov. Dec. American Water Works
Association, 1979, vol. 71, N 2, p.61-75, the use of infrared detectors to check for leaks (see for example nVakuum-Technickn, 1980, vol.29, N04, p.

100-115).

 All the devices mentioned are made, for the most part, in a manner analogous to the device according to the author's certificate of URUS N 428242, and possess, like this device, a low sensitivity and precision of control.

 The present invention relates to a method for analyzing gas-air mixtures and a device for its implementation, making it possible to ensure the conditions which give the possibility of stabilizing the parameters of the gas-air mixture to be controlled during its admission into the working chamber and making it possible, in the working chamber itself, to improve the sensitivity to the presence of the test gas and the accuracy of against tightness of the devices.

 It therefore relates to a process for analyzing gas-air mixtures, which consists in causing the gas-air mixture to be analyzed in a working chamber, to act on this mixture with infrared or ultra-violet radiation modulated in the absorption bands of the test gas, and to determine from the variation in the intensity of the radiation the presence of the test gas in the gas-air mixture, said method being characterized in that the gas-air mixture is admitted into said chamber until its pressure there exceeds the atmospheric pressure and this pressure is maintained at a constant level during at least three modulation cycles, the action of infrared or ultraviolet radiation being ensured from time the gas-air mixture reaches a pressure exceeding atmospheric pressure.

 It is advantageous to complete the method of analysis of gas-air mixtures, by a blowing operation of the working chamber carried out before bringing the az-air mixture into the latter, the blowing being done with a non-absorbent gas. not infrared or ultraviolet radiation, and by an evacuation operation by pumping until a pressure lower than atmospheric pressure is obtained, to increase the concentration of the exhaust gas in the gas-air mixture at inside the working chamber.

 The invention also relates to a device implementing the method for analyzing a gas-air mixture, comprising a working chamber having its inlet connected to a device for taking the gas-air mixture and its outlet connected to a vacuum pump, a source of infrared or ultraviolet radiation being placed in a determined position relative to a window of said vacuum chamber, a radiation switch and a modulator forming optical paths of retention and work being successively placed on the path of said radiation between the source and the window, while on the path of radiation which has passed through the gas-air mixture, is placed an infrared or ultraviolet radiation receiver electrically connected to the corresponding inputs of a comparator circuit whose output is connected to an indicator block, said device being characterized in that it further comprises a pressurizing pump located at the entrance to the working chamber vail, two solenoid valves placed directly respectively at the inlet of the working chamber and at its outlet, a pressure sensor connected to the working chamber, a control block of which an information input is connected to the pressure sensor and of which another information input is connected to a second output of the comparator circuit, a control output of said block being connected to the corresponding input of the comparator circuit, and other control outputs being connected to the inputs of each of the solenoid valves, as well as a timer block whose output is connected to a corresponding information input of the control block.

 In this method of analyzing a gas-air mixture as well as in the device implementing it, the analysis is carried out at constant pressure in the working chamber and at zero speed due to the mixture to be analyzed.

The absolute value of these two parxseter3 is chosen so that during the analysis process according to the proposed method the device exhibits the best possible limit sensitivity Qmin with respect to the concentration of the test gas. During the analysis these parameters are automatically kept in the device at a constant level.

 This makes it possible to improve the sensitivity of the process and the device as well as the control precision when detecting a piercing-type defect.

The characteristics of the invention will emerge more particularly from the following description given by way of example and made with reference to the drawings given in the appendix in which:
- Fig. 1 is the functional diagram of a device for carrying out the method for analyzing a gas mixture, according to the invention
- Fig. 2 is a time diagram of the variation of the pressure of a gas-air mixture in the working chamber during the analysis of a mixture according to the method of the invention.

 The process for analyzing gas-air mixtures consists of the following.

 A gas-air mixture to be analyzed, taken from the controlled surface of the verified objective in the event of a piercing-type defect, is sent to the working chamber.

The gas-air mixture is brought there until its pressure in said chamber exceeds atmospheric pressure. From this moment, the gas-air mixture is acted on by infrared or ultraviolet radiation modulated according to the absorption bands of the test gas; moreover, during the radiation action, the pressure of the gas-air mixture in the chamber is permanently maintained at the level reached, at least during three modulation cycles.

 The action of the radiation indicated on the gas-air mixture to be analyzed causes the intensity of the radiation to vary, which makes it possible to detect the presence of test gas in the gas-air mixture. It is possible to determine in this way the presence of defects of the piercing type in the objective checked, and to give a quantitative assessment of the volume concentration of the test gas in the gas-air mixture analyzed.

 The analysis process of the gas-air mixture can be carried out either statically when the mixture has already filled the volume of the chamber and its supply ceases, - or in dynamic regime, when the mixture incessantly passes through the chamber. In this case, a pressure of the mixture in the chamber is obtained which exceeds atmospheric pressure by adjusting the flow rate of the mixture.

 A device implementing the method for analyzing gas-air mixtures according to the invention comprises a device for taking samples 1 (FIG. 1) connected to the inlet of a working chamber 2 by the through an air filter 3, a pressurizing pump 4 and an electro-valve 5, the latter being mounted directly at the inlet of chamber 2. At the setting of chamber 2 is mounted a solenoid valve 6 by means of which the chamber 2 is connected to a vacuum pump 7.

 A source of infrared or ultraviolet radiation is disposed relative to the inlet 8 of the chamber 2; in the variant described it is a source 9 of infrared radiation. On the path of the infrared radiation beam, between the source 9 and the window 8, are arranged in series a radiation switch 10 and a modulator 11 which form optical reference and working channels.

 On the path of the radiation having crossed the chamber 2 containing gas-air mixture there is installed an infrared or ultraviolet radiation receiver common to said optical channels; in the variant described it is an infrared radiation receiver 12. The sensitive element 13 of the receiver 12 is electrically connected to the inputs 14, 15 of a comparator circuit 16, to which the information coming from the reference optical channels arrives and of work respectively. The output of the comparator circuit 16 is connected to an indicator block 17.

 The device also includes a pressure sensor 18 connected to the working chamber 1 and connected to an information input 19 of a control unit 20. A control output 21 of the control unit 20 is connected to the solenoid valves 6, 5 and sends control signals for their opening, while control outputs 22, 23 are connected to the same solenoid valves 5, 6 to send closing control signals. A control output 24 of the control block 20 is connected to the switch 10 produced in the variant described in the form of a curtain 25 performing a back-and-forth movement under the action of an electric stepping motor 26. A control signal comes from output 24 for switching on the electric stepper motor, the stop command signal from the latter coming from a control output 27 of the control unit 20.

 The device also includes a timer block 28, the output of which is connected to an information input 29 of the control unit 20, the control output of which is connected to a corresponding input of the comparator circuit 16. The corresponding output of the comparator circuit 16 is connected to an information input 31 of the control unit 20.

 The device also comprises a synchronization block, comprising in the embodiment described a light source 32 and a photodiode 33 which are arranged on the two sensed sides of the curtain 25 of the switch 10, this curtain having an opening 34. The block of synchronization is connected by the output of the photodiode 33 which forms part of it, to an information input 35 of the control block 20.

 In the embodiment described, the source 9 of infrared radiation consists of 'e. nichrome spiral 36, mounted in a reflector 37.

The modulator it is made up of three gas filters 38, 39, 40. The filter 38 is filled with nitrous oxide, the filter 39 is filled with nitrogen, and the filter 40 is filled with constituents whose spectral characteristic is located close to the spectral characteristic of nitrous oxide used as test gas
When using the device proposed to detect a fault of the piercing type, the indicator block 17 takes the form of a light or sound signaling device, an output of which can be connected to a recording block. indicated above, information on the volume concentration of the test constituent in the gas-air mixture analyzed, the indicator block 17 may include a recording device graduated in% by volume of the test gas.

 The operation of the apparatus for carrying out the method of analysis of gas-air mixtures is as follows.

 When a control signal arrives from the control block 20 (Fig.l) from the control output 21, on the solenoid valves 5, 6, the latter are open, and with the help of the vacuum pump 7 the work 2 is blown with a yaz which does not absorb infrared radiation, for example with clean air. The blowing is carried out in accordance with the ventilation cycle tl represented in FIG. 2, which gives the time diagram of the variation of the pressure P in the working chamber during the operation of the device.

 When the ventilation cycle tl is finished, when a signal arrives from the timing block 28 and attacks the input 29 of the control block 20, the latter delivers at its control output 23 a command to close the solenoid valve S The solenoid valve S is closed, after which, using the vacuum pump 7, the pressure in the working chamber 2 is reduced to a value below atmospheric pressure, so that in the chamber 2 a depression Pmin is created, controlled using the pressure sensor 18. The pumping for the evacuation of the working chamber 2 carried out during the depression cycle t2, represented in FIG. 2.

 The cycles tl and t2 are preparatory cycles which make it possible to improve the sensitivity and the precision by virtue of an increase in the content of test gas of the gas-air mixture in the working chamber, ie d '' obtain in the same volume of the working chamber 2 a greater value of the equivalent thickness of the test gas in the gas-air mixture, absorbing infrared or ultraviolet radiation, in comparison with the concentration of the test gas in room 2 if the indicated preparatory operations are not carried out.

 When the vacuum cycle t2 is finished, the control unit 20 delivers at its control output 22 a command to close the solenoid valve 6 and, simultaneously, it outputs at the control output 21 a command to open the solenoid valve 5. The valve 6 is closed and the valve 5 is open; from this instant the gas-air mixture to be analyzed arrives in the working chamber 2 through the sampling device 1 and the air filter 3, using the pressurization pump 4. The intake of the gas-air mixture to be analyzed takes place until its pressure exceeds atmospheric pressure. The admission of the gas-air mixture to the working chamber 2 corresponds to the cycle t3 of creating an overpressure in the working chamber 2 shown in FIG. 2.

 In principle, the proposed process for supplying the gas-air mixture to the working chamber 2 can be carried out without cycles T1 and T2, which are preparatory cycles. In this case, it is possible to increase the pressure of the gas-air mixture in the working chamber 2 from atmospheric pressure in the working chamber itself, which corresponds to cycle I of creation of an overpressure in the work represented in figure 2 by a dotted line.

In accordance with cycle t3, the pressure P of the met
max gas-air change in working chamber 2 is high, par.

example, up to l, 6.105Pa and it is checked using the pressure sensor 18.

 When the cycle t3 of supplying the gas-air mixture to the working chamber 2 is finished, the control unit delivers at its control output 23 a command signal to close the solenoid valve 5, and the valve 5 closes .

 During the blowing operations of the working chamber 2, of creating the vacuum and of filling the chamber with the gas-air mixture to be analyzed, corresponding to the cycles tl, t2, t3, the infrared radiation from the source 9 is masked by the radiation switch 10; therefore infrared radiation does not reach the chambers 38, 39, 40 of the modulator ll to the working chamber 2 and to the measurement volume of the receiver 12 of infrared radiation.

During said cycles tl, t2, t3 the measurement volume 12 is cooled and its thermal regime in the initial state (by initial state is meant the state corresponding to the preparation of the receiver for the analysis of the gas-air mixture after the previous measurement).

 When the valve 5 is closed, the control unit 20 delivers at its control output 24 and a signal for controlling the engagement of the stepping electric motor 26 of the radiation switch 10. Then the electric motor 26 moves the curtain 25 letting the infrared radiation pass in turn through the chambers 38 and 39 of the modulator 11; therefore the radiation is modulated in the absorption bands of the test gas (nitrous oxide) with a constant frequency.

In accordance with the cycle + t4 of action of the infrared radiation, on the gas-air mixture, from the moment the gas-air mixture reaches a maximum pressure, the action by infrared radiation is carried out at least for three cycles. modulation, P then being maintained at a level
max constant.

When the cycle t4 is finished the timer block 28 outputs a signal attacking the input 29 of the control block 20, which outputs by its control output 30 a control signal to the comparator circuit 16 and allows the reception of electrical signals from the receiver 12 of infrared radiation on the inputs 14, 15 and the subsequent transmission of the result of the comparison to the indicator block 17, according to the cycle t5 of fixing the presence of the test gas in the chamber 2 with a constant pressure
P of the gas-air mixture, shown in FIG. 2.

max
After the statement of the result. from the comparison to one of the outputs to the comparator circuit 16 a signal is sent from another output of the comparator circuit 16 to the information input 31 of the control block 20, after which the control block 20 outputs at its control output 21 a command signal to open the solenoid valves 5, 6.

The valves 5, 6 open and the gas-air mixture is pumped by the vacuum pump 7, according to the cycle t6 shown in FIG. 2 during which the pressure in the working chamber 2 reaches the value of atmospheric pressure .

 Simultaneously with the opening of the solenoid valves 5, 6, at the control output 27 of the control unit 20 appearing a stop signal of the stepping electric motor 26, the latter stops by placing the curtain 25 in the position of occultation of infrared radiation arriving at the working chamber. The command for stopping the electric stepper motor 26 is formed after the arrival of the signal from the output of the comparator circuit 16 which attacks information input 31 of the control block 20.

 The position in which the infrared radiation is concealed by the curtain 25 of the radiation switch 10 is controlled by a synchronization block, the photodiode 33 of which outputs a signal attacking the silver information 35 of the control block 20.

P étant la pression statique du mélange gaz-air dans le
o
volume de mesure du récepteur de rayonnement infrarouge
(ultraviolet)
T est la température absolue
G est la conductibilite thermique du système gaz-volume
de mesure
C est la capacité thermique du mélange gaz-air
v & est la pulsation de la modulation e est l'amplitude du flux thermique dégagé dans le volume
de mesure par le flux de rayonnement infrarouge absorbé
par le gaz remplissant le volume de mesure.To make it easier to understand what is going on in our presentation, we give below the relation dQ defining the amplitude P of the pressure oscillations in the measurement volume of the receiver (for an infinitely large acoustic resistance of the walls of the volume of measurement) which is given approximately by the formula

P being the static pressure of the gas-air mixture in the
o
infrared radiation receiver measurement volume
(ultraviolet)
T is the absolute temperature
G is the thermal conductivity of the gas-volume system
measurement
C is the thermal capacity of the gas-air mixture
v & is the pulsation of the modulation e is the amplitude of the heat flux released in the volume
of measurement by absorbed infrared radiation flux
by the gas filling the measurement volume.

When the gas in the measurement volume is gradually heated, in the known diagrams the absolute temperature T, the thermal conductivity G, the thermal capacity C increase and the amplitude 9 of the flow
v thermal, which is released in the measurement volume as a result of the absorption of radiation by the test gas decreases, which causes (as is deduced from formula 2 given above) an appropriate decrease in l amplitude P of the pressure oscillations in the measurement volume of the receiver, and therefore a decrease in the sensitivity Xin of measurement of the test gas in the mixture to be analyzed, which occurs in all the measurement setups of the gas analyzers without exception.

In the process, offer thanks to the fact that the irradiation of the gas-air mixture to be analyzed in the working chamber by an infrared or ultraviolet xayonnenellt only takes place during cycles t4, the absolute mean temperature T of the gas in the measurement volume of the receiver during the flow of cycles tl, t2 t3, t5 has time to decrease and at the start of cycle t4) it returns to its initial value
As a result, the amplitude P of the pressure oscillations in the measurement volume has its maximum value equal to the theoretical value thanks to which the measurement sensitivity of the test gas does not decrease with respect to the theoretical value and remains constant for the entire operating time of the device.

According to the invention proposed the introduction of blowing operations of the working chamber by a neutral gas which does not absorb infrared or ultraviolet radiation, for example pure air and creating in the working chamber a depression relative to atmospheric pressure by reducing the pressure in the chamber for example to a value of 3.3.104 Pa, and filling the constant volume of the working chamber with gas-air mixture to be analyzed up to a pressure constant exceeding atmospheric pressure, for example up to 1.6 × 10 5 Pa, makes it possible to obtain in the same volume a greater value for the equivalent thickness of the test gas absorbing infrared or ultraviolet radiation, that is to say -say
u = ci, (3) where: u is the equivalent thickness of the gas layer
erect absorbing the flux of radiation, for example,
infrared
c is the volume concentration of the test gas in the
gas-air mixture; is is thickness of the layer of gas drawn up in the
gas-air mixture inside the tra
vail, that is, the length of the
work (Fig.l).

où #oγ représente le flux de rayonnement infrarouge arrivant
perpendiculairement sur la couche étudiée du gaz d'es
sai, au centre de sa bande d'absorption ;
est la fréquence du rayonnement infrarouge ;
k est une constante caractérisant l'absorption de la
couche, calculée par unité d'épaisseur pour p cons
tante, appelee coefficient d'absorption.
The parallel flow #O of infrared radiation
o absorbed by the test gas layer is equal to

where # o γ represents the incoming infrared radiation flux
perpendicularly on the studied gas layer
sai, in the center of its absorption band;
is the frequency of infrared radiation;
k is a constant characterizing the absorption of
layer, calculated per thickness unit for p cons
aunt, called absorption coefficient.

For low values of "u" within the limits of the absorption band (taking # o # = = const,
#o #o being the center of the band) we obtain: #o = ## o α U, where d is the integral intensity of the absorption band.

 The expression (5) indicated highlights the fact that the greater the equivalent thickness "utt of the gas layer, the more the flux of infrared or ultraviolet radiation is absorbed. This in turn does that in the measuring volume of the receiver, under equal conditions, that there is an increase in the amplitude p of the pressure oscillations, thanks to the increase in the amplitude e of the heat flux (formula 2). Thanks to the increase in the amplitude p of pressure oscillations the acoustic oscillations of the membrane of the sensitive element of the receiver increase, which, in turn, ensures the increase of the useful electrical output signal.

Regardless of the type of radiation receiver, the maximum sensitivity of the device is regulated by the minimum possible sensitivity value of the threshold for transformation of the flux 00 of the radiation absorbed in the equivalent layer of the test gas into an electrical signal U at the output of the radiation receiver. When the converter is linear the sensitivity of the radiation receiver can be written in a simplified form
K = U / 0 or U = Ko (6)
o
In the proposed method of analyzing a gas-air mixture, by increasing the equivalent thickness of the layer of the test gas, for example nitrous oxide (expression (3) the flux O of the infrared radiation absorbed in this layer increases (expression (5)) and this increases the sensitivity of the proposed radiation receiver or what is equivalent, the electrical output signal U.

Claims (3)

R E V E N D I C A T I O N S  1 - Process for the analysis of gas-air mixtures, in which the gas-air mixture to be analyzed is brought into a working chamber, the mixture is acted on by infrared or ultraviolet radiation modulated in the gas absorption bands test, and according to the modification of the intensity of the radiation the presence of the test gas in the gas-air mixture is determined, characterized in that the gas-air mixture is brought into the working chamber until its pressure in this chamber exceeds atmospheric pressure and this pressure is kept constant for at least three radiation modulation cycles, the action of infrared or ultraviolet radiation being carried out from the moment when the gas-air mixture reaches a pressure exceeding atmospheric pressure.  2 - Analysis method according to claim 1, characterized in that before bringing the gas-air mixture to the working chamber, the latter is subjected to a blowing with a gas which does not absorb infrared or ultraviolet ul radiation, and a vacuum is created there so that the pressure there becomes lower than atmospheric pressure 2 in order to increase the concentration of the test gas in the gas-air mixture inside the working chamber.  3 - Device for implementing the method of analysis of gas-air mixtures according to claim 1, which comprises a working chamber (2) connected by its inlet to a device for taking samples (1) of the gas mixture -air and by its outlet, to a vacuum pump (7), a source of infrared radiation (or ultraviolet) disposed relative to the inlet window (8) of said working chamber; a radiation switch (10) and a modulator (11) forming optical reference and working channels, being arranged in series on the radiation path between the source and the window (8) while on the radiation path having passed through the chamber (2) containing gas mixture is placed an infrared radiation receiver (or ul traviolet) electrically connected to the inputs (14, 15) of the comparator circuit (16) whose output is connected to an indicator block (17) , device characterized in that it comprises a compression pump (4) located at the inlet of the working chamber (2), two solenoid valves (5, 6), mounted directly, respectively, on the inlet and the outlet of the chamber working (2), a pressure sensor (18) connected to the working chamber (2), a control unit (20) which is connected by its information input (19) to the pressure sensor (18), by its information input (31), at the other output of the comparator circuit (16), by its output control e (30) at the corresponding input of the comparator circuit (16), and by its control outputs (21, 23), (21, 22), at the respective inputs of the solenoid valves (5, 6), and a block timer (28) whose output is connected to the information input (29) of the control unit (20).