SU894494A1 - Method of optical absorbtion gas analysis - Google Patents

Description

The invention relates to gas analysis, and more specifically to optical absorption gas analysis, and can be used, for example, in analyzing the composition of air in life-i. out and production facilities. The known method of optical absorption analyzer by measuring the 1T1 level by measuring radiation with a pair of non-selective receivers, such as bolometers {Ts .. The closest to the proposed method is an optical absorption gas analysis method based. absorbed by the absorption of the modulated radiation by the detectable component of the analyzed gas mixture by measuring the fluctuations of the temperature difference in the two chambers, at least one of which is receptive. In this method, the measurement of the intensity of absorption of radiation by ocytqecT is measured by measuring the pressure fluctuations that occur when the analyzed mixture heats up under the influence of a modulated radiation flux. The conversion of pressure oscillations into an electrical signal is performed using a microphone. 2. The disadvantage of this method lies in its low sensitivity caused by the limited volume of the receiving radiation of the analyzed gas mixture. The purpose of the invention is to increase the sensitivity. This goal is achieved by the fact that in an optical absorption gas analysis method based on the absorption of modulated radiation by a detectable component of an analyzing gas mixture, by measuring the temperature difference fluctuations in two chambers, at least one of which is ray-receptive, the flow of the analyzed gas is excited from one chamber to another and measure the intensity of this flow by converting the flow rate of the analyzed gas mixture into an electrical signal, while the number of -qecTBO The analyzed gas mixture is selected from the conditions for providing an increased intensity of heat exchange between the analyzed gas mixture and the environment, which is increased in comparison with the value at which the maximum temperature signal is reached.

The drawing shows the device implementable method.

The device contains a radiation source 1, a reflector 2, an input window 3 of the receiving-ground chamber 4 with a wall 5, a synchronous motor 6, optical filters 7 and 8 forming the obturator, a reference signal receiving circuit comprising a setting device 9 and a converter 10, an outer chamber 11 separated from the surrounding environment wall 12f mirrors 13 and 16, shut-off valve 17, hole 18 in the wall 5 of the receiving chamber 4, thermistors 19 and 20, e-bearing valve 21 a measuring system containing condensate 22 and 23, forming, with thermistors 19 and 20 nonequilibrium bridge, 24 pytaki source, separation capacitor 25, variable signal generator 26, synchronous detector 27, device 28 linearizing gradient optical gain recorder 29, pressing 30 corrector 31 flatness, SOURCE 32 adjustable voltage of the current.

The device works as follows.

radiation from the source 1 by the reflector 2 ipraal efs through the input bk but 3 into the radiating chamber 4, bounded by the wall 5. The syphons and the motor are equipped with an 8-way obturator, two optical 7 and 8 of which are emitted radiation and nonycKsaof radiation in the picture. no detectable component of the mixture being mixed and almost equally transmitting radiation 9 regions of the spectrum, where it’s absorbed by the Hi-Tepe ejineiiKite component 4 and 3 of the mixture

With a zeda gchv {guv 9, filled in in M (here from magiforno material, on the transducer 10), a reference is obtained to control the operation of the synchronous detector 27.

Radiation chamber 4 is inside the outer junction of the Jurassic 11, which is separated from the surroundings by the wall 12. The inner chamber contains a concave spherical helix of the same radius of curvature, and mirrors 13 and 14 are removed from the mirror 15 for a distance equal to this radius, | The center of curvature of the mirror 15 lies between the mirrors 13 and 14, and the centers of curvature of these mirrors locate at some distance from each other on the surface of the mirror 15. The radiation after a certain number of reflections from the mirrors (this number depends on um from the angle of rotation of mirrors 13 and 14 around the center located between these mirrors) falls on an additional mirror 16. The latter is made of

cylindrical rod and head in the form of a piston, the front mirror surface of which is beveled at an angle that allows to change the direction of the reflected radiation to the necessary extent (by rotating the mirror around the axis of the rod) and thereby increase and regulate the path length of the rays in the chamber.

When the radiation detector Q is filled with the analyzed gas mixture, it is passed successively through the open shut-off valve 17, the receiving-chamber 4, the opening 18 in the wall 5 of the receiving-chamber 4, the channel with thermistors 19 and 20, the outside chamber 11 and through the open-closing check valve 21 to discharge into the surrounding the atmosphere.

When the filters 7 and 8 are rotated, the radiation entering the receiving-chamber 4 is modulated. In the part of the spectrum where the component being detected is absorbed by the analysis of the mixture under study. The modulated radiation being absorbed in the receiving cell 4 causes, in the latter, fluctuations in the temperature of the gas mixture. The mixture is analyzed periodically (with a modulation frequency) flows from radiation-receiving chamber 4 into outer chamber 11 and back through aperture 18 and a channel in which the heating resistors 19 and 20, which receive this gas flow, are de-energized by the flow of gas. Indeed, in the absence of a gas flow between the chambers, the gaseous medium, surrounded by thermistors 19 and 20, is fixed. Both thermistor Joule heat almost

up to the same temperature limit. When a flow occurs between chambers, the cooling conditions change; thermoresistors 19 and. 20. These of Meenia are not identical, since the gas

The yoke carries heat from one thermistor to another. The flux from the radiofrequency 1SHORE 4 to the outer chamber 11 carries heat away from the thermistor of the resistor 19 to the thermistor 20. The latter turns out to be more heated than the first. On the contrary, the opposite is directed: the new gas flow due to ablation from the thermistor 20 to the thermoresis TOpy 19, the first one cools more.

Claims (1)

Since the direction of the gas flow changes with the modulation frequency of the radiation, a variable additional heat flow occurs between the thermistors 19 and 20 due to the partial transfer of heat by the gas flow. Depending on changes in the direction of the gas flow, the temperature difference between thermistors 19 and 20 also changes. Periodic oscillations of the temperature difference between thermistors 19 and 20 are sensed and converted by the measurement system into a signal of measurement information. The measuring system on the course has capacitors 22 and 23, which form a non-equilibrium bridge with thermistors 19 and 20. One of its diagonal is connected to the DC power supply 24, and the other via a coupling capacitor 25 to the input of the AC amplifier 26. The amplified signal is rectified by a synchronous detector 27 (synchronous detection commutation is performed with the radiation modulation frequency in the usual manner - the reference signal from the converter 10) and is fed through the device 28, which linearizes the calibration characteristic (it can be performed on a nonlinear element, for example, a semiconductor diode) to the registrar entry. The switch 30 and the error corrector 31 serve to periodically monitor the transmission coefficient of the output electrical circuit with an amplifier. The source 32 is adjustable DC voltage is designed to correct the zero signal. The advantages of this re-known method are as follows. In the known methods of optical absorption gas analysis for each given concentration range of measurements it tends to achieve the maximum possible or close to it sensitivity of the gas analysis (the ratio of the electrical signal to the cause of its change in the concentration of the component being determined in the analyzed mixture), choosing the optimal number of senses radiation of the inherent mixture from the condition of reaching the maximum possible (or close to it) amplitude of temperature fluctuations ry 6 luchepriemnoy gas mixture, in particular, the optimum thickness is selected layers 6 luchepriemnoy mixture value which generally does not exceed 5 mm. The latter value is taken for a series of currently available optoacoustic gas analyzers, a further increase in the amount of radiation perceived by the receiving mixture, i.e., greater than the optimum value corresponding to the maximum temperature amplitude (in particular, an increase in the thickness of the receiving gas mixture) more than 5 mm), leads to a decrease in the sensitivity of the optical absorption analysis, based on measuring the difference of comparison "x streams (one of which is passed through uemuyu mixture largest acoustic pressure amplitude, dependent on the temperature signal present), the latter is caused by the difference compares "nx radiation fluxes. This measurement also does not increase the sensitivity of the optical absorption gas analysis and the increase in the number of perceived radiation of the light-receiving mixture by increasing the overall dimensions limiting the light-receiving mixture in two directions perpendicular to the radiation flux axis. Replacing in this method an optoacoustic method based on measuring the vibrations of a microphone membrane with a method based on measuring the intensity of a part of the mixture being analyzed from one chamber to another allows increasing the number of cells in the cameras compared to the amount icoTopoe is optimal for opto-acoustic conversion. In this case, the absolute value of the temperature signal (amplitude of oscillations of the temperature difference) decreases and the dimensionless GrPr complex increases, i.e., the intensity of heat exchange between the receiving chamber and the surrounding medium. The method has advantages over the known values of Gr-Pr 0, l, i.e., with an increase in the volume of the light-receiving mixture, see Formula of Invention two chambers, at least one of the hours, which is only receiving, is characterized in that, in order to increase the sensitivity of the FIRST, excite the flow of the analyzed gas mixture from one and other measured intensivioet this pe- retekani. by converting the flow rate of the analyzed gas mixture into an electrical signal, the amount of the analyzed gas mixture is selected from the condition of increased heat transfer between the environment being analyzed by the gas mixture, increased compared with the value at which the maximum temperature signal is reached. Sources, information taken into consideration during the examination 1. Aiken A, Physico-chemical analysis in production, ONTIL, 1936, p. 99, 2, Automatic gas analyzers. Under Re B, A, Pavlenko, M ,, TsINTI Electroprom, 1961, s, 180-181 (prototype),