SU1485117A1 - Method for analysis of gas mixtures - Google Patents

Description

The invention relates to gas analysis and can be used to control the composition of gaseous media, mainly in baroz.The invention relates to a gas analyzer and can be used to control the composition of gaseous media mainly in barocomplexes and other inhabited aquanawtic objects.

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The aim of the invention is to improve the accuracy of the analysis in the specified ranges of temperature and pressure.

FIG. Figure 1 shows the temperature dependences of the output signal of the thermoconductometric sensor on temperature ύ; in fig. 2 barometric signal C, pressure sensor P.

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complexes and other objects of aquanautics. The purpose of the invention is to improve the accuracy in determining the composition of the gas mixture thermoconduction method in a wide range of pressures. In the analysis, the thermoconductometric sensor constants are pre-determined - the normalized calibration characteristic and its nonlinearity coefficient, temperature and barometric dependence of the output signal of the Sensor. Signals of temperature and pressure sensors are recorded synchronously with the sensor output signal. The volumetric content of the measured component is determined using predetermined constants by means of transformations. 2 Il.

Pre-determine the constants of the thermoconductometric sensor, with which the method is implemented. To do this, carry out the following operations.

Maintaining temperature C and pressure P of test gas mixtures (CBC) equal respectively to the lower values of the set ranges of measuring temperature C _n and pressure P _h and passing the reference gas through the comparative sensitive elements (SE) of the sensor with a volume content of the measured component equal to the upper limit of the C ₈ measurement , they pass through a set of ASGs through the working CEs of the sensor, in which

WZ. . ,, 1485117 A1

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the volumetric content of the measured component C is consistently increasing within С _n <С <, where С „is the lower limit of measurement. By registering on each of the ASGs the corresponding steady-state value of the signal, sensor and, (C), determine the normalized calibration characteristic of the sensor

£ (c)

₌ Μθ „- ^С d) и, (с, - с„) '

using which one determines, for example, graph-analytically, the coefficient of its nonlinearity b by the formula

ten

15

£ (C _th ) _ 2

£ (SSR)

(ABOUT

20

where c <

Place the sensor in a thermostat. Passing through the working ChE sensor ASG from volumetric content of the measured component C _av at a pressure P ^ ·, change the sensor temperature and ASG in the range from the lower £ "to the upper £ _in predetermined limits the temperature change range by registering at discrete steady temperatures £ ranging £ $ g. <. £ _to appropriate values

sensor output signal (£, (¾). 'Using the temperature dependence ϋ (£, C _cr ) found on the output signal of the sensor, for example, the values of the first and second derivatives of this dependence are determined graphically and analytically at a temperature £ _n .

Place the sensor in a thermobaric chamber. Passing through the working cells at a temperature £ _n PGS with a volumetric content of the measured component equal to С „, is increased in steps in the range Р _n <Р <Р _{to the} pressure of the PGS in the pressure chamber and, therefore, in the ampoules of the workers SE by letting in the PGS temperature chamber from the cylinder under pressure. At each steady-state value of pressure P, the corresponding value of the output signal of the sensor ΙΤ (P, C „) is recorded, after which, using the found barometric dependence C. (P, C„) of the output signal of the sensor, the value of the first is determined graphically and analytically.

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derivative of this dependence at pressure P „. Making further similar operations when passing through the work stations with the content of the measured component equal to С _е , determine the value of the first derivative of dependence II (Р, С _в ) at pressure Р „.

The analyte gas is passed through the working sensors of the sensor, and through the reference ones the reference gas. with a volumetric content of the measured component equal to the upper limit of the measurement of C _in , and synchronously with the output signal of the thermoconductometric sensor, the signals of the temperature sensor 11 ^ and the pressure sensor are recorded. The signals of these sensors have linear characteristics and can be used to further correct signal II,.

The volumetric content of the measured component is determined by, for example, using a microcomputer. the following operations with signals and, P ₄ and 1! _p using predefined constants:

enter into the output signal of the thermoconductor sensor and temperature correction by conversion.

MAX

^{G (} ι-ΣΰΓ7ϋ " ^:

+ 0.5 / 3 (¾

(2)

where χτ '* ¹⁴ ' * - is the maximum output

the signal of the thermoconductometric sensor, corresponding to the transmission through the working CEs of the analyzed gas with a volumetric content of the measured component C _and at a temperature £ _n and pressure P _m ;

_ _maximum temperature sensor signal corresponding to the temperature q;

enter the signal P, the pressure correction by the following conversion

g, ₊ ^ -c- (g _n -g _in ) and ₍ ^MAX

where and _p - the maximum signal of the pressure sensor corresponding to the pressure P _in ;

produce a linearization of the signal G _{2 the} following conversion:

(four)

invert the signal P ₃ with the transformation = 1 - P ₃ ; (five)

calculate the volumetric content of the measured component in percent by the formula

С = (С _е - С _Н ) Р ₄ + С „. (6)

An example, The method was tested in the development of a helium gas analyzer having two measuring ranges of 0-100% He and 80-100% He and intended for analyzing binary helium-oxygen gas mixtures under the following conditions:

C _p = 100% He; ϋ _β = 50 ° C; P _in = 10 MPa;

C _th = 0% He; C _n = 0 ° C; P = 0 MPa,

(7)

Pre-determine the constants of the thermoconductometric sensor, the comparative SE of which 'are filled with pure helium. The sensor bridge is supplied with stabilized DC voltage. The output signal is measured with a digital voltmeter of class 0.15. Temperature measurement with an accuracy of 0.5% is performed using a platinum thermo-. resistance meter mounted on the metal housing of the sensor. Resistance as a function of temperature is measured by a digital voltmeter of class 0.1. The helium-oxygen CBC passed through the sensor has a metrological ^ accuracy of certification + 0.15% of the volume fraction. Determine the normalized calibration characteristic of the sensor, the normalization of which is carried out by assigning the current values of the output voltage of the sensor II, to the maximum value and, ^MAX , determined at C _ns = 0% (pure oxygen); C = =

= 0 ° C; <P = P _n = 0 MPa (atmospheric pressure). The value of the nonlinearity coefficient b found by formula (1) is 0.13.

The study of the dependence of the output signal on temperature and pressure is carried out as follows.

The sensor is placed in a high-pressure chamber, which is installed in the climate chamber. Pressure in

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the chamber is adjusted in the range of 0.1 - 10 MPa (1-10 kgf / cm ^g ) by inlet into the chamber of the corresponding gas mixture from the cylinder, Accuracy

θ maintain the temperature? ^- 0.5 pressure ± 0.05 MPa,

The resulting dependences of the output signal on temperature and pressure are shown respectively in FIG. 1 and 2,

The graphoanalytically determined values of the corresponding derivatives of these dependencies are equal to:

⁼ ° 4; G _n - 0.09;

> = 0.1; = 0.08.

After processing the data, it was found that as a result of using the proposed method, the accuracy of analysis compared to the known increases in a wide pressure range.

Claims (1)

Claim A method of analysis of gas _mixtures, comprising: determining if the normalized values of the temperature 30 and pressure calibration characteristics of the measured component thermal conductivity sensor by passing therethrough, at least three calibration gas sme35 this corresponding to specify the lower C "and top _C0 limits measurement and the mean value C _{CP the} concentration of the measured component, the subsequent registration signal and ₍ 40 sensor when passing through it the analyzed gas and calculating the desired concentration of the measured component by comparing the values of signal II, and the calibration 45 characteristics of the sensor, characterized in that, in order to increase the accuracy of the analysis in given ranges of temperature variation C and pressure P, before recording the signal using the test gas mixtures at a lower value of P _{n in the} range, determine the temperature dependence of the signal of the sensor P, (C _av ) in a given range of not temperatures n the value at least measure the first derivative of this dependence at the point corresponding to the lower value of the temperature range, at temperature - barometric7 1485117 eight The dependences of the sensor signals V, (С „) and Г _у (С _в ) in a given pressure range and the value of at least the first derivative dependencies at the point R _h , and in the process of recording the signal 11 ^ of the sensor during transmission through it, the analyzed gas is determined synchronously current, the values of temperature and gas pressure and taking into account these values, the desired value of the concentration of the measured component is calculated. Redak'tor V. Petrash