SU1427276A1 - Method of checking fuel gas - Google Patents

Abstract

The invention relates to gas analysis and can be used in instruments for controlling the explosion of the atmosphere by the content of combustible gases in it. The purpose of the invention is to improve the accuracy of controlling the explosion hazard of multicomponent gas mixtures. When the concentration of combustible gases changes from zero to the upper limit of measurements, the supply voltage of the thermocatapitate sensor decreases from the initial value corresponding to the middle of the diffusion region of the catalytic oxidation process to the value corresponding to the boundary of the diffusion and kinetic regions of the catalytic oxidation process. The supply voltage is reduced in accordance with the expression -KS, where and is the voltage of the psta and sensor; Uo is the initial supply voltage of the sensor; S - sensor output signal; K is the coefficient of voltage reduction of the sensor supply voltage, K (Uo-Ur) / is the sensor supply voltage corresponding to the boundary of the diffusion and kinetic regions of the catalytic oxidation process, Maxmax is the sensor output signal corresponding to the upper limit of measurements. 4 il. (Lu e oi

Description

The invention relates to gas analysis and can be used in instruments for controlling the explosion of the atmosphere by the content of combustible gases in it.

The purpose of the invention is to improve the accuracy of monitoring the explosion hazard of j-iHoro component gas mixtures while reducing the sensor supply voltage.

The method of controlling combustible gases consists in their thermocatalytic oxidation on the surface of the sensing elements of the sensor, included in the bridge measuring circuit for reducing the sensor supply voltage when a signal appears at its output and determining the concentration of gases based on the value of the sensor voltage reduction. When the concentration of combustible gases changes from zero to the upper limit, the supply voltage decreases from the initial value corresponding to the middle of the diffusion region of the catalytic oxidation process to the value corresponding to the boundary of the diffusion and kinetic regions of the catalytic oxidation process, and the voltage reduction of the sensor is carried out according to the expression

P-

and and „-kz.

e and

and.

S K

sensor supply voltage; initial sensor supply voltage 35 (supply voltage in the absence of combustible gases in the analyzed medium);

sensor output; 40 coefficient of voltage reduction of the sensor power supply.

TO

- iiHi

mlkg

where and is the sensor supply voltage,

corresponding to the boundary of the diffusion and kinetic regions of the catalytic oxidation process; sensor output signal corresponding to the upper measurement limit. At this m, a decrease in the voltage supply of the sensor excludes the overheating of the sensitive elements, but the fan of characteristics for various combustible gases does not expand, since the operating points of the sensitive elements are not

x,

e10

15 20 25

thirty

35

40

45

- about 55

go beyond the diffusion region of the catalytic oxidation process, as may be the case when using a power reduction as a function of the resistance of the sensing elements or maintaining the output signal of the sensor at zero.

FIG. 1 is a schematic diagram of an apparatus for implementing a method for monitoring combustible gases; in fig. 2 and 3 are graphs of the transfer characteristics of the sensor when using, respectively, the proposed and known methods, where the explosiveness of the mixtures in% LEL is plotted along the same axis, and the output signal of the combustible gas control device (); in fig. 4 is a graph of the output signal of sensor S versus the supply voltage U on the same gas mixture necessary for determining the values of U and P ,.

The flammable gas monitoring device contains sensing elements 1-4, constituting the two arms of the bridge measuring circuit of the sensor 5, the other two arms of which comprise a resistor 6, which is used for balancing. The output of sensor 5 through resistors 7 and 8 is connected to the inputs of amplifier 9, the amplification factor of which, determined by the ratio of the resistance values, resistors 10 and 7, is K, the output of amplifier 9 is connected to the base electrode of the transistor 11 regulating the supply voltage (current ) sensor 5, Resistor 12 serves to set the value of Uo. A resistor 13 installed in the power supply circuit of the sensor 5 is connected to the input of the amplifier 14 through a resistor 15. The gain of the amplifier 14 is determined by the ratio of the resistance values of resistors 16 and 15. For balancing the amplifier 14 there is a resistor 1 7 connected to its input through a resistor 18, The power supply circuits of amplifiers 9 and 14 are not shown in the diagram of FIG. 1,

The device works as follows.

In the absence of combustible gases in the analyzed medium, the supply voltage of the Danes a. In this case, the sensor signal, the voltage drop across the resistor 13 supplied to the input of the amplifier 14, is compensated by the voltage supplied to the other input of this amplifier from the resistor 17, and the voltage at the output of the device When the analyzed medium at the output of the combustible gases at the output of the sensor 5 a signal S is generated, which is amplified by amplifier 9 by a factor of K and fed to the base of transistor 11. At the same time, the voltage at the emitter of transistor II is reduced by the value of KS. The voltage of the power supply and the sensor 5, which becomes equal to UO-KS, decreases by the same amount. This reduces the voltage drop across the resistor I3 and at the output of the device, a signal Ujy is formed, proportional to the measured value. As can be seen from the graphs depicted in FIG. 2 and 3, when using the proposed method, the width of the fan characteristics of the sensor for various combustible gases, and, consequently, the sensor error when determining the explosion hazard of many of the gas mixtures is about 5 times less than when using the known method.

I.

PRI me R. Measuring range

sensor 0-50% LEL. To select the parameters of its power, the dependence of the sensor output signal on the supply voltage on the same mixture within the measurement range, for example, 2% methane in air, is removed.

(38% LEL) (figure 4). According to the graph of S (U), the values of Uo and DI are determined, the DO value (for example, 1 1j9 в) is selected in the middle of the section of the characteristic that is closest to the horizontal (in the middle of the diffusion region). This ensures the most stable operation of the sensor. The value and (for example, And 1.5 in) is determined by the inflection point of the characteristic - by the boundary of the diffusion and kinetic regions. Detecting the sensitivity of the sensor at the end of the measurement range (for example, max mV) is determined. Determine the voltage reduction factor:

V- -t; 0.08

14272764

The supply voltage of the sensor but decrease in accordance with the

Claims (1)

and 1.9-5 S. The formula of the invention The method of controlling combustible gases, which consists in their thermo-catalytic oxidation on the surface of the sensor sensitive elements included in the pavement measuring circuit, reducing the sensor supply voltage when a signal appears at its output and determining the concentration of combustible gases according to the decrease in sensor supply voltage, about l that, in order to improve the accuracy of control of the explosion hazard of multicomponent gas mixtures, the voltage supply of the sensor when the concentration of combustible gases changes from zero to top its detection limit is reduced from the initial value corresponding to the middle of the diffusion region of the catalytic oxidation process, to a value corresponding to the boundary of kinetic and diffusion regions of the catalytic oxidation wherein a decrease in the supply voltage sensor wasp schestvl dissolved in accordance with the expression , -KS, where and is the sensor supply voltage; UQ is the initial supply voltage of the sensor (the supply voltage in the absence of combustible gases in the medium being analyzed); S - sensor output signal; K is the coefficient for reducing the voltage supply of the sensor. to S MQKt where is ut. - sensor supply voltage corresponding to the boundary of the diffusion and kinetic regions of the catalytic oxidation process; -output sensor signal corresponding to the upper limit of measurement. S Max.  / 7 (// 7 j t fc / Jf, B 17.4 0.2 - / / U / 7 Compiled by V.Ekaev Editor A.Lezhnina Tehred M.Hodanich E f Proofreader N.Korol