JP4953087B2 - Concentration measuring method and apparatus - Google Patents

Description

  The present invention relates to a measuring method and apparatus for measuring the concentration of each gas in a mixed gas composed of three or more types of gases whose types of gases are known in advance.

The present applicant has developed an invention for measuring the concentration of mixed binary gas (see Patent Document 1, hereinafter referred to as “Prior Art 1”).
The measurement method of the present invention mainly uses the fact that the output of a pressure gauge by a quartz crystal sensor changes depending on the type of gas at the same absolute pressure, thereby allowing the concentration (partial pressure) of each component gas in the mixed gas. ).
In addition, the present applicant has further expanded the conventional technique 1 and proposed an invention for measuring the partial pressure of a multi-component gas, which is the same problem as that of the present invention (see Patent Document 2 below). 2 ”).

Furthermore, as an application of the above-described prior arts 1 and 2, there is an invention for performing gas detection (see Patent Document 3; hereinafter referred to as “prior art 3”).
In addition to the above, an invention has been proposed in which an airtight test is simply performed (see Patent Document 4; hereinafter referred to as “Prior Art 4”).
On the other hand, there is also an invention relating to a gas density meter using a microflow sensor having a thermopile (see Patent Document 5, hereinafter referred to as “Prior Art 5”).
JP 2001-330543 A JP 2004-198328 A JP-A-60-238742 JP 2003-194654 A JP 2004-125684 A

The prior art 1 can be applied only to a gas composed of two components.
Moreover, the above prior art 2 assumes only a mixed gas composed of three components, and the case where the concentration of one of the constituent gases is self-evident or the concentration ratio of the two gases is constant. Furthermore, it is limited only when the object can be reduced to the partial pressure measurement of the binary gas mixture.
Moreover, in the said prior art 3, although it can detect that the composition of gas changed, the method of calculating | requiring each partial pressure of the gas which comprises mixed gas in any before and behind a composition change is not described.
Further, the above prior art 4 is a method for performing a gas pipe airtightness test, and the concentration measuring portion uses a conventional densitometer, and discloses a new technology in terms of concentration measurement. It is not a thing.
Furthermore, the above prior art 5 measures the density of one kind of gas whose components are known, and cannot distinguish the gas type.

The present invention provides a method and apparatus for determining the concentration of each gas in a mixed gas composed of three or more known gases by using a crystal resonator that can overcome the above-described difficulties and can be measured easily and safely. With the goal.
In the present specification, the “concentration” of gas means “concentration or partial pressure” of gas.

In order to achieve the above object, the concentration measuring method of the present invention is a method for measuring an unknown concentration of each gas constituting a mixed gas composed of three or more kinds of known gases , wherein the mixed gas is measured by a sensor. A physical property-dependent output that depends on a physical property value that varies depending on the concentration of each constituent gas is measured, and for each combination of two types of gases among the gases contained in the mixed gas, the distribution of one type of gas A calibration curve group is obtained in advance by changing the partial pressure ratio of the other type of gas to the pressure ratio from 0% to 100%, and from the relationship between the measured physical property-dependent output and the calibration curve group, the one type of gas and The partial pressure ratio with the other kind of gas is narrowed down, and the concentration of each gas constituting the mixed gas is obtained.
Here, the prior art 1 measures the concentration of each gas constituting a mixed gas composed of two known components by using one calibration curve. On the other hand, when the gas constituting the mixed gas has three or more components, the concentration of all gases cannot be determined completely from only one calibration curve, but can be narrowed down to some extent. Therefore, the concentration of each gas can be further narrowed down by using the gas concentration dependency of a plurality of physical property dependent outputs. If the concentration of each gas is narrowed down to a measurement error range or a practically sufficient range, it is synonymous with determining, that is, obtaining the concentration of each gas constituting the mixed gas.
In order to narrow down the above gas concentration, it is necessary to obtain a plurality of physical property dependent outputs depending on the concentration of each constituent gas. Physical property values contributing to these physical property dependent outputs include viscosity, thermal conductivity, density, A quantity such as molecular weight can be used. Furthermore, in this measurement, if different types of sensors are used for the same physical properties or sensors with different relative sensitivities to different gases, the dependence of the physical property-dependent output on the gas concentration will be different. And the concentration measurement accuracy of each constituent gas is improved.
In order to implement the above invention, at least a device for introducing a gas and a plurality of types and a plurality of sensors for directly and indirectly obtaining the above-described physical property dependent outputs are necessary.
Further, for the concentration measurement, a calibration curve that is dependent on the gas concentration of the physical property dependent output is necessary, and these can be obtained by using the above-mentioned apparatus. In order to speed up and refine the concentration measurement, an electronic computer that derives the concentration from the known calibration curve group is required.

The present invention has the following excellent effects.
(1) In a multi-component gas mixture in which a pre-configured gas is known, the inside of the container in which the gas mixture exists is measured by using only a physical sensor such as a quartz crystal sensor and an absolute pressure gauge. It is possible to easily measure the concentration of each constituent gas present in the. This measurement enables high-speed measurement without consuming the gas measured at the time of measurement, and can always measure the exact composition even when the pressure of the mixed gas is other than atmospheric pressure or even when the pressure changes. it can.
(2) Furthermore, when using a piezoelectric element including a quartz resonator, it is a measurement method that does not irradiate heat or light, so it can safely measure even highly reactive gas mixtures that cause an explosion due to stimulation by heat or light. be able to. The measurement does not require an ultraviolet lamp having a specific wavelength, is easy to maintain, and can immediately measure the composition in response to changes in the gas composition.

  Hereinafter, embodiments of a concentration measuring method and a concentration measuring apparatus according to the present invention will be described in detail with reference to the drawings. However, the present invention is not construed as being limited thereto, and the scope of the present invention is not limited thereto. Various changes, modifications, and improvements can be made based on the knowledge of those skilled in the art without departing from the scope.

  The basic principle of the present invention is that the physical property value of a mixed gas such as viscosity, thermal conductivity, density, and molecular weight depends on the concentration of each constituent gas, and measures a specific physical property value or a plurality of physical property values. Thus, the concentration of each gas is calculated. When viscosity is used as one of the physical property values, if the target gas mixture is measured using the probe A sensitive to pressure and viscosity and the probe B sensitive only to pressure at the same time, the influence of the pressure is eliminated by the calculation process. Therefore, the viscosity of the mixed gas can be calculated by using this measurement method, and each of the components constituting the mixed gas is compared with the gas concentration dependence of the viscosity of the mixed gas obtained in advance. The concentration of gas is obtained.

  Concentration calibration is performed by preparing standard gases of various concentrations by mixing each pure gas constituting the mixed gas at a known ratio in advance, and measuring the standard gas with the various sensors to obtain a calibration curve. This can be done by recording the line in a density calculator.

  As an example of the measuring probe B used in the present invention, for example, a pressure sensitive sensor such as a liquid column differential gauge, a compression gauge, a diaphragm gauge, a Bourdon tube gauge, etc. can be used. A varies depending on the pressure, and changes in frictional force that the moving solid receives from the gas, changes in the thermal conductivity from the solid to the gas, and heat generated by the solid when the gas reacts near the solid surface. Among them, a pressure gauge whose physical quantity changes can be used.

  Similarly, as the pressure gauge such as A, in which the physical quantity changes as the pressure changes, for example, a friction vacuum gauge equipped with a quartz vibrator sensor that uses viscosity (friction), a spinning rotor gauge, or heat conduction is used. Thermocouple vacuum gauges, Pirani vacuum gauges, other Knudsen vacuum gauges, etc. can be used, and hot cathode ionization vacuum gauges, cold cathode ionization vacuum gauges, radiation ionization vacuum gauges, etc. that use ionization phenomena can be used. it can. These probes can be used properly depending on the gas properties such as flammability and explosiveness, the concentration and pressure of the target mixed gas.

FIG. 1 shows the characteristics of a friction vacuum gauge equipped with a crystal resonator sensor.
FIG. 1 shows the value of a diaphragm vacuum gauge sensitive only to pressure on the horizontal axis, and the value of a friction vacuum gauge equipped with a quartz vibrator sensor whose physical quantity changes as the pressure changes on the vertical axis. It can be seen that even if the value of the diaphragm vacuum gauge is constant, the indicated value of the friction vacuum gauge equipped with the quartz crystal sensor is apparently different depending on the type of gas.

As a study of how the electrical impedance and resonance frequency at the time of resonance of a quartz crystal change with respect to the surrounding gas pressure, ["Theory of a friction vacuum gauge using a quartz crystal", "Vacuum “Vol. 29, No. 2 (1986), Kiyohide Kokubun, Masatoshi Hirata, Masatoshi Ono, Hiroshi Murakami, Yoshitsugu Toda”.
This document states that the impedance component ΔZ resulting only from the friction between the vibrator and the surrounding gas is proportional to the coefficient f ₁ of the velocity term of the drag resulting from the friction between the vibrator and the gas, and It is described that the value of ΔZ decreases as the gas pressure decreases.

FIG. 2 is an explanatory view showing one form of the concentration measuring apparatus according to the embodiment of the present invention.
As shown in the figure, a vacuum device 8 to which a mixed gas to be measured is supplied is provided, and an absolute pressure at which the measured value does not change due to physical properties such as the viscosity and molecular density of the mixed gas is measured. A diaphragm vacuum gauge 1 that can be used is connected, and a pressure measuring element whose characteristics change in advance depending on the viscosity of the gas and whose characteristics are known in advance, that is, quartz vibrator sensors 2 to 6 are connected. Further, a concentration calculator that obtains physical property values by inputting the data of the diaphragm vacuum gauge 1 and the quartz vibrator sensors 2 to 6 and calculates the concentration from the data indicating the relationship between the concentration of each gas in the mixed gas and the physical property value. 7 is provided.

Based on the basic principle of concentration measurement according to the present invention as described above, for example, argon, nitrogen, and hydrogen are used as the three-component gases to be evacuated, and then evacuated and then vacuum-isolated from the exhaust system, that is, a closed vacuum. Introduce into device 8 At this time, a gas mixture having a predetermined partial pressure can be produced by sequentially introducing each gas while measuring the absolute pressure with the diaphragm vacuum gauge 1.
3 and 4, when the two-component quartz vibrator sensors 2 to 6 having different sensitivities are simultaneously measured with respect to the ternary mixed gas having the respective partial pressures prepared by the above procedure. The calibration curve groups Amax and Bmax shown in FIG.
FIG. 3 is created by the crystal resonator 2 and FIG. 4 is created by the crystal resonator 3, and the crystal resonators 4, 5, and 6 may be created as necessary.
3 and 4, the three-component gas is represented by A, B, and C for convenience.

In FIG. 3, the horizontal axis indicates the C component partial pressure ratio (vol.%), And the vertical axis indicates the quartz vibrator sensor output (reciprocal of the viscosity value). % (The left end of the figure) is A + B100 vol. %, And C partial pressure ratio 100 vol. In% (the right end of the figure), each calibration curve group coincides with one point, and otherwise, the measurement result falls within the range between the calibration curve Amax and the calibration curve Bmax.
In FIG. 3, the calibration curve Amax and the calibration curve Bmax are shown as straight lines, but are not limited to straight lines.

The calibration curve Amax is B component 0 vol. %, That is, the case where the A partial pressure ratio is maximized, and the calibration curve Bmax is A component 0 vol. %, That is, the case where the B partial pressure ratio is maximized. For example, C partial pressure ratio 50 vol. % On the calibration curve Amax and the calibration curve Bmax are respectively A50 vol. % + C50 vol. %, B50 vol. % + C50 vol. % Means the state.
When attention is focused on the viscosities of the components A, B, and C, these viscosities correspond to the order of C <B <A.

  Although FIG. 3 can be produced by the method described in the paragraph [0016], it is possible to obtain a total of three types of calibration curve groups by further expressing the same measurement results with respect to the partial pressure ratio of A and B. it can. Such calibration curve groups with respect to the partial pressure ratio of A and B are shown in FIGS. 5 and 6, respectively.

Assuming that the quartz resonator sensor output is 5.0 as a result of the measurement, the C component is 20 to 50 vol. %, The A + B component is accordingly 80-50 vol. %.
Similarly, also in FIG. 5, since the quartz vibrator sensor output is 5.0, the A component is 0 to 50 vol. % For the B + C component corresponding to 50 to 0 vol. %.
Similarly, when the same result is applied in FIG. 6, 0 to 80 vol. %, And the A + C component is correspondingly 100 to 20 vol. %.
Since the results of FIGS. 3, 5 and 6 are established at the same time, when the above is combined, the A component is 0 to 50 vol. %, B component is 0 to 50 vol. %, C component is 20-50 vol. %, And the A + B component is 0 to 80 vol. %, B + C component is 0 to 50 vol. %, A + C component is not limited.

As described above, even when one sensor is used, it is possible to limit the concentration of each gas constituting the mixed gas.
Further, as described above, if measurement is performed using sensors having different relative sensitivities to each gas, the mixed gas composed of three kinds of gases having the same partial pressure is different from FIG. 3, for example, as shown in FIGS. Results are obtained and the concentration of each gas is further limited.

In FIG. 4, C component is 40-70 vol. %, The component A is 0 to 40 vol. %, B component from 0 to 60 vol. %.
When the above results are combined, the concentration of each gas is 0 to 40 vol. %, B component is 0-60 vol. % C component is 40-50 vol. %. The concentration of each of the three types of gases in the mixed gas can be limited in this way even by using only two sensors.

  On the other hand, as shown in FIG. 9, it is possible to take the relative concentrations of the A component and the B component on the horizontal axis and the sensor output on the vertical axis. In this case, the calibration curve is a different calibration curve group depending on the concentration of the C component. In this figure, the concentration of the C component is shown as a relative concentration with respect to the total concentration of the A and B components.

If the number of sensors is further increased by the above-described method and measurement is performed, each partial pressure is limited, and finally the concentration of one component, for example, C component within the range of the measurement error, is obtained. Since the gas mixture is a gas mixture in which the concentration of one of the three gases in the prior art 2 is known, the two-component gas concentration measurement method can be applied, and the remaining two gas concentrations can also be obtained.
Specifically, since the relative partial pressure ratio between A and B is obtained by applying the measurement result and the C component concentration to FIG. 9, the partial pressures of all three components can be obtained as a result.

  In this case, the concentration of the C component is further limited in the above-described measurement, and the C component is 45 vol. %, The measurement result of FIG. 9 and the C component are 45 vol. %, The relative concentration ratio of the A component and the B component is required to be about 7: 3. From this result, the A component has a C component concentration ratio of 45 vol. % Is 100 vol. About 38 vol. %, B component is 17 vol. %, And as a result, the concentration of all gases constituting the mixed gas can be obtained. This result is of course consistent with the density range of the preceding paragraph 22 obtained from all the figures from FIG. 3 to FIG.

  In this patent, it is an important point to measure using a crystal resonator having different sensitivities to each gas. Quartz resonators with different sensitivities to different types of gases are produced mainly by changing their shapes. Changing the shape of the crystal resonator changes the resonance frequency, but also changes the sensitivity to the type of gas. Currently used quartz oscillators have the best signal-to-noise ratio and a resonance frequency of 32 kHz.

  In the actual measurement examples so far, as shown in FIG. 10, when the measurement is performed using different crystal resonator sensors I and II with respect to the same kind of gas, the inclination of the approximate straight line of the pressure dependence measurement result is obtained. Different measurement results are obtained. The result that the absolute pressure dependency differs depending on the individual sensor is due to the difference in sensitivity to the gas viscosity of each sensor. Therefore, if a plurality of such sensors are used, a mixed gas as shown above is formed. It can be seen that the concentration of each gas can be measured.

Comparing FIG. 3 and FIG. 4, the sensitivity to the type of gas is worse in FIG. 3 compared to FIG. 4, but the greater the difference in sensitivity, the higher the accuracy of partial pressure measurement.
Furthermore, instead of using a quartz crystal sensor with different sensitivity to gas species, this heat is generated by generating an output that depends on the ceramic vibrator, which is another piezoelectric element sensor, or the thermal conductivity, which is another physical property value of gas. By using a thermopile microflow sensor capable of measuring conductivity, it is possible to measure the partial pressure of a multi-component mixed gas by utilizing the difference in sensitivity with respect to gas species.

Since the physical properties of gas are clearly different in viscosity and thermal conductivity, it is natural that the dependence of these values on the type of gas is different. Therefore, if a plurality of physical property values are measured, the dependency on each gas type is different, so the concentration of each gas constituting the mixed gas is limited.
In principle, the measurement of different physical property values and the measurement by different sensors are synonymous in the sense of obtaining gas concentration dependency of different physical property dependent outputs.

  In principle, it can also be applied to mixed gases consisting of four or more gases, and if the concentration of a single component is determined from a plurality of measurement results, the mixed gas is constructed by sequentially applying this method. The concentration of each gas can be determined.

  When only the viscosity is used as the physical property value of the gas, the measurement can be performed with a pressure gauge such as a quartz crystal sensor, so the measured gas is not consumed and energy such as heat and light is consumed. Since it is not necessary to directly contact the specific measurement gas, even a highly reactive gas can be measured safely.

It is a graph which shows the characteristic of the friction vacuum gauge provided with the crystal oscillator sensor used by embodiment of this invention. It is explanatory drawing which showed the outline | summary of the density | concentration measuring apparatus which concerns on embodiment of this invention. In the ternary mixed gas according to the embodiment of the present invention, when the measurement result obtained by the friction vacuum gauge equipped with the quartz resonator sensor having a specific sensitivity is taken, the horizontal axis represents the partial pressure ratio of the C component. It is a graph which shows the calibration curve group of A component and B component. 3 is a graph showing a calibration curve group of the A component and the B component when measured by a friction vacuum gauge having a quartz crystal sensor having a sensitivity different from that of the friction vacuum gauge having the quartz crystal sensor used in the measurement of FIG. It is. In the case of FIG. 3, it is a graph which shows the calibration curve group of the B component and C component at the time of taking the partial pressure ratio of A component on a horizontal axis. In the case of FIG. 3, it is a graph which shows the calibration curve group of A component and C component at the time of taking the partial pressure ratio of B component on a horizontal axis. In the case of FIG. 4, it is a graph which shows the calibration curve group of the B component and C component at the time of taking the partial pressure ratio of A component on a horizontal axis. In the case of FIG. 4, it is a graph which shows the calibration curve group of A component and C component at the time of taking the partial pressure ratio of B component on a horizontal axis. It is a graph which shows the calibration curve group of C component at the time of taking the relative density | concentration of A component and B component as a horizontal axis for the measurement result of FIG. It is a graph explaining that the inclination of the approximate straight line of the measurement result of the pressure dependence becomes a different measurement result when the measurement is performed using the different crystal resonator sensor for the same kind of gas.

Explanation of symbols

1 Diaphragm gauge 2-6 Quartz crystal sensor 7 Concentration calculator 8 Vacuum device

Claims (2)

A method of measuring an unknown concentration of each gas constituting a mixed gas composed of three or more types of known gases,
The physical properties dependent output that depends on the physical properties that vary depending on the concentration of the gas constituting the mixed gas was measurement by the sensor,
For each combination of two types of gases included in the mixed gas, the calibration curve group is changed by changing the partial pressure ratio of the other type of gas to the partial pressure ratio of one type of gas from 0% to 100%. Ask in advance,
From the relationship between the measured physical property dependent output and the calibration curve group, the partial pressure ratio between the one kind of gas and the other kind of gas is narrowed down,
A concentration measuring method, wherein the concentration of each gas constituting the mixed gas is determined. In each gas concentration measuring device that constitutes a mixed gas of three or more types of gases that are known in advance,
And sensors for obtaining an object dependency output corresponding to the concentration of each gas constituting,
Calibration obtained in advance by changing the partial pressure ratio of the other type of gas to the partial pressure ratio of one type of gas for each combination of two types of gases included in the mixed gas, from 0% to 100% With line groups,
A plurality of calibration curve group is gas concentration dependence of physical properties dependent output obtained by said sensor, narrowing of the concentration range of each gas by applying the values of physical properties dependent output of the sensor obtained in the measurement of a mixed gas of unknown concentration A concentration measuring device for determining the concentration of each gas constituting a mixed gas, comprising a processing device for performing a calculation.

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