JP2004219386A - Concentration measuring instrument for gas mixture comprising two kinds of gases - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simplify instrument constitution by using two pressure measuring probes of the same type, and to simply read data in from the respective probes. <P>SOLUTION: This concentration measuring instrument for two component gas mixture of which the constitutive gases are known and of which the concentrations are unknown has the first and second pressure measuring probes 20, 40. The first probe 20 is displaced in response to pressure of the gas mixture supplied to piping 10, and is sensitive to a physical property of the gas mixture. The second probe 40 is arranged inside a bellows container 30. The bellows container 30 is stored, in its inside, with known gas of which the physical property is not substantially fluctuated, and changes its volume in response to the pressure of the gas mixture. The second probe 40 is displaced in response to the pressure of the gas inside the container 30, and is sensitive to the physical property of the gas in the container 30. The concentrations in the gas mixture are measured based on outputs from the first and second pressure measuring probes 20, 40. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an apparatus for measuring the concentration of a mixed gas composed of two types of gases. In particular, the present invention relates to a concentration measuring device that can detect a pressure reflecting a physical property value of a mixed gas and an absolute pressure not reflecting a physical property value of a mixed gas using the same type of pressure gauge.
[0002]
[Background Art]
Conventionally, as a method for determining the concentration of a mixed gas composed of two types of gases, an ultraviolet absorbance measurement method is known. In this method, for example, when measuring the ozone concentration in the ozone-oxygen mixed gas, the mixed gas is irradiated with a specific wavelength of ultraviolet rays that absorbs ozone but hardly absorbs oxygen. Then, the concentration was determined by measuring the absorptivity of ultraviolet rays.
[0003]
In order to solve various problems of this UV absorbance measurement method, the viscosity, thermal conductivity, density, molecular weight and physical properties of the mixed gas as a function of them are measured, and based on the physical properties of the pure gas, A technique for calculating the concentration of gas has been developed (Patent Document 1).
[0004]
For this purpose, two types of pressure gauges are used. One is a pressure gauge that is sensitive to the physical properties of the gas mixture, and the other is a pressure gauge that is not affected by the physical properties of the gas mixture. In Patent Document 1, a quartz friction vibrator is cited as the former pressure measuring element, and a diaphragm vibrator is cited as the latter pressure measuring element.
[0005]
Further, a crystal resonator that can be temperature-compensated has been proposed (Patent Document 2).
[0006]
[Patent Document 1]
Japanese Patent No. 3336384 [Patent Document 2]
U.S. Pat. No. 5,228,344 (Japanese Patent Publication No. 7-97060)
[0007]
[Problems to be solved by the invention]
The method of Patent Document 1 employs a method that can always accurately measure the concentration even when the pressure of the mixed gas is other than the atmospheric pressure, and even when the pressure changes, and that does not irradiate heat or light. Therefore, it is excellent in that it can safely measure even a gas mixture in which an explosion occurs due to heat or light stimulation. Further, it is excellent in that it does not require an ultraviolet lamp or the like having a specific wavelength, maintenance is easy, and the concentration can be measured immediately in response to a change in gas concentration.
[0008]
However, the method disclosed in Patent Document 1 uses two types of pressure gauges having completely different principles according to the principle of the present invention, so that the apparatus configuration becomes complicated, and the consistency of data from the two types of pressure gauges, etc. New challenges have arisen. In addition, a pressure gauge using a diaphragm is suitable as a pressure gauge that is not affected by the physical property value of the gas mixture. was there.
[0009]
Therefore, an object of the present invention is to measure the pressure affected by the physical property value of the gas mixture and the pressure not affected by the physical property value, and to measure them with the same type of pressure element, thereby increasing the size and complexity of the apparatus. It is an object of the present invention to provide an apparatus for measuring the concentration of a mixture of two gases, which can solve the above problem.
[0010]
[Means for Solving the Problems]
One embodiment of the present invention is a concentration measurement device for a two-component gas mixture whose constituent gas is known and whose concentration is unknown.
A first pressure gauge that is displaced in accordance with the pressure of the gas mixture and is sensitive to the physical property value of the gas mixture;
A known gas whose physical property value does not substantially fluctuate is housed therein, and a container that changes its volume according to the pressure of the mixed gas,
A second pressure gauge disposed in the container, displaced in accordance with the pressure of the gas in the container, and sensitive to the physical property value of the gas in the container;
A concentration detector that measures the concentration of the mixed gas based on the outputs of the first and second pressure gauges.
[0011]
According to one embodiment of the present invention, a pressure dependent on the physical properties of the gas mixture is determined from the first pressure gauge, and an absolute pressure independent of the physical properties of the gas mixture is determined from the second pressure gauge. The concentration detector obtains the physical properties of the mixed gas excluding the influence of the pressure based on the two types of pressure values, and can detect the concentration of the mixed gas based on the physical properties.
[0012]
Moreover, both the first and second pressure gauges are of the same type that are sensitive to the physical property values of the gas to be measured. Therefore, as compared with the invention of Patent Document 1 in which different types of pressure gauges are used, the apparatus configuration is simplified and the data from each pressure gauge is matched, so that the data capture is simplified.
[0013]
As the first and second pressure measuring elements, a tuning-fork type crystal resonator can be suitably used.
[0014]
The concentration detector may include an oscillator connected to the first and second pressure gauges. The concentration detector further includes the mixed gas based on a resonance resistance of the first and second pressure measuring elements, which are outputs from the oscillator, and a specific resonance resistance of the first and second pressure measuring elements. May be included.
[0015]
In this case, the oscillator includes a first oscillator connected to the first pressure gauge,
A second oscillator connected to the second pressure gauge. Alternatively, the oscillator may be shared by the first and second pressure gauges. At this time, a switch may be provided for selectively connecting the output from the first and second pressure gauges to the oscillator.
[0016]
The concentration detector is configured to determine a resonance resistance value of the first and second pressure measuring elements from the oscillator and a difference between each of the natural resonance resistance values of the first and second pressure measuring elements. The concentration of the gas mixture can be measured.
[0017]
In this case, the oscillator outputs the respective resonance frequencies of the first and second pressure measuring elements, and the concentration detecting section is configured based on the respective resonance frequencies of the first and second pressure measuring elements, It is possible to correct the specific resonance resistance value having the temperature dependency of the first and second pressure measuring elements.
[0018]
Further, the concentration calculating unit further includes a memory for storing a calibration result for calibrating a variation in resonance resistance-pressure between the first and second pressure gauges at at least two points where the pressure of the mixed gas is different. Can have.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
As a premise of the concentration detection principle of the present invention, as described in Patent Document 1 (Japanese Patent No. 3336384), pressure affected by physical properties such as viscosity, thermal conductivity, density, molecular weight, and the like, and the influence of the physical properties are described. The method adopts a method of calculating the concentration of the mixed gas based on the pressure that does not receive the gas. As an improvement of the present invention, two pressure gauges that are sensitive to physical property values, such as viscosity, that vary depending on the concentration of the mixed gas are used. One of the pressure gauges is brought into contact with the gas mixture to measure the pressure, and the other is housed in an airtight container whose volume changes according to the pressure of the gas mixture, and is not in contact with the gas mixture, but is affected by the physical properties of the gas mixture. Measure the absolute pressure that will not be affected. Then, based on the pressure value reflecting the physical property value and the absolute pressure value, the physical property value such as viscosity of the mixed gas is calculated by an arithmetic processing, excluding the influence of the pressure, thereby obtaining the mixed gas corresponding to the physical property value. Is determined.
[0020]
Examples of the measuring element used in the present invention include a pressure gauge in which a physical quantity changes with a change in pressure of a mixed gas. Examples of the pressure gauge include a quartz oscillator using viscosity (friction), a spinning rotor gauge, and a thermocouple using heat conduction. A vacuum gauge, a Pirani vacuum gauge, a Knudsen vacuum gauge, or the like can be used. Further, for example, a hot cathode ionization vacuum gauge, a cold cathode ionization vacuum gauge, a radiation ionization vacuum gauge, or the like using an ionization phenomenon can be used. These probes can be used properly depending on the properties of gas such as flammability and explosiveness, the concentration and pressure of the target mixed gas.
[0021]
<First embodiment>
FIG. 1 shows a concentration measuring device according to a first embodiment of the present invention. In FIG. 1, a pipe 10 supplies a mixed gas, for example, a mixed gas of two kinds of ozone / oxygen. A gas supply source is connected to one end of the pipe 10. The other end of the pipe 10 is connected to a semiconductor manufacturing apparatus that forms, for example, an oxide film on a substrate. When a cylinder containing liquefied ozone is used as a gas supply source, for example, vaporized high-concentration ozone can be supplied to the pipe 10, and the film forming speed can be increased. The invention is not limited thereto, and low-concentration ozone and high-concentration oxygen may be supplied to the pipe 10. Since the concentration of the mixed gas supplied to the pipe 10 fluctuates, it is necessary to measure the concentration.
[0022]
The measurement chamber 12 communicating with the pipe 10 is provided with a first pressure measuring element 20 and an airtight container such as a bellows container 30 whose volume changes according to pressure. In this bellows container 30, a second pressure gauge 40 is arranged. The measurement chamber 12 may not be provided separately, and the inside of the pipe 10 may be used as the measurement chamber.
[0023]
Each of the first and second pressure gauges 20 and 40 is a pressure gauge that measures a pressure reflecting a physical property value that changes according to a change in the concentration of the gas to be measured. Both of the pressure measuring elements 20 and 40 use a tuning fork type crystal resonator. The principle of pressure detection by a quartz oscillator is that the frictional force between the quartz oscillator that is in contact with the gas to be measured and the gas is equal to the square of the product of the molecular weight of the gas and the viscosity coefficient of the gas when the pressure is in a viscous flow region. It is proportional. This crystal oscillator operates at room temperature and has only gold, quartz, and stainless steel in contact with gas, and has no factor for decomposing ozone.
[0024]
A constant concentration of gas, preferably argon or nitrogen gas, which is an inert gas, is sealed in the bellows container 30, and before the mixed gas is introduced into the pipe 10, the pressure in the bellows container 30 is constant, for example, atmospheric pressure. Is set to
[0025]
Here, since the first pressure measuring element 20 is in direct contact with the gas mixture to be measured, the first pressure measuring element 20 measures a pressure that fluctuates depending on its physical properties, for example, viscosity or molecular density.
On the other hand, the second pressure measuring element 40 is housed in the bellows container 30 and is not in contact with the gas mixture to be measured. The volume of the bellows container 30 changes depending on the pressure of the mixed gas. That is, if the pressure of the mixed gas is higher than the pressure in the bellows container 30, the volume of the bellows container 30 contracts, and if the pressure is opposite, it expands. As a result, the pressure of the inert gas in the bellows container 30 also changes. The second pressure gauge measures the pressure that changes due to the physical properties of the inert gas. The concentration of the inert gas is constant. After all, the second pressure gauge 40 in the bellows container 30 functions as an absolute pressure gauge that can measure an absolute pressure whose measured value does not change due to physical properties such as viscosity and molecular density of the mixed gas.
[0026]
As shown in FIG. 1, a first oscillator 50 is connected to the first pressure gauge 20, and a second oscillator 60 is connected to the second pressure gauge 40. Further, a frequency counter 70 and an A / D converter 80 shared by the first and second oscillators 20 and 40 are provided. The frequency counter 70 and the A / D converter 80 are connected to a CPU 90 functioning as a density calculator. A memory 92 is further connected to the CPU 90, and information necessary for density calculation is stored in the memory 92 in advance.
[0027]
FIG. 2 shows an example of an oscillation circuit shared by the first and second oscillators 50 and 60. Although FIG. 2 illustrates the first oscillator 50, the second oscillator 60 has the same configuration.
[0028]
FIG. 2 has the same configuration as the oscillation circuit disclosed in US Pat. No. 5,228,344. The first oscillator 50 shown in FIG. 2 is for compensating for a measurement error caused by a temperature change of the crystal unit 50. The first oscillator 50 includes a current-voltage converter 100, a first full-wave rectifier 102, an attenuator 104, a comparator 106, a voltage-controlled attenuator 108, and a second full-wave rectifier 110.
[0029]
Here, the natural resonance resistance of the crystal oscillator 20 and Z _0. When the crystal oscillator 20 is placed in an atmosphere of a mixed gas, the crystal oscillator 20 oscillates via the first oscillator 50, from the second full-wave rectifier 110, the measured resonance resistance Z ₁ reciprocal 1 / _{Z 1} is obtained. The difference between the natural resonance resistance Z0 and the measured resonance resistance _{Z 1 ΔZ (Z0-Z 1} ) corresponds to the pressure of a mixed gas depending on the viscosity (concentration). However, the natural resonance resistance Z ₀ is stable over a wide temperature range (-20 to + 60 ° C.), the change can not be ignored in vacuo.
[0030]
Thus, in the present embodiment, a temperature-dependent natural resonance resistance (Z ₀ + Zt) is obtained, and a difference ΔZ (Z ₀ + Zt−Z ₁ ) between the natural resonance resistance (Z ₀ + Zt) and the measured resonance resistance Z is calculated. And the pressure of the mixed gas depending on the viscosity (concentration).
[0031]
The first oscillator 50 is configured to output a resonance frequency f ₁ of the crystal oscillator 50. The resonance frequency f ₁ is measured to determine the street temperature T to be described later.
[0032]
The first resonance frequency f ₁ from the first oscillator 50 is input to the CPU 90 as a digital value after being counted by the frequency counter 70 shown in FIG. The reciprocal 1 / Z ₁ (analog value) of the resonance resistance Z ₁ from the first oscillator 50 is input to the CPU 90 via the A / D converter 80 shown in FIG.
[0033]
Similarly, the resonance frequency f ₂ from the second oscillator 60, after being counted by a frequency counter 70 shown in FIG. 1, is input to CPU90 as a digital value. The reciprocal 1 / Z ₂ (analog value) of the resonance resistance Z ₂ from the second oscillator 60 is input to the CPU 90 via the A / D converter 80 shown in FIG.
[0034]
Next, the density calculation in the CPU 90 will be described.
[0035]
(Temperature correction)
First, based on the data f ₁ , f ₂ , 1 / Z ₁ , 1 / Z ₂ from the first and second oscillators 50 and 60, temperature-corrected natural resonance resistances (Z ₀ + Zt) are obtained. Hereinafter, the first crystal oscillator 20 is obtained, but the second crystal oscillator 40 is similarly obtained.
[0036]
The first crystal oscillator 20, as shown in FIG. 3, the natural resonance resistance was dependent on the characteristics of the straight line a, and it temperature T between the temperature T and the resonance frequency f ₁ (Z 0 ₊ Zt) And has the characteristic of the curve b.
[0037]
In CPU 90, from the resonance frequency f ₁ determined by the first oscillator 50, for example, determine the point A in FIG. 3, by obtaining the point B in FIG. 3 from a temperature corresponding to the point A, followed by And the natural resonance resistance (Z ₀ + Zt) depending on the temperature of the crystal unit 50 can be obtained.
[0038]
Similarly, the temperature-dependent natural resonance resistance of the second crystal resonator 40 can be obtained.
[0039]
(Calculation of gas mixture concentration)
As described above, the temperature-dependent natural resonance resistance (Z ₀ + Zt) is obtained, and the difference ΔZ (Z ₀ + Zt−Z) between the natural resonance resistance (Z ₀ + Zt) and the measured resonance resistance Z is determined by the viscosity ( Concentration) depending on the gas pressure. FIG. 4 is a measurement diagram in which the difference ΔZ is obtained by changing the gas pressure P. In the same manner as in FIG. 4, the relationship between the resistance difference ΔZ and the gas pressure P is determined for each of the ozone / oxygen mixed gas having two concentrations and the inert gas having a constant concentration in the bellows container 30 as the gas to be measured. Measure in advance.
[0040]
Next, a calibration curve shown in FIG. 5 is created from these three types of measurement data. The horizontal axis in FIG. 5 is the pressure (absolute pressure) obtained from the data on the second crystal resonator 40 side. The vertical axis in FIG. 5 is a pressure dependent on the viscosity of the gas mixture obtained from the data on the first crystal resonator 20 side. FIG. 5 plots a characteristic C in the case of 100% oxygen and a characteristic D in the case of a mixed gas of 95% oxygen / 5% ozone.
The calibration curve data shown in FIG. 5 is stored in the memory 92 of FIG.
[0041]
Here, when the mixed gas whose concentration is unknown passes through the pipe 10, based on the information from the first crystal resonator 20, the pressure (FIG. 5 (vertical axis coordinate position). On the other hand, based on information from the second crystal resonator 40, an absolute pressure (the horizontal coordinate position in FIG. 5) that does not depend on the viscosity (concentration) of the gas mixture is obtained. The coordinate position E in FIG. 5 of the unknown gas mixture is determined from the vertical and horizontal coordinate positions. The CPU 90 can measure the ozone concentration in the unknown gas mixture based on the coordinate position E in FIG. 5 and the characteristics C and D.
[0042]
Note that there may be variations in characteristics between the first and second crystal units 20 and 40, that is, the resonance resistance-pressure characteristics. If this characteristic variation is made up of two different pressure points, for example, two points of atmospheric pressure and vacuum, the pressure can be calculated with sufficient accuracy from the resonance resistance Z under the pressure between them. For this purpose, for example, two calibration results of atmospheric pressure and vacuum are stored in the memory 92 shown in FIG. The pressure value may be corrected based on the pressure value.
[0043]
<Comparative example>
FIG. 6 shows an embodiment disclosed in Japanese Patent No. 3336384. In FIG. 6, members having the same functions as those in FIG. 1 are denoted by the same reference numerals. The quartz friction vacuum gauge 100 includes a quartz oscillator 20, an oscillator 50, a frequency counter 70, an A / D converter 80, and a CPU 110. A method for measuring a pressure depending on the physical properties (eg, viscosity) of a mixed gas is as follows. , And the same as the first embodiment.
[0044]
In FIG. 6, a diaphragm gauge 120 is used to obtain a pressure independent of the physical properties of the gas mixture. The diaphragm vacuum gauge 120 has an amplifier 122, a phase detector 124, an A / D converter 126, an oscillator 128, a CPU 130, and the like, in addition to a diagram 121 displaced by the pressure of the mixed gas and its peripheral detection circuit. The CPU 140 to which the outputs of the CPU 110 of the quartz friction gauge 100 and the CPU 130 of the diaphragm gauge 120 are input functions as a concentration calculator. The calculation result and the like are displayed on the display 150.
[0045]
As described above, the measurement device of the comparative example shown in FIG. 6 uses two types of vacuum gauges whose detection principles are completely different from each other, so that data acquisition is more complicated than that of this embodiment, and the detection accuracy is the diameter of the diagram 121. , It is difficult to reduce the size of the diaphragm gauge 120.
[0046]
On the other hand, in the present embodiment, by arranging the quartz oscillator 40 in the bellows container 30 without using the relatively large diaphragm gauge 120, pressure measurement independent of the physical properties of the mixed gas is enabled. . In the present embodiment, since the same type of, for example, two crystal units are used, data acquisition is commonized. For example, the frequency counter 70 and the A / D converter 80 are connected to the two crystal units 20 and 40 as shown in FIG. Can be used for Moreover, since the quartz oscillators 20 and 40 can be configured with a diameter of about 2 mm and a length of about 10 mm, the size can be reduced as compared with the diaphragm gauge 120.
[0047]
<Second embodiment>
FIG. 7 shows a concentration measuring device according to a second embodiment of the present invention. As shown in FIG. 7, by providing a double switch 200 at the output terminals of the first and second crystal units 20 and 40, the first and second oscillators 50 and 60 in FIG. 210. The dual switch 200 can be configured by a semiconductor switch or the like that can be switched at high speed.
[0048]
By doing so, the oscillator 210 can be shared with the first and second crystal units 20 and 40 in addition to the frequency counter 70 and the A / D converter 80, and the measurement and measurement device can be further configured. It is downsized.
[0049]
The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the present invention. For example, a quartz oscillator is used as the first and second pressure measuring elements in the above embodiment, but the present invention is not limited to this. However, especially when the mixed gas is an active gas such as ozone, it explodes when there is a heating element.However, since a quartz oscillator is not used, there is no danger of explosion. Excellent.
[0050]
In the above-described embodiment, the natural resonance resistance of the crystal unit is temperature-compensated. However, the compensation operation can be omitted in a pressure band where temperature compensation is not required, for example, near the atmospheric pressure. In this case, a circuit for detecting the resonance frequencies f ₁ and f ₂ and a frequency counter for counting them are not required.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory view of a concentration measuring device according to a first embodiment of the present invention.
FIG. 2 is a diagram illustrating a circuit configuration example common to first and second oscillators in FIG. 1;
FIG. 3 is a diagram showing a temperature dependence characteristic of a resonance frequency and a natural resonance resistance of the crystal unit shown in FIG. 1;
FIG. 4 is a characteristic diagram showing a relationship between a difference between a natural resonance resistance and a resonance resistance of the crystal unit shown in FIG. 1 and a pressure of a gas to be measured.
FIG. 5 is a characteristic diagram showing an example of a calibration curve stored in a memory in FIG.
FIG. 6 is a schematic explanatory view of a concentration measuring device as a comparative example of the present invention.
FIG. 7 is a schematic explanatory view of a concentration measuring device according to a second embodiment of the present invention.
[Explanation of symbols]
Reference Signs List 10 piping, 12 measuring chamber, 20 first pressure measuring element (crystal oscillator), 30 bellows container, 40 second pressure measuring element (crystal oscillator), 50 first oscillator, 60 second oscillator, 70 Frequency counter, 80 A / D converter, 90 CPU (concentration calculator), 92 memory, 200 double switch, 210 oscillator

Claims (8)

In a concentration measuring device for a mixture of two gases whose constituent gases are known and whose concentration is unknown,
A first pressure gauge that is displaced in accordance with the pressure of the gas mixture and is sensitive to the physical property value of the gas mixture;
A known gas whose physical property value does not substantially fluctuate is housed therein, and a container that changes its volume according to the pressure of the mixed gas,
A second pressure gauge disposed in the container, displaced in accordance with the pressure of the gas in the container, and sensitive to the physical property value of the gas in the container;
A concentration detector for measuring the concentration of the mixed gas based on the outputs of the first and second pressure gauges. In claim 1,
The apparatus for measuring the concentration of a mixture of two gases, wherein the first and second pressure measuring elements are both tuning-fork type quartz vibrators. In claim 1 or 2,
The concentration detector,
An oscillator connected to the first and second pressure gauges;
A concentration calculating a concentration of the gas mixture based on a resonance resistance of the first and second pressure measuring elements, which are outputs from the oscillator, and a specific resonance resistance of the first and second pressure measuring elements; An apparatus for measuring the concentration of a mixture of two gases, comprising: a computing unit. In claim 3,
The oscillator comprises:
A first oscillator connected to the first pressure gauge;
A second oscillator connected to the second pressure gauge;
An apparatus for measuring the concentration of a mixture of two gases, comprising: In claim 2,
The oscillator is shared by the first and second pressure gauges,
An apparatus for measuring the concentration of a mixture of two gases, further comprising a switch for selectively connecting the outputs from the first and second pressure gauges to the oscillator. In any one of claims 3 to 5,
The concentration detector is configured to determine a resonance resistance value of the first and second pressure measuring elements from the oscillator and a difference between each of the natural resonance resistance values of the first and second pressure measuring elements. An apparatus for measuring the concentration of a mixture of two gases, which measures the concentration of a mixture of gases. In claim 6,
The oscillator outputs each resonance frequency of the first and second pressure gauges,
The concentration detector corrects the specific resonance resistance having the temperature dependency of the first and second pressure measuring elements based on the respective resonance frequencies of the first and second pressure measuring elements. An apparatus for measuring the concentration of a mixture of two gases. In any one of claims 1 to 7,
The concentration detecting unit further includes a memory for storing a calibration result for calibrating a variation in resonance resistance-pressure between the first and second pressure gauges at at least two points where the pressure of the mixed gas is different. An apparatus for measuring the concentration of a mixture of two gases.

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