JPS587931B2 - Kongo Kouseigas no Chiyouseihouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for continuously generating highly accurate calibration gas.

Various instrumental analysis or chemical analysis methods are applied to measure atmospheric pollutants, and a gas with a known concentration and similar composition to the pollutant to be measured is used as a measurement standard material (calibration gas). .

In general, it is relatively easy to produce calibration gases for contaminant components in the concentration range of several 10 ppm or more and with extremely low chemical activity, and these gases are used filled in high-pressure containers. Thick or number 1 0
In the case of a calibration gas with a trace concentration such as ppm or less,
It is impractical and desirable to fill a high-pressure container because instability occurs in the concentration value of the extracted gas due to reactions between gases, reactions between gases and the container, differences in gas density, or temperature gradients in the container. do not have.

Therefore, a method has been adopted in which a mixed calibration gas having a concentration of the contaminant gas determined by an appropriate dilution rate is continuously created by mixing the contaminant gas at an appropriate concentration with a diluent gas such as high-purity nitrogen.

Of course, the actual flow rate (actual measurement value) of the flowmeter used at this time must be accurately verified using a soap film flowmeter or a wet rotary flowmeter.

However, when preparing a calibration gas in this way, if the concentration of the desired calibration gas is over a wide range from several ppb to several ppm, the type and concentration of the dilution gas (raw material contamination gas) to be used must be adjusted. , specific heat, density, flow rate range, etc., require multiple verification operations for each flow rate detection device, making practical implementation extremely difficult.

The present invention aims to improve the above-mentioned conventional method and provide a method that allows calibration gases in a wide range of concentrations to be freely and continuously adjusted with a minimum of verification operations.

That is, the gist of the present invention is to produce a low concentration mixed calibration gas from at least two types of gases.
A process in which a calibration gas with a known concentration of several hundred ppm or less of each type is used as a dilution gas and is flowed in fixed amounts through a quantitative flowmeter, and a dilution gas with a substantially 100% concentration is passed through a variable flowmeter in accordance with the desired concentration. Low concentration calibration of several tens of ppm or less can be performed by quantitatively flowing the diluted gas flow rate and controlling the dilution gas flow rate, which includes a step of flowing the diluted amount at a time and a step of supplying the gas flow after mixing. This is a method for preparing a low concentration mixed calibration gas characterized by continuously supplying gas.

In the present invention, as described above, a dilution gas of a known concentration, which has been prepared in advance, is constantly flowed in a fixed amount, and various desired concentrations are adjusted by accurately measuring the flow rate or easily changing the flow rate of the dilution gas. Therefore, the flow rate verification operation is minimized, and a calibration gas having a concentration lower than the concentration of the diluent gas to be used can be freely prepared.

Generally, dilution gases with high purity close to 100% or gases with low chemical activity are used, so there is little change in physical properties such as specific heat and density, and the gas to be diluted must be diluted in a stable state. The measurement accuracy is also high.

In the present invention, two types of flowmeters are used to measure the gas to be diluted and the flow rate of the dilution gas, but the flowmeter in this case is not a specific one, and may be any instrument that is generally used for measuring gas fluids. Any of these can be used, including capillary orifices, marginal orifices,
Such as a mass flow meter.

In addition, it is desirable that the dilution gas be as pure as possible and have minimal reactivity, but the gas to be diluted may include carbon monoxide, oxygen, synthetic air, etc. in addition to nitrogen, helium, argon, and carbon dioxide. It can be used in consideration of the range of stability mixing ratio.

The present invention will be explained below using specific examples shown in the drawings.

In Figure 1, 1 is a calibration gas to be diluted with a known concentration, 2 is a high-purity diluent gas with a single composition, such as nitrogen, and 3 is a constant, stable gas that is composed of a quantitative flow meter such as a limit orifice and a control mechanism that interlocks with it. A device for obtaining a flow rate, 4, is a device that can vary the flow rate within a certain range, and includes a variable flow meter such as a mass flow meter or an orifice flow meter, and a control mechanism interlocked with the variable flow meter.

Furthermore, numerals 5 and 6 are mixing tanks for uniformly mixing gases, and a desired number of mixing tanks can be installed.

As an example of an embodiment, the chamber is filled with a nitric oxide calibration gas diluted with high-purity nitrogen at a concentration of 100 ppm,
This gas was flowed at a constant rate of 1 cc/min into the limit orifice flowmeter at 3, while using high purity nitrogen at 2, the gas was
While setting the flow rate within the range of 100cc to 1000cc/min using a mass flowmeter, the concentration of the nitrogen monoxide mixed calibration gas discharged from the mixing tank 6 was measured, and the concentration ranged from 1 ppm to 0. Calibration gas in the range of 1 ppm was obtained stably and freely as calculated.

At this time, if you try to obtain a calibration gas while changing the flow rate using a mixed standard gas of various concentrations in 1, the flowmeter 3 will be asked to check the type, concentration, and flow rate range of the mixed standard gas to be used. A large number of calibration curves of actual flow rate versus flow rate indication corresponding to combinations of variables would be required, making practical application impossible.

On the other hand, in the present invention, the raw material dilution gas concentration and flow rate are kept constant, and a high-purity gas is used as the dilution gas, so the desired mixed calibration gas can be determined by creating a very small number of calibration curves related to the gas type and flow rate range. can be obtained easily.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the steps of the present invention.

Claims (1)

[Claims] 1 In producing a low-concentration mixed calibration gas from at least two types of gases, a process of flowing a fixed amount of at least one type of calibration gas with a known concentration of several hundred ppm or less as a dilution gas through a quantitative flowmeter. and essentially 10
A step of flowing a dilution gas having a concentration of 0% through a variable flowmeter in dilution amounts according to a desired concentration, and a step of supplying the gas flow after mixing, quantitatively flowing the dilution gas flow rate and producing the dilution gas. A method for preparing a low concentration mixed calibration gas, characterized by continuously supplying a low concentration calibration gas of approximately several tens of ppm or less by controlling the flow rate.