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Standard Gas Determination Method to Determine the Concentration of Standard Gas
Source: | Author:sirloong | Published time: 2020-07-03 | 84 Views | Share:
In theory, there are two main methods of standard gas setting.
First, the direct determination method is used to determine the method.

In theory, there are two main methods of standard gas setting.

First, the direct determination method is used to determine the method. But so far, people have not found a definition of the standard gas is suitable for the definition of law, and many chemical analysis method in the gas concentration below lo-4 when the measurement error is large, often can not meet the requirements of the emblem.

Second, the indirect measurement method, that is, with the quality of the measurement (mass ratio of mixing method), pressure measurement method (pressure ratio method), volume measurement method (volume ratio method) and other physical measurement method to determine the standard gas concentration value. In other words, the standard gas in the container (high pressure cylinder) is measured by the mass measurement method, and the standard gas formulated in accordance with the standard gas generation method is measured by the flow rate method. However, this physical measurement method is based on the composition of gas and dilution gas can be mixed evenly, different gas mixture does not produce chemical reaction (composition changes) as the premise. In some cases, the physical method can not be accurately determined by the mass method, so that the method and the chemical analysis method are used in the standard gas setting at the same time.

Standard mass mixing method is the use of ultra-large high-precision balance were measured high-purity gas and dilution gas, and quantitative mixing and preparation of standard gas method. It is characterized by its quality measurement can be traced back to the international kilogram of the original, but also in the gas when the gas does not need the pressure, temperature, viscosity and other parameters to be corrected, so the measured value is accurate and reliable. However, this method only determines the concentration of a method to determine the concentration value, so it is the high precision of the balance and the cylinder of the high stability of the gas as a prerequisite. In addition, the quality of the cylinder is much greater than that of the component gas or diluent gas. And the weight and the cylinder in the size, material and density vary widely, and thus require a high quality measurement technology. Generally use a wide range of quality measurement, measurement accuracy and can meet the requirements of large precision flat, and the use of counterweight instead of weighing method. Although the quality ratio is more problematic than the hybrid method, it is much more accurate than other methods.

Standard gas rating The procedure for determining the standard gas concentration value by mass determination is as follows:

(1) first with a dilution gas to clean the high-pressure cylinder, and then vacuum to 10-2Pa below, with the balance accurately weighing the quality of high-pressure cylinder W0.

(2) filling the high pressure cylinder with the component gas to be formulated and measuring its mass W1.

(3) The high pressure cylinder is again filled with the diluted gas and the mass W2 is weighed.

In the determination of the quality of large-capacity cylinders, the weight and the container in the surface state (such as rough, rust, paint off, etc.), the average density, size and other aspects of the problem, will give the quality measurement error. In order to overcome the above-mentioned factors on the measurement results, you can use alternative weighing method, that is, select a size, the village and the outer surface of the state and the gas filled with the container is very similar to the alternative container, And to offset the impact of the determination of the environment. The standard value determined by the mass method (mass ratio mixing method) is consistent with that of the mass spectrometry method, but the method is not suitable for the mixed gas or the chemically reactive gas.


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