Blending techniques for standard gases
Homogeneity is an important index to evaluate the performance of standard gases. The characteristic of a standard gas should be uniform that is, its magnitude is not changed over a specified range. Standard gases prepared by either method need to be mixed. Standard gas mixing methods are: heat treatment method, cylinder rolling method, special filling method, natural diffusion method, other mixing methods, etc., and Xiaobian take a look.
1. Heat treatment method: generally, the prepared standard gas container is heated in a warm water bath below 40℃, so that the gas components can be mixed evenly faster.
2. cylinder rotation rolling method: the cylinder is placed horizontally on the mixed half-placed rolling shaft, so that it rotates around the axis. This method requires short time to blend and is simple to operate.
3. Special filling method: when filling some gases, the cylinder can be upside-down and keep the incline of 45℃, and inflated from the lower end to promote the adiabatic expansion of the gas and produce exothermic effect. The gas can be mixed evenly while filling.
4. natural diffusion method: into the standard gas cylinder inverted in the appropriate position, static, by the natural diffusion of the gas itself to achieve uniform mixing, but this method requires a long time.
5. other mixing methods: using static mixing container or the use of special structure of the container valve, can make the standard gas in a very short time to mix evenly.
Calibration gas production plant
Whichever method is used for blending, another analytical method with high accuracy must be used for testing. In the standard gas research stage, the uniformity of the standard gas studied should be investigated. Gas chromatography is generally used to determine the uniformity of the standard gas under the same operating conditions. The uniformity of the standard gas is usually determined by the consistency test method of the mean value. Since uniformity is the measurement of how long it takes for the quantity of the same bottle of standard gas to reach stability after preparation, the average value obtained from a finite number of measurements should not be significant within the uncertainty range of the method. If the difference is significant, the factor is due to the inhomogeneity of the standard gas.