GB/T 5275.7-2014

This part of GB/T 5275 details the method of using commercially available thermal mass flow controllers to continuously prepare calibration gas mixtures containing two or more components from pure gases or mixed gases. The best achievable level of calibration gas mixture preparation using this method is as follows: the relative measurement expanded uncertainty (obtained by multiplying the synthetic standard uncertainty by the inclusion factor k=2) U is no greater than 2%. If pre-mixed gases are used instead of pure gases, mixtures with a molar fraction lower than 10-6 can be prepared. The measurement of mass flow is not absolute, and the mass flow controllers need to be calibrated separately. The advantage of this preparation method is that it can continuously prepare a large number of gas mixtures, and as long as an appropriate number of thermal mass flow controllers are used, it can easily prepare multi-component gas mixtures as easily as preparing binary gas mixtures.