In the field of gas flow rate metrology, there are two basic methods of measurement that give the desired value of the observed quantity with a sufficiently good measurement uncertainty that they can be considered as the primary standard. The two methods are gravimetric and volumetric, which can be performed with a volume that changes or remains constant.
The doctoral work presents the development of the primary standard for micro gas flow rates (from $0.12\;\si{\milli\gram\per\minute}$ to $12\;\si{\milli\gram\per\minute}$) based on the volumetric method with constant volume, the use of the flying start-stop method and the static method of mass determination.
The flying start-stop method requires the use of a diverter to start and end the measurement. The time measurement error originates from diverters operation, which we analyzed, defined two methods of error measurement, and defined the method of error compensation and reduction.
During the measurement, the gas is compressed within the constant volume. Therefore the gas heats up, which makes it difficult to use the dynamic method of mass determination. By defining an analytical model, we predicted this temperature change and successfully used it in the test execution of measurements using the dynamic method.
A comprehensive system uncertainty analysis was performed. For a part of the measurement range above $3\;\si{\milli\gram\per\minute}$, an expanded uncertainty of less than 0.2 \% was confirmed by internal validation. A portable standard was also developed, which will enable external inter-laboratory comparison and confirmation of uncertainty in the lower part of the measurement range.
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