The uncertainty of a new primary standard for hydrocarbon flow measurements has been evaluated analytically and experimentally in detail in accordance with the “ISO Guide to the expression of uncertainty in measurement”. The expanded uncertainty has been estimated to be 0.03% for volumetric flow rate and 0.02% for mass flow rate (coverage factor : k=2). This evaluation shows that the uncertainty of duration time when liquid is accumulated into the weighing tank is negligible by using the new diverter, and that the dominant sources of combined uncertainty of flow rate are the mass of oil accumulated in the weighing tank and the density of oil flowing through the flowmeter under test. In particular, the uncertainty in the low flow rate at the kerosene test rig using the 10t weighing system is quite larger than those at the other test rigs due to the loss of oil caused by oil mist and vapor discharged from the diverter and the weighing tank. Furthermore, the uncertainties of temperature measurements at the test meter and the density meter have large effect of the combined uncertainty of volumetric flow rate.
