Measurement Equation of State Primary Special Measurement Standard for the Unit of Volumetric Natural Gas Flow Rate at Pressure up to 10 MPa

In the Russian Federation, a development type of a state primary special measurement standard for the volumetric flow rate of natural gas at pressures up to 10 MPa has been created on the base of a piston prover with four parallel-connected cylinders with an internal diameter of 500 mm. The design of measurement standard utilizes simultaneous active actuation of the four pistons within the cylinders via piston rods connected to a common hydraulic system piston rod.In paper the measurement equation compiled that includes more than twenty influencing parameters and determines the value of the volumetric flow rate through a calibrated transfer standard as part of the state primary special standard. Equation takes into account the volumetric flow rate of gas reproduced by the piston prover, the change in the volumetric flow rate as a result of the change in the amount of gas in the attached («dead») volume during the measurement time, and the volumetric flow rate of gas leaks between the cylinder chambers through the piston seals.Based on the measurement equation, an assessment of the expanded uncertainty ( k = 2) of the reproduction of the volumetric gas flow rate carried out and the percentage contribution to this value of individual input parameters under different modes determined.From the results of the calculations, the accuracy measurements indicators of the state primary special standard declared in the technical specifications for its creation confirmed.