Uncertainty Analysis of Primary Standard for
Hydrocarbon Flow at NMIJ

The present article, first, an outline of the new hydrocarbon flow calibration facility is described, then uncertainty of calibration of the flowmetre is analitically estimted in accordance with ISO guide say Takashi Shimada, Ryouji Doihara, Yoshiya Terao and Masaki Takamato

 

Introduction
The primary standard for hydrocarbon flow at NMIJ[1] has been designed to calibrate hydrocarbon flowmeters at flow rates in the range between 3 to 300 m3/h with expanded uncertainty better than 0.04% for volumetric flow rates and 0.03% for mass flow rates (coverage factor: k = 2). This calibration facility has special features that enable highly accurate calibration. In the present article, first, an outline of the new hydrocarbon flow calibration facility is described. Second, the uncertainty of calibration of the flowmeter is analytically estimated in accordance with ISO Guide[2]. Fi- nally, a Coriolis flowmeter, a positive displacement flowmeter, a turbine meter and an ultrasonic flowmeter and calibrated in both test rigs in order to verify the performance of the facility.

Primary Standard for Hydrocarbon Flow Measurement in Japan
Outline of the calibration facility A schematic and the specifications of the primary standard for hydrocarbon flow are shown in Table 1. Light oil and kerosene are used as the working liquids; each oil has a separate test line. Although the flow rate range of the facility capacity is from 3 to 300 m3/h, the normal calibration flow rate range is limited from 15 to 300 m3/h. This primary standard is based on static and gravimetric methods with a flying start and finish, i.e., the total mass of fluid passing through the flowmeter via the diverter in a given time is measured. It consists of a 10 t weighing scale, a 1 t weighing scale, a density meter and the diverter system was developed by NMIJ[3] and was applied to minimize the uncertainty in the collection collection time of the hydrocarbon into the collection time of the hydrocarbon into the weighing tanks. The test line diameters for the flowmeters are 50, 100 and 150 mm. Two 43 m3 storage tanks are used for the two lines. The temperature stability of working fluids have a significant effect on the uncertainty of density, and hence, a sophisticated heat exchanger is installed in the test lines. Almost all the test lines and tanks are sufficiently covered by thermal insulator. A weighing system with dead weights is one of the advantages that enable high-performance calibration. Three servo PD flowmeters[4] are installed in each of the test rigs as working standards. In the servo PD flowmeter, the spiral motors are driven by a servomotor so that the differential pressure between the inlet and outlet of the flowmeter remains zero or at a certain value that results in reduced differential pressure across the rotors. Thus, a wide range of flow rate can be measured at a high accuracy. These flowmeters of 50, 100 and 150 mm diameter are used in the flow rate ranges from 3 to 30, 7.5 to 75 and 30 to 300 m3/h, respectively. The long stability of the servo PD flowmeter has been investigated by simultaneous calibration with a test meter. Calculation of the calibration factor of the flowmeter (K-factor) The calculation of the K-factor obtained at the hydrocarbon flow calibration facility is based on the same concept as that of the large water facility at NMIJ, where static and gravimetric methods with flying start and finish are applied[5]. Furthermore, the K-factor for the volumetric flowmeter, Kf, is described by ...

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