Based on the policies of efficient energy utilization, environmental protection, particularly in reduction in CO2 emissions, and stable economical growth, Taiwan government adopted natural gas as a source of clean energy since 1980s. Each year, over 3 million tons of Liquefied Natural Gas is imported from Indonesia and Qatar for electrical power generation from nationally-owned and private industrially-owned companies. It is estimated by the year 2020, the appropriation of natural gas consists of 25% of national energy sources. To safeguard fair trade of energy transactions and validation of gas emission on the effects of global warming, accurate measurement of natural gas consumption and traceability to national primary standards is essential. Roughly, a 1% error in measurement causes 40 million USD unaccounted losses per year for NG supplier. Thus, a project to construct a national measurement infrastructure to serve this purpose was initiated since the 1990s. This paper describes the use of three different flow design principles to construct an unbroken chain of traceability hierarchy and demonstrates calibration with well-proven uncertainties. For each standard facility, ultrasonic meters are used in parallel to cascade up from Dia: 150 mm, 10 bar pressure, 1000 Actual m3/h; to Dia: 600 mm, 55 bar pressure, and 16000 Actual m3/h. For two years of successive on-site measurement for six meters, relative errors are within ±0.1%, with uncertainty less than 0.35%. The daily difference between custody transfer and check meters remains within ±0.2%.

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