PTC 6-2004 Performance Test Code on Steam Turbines  delineates fabrication and calibration requirements for throat tap flow nozzles with the purpose of obtaining the best feasible accuracy of flow measurement, a primary measurement to determine turbine performance. The Code requires nozzle discharge coefficient calibration results meet tight specifications for average value and rate of change with throat Reynolds number. Performance specifications were developed from large historical, empirical bases and an extensive theoretical analysis. Calibration uncertainty for PTC-6 Flow Meters using gravimetric flow measurement method in accordance with ASME/ANSI MFC 9M Measurement of Liquid Flow in Closed Conduits by Weighing Method  using a 100,000 lb capacity weigh tank is estimated. Calibration results are compared to Code requirements for about 330 meters with 1320 individual tap sets.
Calibration Uncertainty of PTC-6 Flow Sections
Nystrom, JB, & Stacy, PS. "Calibration Uncertainty of PTC-6 Flow Sections." Proceedings of the ASME 2006 Power Conference. ASME 2006 Power Conference. Atlanta, Georgia, USA. May 2–4, 2006. pp. 749-756. ASME. https://doi.org/10.1115/POWER2006-88058
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