【国外标准】 Standard Practice for Calibrating U-tube Density Cells over Large Ranges of Temperature and Pressure

5.1 This practice covers a series of methods offered to aid users in calibrating U-tube density meters to provide a measure of density and an associated expanded uncertainty. The reference density, as obtained from either an equation of state (EOS) or CRM has an uncertainty that arises from the uncertainty of the measurements of temperature, pressure, and also the chemical purity of the substance studied (origin) or for that matter of the certified reference material. This uncertainty results in an additional uncertainty for the density of these samples. Because the measurements made with U-tube density meters are not absolute, the uncertainty with which the instrument calibration is determined is directly related to the uncertainty of the density obtained.1.1 This practice outlines procedures for the calibration of U-tube density cells. It is applicable to instruments capable of determining fluid density at temperatures in the range –10 °C to 200 °C and pressures from just greater than the saturation pressure to 140 MPa. The practice refers to density cells as they are utilized to make measurements of fluids primarily in the compressed-liquid state. Examples of substances for which the density can be determined with a calibrated U-tube density meter include: crude oils, gasoline and gasoline-oxygenate blends, diesel and jet fuels, hydraulic fluids, and lubricating oils.1.2 This practice specifies a procedure for the determination of the expanded uncertainty of the density measurement.1.3 This practice pertains to fluids with viscosities < 1 Pa·s (1000 centipoise) at ambient conditions.1.4 4 The values listed in SI units are regarded as the standard, unless otherwise stated. The SI unit for mass density is kilograms per cubic metre (kg·m-3) and can be given as grams per cubic centimetre (g·cm-3).1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.