This guide outlines procedures for the accurate calibration of U-tube density cells over large ranges of temperature and pressure. It refers to density cells as they are utilized to make measurements of fluids primarily in the compressed-liquid state. The practice is applicable to instruments capable of operating in the temperature range 263 K 473 K at pressures from just above saturation to as much as 140 MPa. Some examples of products that may be tested after a successful calibration using this procedure include: crude oil, gasoline and gasoline-oxygenate blends, diesel and jet fuels and lubricating oils. 1.1 The guide specifies a procedure for the calibration of the density meter and for the determination of the overall uncertainty of the density measurement when procedures outlined in this guide are followed.
4.1 The use of commercial instruments that use the U-tube method to measure density over large ranges of temperature and pressures largely above ambient conditions has become wide spread. The instruments are robust and capable of producing repeatable and accurate density measurements on a wide variety of fluids and gases; however the measurement is not direct and the instruments must be adjusted prior to measurements. This standard practice covers a series of methods provided to aid users in adjusting U-tube density meters to achieve accurate density measurements and to accurately determine the overall uncertainty of the measurements. Any parameter describing the equation of state (EOS), such as temperature, pressure or purity (origin) of the certified reference material, has an influence on the achievable total accuracy of density measurements of these samples. Because the measurements made with these instruments are not absolute, the accuracy with which the instrument is adjusted largely determines the uncertainty of the measurements.
Keywordsvibrating-tube density meter; specific gravity
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