Endress+Hauser NXA820 - Page 35

Tankvision Calculations
Endress+Hauser 35
8.1.11 Density calculations
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We have to distinguish between: observed and reference density
• Observed density is the density of the product at actual (observed) temperature
• Reference density is the density the product would have if we heat/cool it until the
reference temperature (usually 15 °C/60 °F)
• Reference density is used to calculate VCF, FR and mass
• If you know the RefDens you can easily geht the ObDens
ObsDens = RefDens x VCF
• If you know the ObsDens you need (API/ATSM) tables and the sample temperature to get
the RDC (reference density correction factor).
• You can also correct for the thermal expansion of the hydrometer glass (HYC)
RefDens = RDC x ObsDens x HYC
Hydrometer Correction - HYC
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with:
• HYC = Hydrometer correction
•A
HYC
, B
HYC
= Thermal expansion coeff. for glass
• t = Temperature of sample
•T
Cal
= Calibration temperature of glass hydrometer
Hydrom. corr.
Product Code
Obs. density &
Obs. temp.
Ref. Density
Obs-Ref
density
conversion
9.
Reference Density
Calculation
HYC = 1.0 - A (t - T) - B(t - T)
HYC Cal HYC Cal
´´
2
T
Cal
A
HYC
B
HYC
15 °C 0.000 0230 0 0.000 000 020
60 °F 0.000 0127 8 0.000 000 062