Calculations
Tankvision
44
Hauser
8.3
Mass Measurement
Today, most hydrocarbons in the western world are bought and sold using volume
measurement. However, in many eastern countries and in some specialised industries,
product are sold based on mass due to traditions in particular markets, so mass calculation
can be important in those areas of trade. Mass-based measurement offers other advantages,
since mass is independent of product temperature and other parameters.
For custody transfer, high accuracy tank gauging is required, and mass-based calculation is
often used.
8.3.1
Hydrostatic Tank Gauging
The advantage of HTG is that it provides direct mass measurement with only pressure
transmitters to measure hydrostatic pressure in determining density via a fixed distance and
vapour pressure. Therefore, it is a low-cost solution for mass measurement. However, there
are substantial disadvantages:
• Level and volume measurements are less accurate, especially when density stratification
occurs.
• Density is only measured at the between the two pressure sensors.
• Difficult to verify, commission and calibrate
L00-HTGSxxx-05-00-00-xx-001_
The middle or P
2
transmitter is unique to Hydrostatic Tank Gauging.
P
3
P
2
P
1
Y
L
=
Y
Y
L
P
-
P
1
3
P
-
P
1
2
P
-
P
1
2
D
=
obs