Hydrostatic Tank Gauging (HTG) Calculator
Hydrostatic tank gauging (HTG) uses two or three pressure transmitters to measure density, level and mass. This calculator shows how the readings combine for a vertical tank.
- ρ = (P1 − P2) ÷ (g × h12) = 20,000 ÷ (9.807 × 2.4) = 849.8 kg/m³
- Level = (P1 − P3) ÷ (ρg) + z = 9.3 m
- Mass ≈ (P1 − P3) × A ÷ g + ρ × z × A = 620.7 t
HTG Equations
Level = (P1 − P3) ÷ (ρ × g) + z
Mass = (P1 − P3) × A ÷ g + ρ × z × A
P1, P2 and P3 are the bottom, middle and vapour space pressures, h12 the vertical distance between P1 and P2, z the height of P1 above the tank bottom and A the tank cross section. The mass equation is exact for a vertical cylinder; real tanks need a strapping table and corrections for tank expansion.
Worked example
With P1 = 0.8 bar, P2 = 0.6 bar, P3 = 0.05 bar, 2.4 m between P1 and P2 and P1 0.3 m above the floor of a 10 m tank: ρ ≈ 849.8 kg/m³, level ≈ 9.30 m and mass ≈ 620.7 t.
Frequently Asked Questions
What is hydrostatic tank gauging?
A method that uses pressure transmitters at known heights on a tank to calculate density, level and mass.
Why is a top transmitter needed?
For tanks with vapour pressure or blanketing, P3 subtracts the gas pressure from the liquid readings. Atmospheric tanks can omit it.
When is the density valid?
Only when the liquid level is above the middle transmitter, so both P1 and P2 are in liquid.
Learn more on the blog
Basics of level measurement
A practical, field focused guide on instrumentationblog.in that explains the theory behind this calculator and how engineers apply it on real plants.
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