Local Gravity and Deadweight Tester Correction
Deadweight testers generate pressure from masses, so the pressure depends on local gravity. Calculate local gravity from latitude and altitude and correct the nominal pressure.
- g = 9.780327 × (1 + 0.0053024 sin²φ − 0.0000058 sin²2φ) − 3.086 × 10⁻⁶ × h = 9.78381 m/s²
- P = Pnominal × glocal ÷ gcal = 99.7671 bar
International Gravity Formula
Pactual = Pnominal × glocal ÷ gcal
φ is latitude and h altitude in metres (free air correction). For the best accuracy use a measured gravity value for the laboratory, and also correct for air buoyancy and piston temperature.
Worked example
Pune (18.52° N, 560 m): g ≈ 9.7838 m/s². A tester calibrated to standard gravity (9.80665) generates 99.767 bar when loaded for 100 bar, a 0.23 % difference.
Frequently Asked Questions
Why does a deadweight tester need gravity correction?
Pressure equals force divided by area, and the force from the masses equals mass times local gravity.
What is standard gravity?
9.80665 m/s², a defined conventional value used for kgf and many instruments.
Is the formula accurate enough?
It is typically within about 0.005 % of measured values. For accredited work, use a surveyed local gravity value.
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