Level Measurement · Glossary

What is DP Level Measurement?

closed and pressurised tanksLevel Measurement

DP level measurement uses a differential pressure transmitter between a bottom tap and a top tap to measure level in closed tanks.

DP Level Measurement Explained

The high side connects to the bottom of the vessel and the low side to the vapour space. The vapour pressure acts on both sides and cancels, leaving only the liquid head.

The low side line is either a dry leg (gas filled) or a wet leg (liquid filled). A wet leg adds a constant head that shifts the range to an elevated zero.

DP Level Measurement Formula

ΔP = ρ g h − ρ_wl g H_wl

ρ, h	process density and level above the HP tap
ρ_wl	wet leg fill density (0 for dry leg)
H_wl	wet leg height

Example: Taps 3 m apart, water process and water wet leg: LRV = −29.42 kPa (empty), URV = 0 kPa (full).

Calculators for DP Level Measurement

CalculatorDP Level Transmitter CalculatorFree online calculator with formula and worked example.CalculatorDensity from DP CalculatorFree online calculator with formula and worked example.CalculatorPressure Transmitter Elevation CorrectionFree online calculator with formula and worked example.

Free Downloads

Free downloadDP Level Transmitter Calculation ExcelFree download in Excel and PDF.Free downloadLevel Transmitter Datasheet Template in ExcelFree download in Excel and PDF.

Frequently Asked Questions

What is DP Level Measurement?

DP level measurement uses a differential pressure transmitter between a bottom tap and a top tap to measure level in closed tanks.

Why does a full tank read 0 kPa with a wet leg?

When full, the process head on the HP side equals the wet leg head on the LP side, so DP is zero. When empty, DP is negative.

What if the wet leg loses fill?

The LP head falls and the transmitter reads too high. Check wet legs regularly, or use remote seals.

Learn more on the blog

DP level transmitter calibration: zero suppression and zero elevation

A practical guide on instrumentationblog.in with more detail on DP level measurement and how it is applied on real plants.

Read Full Article

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