Level Measurement · Glossary

What is Interface Level?

boundary between two liquidsLevel Measurement

Interface level is the height of the boundary between two liquids of different densities in a vessel, such as oil on water.

Interface Level Explained

Separators and settlers need to know where the heavy liquid ends and the light one starts. DP, displacer, guided wave radar and capacitance instruments can measure it.

DP and displacer methods need a clear density difference. Emulsion layers make the interface fuzzy for every technology.

Interface Level Formula

x = (ΔP ÷ g − ρ_L H) ÷ (ρ_H − ρ_L)

x	interface height above the lower tap
ΔP	DP between taps with both submerged
H	tap spacing
ρ_H, ρ_L	heavy and light liquid densities

Example: H = 1 m, ρ_H = 1000, ρ_L = 800 kg/m³, ΔP = 9.0 kPa: x ≈ 0.59 m.

Calculators for Interface Level

CalculatorInterface Level CalculatorFree online calculator with formula and worked example.CalculatorDisplacer Level CalculatorFree online calculator with formula and worked example.

Free Downloads

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

Frequently Asked Questions

What is Interface Level?

Interface level is the height of the boundary between two liquids of different densities in a vessel, such as oil on water.

Must both taps be covered?

Yes, for DP interface measurement both taps must always be below the total liquid surface.

What is the minimum density difference?

It depends on the instrument; small differences give a small signal span and poor resolution. Check the maker data.

Learn more on the blog

Types of level transmitters

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

Read Full Article

More Level Measurement Terms

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