Level Measurement · Glossary

What is Dielectric Constant?

Symbol: εrdimensionlessLevel Measurement

Dielectric constant is the relative permittivity of a material; it sets how strongly a liquid reflects radar and affects capacitance probes.

Dielectric Constant Explained

Radar echoes are strong from high εr liquids like water and weak from low εr liquids like oils and LPG. Capacitance probes rely on the difference in εr between the product and air.

In GWR, the signal also slows down when passing through an upper liquid layer, which is used for interface measurement.

Dielectric Constant Formula

Reflection ≈ [(√εr − 1) ÷ (√εr + 1)]²

εr	relative permittivity of the liquid

Example: Water (εr 80): about 64 % reflected; oil (εr 2): about 3 %.

Dielectric Constant: Typical Values

Water	about 80
Alcohols	about 18 to 33
Oils and hydrocarbons	about 1.8 to 4
Air	1.0

Calculators for Dielectric Constant

CalculatorRadar Level Dielectric CalculatorFree online calculator with formula and worked example.CalculatorCapacitance Level CalculatorFree online calculator with formula and worked example.

Frequently Asked Questions

What is Dielectric Constant?

Dielectric constant is the relative permittivity of a material; it sets how strongly a liquid reflects radar and affects capacitance probes.

What εr is too low for radar?

It depends on the radar type and conditions; GWR coaxial probes handle the lowest values. Check maker limits.

Does εr change with temperature?

Yes, slightly for most liquids, and strongly for water close to boiling.

Learn more on the blog

Guided wave radar vs non contact radar

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

Read Full Article

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