Level · Comparison

Displacer vs Guided Wave Radar

Side by side comparison: how they work, where each fits, and which to choose.

Quick answer: Displacers are proven for level and interface but density dependent with moving parts; GWR has no moving parts, is density independent and often fits the same chamber.

Displacer vs Guided Wave Radar: Comparison Table

Aspect	Displacer	Guided Wave Radar
Principle	Buoyancy on a heavy cylinder	Microwave pulse along a probe
Density dependence	Yes	No (for total level)
Moving parts	Torque tube or spring	None
Interface	Yes, with density difference	Yes, with dielectric difference
Range	Displacer length	Probe length, up to many metres
Maintenance	Recalibration, torque tube wear	Probe cleaning in sticky service

Choose Displacer when

Existing installations with proven performance
Extreme conditions where GWR is not certified

Choose Guided Wave Radar when

Retrofits into displacer chambers
Changing density, foam, vapour

Key Differences Explained

Replacing displacers with GWR in existing cages is a common upgrade. Check the chamber size, probe type and process conditions.

For interface, the upper liquid must have a lower dielectric constant than the lower one for GWR to see both.

Related Glossary Terms

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Free Calculators

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

Frequently Asked Questions

What is the difference between Displacer and Guided Wave Radar?

Displacers are proven for level and interface but density dependent with moving parts; GWR has no moving parts, is density independent and often fits the same chamber.

Can GWR fit a displacer chamber?

Usually yes, with a rod or coaxial probe sized for the chamber.

Why do displacers drift?

Density changes, buildup on the displacer and torque tube fatigue.

Is GWR affected by steam?

At high pressure steam the signal speed changes; special compensation exists.

Learn more on the blog

Guided wave radar vs non contact radar

A practical guide on instrumentationblog.in that goes deeper into this topic with field examples.

Read Full Article

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