Radar, ultrasonic, guided-wave radar, hydrostatic and float each solve level measurement a different way. Understanding the physics is the fastest way to avoid buying the wrong instrument. Below, each technology gets a plain-English explanation and a best-for / watch-out summary, then all five are compared side by side.
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Radar sends a microwave beam at the surface and measures the round-trip time. Because it never touches the medium, it is immune to corrosion, buildup and most surface conditions. The move to 80 GHz matters: the beam is far narrower (around 3°), so it reads small tanks and silos without false echoes from the walls, and it penetrates dust, foam and vapour that defeat older 26 GHz units.
Best for difficult media — foam, turbulence, dust, hazardous areas and long range.
Watch out it still has a blind zone at the top; very low-dielectric gases can weaken the echo.
Ultrasonic transmitters use sound waves instead of microwaves. They are simple, cheap and accurate on calm, clean liquids, which makes them a popular choice for water tanks and simple vessels. Their limits are physical: sound is absorbed by foam and vapour, reflected by condensation on the face, and blocked by heavy dust, so range and reliability drop in tough conditions.
Best for calm, clean liquids on a budget — water tanks and simple vessels.
Watch out foam, vapour, condensation on the face and heavy dust will degrade or block the echo.
For placement rules that make or break an installation, see the ultrasonic installation guide.
GWR runs the microwave along a probe immersed in the medium. Because the signal is guided, it performs well on turbulent, low-dielectric or boiling liquids and can measure interface between two liquids. The trade-off is that the probe contacts the process, so it is vulnerable to coating, corrosion and mechanical damage, and it is harder to clean.
Best for turbulent, low-dielectric or boiling liquids, and liquid-to-liquid interface.
Watch out the probe contacts the medium — coating, corrosion and mechanical damage, and harder to clean.
A pressure transmitter at the bottom infers level from the weight of the column above it. It is the simplest and often cheapest option for open, still, conductive tanks, but the reading depends on liquid density — so it drifts if the product changes, and it cannot handle gases or solids.
Best for open, still, conductive tanks — the simplest and cheapest option.
Watch out the reading depends on density, so it drifts if the product changes; not for gases or solids.
Mechanical float systems track a floating element; magnetostrictive versions read its position very precisely. They are robust and inexpensive for clean liquids but are moving parts in the tank — subject to wear, sticking and limited range, and unsuitable for solids or aggressive media.
Best for clean liquids over a short range at low cost.
Watch out moving parts wear and can stick; not suitable for solids or aggressive media.
| Technology | Contact | Foam / dust | Cost | Best for |
|---|---|---|---|---|
| 80 GHz radar | No | Excellent | Medium | Difficult media, hazard, solids |
| Ultrasonic | No | Poor | Low | Calm clean liquids |
| Guided-wave radar | Yes | Good | Medium | Turbulent / interface |
| Hydrostatic | Yes | n/a | Low | Open still tanks |
| Float | Yes | No | Low | Clean liquids, short range |
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