Radar vs Ultrasonic Level Measurement: How to Choose
The one-line answer
Radar for foam, vapour, dust, condensation and long range. Ultrasonic for clean water in a simple tank where cost matters. Everything else is a detail.
How the two technologies fail
Ultrasonic depends on sound travelling through air and reflecting from a surface. Anything that changes the air or absorbs the sound changes the measurement: temperature gradients, steam, foam, dust, wind and condensation on the transducer face. The failure is rarely a clean fault. It is a plausible reading that drifts.
Radar depends on a radio reflection. Vapour, dust and most foam are largely transparent at 80 GHz, and the narrow beam means the reflection comes from the surface directly below the antenna rather than from a wall or an agitator blade. The failure mode is a false echo from a fixed obstruction, which is visible during commissioning as a constant distance.
Surface conditions
| Condition | Ultrasonic | 80 GHz radar |
|---|---|---|
| Clean water, still surface | Good | Good |
| Foam layer | Poor, absorbs pulse | Good, reads through most foam |
| Steam or vapour | Poor | Good |
| Dust in a silo | Poor | Good |
| Condensation on the face | Poor | Good, dripping can interfere |
| Agitated surface | Marginal | Good with damping |
| Very low dielectric media | Good | Marginal, needs guided radar |
Vessel geometry
Radar needs a clear cone. A nozzle that protrudes more than its own diameter, a heating coil close to the beam, or a manway directly beside the antenna will all produce a reflection. The 4 degree beam of an 80 GHz unit makes this manageable in most tanks, but check the beam diameter at maximum range against the internals before ordering.
Ultrasonic needs a clear acoustic path too, but the wider beam means it is more tolerant of a slightly off-centre mounting and less tolerant of internals.
Cost and maintenance
Ultrasonic is roughly half the price of radar at the same range. That difference disappears the first time a unit needs a site visit, which is why water utilities with remote pump stations increasingly specify radar for anything that is not a clean tank.
What we recommend in practice
- Wet wells and pump stations: 80 GHz radar plus an independent low-level switch for protection
- Clean water reservoirs and cooling tower basins: ultrasonic, unless the site is remote
- Fermentation, flotation and chemical reactors: radar, always
- Silos and hoppers: radar with dust suppression, or guided radar for low-dielectric powders
- Sealed metal vessels: guided-wave radar, since neither non-contact technology can see through the wall
Whatever the technology, keep the protection function separate from the control function. One instrument doing both jobs is how tanks overflow.
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