Skip to content

LEVEL MEASUREMENT TECHNOLOGIES

Radar level measurement: non-contact and guided wave radar

A radar level transmitter measures the distance to the surface with microwaves and gives the level of liquids and bulk solids — through vapour, at high temperature and pressure, and in tall tanks and silos. It comes in two forms: non-contact radar, which sends the signal through the air from an antenna, and guided wave radar, which sends it along a rod or a cable. We supply KROHNE radar level transmitters.

See how we supply them

How radar level measurement works

The transmitter sends microwaves towards the surface and receives their echo. Microwaves travel at the speed of light, so the times are tiny — a few nanoseconds for every metre — and the electronics measure them precisely, either as the travel time of a short pulse or as the frequency difference of a continuous sweep. The distance taken from the height of the tank is the level.

Non-contact radar sends the signal through the air above the medium from a horn, drop or lens antenna. Nothing touches the product, so it suits aggressive, hot, sticky or hygienic media, and tall tanks and silos.

Guided wave radar sends a pulse along a rod, a coaxial probe or a cable that reaches down into the medium. The probe guides the energy to the surface and back, so foam, vapour, dust and the shape of the tank matter less, and a second echo from a lower interface — oil on water, for example — can be measured as well.

How well a surface reflects depends on its dielectric constant: water and most water-based liquids reflect strongly, oils and many powders less. That decides the antenna or the probe, and it is one of the first questions we ask.

  • The microwave signal leaving the antenna, and its echo returning from the surface
  • Guided wave radar: the pulse travelling along the probe and reflecting at the surface
  • The electronics, which measure the time of flight and calculate the level
  • The 4–20 mA signal, usually with HART, to the control system

Where radar fits — and where it does not

A strong choice for

  • Tall tanks and silos, of liquids or of bulk solids
  • Vapour, temperature and pressure in the tank, which hardly affect microwaves
  • Aggressive, sticky or hygienic media, measured without contact
  • Foam, and the interface between two liquids, with guided wave radar
  • Storage tanks where an accurate inventory matters

Think twice when

  • You only need a high or a low alarm: a switch is simpler and cheaper
  • Internals near the antenna — agitators, ladders, heating coils — or the filling stream are in the beam: they give false echoes
  • Heavy, sticky build-up forms on the antenna or the probe
  • The liquid has a very low dielectric constant and the installation is non-contact: the echo is weak, and guided wave radar or another technology may suit better

How it compares with the other technologies

Typical process temperature of each technology, in °C. The technology of this article is highlighted.
  • Hydrostatic level transmitters−20…+100 °C
  • Radar level (the technology of this article)−40…+200 °C
  • Ultrasonic level−40…+80 °C
  • Vibrating level switches−40…+120 °C
  • Floats and displacers−60…+320 °C
  • Conductive and HF level switches−30…+150 °C
  • Rotating paddle−20…+80 °C

Typical process temperatures, not a model commitment; several technologies have versions for higher temperatures. We confirm the figures of each instrument for your application.

 All technologies

Installing a radar level transmitter

Mount a non-contact antenna on a nozzle away from the tank wall and away from the inlet, so that the beam reaches the surface clear of internals. Keep the nozzle short and smooth inside, or let the antenna reach past it into the tank.

Then:

Away from the inletThe filling stream and the wall reflect the signal: mount the antenna between the centre and the wall, out of the inlet stream.
In a siloSolids form a heap and a slope: aim the antenna towards the outlet, so that the level is measured over the whole range.
Guided wave: foam and interfacesThe probe guides the pulse through foam and vapour, and reflects it both at the surface and at the interface between two liquids.
  • Tell us the medium, or its dielectric constant, so that we can choose the antenna or the probe.
  • Keep a guided wave probe clear of the wall and of internals; a coaxial probe or a stilling well helps in small or crowded tanks.
  • Map the echoes of the empty tank at commissioning, so that the transmitter ignores them.
  • In silos, check the pulling force of the moving solids on a cable probe.

Radar level by industry

Oil & GasStorage tanks, separators and process vessels, with guided wave radar for the interface between oil and water.ChemicalReactors and storage tanks of aggressive or toxic liquids, measured without contact.Power & EnergyFeedwater and condensate tanks, and silos of fuel and ash.Mining, Minerals & MetalsSilos and bins of ore, cement, lime and other bulk solids.Food & BeverageProcess and storage tanks, and silos of flour, sugar and grain.

Radar level transmitters from KROHNE

We supply KROHNE radar level transmitters — the OPTIWAVE non-contact radar series and the OPTIFLEX guided wave radar series. Tell us the application: the medium, the tank or silo and its height, the process temperature and pressure, and the connection — and our engineers will suggest the right transmitter, with price and delivery time.

KrohneKrohneProcess instrumentation — flow, level, temperature, pressure and analysis Learn more

Radar level: frequently asked questions

Ask about a radar level transmitter

Tell us the medium, the tank or silo and its height, the process temperature and pressure, the connection and the output you need — and our engineers will suggest the right radar transmitter, with price and delivery time.