Level Measurement

What is a guided wave radar level transmitter?

A guided wave radar sensor is a type of radar level sensor there are two types of radar level sensors they are through the air and guided type. This device can be used to measure the liquid level and it can also be used to do the liquid-liquid interface level measurement and this can be done for both process and ESD applications. GWR working is based on the principle of time-domain reflectometry.

So the level is measured by providing low-power nanosecond pulses and these pulses are guided along with the probe which is submerged in the process media. So when the pulse reaches the surface of the material it is measuring, then a part of the energy is reflected back to the transmitter and this time difference is taken to do the level measurement. So there is a time gap between these pulses which are the generated and reflected pulses and this time gap is converted to a distance and the level is calculated. The speed of the travel of the pulse would have an impact on the dielectric of the medium.

How do a guided wave radar transmitter operates?

The operation of the guided wave radar is based on TDR technology and it is based on a pulse of electromagnetic energy that is transmitted down the probe tube. So when the radar pulse reaches the liquid surface which has a higher dielectric constant than air in the process tank then the pulse will be reflected back to the electronic unit. There is a high-speed electronic timing circuit that can calculate the transit time and also measure the liquid level in the tank. It can accurately measure the level of the liquid.

How to select a guided wave radar transmitter for our application?

  • It must be selected according to the dielectric constant of the process liquid
  • Process temperature and pressure must be considered
  • Possibility of foam formation
  • Possibility of coating and build-up
  • Cleaning of probe
  • It must be selected according to the installation as if it is top-mounted, or side-mounted, etc.
  • Viscosity and suspended solids, particle size, etc must be considered

What are the advantages of GWR transmitter?

  • It can be used with liquids that have low dielectric values
  • It can be used with turbulent liquids
  • It is also applicable for low specific gravity liquids
  • It is applicable for heavy foam layers and problematic solids
  • The measurement is completely independent of the density

The measuring signal and reflection are concentrated around the waveguide or inside the waveguide. There won’t be any impact of stray signals because of the narrow path of the signal propagation. The signal concentration on the waveguide would result in a cleaner stronger signal of the echo reflection.

Guided wave radar is virtually not affected by the following process conditions

  • Conductivity
  • Temperature
  • Pressure and vacuum
  • Dielectric constant
  • Specific gravity
  • Vapor, steam, or dust

What are the limitations of guided wave radar?

  • It can’t be used to measure the interface of two liquids
  • The ability of the detection is limited for the GWR in the case of foam
  • During the water sand interface, the transmitter can only detect the water
  • Chances of corrosion are high
  • The movement of the product in the tank could bend the waveguide

What are the application of guided wave radar?

  • It is used in accumulators
  • Separators
  • Distillation and rectification towers
  • Reactor tanks and scrubbers
  • Liquefied gas containers
  • Boiler and feed-water systems


post-graduate in Electronics & communication.

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