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GWR - Guided Wave Radar Guided Wave Radar: Nr.1 Alternative to Mechanical Level Measurement

Author / Editor: Anna Olander / Dr. Jörg Kempf

Guided wave radar (GWR) has become increasingly popular as an alternative to mechanical technology for level and interface measurements in bypass chamber applications. This measurement method, which has no moving parts and is not affected by density changes, provides reliable and accurate level and interface measurements.

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Guided wave radar provides an accurate and low maintenance alternative to mechanical technology for many applications, including both level and interface.
Guided wave radar provides an accurate and low maintenance alternative to mechanical technology for many applications, including both level and interface.
(Pictures: Emerson)

Traditionally, displacers and other mechanical technologies have been used for level, interface and density applications involving short measurement ranges. GWR is now being considered for many of these applications as it offers significant benefits over mechanical technologies.

A displacer is a robust level device that can handle a wide range of pressures and temperatures. As the primary measurement principle is the buoyancy of the displacer in the fluid, fluid density is a key factor in sizing the displacer and determines the stability of the signal, with variations in density affecting accuracy. Build-up on the displacer element also affects accuracy.

GWR, on the other hand, relies on low-energy microwave pulses sent down a probe. When a pulse reaches the surface of the medium, its reflection travels to the transmitter, which uses the time of flight principle to calculate the position of the reflecting surface. As GWR is not density-dependent, changes in the density of the medium or material build-up have practically no effect on accuracy. Unlike mechanical devices, GWR measurements are also unaffected by turbulence or vibration. With no moving parts to stick or wear, maintenance costs are reduced and false readings, which can result in hazardous situations, are avoided.

For these reasons, GWR level and interface measurement transmitters have shown significant cost savings in some of the most difficult applications. For example, users of Emerson’s Rosemount GWR report annual maintenance and repair savings in the range of $1,000–8,000 per unit.

A GWR unit is mounted on top of the tank or chamber, with a probe extending to the full depth of the vessel. Manufacturers offer a wide range of probe styles to suit different tanks and media. For example, Emerson offers coaxial, rigid single, flexible single, rigid twin, and flexible twin probes. There are also probes for aggressive environments and extreme temperatures. GWR transmitters are quick and easy to install, and can generally be retrofitted to chambers formerly used for mechanical transmitter.

GWR is recommended over non-contact radar in most chamber applications because it is unaffected by the size and shape of the chamber and is better at managing shorter measuring ranges. Unlike GWR, non-contact radar cannot detect liquid-liquid interfaces, and may have problems with surface layers of liquid or foam.

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