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Guided Wave Radar

Level Measurement: How to Make the Best of GWR

| Author / Editor: Phil Lever / Dr. Jörg Kempf

On the radar: Each peak of the ‘echo curve’ corresponds to a reflection of the signal: The ‘Reference’ pulse is caused by the transition between transmitter head and probe. A further peak is caused by a reflection on the product surface.
On the radar: Each peak of the ‘echo curve’ corresponds to a reflection of the signal: The ‘Reference’ pulse is caused by the transition between transmitter head and probe. A further peak is caused by a reflection on the product surface. (Picture: Emerson)

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Guided Wave Radar (GWR) technology has transformed the way process companies measure level in challenging applications: Providing accurate and reliable results, GWR modules have no moving parts, reducing maintenance to a minimum. Critical for a GWR application is, nevertheless, the correct installation.

In a Guided Wave Radar installation, the GWR is usually mounted on top of the tank or chamber with a probe extending to the full depth of the vessel. A low energy pulse of microwaves is sent down the probe that is reflected back when the pulse reaches the media surface. The transmitter measures the time taken for the pulse to reach the media surface and be reflected back with an on-board microprocessor that accurately calculates the distance to the media surface using ‘time-of-flight’ principles.

GWR level transmitters are accurate and reliable: They are not density dependent and are relatively unaffected by high turbulence or vibrations. Since there are no moving parts to stick or wear, maintenance costs are reduced. As this setup reduces the problems of false readings, possible hazardous situations can often be avoided.

Level Measurement in a Wide Range of applications

Guided Wave Radar measurement technology is suitable for a wide range of applications, but as with any measurement technology, installation good practices are important and there are some situations where the mechanical installation, the process media itself, as well as the effects of electromechanical noise may interfere with the basic measurement.

One Ping Only: The Echo Curve

To simplify the commissioning process, GWR level transmitters can be pre-configured at the factory to include parameters such as tank height and media properties. Some applications can however be quite challenging — this is where being able to view the echo curve can be a valuable tool for troubleshooting difficult applications. The echo curve represents the tank, as seen by the radar transmitter. Each peak corresponds to a reflection of the radar signal (e.g. the surface of the level or interface, an obstacle, or something else).

By viewing single instances or movies of the echo curve, the transmitter configuration can be adjusted to achieve a reliable measurement. Additionally, the echo curve gives insight into transmitter functionality and changes in application conditions. The software includes functions for viewing and recording the echo curve, and advanced functions for configuring the amplitude thresholds. Emerson’s Rosemount 3300/5300 and the new wireless 3308 Series level transmitters for example allow the user to adjust threshold settings and suppress or block out noise that may be present at the top of the measuring range.

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