Flow, level & control
ENSURING ACCURATE AND RELIABLE LEVEL MEASUREMENTS IN TANKS WITH OBSTRUCTIONS
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Sara Anderberg, non-contacting radar product manager at Emerson, explains how intelligent signal processing technology in modern transmitters enables organisations to meet the challenges of tank obstructions interfering with radar signal reflections.
on-contacting radar level transmitters are widely implemented throughout the manufacturing and process industries, especially in measurement applications
where high accuracy, reliability and minimal maintenance are important requirements. These versatile devices are suitable for measuring the level of liquids, sludges, slurries and solids. However, one of the most challenging applications for this technology has traditionally been measuring level in tanks with internal obstructions (figures 1 and 2), such as agitators, heating coils, pipes, ladders or baffles, for example. Vessels containing these types of structures can create difficulty for non-contacting radar devices because they can interfere with their signal processing. Radar level sensors work by emitting microwave signals that bounce off the material surface and are reflected back to the transmitter. These reflected signals are known as echoes, and they enable the material level to be calculated. Obstructions within a tank can, however, also reflect microwave signals, creating what are known as false echoes. When this happens, it can become challenging for the radar device to identify which echo is from the material surface and which are false echoes coming from obstructions. As some liquids have a low dielectric constant – meaning that they poorly reflect radar signals – even slight interference from obstructions can have a major impact on the signal in these cases, which further complicates level measurement.
THE CONSEQUENCES OF FALSE ECHOES When a radar device interprets a false echo as a surface echo, it results in an inaccurate level reading which could have serious consequences, including an overfill and subsequent spill. In tanks containing volatile or flammable substances, a spill would not only create an obvious safety
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Figures 1 and 2: Internal obstructions in tanks. June 2025 Instrumentation Monthly
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