Level measurement for low dielectric constants

Low dielectric constants present most guided radar (TDR) level meters with almost insoluble problems. Under such conditions, OPTIFLEX from KROHNE has already proven its effectiveness repeatedly. At Xella, the leading supplier of calcium-silicate brick and aerated concrete products and services, OPTIFLEX performed convincingly even at a dielectric of 1.16. At Xella Trockenbau-System GmbH’s Calbe plant near Magdeburg, perlite had to be measured in a 15 m high silo. Perlite is an extremely light powder and is used for the manufacture of AESTUVER-brand dry lining boards. A particular feature of perlite is its low dielectric constant, which has prevented conventional TDR meters from reliably measuring the level.

However, KROHNE’s new level meters, including OPTIFLEX, feature the so-called TBF (tank bottom following) mode, which detects the probe end return signal rather than a direct reflection from the product surface. In the case of products with poor reflective properties the level meter is able to see through the product and determine the position of the probe end.

However, as the transit time of the emitted pulse is delayed in the product, the reflection of the probe end appears with a time delay. The transit time delay depends on the dielectric constant of the product. This means that if the dielectric constant is known, the actual level can be calculated from the displacement of the probe end pulse. In automatic mode, OPTIFLEX is capable of autonomously switching from standard direct mode to TBF mode, and thus always selects the most reliable measuring method for the client.

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