An Ultrasonic pulse is transmitted via a coupling media through the wall of a tank into the liquid, reflected at the liquid's surface and travels back to the sensor. The time of flight is proportional to the level height. Interface measurement is also possible when there is a sharp interface.

The wall's material may be metallic, plastics, GFK or glass, which thickness may be between 0,5 and 50 mm. Any gas content like in foam or with linings should be avoided, as these cause stray dispersion for the ultrasonic pulse and so reduce the signal quality. The thicker the wall is the bigger the minimum measurable liquid level will be.

A big advantage of this measuring principle is that there is no influence by the gas atmosphere. Especially the thermal coefficient for ultrasonic velocity of liquids is much smaller than those of gases, which results in less influence on the measuring results compared to those principles measuring from top through the gaseous atmosphere. Heavy crustings and sediments on the bottom also reduce the signal quality by damping and straying effects which may also occur with highly viscous dispersed or bubbling media.

The wall may made of metal, plastic, glass and also on these, air-free applied coatings, as email or color exists and the wall thicknesses may here between 0,5 and 50 mm amount to. Dependent on the thickness as well as the material of the container wall a neutral zone of 30...300 mm results. Besides from this a constant offset error, which amounts to with a steel wall e.g. ¼ the thickness, results. (example: 6 mm of wall thickness = > 1.5 mm of offset). With porous or foamed layers or walls no measurement is possible.

The sensor will be installed into a fixing part which may be clamped, cemented or welded onto the wall. For installation you will have a big advantage because you do not need openings in the containment and therefore retrofitting can be performed during operation. Additionally there is no need of taking into account corrosive aspects which results in safe operation in aseptic application or with highly aggressive media. There is no problem  with leakage any more!

Calibration of the sensor can be made without emptying the containment!