Humble limit switch becomes inline density meter

07 July 2008

AFor 25 years, Endress+Hauser’s Liquiphant sensor has been used for the reliable limit detection of the liquid levels in pipelines and storage tanks.

Liquiphant density meter
Liquiphant density meter

With the advent of microelectronics and modern signal processing techniques, it has been cast in a new role. In combination with the newly developed FML621density calculator, it can be adapted to monitor the quality of liquids in many manufacturing processes. It not only determines the relative and standard density, but also measures the concentration of liquids and thus is able to identify the liquid itself.

The liquid’s density is computed through the input value of the Liquiphant frequency, the temperature, and the pressure. These last two values can be supplied and integrated using separate instruments. A data logger function in the FML621 supports operation and servicing.


Determining the concentration of materials is today an important factor for quality in the chemical and the food industry. In liquids, it is often found by peripheral off-line and laboratory measurements.

The newly developed Liquiphant density system offers in-line concentration measurement without the use of expensive and time-intensive analytical procedures and it can also easily be adapted to current applications.

For example, Endress+Hauser says a soft drink producer wanted to differentiate between cleaning solutions, water, and beverage in the pipeline. Until now the media was identified optically. The advantages of in-line measurement are continuous monitoring, increased measurement accuracy, and reproducibility.

In another example in a crude oil application, a specific salt concentration was required which depended on the depth of the drill hole so that the oil/water mixture is brought to the surface by the greater density of the salt mixture. The Liquiphant density function ensured that the required salt concentration was continuously mixed in the tank automatically. When compared to previous tests, this method has much greater precision (0.002 g/cm3) with excellent reproducibility (0.0007 g/cm3).

Endress+Hauser Messtechnik GmbH+Co. KG

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