Carlsberg in Denmark uses Baumer’s LSP sensor for level measurement ensuring tank levels in its bottle and can ­filling machines are kept at a constant height

In the bottling plant with its six filling machines, the beer is filled into 0.33 litre bottles as well as 0.33 or 0.5 litre cans. Placed above each of these machines is a rotating barrel tank with a capacity of 300 litres from which the beer falls through the filling valves into the bottles. The bottle filler with 104 filling valves is able to fill about 700 to 800 bottles per minute, or about 50,000 bottles per hour. The can filler follows the same principle, but it has 130 filling valves and fills more cans as a consequence. The production runs day and night in three shifts only interrupted for cleaning.

Carlsberg was looking for a new level measuring system for the barrel tanks above the filling machines because the existing solution was too sensitive in humid surroundings occasionally leading to inaccurate results. This measuring method generated a frequency output signal which first had to be translated by an integrated converter into a 4…20mA signal, which is necessary for continuous measuring of levels. The system was also difficult to maintain with not readily available spare parts.

The main requirement for the new level measurement solution was accuracy. As Carlsberg was already using Baumer sensors for pressure and temperature measuring in many other areas, the brewery opted for them in the level measurement in the filling machines as well. For a start, the continuous level measuring sensors LSP 050 were installed and tested on one of the filling machines. The sensor detects the level of liquids with a fixed 300mm long measuring rod and converts it into a 4…20mA output signal. “The direct conversion of the measurement into a linear 4…20mA output signal is very important and has simplified the level measurement considerably compared to the previous solution,” explains Bent Pallesen, engineer at Carlsberg. Moreover, with an accuracy of 0.5 per cent of the programmed full scale, the sensor achieves the required precision.

Level measuring with the LSP

The LSP 05x is able to precisely measure all homogeneous liquids with a minimum conductivity of 50 µS/cm. Changes in conductivity through different media or temperatures do not affect the accuracy of the level measurement. Neither does the different concentration of media affect the measuring result. Due to the fast response time of up to 10 ms (T66), the analogue output signal of the precise level measurement allows the control of very fast filling processes. The level sensor can be installed in a container from above, below or from the side. Different process connections are available to ensure hygienic installation. All parts in direct contact with the media are made of PEEK thermoplastic and stainless steel. At a maximum pressure of 16 bar, the process temperature can rise up to 140°C for up to half an hour. A 3A-approval certifies that the device complies with the specific FDA and EHEDG requirements. If a measurement only requires part of the rod length, then push buttons in the measuring head allow programming of the span over any section of the rod, with the smallest selectable measuring range being 50mm.

Another crucial factor for use of the LSP in the beer bottling machine is that it can also be used in pressurised tanks. Like all carbonated beverages, beer is bottled under pressure to avoid foaming and loss of carbonic acid. In fact, it is impossible to totally exclude a certain amount of foaming, but even then the LSP reliably measures the actual level of the liquid because its potentiometric measuring system does not detect foam at all, which ensures that foam does not affect the result.

Average of four measurements

Since the tank above the filler is constantly rotating and, therefore, the content is always moving, the level is measured at four points. For this purpose, four LSP sensors were mounted on top of the tank. The average value calculated from the individual measurements indicates the actual level very precisely. A PID (proportional integral derivative) controller takes the measurement of the LSP sensors and makes sure enough beer is constantly being refilled from the brew house in order to keep the tank level of the filling machines constant. This is necessary to guarantee a correct and complete filling of the bottles.

After the test run on the first machine, Carlsberg was satisfied with the new level measurement, and subsequently replaced the measuring devices in other filling machines with LSP sensors. The LSP sensor’s convincing price-performance ratio was in its favour as one LSP costs only a quarter of what Carlsberg would have had to pay for the replacement of a defective probe of the old system. “It’s a low-priced solution that provides a reliable measuring result and is easy to install and maintain,” says Pallesen.