Arla dairy standardises level measuring

Slagelse, Denmark - With around 8.5 billion litres inflow of raw milk and an annual turnover of 6 billion Euros, Arla Foods is Europe’s biggest dairy corporate. As process control plays an important role in the efficient and flexible dairy processing routines, the measuring devices controlling these processes have to meet highest demands.

One of Arla's 40 manufacturing facilities is located in Slagelse on the Danish island of Zealand, where 400 people are employed. The processing of 245 million litres milk per year makes this site not only the largest Danish dairy for fresh milk, butter, yoghurt and desserts, but one of the biggest dairies for organic products worldwide.

Over the past years, Arla has been expanding their production facility in Slagelse. In the course of that, Europe’s biggest dairy installed sensors from Swiss company Baumer for the level process monitoring and started the gradual standardisation of level measuring devices throughout the entire facility. 

Arla has employed Baumer devices for their pressure, temperature and level measuring for over 15 year. In 2003, the dairy formalised a preferred supplier agreement with the Danish Baumer subsidiary.

Point level measurement is one of the most common applications in the food and beverage industry. Regardless of tank size and type or the cleaning method, the equipment has to be designed for highest possible food safety standards. Therefore, only FDA-approved materials can be used, whereas at the same time, the equipment has to be easy to clean.

The level switch LSM 020.1, installed in the new CIP unit in Slagelse, is also used in other production processes like for example the filling unit. The hygienic measuring device is available with different 3A approved process connections. It fulfils the FDA demands and follows the EHEDG guidelines regarding design, materials and finishing.

The LSM is especially suitable for CIP and SIP measurements. Thanks to integrated electronics and no moving parts, the switch is virtually maintenance-free. All wetted parts are made of acid-proof stainless steel or PEEK thermoplastic respectively. It measures the level of liquids, viscous fluids and even some dry media regardless of its mounting position and without being influenced by foam, bubbles, lumps or vibrations. An LED level indicator shows the detection of liquid. The precise switching point is reached without calibration. The LSM’s process temperature ranges from -20 to 85°C.

Inserted into a metal tank, the LSM sends out an electro-magnetic wave, and its reflection is measured through the tank wall. As soon as the media reaches the sensor tip, the reflection of the electromagnetic field changes depending on the dielectric value of the media. Again, the LSM switch measures this change through the tank wall and opens or closes respectively. The switch can be electrically installed as normally opened or normally closed; a jumper on the electronics enables the setting of the sensitivity and response time.

Continuous Level Measurement with LSP

However, some processes require the precise level measurement of the tank content, for instance if liquids are to be dosed or mixed, or if adjustments, consumption or leakage are to be monitored. With a continuous measurement, the level is measured via an analogue output signal enabling an accurate monitoring of the tank content. In Arla’s factory, this is necessary in the pasteurisation process where the level is continuously measured with the LSP 050.1 in a 100-litre tank.

The level sensor LSP 05x can be applied with all media that have a minimum conductivity of 1mS/cm. The measuring method is based on a low resistive measuring rod which dips into a conductive liquid and sends a high frequent current to the tank wall. The voltage drop between the rod and the tank wall is measured in proportion to the length of the wetted part of the rod and its total length. This output voltage is proportional to the tank level which is indicated precisely by the 4 … 20 mA output signal.

The sensor is also suitable for applications with pasty or strong adhesive media, such as yoghurt or rice pudding products. Especially in pressurised tanks where level measurements are usually carried out by more expensive instruments like load cells or differential pressure transmitters, the LSP offers great advantages. On the media side, a maximum pressure of 16 bar and a permanent temperature from -20 up to 140°C are possible. Due to the high temperature limit, the device is well suitable for CIP and SIP processes.

All parts in direct contact with the media are made of stainless steel or PEEK. The Teach-in procedure allows programming of the minimum and maximum level at any interval from 50 mm upwards. The maximum rod length is 3 meters. The excellent measuring accuracy of ± 0.1 per cent of the respective rod length and the short response time of Tm=10 ms enable a precise level control. A stabilised voltage supply of 18 to 36 VDC at 200 mA guarantees secure operation.