01 May 2009
Ideally, the sensors just disregard the foaming, as does the level switch LSM, controlled by electromagnetic waves, which only reacts after the actual filling capacity has been reached.
Foaming – a Challenge within Level Measurement
Although positively seen in many fields of daily life – just think of a hot bubbly bath or the tempting froth on a freshly tapped beer – foaming poses a challenge in the industry of process monitoring as for example in the brewing, fruit juice production or milk industry. Point level detection is one of the most common applications in the process industry, making use of a number of limit switches based on various technologies. The technologies’ suitability depends on the application and therefore the branch’s requirements. Highest hygienic standards have to be met especially in the pharmaceutical, food and beverage industry, where standards like 3A, EHEDG or FDA, certifying the devices’ hygienic capability regarding their construction, material and design, are essential.
During numerous processes of these fields, the foam forming on the surface of the level gauge would be detected by an ordinary level switch, which therefore would initiate even though the required capacity has not yet been reached. Baumer, an instrumentation specialist, offers a limit switch, LSM, designed for the use in hygienic processes. The company says the device’s jumper enables the adjustment of responsiveness and reaction time within the electronic system which allows an easy gating of froth in applications usually prone to foaming, e.g. the brewing industry. The sensor reacts after the actual capacity has been reached, in an effort to avoid error messages caused by false minimum / maximum level indication leading to facility downtimes during the production process.
Functional Principle: Electromagnetic Waves
The LSM sends out electromagnetic waves, undergoing a propagation delay because of the respective medium, which are then returned to the evaluation unit via the metallic tank wall or the metallic welded socket. When the medium reaches the sensor tip, the delay of the electromagnetic waves sent out changes depending on the media’s dielectric value. Since macro- to fine-pored foam possesses a smaller density than the fluid itself, it is often not recognised as detectable liquid. The switching function – whether open or closed – can be realised by changing the type of connection. The advantage of this measuring technology lies in the small conic socket extending into the medium. While with other methods, the device requires a bigger surface to which pasty or adhesive media can easily adhere causing faults, the media can hardly stick to the tiny, small-area adaptor.
A special 3A welded socket ensures the hygiene-approved integration into the process and offers the advantage of a lateral drilling showing any leakage due to abrasion of process fluids.
The device’s 3A standard is only valid in connection with a 3A complement – in this case the welded socket – and the correct mounting position. All components in contact with the media to be measured are made of acid-proof high-quality steel or PEEK thermoplastics and fulfil the FDA, 3A and EHEDG regulations. The device is available with various 3A-approved process connections.
The LSM measures the limit value of fluids (e.g. water, beer, milk), viscous and even various dry substances. It is also suitable for pharmaceutical applications as for example the level detection of ultra-pure water. Foaming, bubbling or lumping do not limit its functionality, neither do vibrations or vorticity. Since the mounting position does not affect its performance, the sensor can be installed sideways or at the bottom of a pipe as used for the protection in case of dry running.
The switching status can be programmed to normally open (NO) or normally closed (NC) with the process temperature ranging from -20 to 85°C. The level switch is also suitable for CIP or SIP processes causing short-term temperatures of up to 140°C. For the use in open or closed tanks, the device withstands a pressure of up to 16 bar. Since the LSM does not contain any moveable parts and its electronic unit is completely integrated, it is practically maintenance-free, allowing precise limit detection without the need of changing the switch-point.
Applications in the food industry
The hygiene-approved LSM models are used primarily in the food and beverage industry. In 2007, the Danish dairy Arla Foods expanded its production facility in Slagelse and now applies the LSM level switch in its filling unit as well as in other production lines. Baumer’s device is also applied for point level measuring in Arla’s new CIP unit, where LSM sensors detect the return tank’s top, medium and bottom level.
When expanding the production plant in South Wales, the British supplier “The Serious Food Company“ standardised its process control measuring equipment and has been deploying numerous Baumer products since then. The LSM is used for the level measurement in various applications (top, sideways, bottom of tank).
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