Measurement Technology for Any Challenge

In the food industry, the improved visibility of all process steps goes hand in hand with the sensors that are used. But finding the optimal sensor can be a challenge for producers. This is also the case at Froneri's Goldach site in Switzerland. The company produces a range of ice creams from well-known licensors here. During the low season, up to 50 tonnes of ice cream are produced daily, which almost doubles in the high season. The prerequisite for producing such quantities is efficient production. As a result, Froneri replaced the floats in the mixing tanks with two Baumer sensors to monitor the fill level as an optimisation measure: The PBMN Flush pressure sensor and CleverLevel LBFS level sensor are used here. Serkan Sezgin, Automation Supervisor at Froneri and responsible for optimising processes, deliberately chose a dual solution consisting of pressure and level sensors because: "The use of an additional pressure sensor was Baumer's idea. Thanks to the precise sensors and the double protection, we were able to significantly minimise downtimes." The CleverLevel LBFS monitors the fill level in real time and reports when the tank is running low. At the same time, the sensor detects which medium is in the tank and verifies whether the correct mixture is being used for the type of ice cream to be produced. The additional PBMN Flush sensor provides an even more accurate level reading thanks to precise pressure measurement over the entire temperature range, ensuring that monitoring is always guaranteed. The level monitoring using this type of process transmitter is based on the hydrostatic measurement method. The transmitter is installed at or near the bottom of the tank and measures the pressure there. A downstream logic then calculates the level in the tank based on this value and the density. However, a requirement for a measurement of this kind is that the container is vented.

The example shows: Before selecting the specific sensors and measuring instruments, first the most suitable measuring method must be determined. Whether it is exposed to moisture, high process and cleaning temperatures, aggressive media and cleaning pressures of up to 100 bar – the sensor technology must function without interference, especially when it comes to processes such as ultra-high temperature (UHT) treatment. They are used to destroy unwanted micro-organisms and at the same time to maintain the physical and chemical properties of the respective product in order to increase its shelf life.

To control the heat transfer, instrumentation is required for measuring the temperature, flow rate and pressure. In view of temperatures of up to 135 degrees Celsius and other challenging conditions such as aggressive cleaning agents, front-flush pressure transmitters are often used for pressure monitoring in a UHT plant. Their diaphragms withstand normal process conditions for a long time without restriction. However, constant exposure to 24-hour operation with the appropriate cleaning procedures can wear out and damage even a solid diaphragm, for example as a result of violent pressure surges (water hammer effect). Pressure-transmitting fluid can seep into the process through the crack or perforation. Conversely, product gets behind the diaphragm, remains there and forms a source of germs.

This worst-case scenario can be avoided with the WIKA DMSU21SA pressure transmitter thanks to its integrated diaphragm monitoring. The measuring system works with a welded double diaphragm with an evacuated space in between. If the process-side diaphragm is damaged, the vacuum is lost and the monitoring device (pressure switch) triggers an alarm signal. The manufacturer is informed of the incident at the same time and can initiate countermeasures immediately. The second diaphragm keeps the process safely closed until the damage has been repaired. The DMSU21SA can easily be put into operation using the plug-and-play principle. The measuring system communicates using the HART protocol and can therefore also be integrated into digitalised structures.

Consistent product quality, plant safety, cost-effectiveness – these are also important aspects when selecting sensors to determine the contents of pipes. A comprehensive selection of different measuring principles is available to food producers for accurately monitoring their fluid flows. These include turbidity sensors, conductivity sensors and mass flowmeters. Another method is based on measuring the dielectric constant of the liquid, i.e. its ability to hold an electrical charge. A sensor is used for this purpose, which identifies the liquid moving through the pipe by inducing a high-frequency electromagnetic field. Different liquids have different dielectric strengths, which makes it possible to distinguish them from one another. For Matti Järveläinen, this fourth method offers tangible advantages, especially in milk-processing operations.

"Flowmeters have a very low accuracy. Turbidity sensors, on the other hand, cannot distinguish transparent liquids, such as concentrated whey, from water and become clogged by thick liquids such as cream," says the CEO of Collo, a Finnish manufacturer of liquid analysis systems. He gives another example in which classic conductivity sensors reach their limits: "The electrical conductivity of milk-based products is close to that of water, which results in low sensitivity when detecting product interfaces," says Järveläinen. Hundreds of litres of product are often lost as the liquid product is displaced by water as it is forced from one processing step to the next.

Often, up to one percent of milk production is wasted between product batches. The losses at the extrusion points, of which there may be hundreds, add up by the end of the process. However, with the right measurement technology, the start of the next batch can be exactly determined. Collo sensors were therefore recently installed at four points in the milk receiving area of a dairy that processes 243 million litres of raw milk a year. The factory had previously used flowmeters to control the extrusion processes. Due to their low accuracy, the timing resulted in losses of 600,000 litres per year. With the higher accuracy of Collo dielectric sensors, the losses were reduced to 5,000 litres – a reduction of more than 99 per cent! But that's not all. "With Collo's versatile technology, we can also help to reduce water consumption in the plants, an area of significant interest to our customers and legislators alike," Järveläinen concludes.