Compensating for Temperature Shocks Using Pressure Transmitters with Wear-Free Ceramic Measuring Cells

The cooking and canning of food is an old, but very reliable method of preservation. A short period of heating food is enough to kill any bacteria and prolong shelf life. (Image credit: monticello/Shutterstock)

What Grandma Already Knows

Although an old method, cooking and canning food remains an extremely reliable preservation method. Bacteria can be killed and a product’s shelf-life prolonged by just a short period of heating. Many years ago, this simple principle was mastered by our grandparents.

For a state-of-the-art production system equipped with precise filling technology and the extremely accurate weighing and portioning of vegetable soups, what problems could this process pose?

A Systematic Error

For one particular canned food manufacturer, it was the measured values of a pressure transmitter that didn’t always make sense. At one step during the production of clear vegetable soups, within seconds the level measurement continuously dropped to a value which was abnormally low.

A quick assessment convinced them that the problem lay with random deviations in the sensor. However, upon further investigation, a systematic error was revealed. This error recurred continuously, whenever significant frozen vegetable quantities were added into the boiling water.

The “Clicking Toy Frog” Effect

A temperature shock triggered this. Food manufacturers have long preferred to use pressure transmitters with ceramic measuring cells because of their high mechanical robustness. However in its standard construction, this wear-free technology based on a virtually fatigue-proof material, is also sensitive to extreme, spontaneous temperature fluctuations.

The impact which boiling water has on deep-frozen vegetables initiates a reaction which is similar to the quenching of a boiled egg. This subjected the sensor’s ceramic membrane to extreme shock, leading it to expand marginally on contact with the heat. This caused it to contort – similar to a “clicking toy frog” – against the ceramic layer behind it.

Following extreme temperature jumps such as these, it can be a number of minutes before conventional ceramic measuring cells can reliably in-contort and once more output sensible values.

A Strong Duo for Hygienic Applications

VEGA is offering the very first ceramic measuring cell which is capable of handling temperatures of 150 °C with 200 times overload resistance, in the form of the VEGABAR 82 pressure transmitter.

This innovative pressure transmitter provides the best of both worlds, particularly in terms of hygienic applications. This is because its chemically resistant CERTEC® high-performance ceramic material can withstand extreme temperatures, and is so robust that it cannot even be damaged by abrasive particles in liquids – including frozen vegetables in clear soup.

However, VEGABAR 82 can do so much more. It compensates easily for the vast temperature fluctuations which occur during CIP or SIP cleaning cycles, or during pasteurization.

This is made possible by an additional temperature sensor which is built into the measuring cell, which complements the standard temperature sensor on the cell body by measuring and giving out a rapid reaction compensating value.

It is situated against the diaphragm’s rear face in an exposed, albeit completely flush position within the glass seam. In this position, directly behind the ceramic diaphragm, it does not miss even minor temperature changes.

Courtesy of a special algorithm which utilizes the difference between the two measurements, the ceramic sensor can totally compensate for temperature shocks.

Clean Measuring Methods from the Clean Room

In the context of food, consumers always expect well-selected and flawless ingredients. Equally important for consumer confidence is the manufacturing process, in which each component plays a vital role.

The whole production chain is ultimately only as strong as its weakest part. VEGA’s special clean rooms are where the high quality of the ceramic-capacitive CERTEC® measuring cells begin.

Special access and air circulation precautions in these rooms ensure that the number of particles does not exceed 352, and they are less than 0.5 µm per cubic meter in size. On average, that is ten-thousand times lower than our cleanest living quarters.

Using thick film technology in this entirely dust-free environment, the CERTEC® measuring cells are printed and fired. The process makes sure that the connection of the glass solder -which links the measuring cell’s base body and the ceramic diaphragm – achieves a precise gap measuring less than the breadth of a hair, with a tolerance of +/-1 μm.

Ceramic Sensors that Follow the Food Trend

As customers come first, and they are increasingly demanding more natural foods, the food industry is faced with the challenge of locating alternative processing methods which do not require the use of artificial preservatives.

Methods for increasing shelf-life which are both traditional and innovative include everyday processes like freezing and pasteurization.

Although these methods may sound familiar, they are used differently nowadays. At present, both processes tread a fine line between freshness and a long shelf-life, while simultaneously preserving vitamins. Consequently, they are being used increasingly frequently.

This pasteurization method typically involves heating the product to 75 °C for a few seconds, while freezing means shock or flash freezing down to as low as -30 °C within just seconds.

The increasing requirements on temperature robustness are perfectly met by VEGABAR 82 pressure transmitters with CERTEC® ceramic cells, which also provide the basis for extremely accurate and reliable measurement. In combination with their high-performance ceramics’ extreme durability, this makes them practically unrivaled in the instrumentation industry.

This information has been sourced, reviewed and adapted from materials provided by VEGA Grieshaber KG.

For more information on this source, please visit VEGA Grieshaber KG.

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