TRANSMITTERS
Ceramic sensors ideal for food processing plants Vega’s range of process pressure transmitters tick many boxes when used in food and beverage manufacturing plants. Food & Beverage Industry News explains why.
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The biggest leaps in technology, however, are being experienced by the ceramic measuring cell CERTEC. Only a few suppliers have ceramic-capacitive cells in their portfolio, and fewer still have the know-how to produce them themselves. Eighty per cent of all units sold operate with ceramic sensors.
ith the introduction of the plics family almost 18 years ago, Vega turned the vision of simple, standardised measurement of level and pressure into reality. The Vegabar 80 series represents a systematic further development of the concept and the products. The clear structure of the new instrument series ensures easy selection when looking for the right instrument for a particular application. The new handling with “quick start” procedure allows fast, simple and reliable setup and commissioning. The integrated diagnostics system makes fast maintenance and servicing possible.
to produce them themselves. Eighty per cent of all units sold operate with ceramic sensors. In principle, both technologies can be used in the majority of applications. But the company is convinced that in many cases ceramic is the better technology, because it is more robust and durable.
Making three from five
Nothing can shock them
With the new Vegabar 80 series, all conceivable applications can be covered with only three process pressure transmitters. There is the all-rounder Vegabar 82 with ceramic measuring cell, which can cover 80 per cent of all applications. Then there is the Vegabar 83 with metallic measuring cell that is designed for high-pressure applications. Finally, there is the classic Vegabar 81 with chemical seal, which is deployed when high temperature and/or chemical resistance is required.
Ceramic measuring cells have many advantages, but also some weaknesses. For example, they are susceptible to thermal shock and moisture. Through intensive further development of CERTEC, both of these problems could be reduced or even eliminated altogether. Equipping Vegabar 82 with temperature-shock compensation resulted in a technological masterpiece. A patent for this worldwide innovation is awaiting approval. When sudden temperature changes occur, it can take several minutes before sensors with ceramic measuring cells begin delivering reliable readings again. Often, users do not know that a sensor is experiencing a temperature shock, which means it is transmitting incorrect values. With the ceramic measuring cell in Vegabar 80, customers can be sure that they are getting correct measurement data. Because now, even fast temperature changes cannot affect
Ceramic versus metallic A lot has happened in the development of both metallic and ceramic measuring cells in recent years. The biggest leaps in technology, however, are being experienced by the ceramic measuring cell CERTEC. Only a few suppliers have ceramiccapacitive cells in their portfolio, and fewer still have the know-how
48 Food&Beverage Industry News | October 2019 | www.foodmag.com.au
the pressure measurement. In addition to the usual temperature sensor on the backside of CERTEC, there is a second sensor in the glass joint directly behind the ceramic diaphragm – this sensor is mounted in a technically challenging process. Due to its exposed position, it doesn’t miss even the slightest temperature change. Any thermal shock is fully compensated by means of a sophisticated algorithm. A side benefit of the second sensor directly next to the process is a temperature measurement of high quality, with an accuracy of ± 2 K. Earlier versions of the measuring cell could also output a temperature signal. However, due to its slowness, the sensor was only suitable for storage tanks, which normally have a stable temperature. In many applications, installation of a separate temperature sensor can be eliminated.
Moisture? No problem The typical moisture sensitivity could also be lowered. The problem with the naked electrodes of capacitive system – ingressing dielectric fluid, such as water – changes the dielectric constant and the capacitance, and therefore the pressure reading. However, the instrument cannot distinguish the reason for the change in capacitance.
The solution? In the new instrument generation, Vega has applied a measurement and a reference capacitor and covered the entire surface of the measuring cell with a thin layer of glass. Due to the glass passivation, there is no longer any contact with the medium, which means the dielectric constant in the entire system changes – for both the measurement and the reference capacitances. A coefficient is then formed from the two values and then computationally balanced for the measuring result. Another special feature of the Vega ceramic is its high overload resistance of up to factor 200 – more than double what other ceramics are able to provide. Progress has also been made with regard to the temperature range. Until recently, 120°C was the limit with the standard version, but CERTEC can now withstand temperatures up to 130°C. These additional 10°C are especially interesting for the food and pharmaceutical industry because, in many cases, customers no longer have to buy the high-temperature version for their sterilisation processes. Application temperatures have increased in relatively small steps, but when it comes to extending the measuring ranges, Vega has put on a pair of proverbial “sevenleague boots”. Vegabar 82 has a tiny measuring range of only 25 mbar (previously 100 mbar). And that is without electronic turndown. The measuring range has also increased in the upward direction, from 60 to 100 bar. This has extended the application limits. Customers will be able to solve more applications with the standard Vegabar 82 sensor in the future.
