Ceramic sensors ideal for food processing plants

With 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.

Making three from five
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.

READ MORE: How Vega has led the way in radar level transmitters

Finally, there is the classic Vegabar 81 with chemical seal, which is deployed when high temperature and/or chemical resistance is required.

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 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.

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.

Nothing can shock them
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 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 “seven-league 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.

No such thing as impossible
CERTEC is the only ceramic measuring cell on the market that allows absolute front-flush mounting, as its radial seal is recessed and protected from the medium.

It can bring this advantage to bear especially in abrasive applications. Build-up is also said to be a thing of the past. This is because the sensor is capable of cleaning itself in the flowing medium.

Safe, reliable operation
Another key topic is the second line of defence. This feature is indispensable, for example, in phosgene applications, in order to prevent the toxic medium from penetrating into the terminal compartment and endangering people and the environment. At present, customers have to resort to encapsulated absolute pressure transmitters with special chemical seal assembly.

Vegabar 82/83 is a fully welded sensor module with a second line of defence, which, in combination with climate compensated electronics, can reliably and accurately measure relative pressure even in such applications.

This unique innovation allows high measurement accuracy to be achieved also with small process fittings.

Reliable and stable measurement data is one of the most important features of a pressure measurement setup.

Vegabar 80 with Safe Integrity Level (SIL) differs from a standard instrument both in hardware and in software.

Vegabar 80 with SIL is a separate instrument developed according to the guidelines of IEC 61508. In single-channel systems, Vegabar 80 can be implemented up to SIL2, and in homogeneously redundant systems even up to SIL3 via the software.

Electronic differential pressure
An innovative software and hardware concept makes it possible to combine any two instruments from the Vegabar 80 family, whether all-rounder, high-pressure or high-temperature sensor, into an electronic differential pressure system. What does this mean in practice?

An example is that a customer only has to take a Vegabar 82, a standard instrument that he or she has in stock anyway, order an additional sensor, select the “slave” electronics version and connect them together.

That is all that is needed to be done. Users benefit from simple selection, identical adjustment and operation as well as simplified stocking.

There are many other features of the electronic differential pressure system.

This includes there are no oil-filled capillary tubes that need to be insulated – usually at great cost – to avoid environmental influences, such as temperature changes or strong vibration and the resulting measurement errors. And oil-filled chemical seal assemblies are usually expensive.

If a customer adds everything up, an electronic differential pressure system is not only a simple solution but also a more cost-effective one for their business.

Vega is the only supplier on the market that has a solution with ceramic sensors in its portfolio.