Chemical Technology July 2015

Real measurement benefits from VEGA’s ceramic pressure transmitters

VEGA’s dry, oil-free ceramic cell technology CERTEC ® is a real alternative for a wide range of measurements, offering major benefits to users.

A s well as improved performance, excellent accuracy, linearity and process hygiene, dry ceramic cells are generally far more robust than traditional oil-filled pressure systems. One of the main issues is that oil-filled transmitter membranes/diaphragms on a pressure sensor are necessarily very delicate by design in order to transmit the pressure, which means they can be easily damaged or compromised. Careful consideration must also be given to the type of fill-oil used for the application. There are many variants, all designed to minimise any contamination should they rupture, but of course, most end users would rather not risk this occurrence at all! Often, to accommodate the various types of oil fills that are needed on a typical plant, multiple oil filled types need to be carried as spares. The VEGABAR series 80 with CERTEC ® dry ceramic sen- sors can be all-rounders across site, as well as being the optimumchoice for each application. They can operatemuch longer in process conditions where traditional filled pressure cells will require regular recalibration, or even replacement on a routine basis. What are ceramic pressure sensors and are they all the same? The ceramic substrate material is made from a highly compressed powder with a binding material. The ceramic itself is extremely durable and hard, based on aluminium oxide, a substance used for many applications in industry. But not all ceramics are structurally the same; the finer and purer ceramic materials produce the highest performance. The best materials are sapphire ceramic based. A dense crystal design provides excellent mechanical strength, corrosion resistance and reliable long term stability. In

these materials, the characteristic surface finish is also very smooth at <0,7 µ m Ra, also making it suitable for use in the most demanding of hygienic applications, including those regulated by FDA and other chemical requirements. Chemical resistance Ceramic as a substance is, of course, resistant to many chemicals with the finer, higher purity ceramics offering the best all round resistance of all, although some care has to be taken with some alkalis and acids. A competent supplier will offer comprehensive resistance lists and advice on this. In general, with the right elastomer seal, eg, Kalrez ® , they can be fully process compatible with some fairly aggres- sive and corrosive media. Some combinations can even have all ceramic/polymer based mountings, threads and flanges providing all non-metallic wetted parts, for excellent resistance to aggressive process environments. These op- tions mean ceramic cells can save costs compared to large flanged, oil filled chemical and capillary seals using special The majority of measurements are ‘gauge’ pressure, which means they have to be referenced and breathe to the at- mosphere. A gauge pressure dry cell will always have the ability to take in moisture from the environment around it. The air will inevitably have moisture in it and, in humid areas (which encourage moisture formation on any temperature differentiated surface - even inside the sensor), microscopic droplets can even form on the sensitive electronics of any measuring cell, thus causing micro short circuits resulting in drift or an offset. This can materialise in days, weeks and often expensive coatings or alloys. Condensation resistance

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Chemical Technology • July 2015