Using Pressure Transmitters with Ceramic Measuring Cell

When the loads are enormous and the demands on the measuring cell are high, there are 7 good reasons for using pressure transmitters with ceramic measuring cells.

The temperature shock-resistant ceramic CERTEC^® measuring cell brings new application possibilities.

Pressure measurement technology in the process industry is one of the most robust and versatile measuring concepts applied for level and pressure because of its high dependability and accuracy.

It presents its abilities, particularly when things get challenging. For example, in hazardous or hygienic areas, chemically aggressive media, applications with quick changes in temperature, extreme temperatures and pressures, or heavy condensation.

Thermal shock or temperature resistance is a frequent challenge for several pressure transmitters with ceramic measuring cells. This is not the case in VEGA's CERTEC^® measuring cell because its unique ability for compensation offers an accurate antidote to this specific limitation.

This problem is solved by the use of an extra temperature sensor circuit towards the rear of the diaphragm, which can discern even the smallest variation in temperature. This temperature value can additionally be utilized as a second output.

The ceramic-capacitive CERTEC^® measuring cell, created from exceptional sapphire ceramic, has even more uses: it is one of the most resilient and robust pressure-measuring cells ever manufactured.

When the loads are substantial and the demands on the measuring cell are equally great, there are seven reasons that it is beneficial to employ pressure transmitters with ceramic measuring cells.

1. Abrasion Resistant

In process environments that are particularly aggressive, metallic measuring cells can easily cease to function due to various stresses. For example, high temperatures, corrosion, impact, friction, and abrasion can all be demanding.

It is a different story with measuring cells produced with CERTEC^® ceramic. They are incredibly hard and resistant to abrasion, along with being 10 times harder than stainless steel.

From challenging production methods such as sand-laden media or slurry containing metallic debris, whenever extreme chemical, temperature, or pressure resistance is required from the measurement technology used, CERTEC^® ceramic is the only choice, as it functions under these environments with ease.

Even mechanical cleaning with a brush or strong cleaning agents does not influence the measuring cell.

2. Minimal Drift = High Long-Term Stability

Pressure transmitters with ceramic CERTEC^® measuring cells provide dependable measuring results because they are essentially free from drift. They far outperform metallic measuring cells when it comes to stability over the long-term.

Drift is an occurrence that steadily develops within pressure measuring systems. In pressure transmitters with metallic measuring cells, long-term drift is a frequent phenomenon because of material aging.

The thin metal diaphragm is exhausted after a specific period of use and no longer restores precisely to the initial zero points. It begins to 'drift' farther away over time. The user then must perform drift compensation in the form of a recalibration.

Ceramic CERTEC^® measuring cells function in a way that is virtually free from drift. The range of motion, hardness, and limited yet precise flexibility of the ceramic material mean that they present essentially no drift or material fatigue.

The self-monitoring ceramic measuring cells increase the cycles of recalibration significantly for that reason.

3. Oil Free

Ceramic measuring cells are dry measuring cells that function with no requirement for oil to be used as a pressure-transmitting medium. This separates them from metallic measuring cells where the pressure is transferred by internal oil to reach the sensor element indirectly.

There is always the possible risk that oil could covertly enter the process when it is used. For example, if a rupture in a membrane causes a leakage, there are related consequences to the end products.

Sensors that are free from oil are being increasingly employed because there is a constant risk of contamination in pressurized and closed manufacturing procedures. Oil-filled measuring systems combined with high temperatures are unsuitable for vacuum applications.

Pressure transmitters with ceramic CERTEC^® measuring cells are engineered to avoid these risks completely. Pressure acts specifically on the sensing diaphragm, which means transmission oil is not required.

This technology meets the need for processes that are oil-free and fully eliminates the danger of whole batches becoming contaminated.

When it comes to zero-point shift, users are guaranteed to be on the safe side. When oil is not used, no air can get trapped within the system, which eliminates the cause of drift.

4. Compatibility For Many Process Media

Two main choices are available for measurement applications in processes that are highly corrosive. These are ceramics or special materials that are commonly very expensive. Measuring cells manufactured with CERTEC^® ceramic reliably avoids interaction with the process media.

Unlike metallic measuring cells, they display a considerably greater chemical resistance to several aggressive gases and liquids. They are suitable for the majority of process media.

In contrast to metal, ceramics are perfect for various applications: from highly acidic liquids to saltwater. Expensive alternatives, for example, measuring cells coated with tantalum, are only necessary for very extreme environments.

5. High Overload Resistance

Ceramic measuring cells cope with extreme changes in load, attaining up to 200 times the overload resistance of metallic cells. This is mostly because of the transmitter design.

A typical measuring cell comprises a ceramic body and a diaphragm. The ceramic diaphragm essentially stops against the bigger base body if very high pressure is applied. The outcome is an exceptional overload capacity.

6. Small Measuring Ranges

Even very small pressure variations, of only a few millibars, are reliably detected using ceramic cells.

Special oil is required as a transmission medium for metallic diaphragm cells to distinguish changes in pressure. This functional concept is the same regardless of the measuring ranges being large or small (just a few millibars).

With very small measuring ranges, a suitably large diaphragm is required to dependably determine the tiny pressure change.

Ceramic CERTEC^® measuring cells do not have this issue as they can handle measuring small ranges. Since they do not need transmission oil, they are highly compact and can be fixed with small process fittings.

7. No Hydrogen Diffusion

Hydrogen can even completely permeate metal, given its small atomic size. The thinner the diaphragm, the quicker this process occurs.

If hydrogen diffuses through and into the diaphragm, it reacts with the transmission oil behind the metallic diaphragm. This creates deposits of hydrogen that result in irreversible changes in measurement performance.

The situation is entirely different from ceramic measuring cells. Even hydrogen fails to diffuse through them and negatively impact their service life. Their advantages regarding hydrogen permeability can be added to the list of benefits of ceramic measuring cells.

Conclusion

Since VEGA has been providing a ceramic measuring cell along with its flexible and highly reliable VEGABAR pressure transmitter, withstanding thermal shock and having superior overload resistance, the arguments for employing metallic measuring cells as standard have become less persuasive.

Even in hygienic applications, commonly the domain of flush-mounted, metallic diaphragms, the pioneering CERTEC^® ceramic has many advantages. It is very chemically resistant, copes with extreme temperatures, and is so hardy that even abrasive, solid particles in liquids cannot damage it.

Ceramic pressure transmitters are produced from one of the most resistant and stable materials in the world.

There are seven persuasive arguments for their use. It is resistant to abrasion, is essentially drift-free, filling oil is not required, it is suitable with the majority of process media, it offers long-term stability, it is resistant from overload, adequate for very small measuring ranges and, last but not least, superior regarding hydrogen permeability.

In any case, they open up limitless and well-suited areas of application for users.

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.