Bangers, burgers and buses

It's that time of year when engineers like to quit the office and get their hands dirty with some back-to-basics engineering such as temperature control, materials handling, sealing, turning, and fine-tuning the carbon-content. Yes, it's barbecue time! But with the widespread adoption of modern technology and the trend away from traditional charcoal and matches, there is one question that springs to mind: why is it that gas barbecues are sometimes so reluctant to light, even when there is a strong smell of gas and a clearly visible spark from the igniter? It's almost enough to make you wonder what all the fuss is about in hazardous areas.

But intrinsic safety is a serious business for many engineers in the process industry, as well as those working in areas where there are paints, solvents, combustible powders and other similarly hazardous substances. Despite - and sometimes because of - the operational difficulties imposed by the hazardous area, there is an increasing demand for remote, automated control of the equipment therein.

Control implies the need to handle inputs from sensors and outputs to actuators. Gathering data from sensors in hazardous areas is not particularly onerous, thanks to the suitability of low-power fieldbuses and simple two-wire data links for conveying digital and analogue signals. But controlling equipment such as valve actuators and positioners can pose rather more of a problem due to the power requirements. Although low-power solenoid-operated pilot valves can be used in hazardous areas, plant operators are still limited to using just one or two on a single fieldbus loop because of the solenoids' power rating (likely to be several Watts per solenoid).

Throughout the world's process industries there has been much discussion of how to solve this problem. And the good news is that there is now a way in which multiple valve actuators and positioners can be directly controlled via a fieldbus. Piezo-pneumatics are very small consumers of energy (around 0.014mW) and, once they have changed state, they require no energy to maintain the new position. Using specially-designed pilot-operated valves, large process valves can easily be controlled in large numbers, all via a fieldbus.

Hoerbiger-Origa has been busy developing the piezo-pneumatic elements for use with valve positioners from Heap and Partners and pilot-operated spool valves from RGS Electro-Pneumatics. All three of these companies firmly believe that the process industry is now ready to make full use of fieldbus systems, and the new products are a major step in the right direction.

Thanks to the ultra-low power consumption of the Hoerbiger-Origa piezo operators, there is simply insufficient energy available to maintain a spark, so the devices are inherently intrinsically safe. At the heart of the operator is a simple three-way, two-position valve in which the airflow is switched by a piezo element. Moreover, by controlling the voltage to the piezo element, it is possible to achieve intermediate positions, so the valve can operate in a proportional mode to provide an analogue pressure output.

Although it is unlikely that many process plant operators will rip out their existing valve actuator and positioner control systems to install the new technology, it is quite possible that piezo-operated units will start to replace conventional devices that fail or are removed for servicing. Extensions or modifications could also benefit, and all-new installations stand to gain the most. Piezo technology could be about to make a big difference to the process industries.

The only irony in this is that a somewhat different application of piezo-electric technology is what makes the gas barbecue igniter work. Needless to say, the piezo devices approved for use in intrinsically safe environments are certainly not capable of lighting any barbecues.