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Explosion Protection in Process Automation
Joerg Fitzek, Managing Director, R. Stahl (P) Ltd. Some of the process industry applications incorporate use of wireless transmission for data transfer from technically challenged locations. Although structures combining hard-wired and wireless communication will dominate the field for the foreseeable future, users will be able to benefit greatly specifically from new, technologically mature and increasingly economically attractive wireless solutions within the next years.

In some process industry applications, wireless data transfer has become part of the daily routine, extending beyond voice communication via radio and mobile phones. Operating and visualization data can often be wirelessly transferred from and to mobile HMI units and notebooks as well. Additionally, plant monitoring cameras are increasingly integrated into wireless networks, especially when they are fitted into existing plants where laying cables would be too costly and/or too much of a technical challenge. The core area of process automation, however, is still dominated by hard-wired components which exchange data via point-to-point connections, fieldbus networks and remote I/O systems. Depending on the type, dimension and topology of a process plant, the greater flexibility of wireless communication may also be of interest for these devices: wireless components are easier to access, meet increased mobility requirements and can facilitate or outright enable the acquisition of additional data for the optimization of production processes. Although structures combining hard-wired and wireless communication will dominate the field for the foreseeable future, users will be able to benefit greatly specifically from new, technologically mature and increasingly economically attractive wireless solutions within the next years. The proven I/O systems, for example, are currently being upgraded for wireless applications. The trend towards so-called WIOs is propelled e.g. by the Fieldbus Foundationís working group dedicated to this technology. Many areas in process plants, however, must be equipped with explosion protected technology. Radioenabled units, e.g. in wireless LANs, must also meet these requirements. Several recent approaches take on a critical point in radio network data transmission: the antennas. Proper antenna breakouts for devices in encapsulated housings, which implement Ex ib (intrinsically safe) type protection and thus allow for communication via an intrinsically safe HF signal, are currently in development. Up to now, explosion protected antennas have been used in zone 1 applications. However, there is only a limited range of such antennas. Since antennas are essential for the performance of radio connections, users would profit considerably from access to the full spectrum of standard antennas. Explosion protection requirements not only stipulate strict demands for WLAN systems, but must also be observed in other wireless data transfer technologies, such as GPRS connections via mobile phone networks. Therefore, GPRS modems with intrinsically safe technology are available e.g. for machine monitoring devices with wireless data transfer functions.

The Wireless Future
According to a study published in 2008 by the market research company ARC Advisory Group, wireless technology suppliers expect a future yearly growth of approx. 30% compared with each previous year in the market for wireless automation. In 2007, the total market volume was less than 300 million US dollars. According the ARC prognosis, it will considerably exceed one billion dollars by 2012. Existing application fields and technologies ranging from RFID labels to wireless LAN will be expanded and users will be offered more comfort, flexibility and new options. This applies e.g. to remote diagnosis and remote maintenance systems and radioconnected portable devices Ė apart from these, wearables will become common for some purposes. Thanks to wireless technology, increasingly precise people tracking and asset tracking systems for operating and service personnel and equipment, intralogistics vehicles and other resources will be established step by step. Robust meshed self-healing networks, as described by the wireless HART and ISA SP 100.11a standards, ensure that wireless data communication becomes increasingly reliable in all fields, including process automation components in hazardous areas. Even if it seems unthinkable now, wireless communication will push forward into safety-oriented applications. This technology will thus probably develop into an alternative to and extension for wireline networks for more and more components and systems in process plants.

GSM/GPRS Data Transfer in Process Automation The General Packet Radio Service (GPRS) is a proven communication standard which enables the transfer of data packets via mobile radio networks. It is, for example, often used to access the internet from notebooks on the road, and is the base for the popular Blackberry technology. In process industry applications, GPRS can be used for remote maintenance and remote monitoring functions in pumping stations, remote tank farms, centrifuges, compressors and other machines. Via GPRS connections, field devices and mobile computers can be integrated into system solutions, which enables them to access the same company-wide MES and ERP databases as process control technology, work stations and remote PCs located elsewhere in the plant and office IT network. This gives technicians easy and immediate on-site access to centrally managed plans, operating manuals, ATEX certificates etc., allowing them to directly confirm service tasks and generate live documentation.

GPRS is an alternative to the widespread WLAN standard and offers the advantage of a dedicated frequency range, which means that less interferences occur in the radio connection than in the ISM bands used by WLAN. Additionally, GPRS is based on the existing, fully developed GSM mobile radio networks. The standard therefore requires no investments into a company-owned network, providing a communication path independent from the companyís or locationís existing IT infrastructure. Apart from direct integration of data communication via GPRS, the technology can also be used for further functions. Possible additional services include alerting responsible staff via text messages or emails in case of malfunctions.

However, some restrictions and weak points must be taken into account. GPRS is, for instance, not yet universally available worldwide. In some countries, like Japan and Korea, GPRS coverage cannot be expected for the future since local mobile radio networks do not use the GSM standard. With a net bandwidth of 50 kBit/s, GPRS is also considerably slower than WLAN. A more extensive worldwide coverage and a better bandwidth will not be achieved until the UMTS service is extended. Additionally, GPRS data transfer charges for each network node currently amount to 10 to 30 Euros per month. These costs have at least considerably decreased within the last years, which makes GPRS solutions attractive for more and more applications. And a final obstacle lies in the fact that GPRS modems for use in hazardous areas must be designed in a way that reliably ensures explosion protection. Zone 1 models, for example, typically have GSM antennas connected via an Ex i interface, and also feature an intrinsically safe Ex i SIM card slot.

Standards and Requirements for wireless operation in hazardous areas Radio emissions that penetrate metallic objects or are induced into electronic circuits with inadequate EMC protection can, in principle, lead to heating and sparking. Because of this danger, the IEC 60079-0 2008 and the upcoming EN 60079-0 for continuous high frequency sources limit the maximum permitted transmitting power in wireless networks, if these are operated in hazardous areas. The location of a node in zone 0, 1 or 2 is irrelevant for the limit, which lies between 6 Watts and (in atmospheres with group IIC explosive gases such as hydrogen or acetylen) 2 Watts emitted power. WLAN standard radio units fall well below these limits, at least during regular operation. Especially in WLAN installations, IT departments usually require the use of standard WLAN units for safe areas. Most standard radio components, however, are not certified for installation in zone 1. A common solution is the installation of conventional radio technology in housings complying with the Ex d protection type (flameproof enclosure) or similar protection types. Such encapsulated housings are mostly made from metal, which would strongly shield the electromagnetic radiation of an antenna installed within. Therefore, users have mostly employed external antennas, which were required to comply with ATEX standards. This was often achieved by implementing an Ex e-type design (increased safety). Special antenna breakouts, which will enable the safe use of any standard antenna with wireless devices thanks to Ex ib-type protection (intrinsically safe), will not be available until some time.

Explosion protection know-how for wireless systems Wireless communication networks provide great flexibility in process automation applications. In plants with hazardous areas, however, their use requires safe technology. The range of available components in suitable protection types is constantly changing, and new approaches can render old restrictions such as the need for ATEX-certified antennas obsolete. In addition, the field of possibly suitable radio standards for process industry applications continues to be in a state of change. It is therefore advisable to seek advice from specialized suppliers for the planning and application-specific design of wireless networks. Users are thus guaranteed to find a stateof- the-art solution that gives them maximum benefit and comfort.