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78 Spring 2019 AUMA's SIMA master station, for example, avoids limitations on cable length that may hamper standard fi eldbus systems. The master station allows rings up to 296 km long and containing up to 247 actuators. Built-in redundancy in the fi eldbus communication and hot-standby confi gurations further enhance data transmission reliability. The use of open fi eldbus standards not only gives the SIMA excellent performance but also ensures long-term future compatibility, in contrast to proprietary communication protocols. Case study 2: Shell Oman tank farm AUMA has supplied 74 electric valve actuators with Modbus RTU communications and a SIMA master station control system for a tank farm operated by Shell Oman Marketing Company near Muscat, Oman. The 15 tanks at the Mina al Fahal tank farm store crude oil, fuel oil, and refi ned hydrocarbon products. For the upgrade project, AUMA supplied SAEx .2 multi-turn actuators with ACExC .2 actuator controls. All 74 devices are centrally controlled by the SIMA master station. Redundant Modbus communication on a ring network ensures that all the actuators remain accessible even in the event of a fault or cable break. Safety at multiple levels Overfi lling, which can create explosive atmospheres and contaminate soil and groundwater, is a constant hazard in tank farms. Managing the risk of overfi lling may require not only multiple level sensors in the tanks but special attention to the reliability of the associated valves and actuators. Depending on the application, different safety concepts may be implemented at actuator level, including hard-wired additional ESD inputs, SIL-certifi ed actuators and fail safe solutions. Case study 3: Koole Tankstorage Minerals terminal, Port of Rotterdam As an application example, actuators with separate inputs for ESD have been installed at the Koole Tankstorage Minerals terminal in the Port of Rotterdam, the Netherlands. AUMA supplied around 500 explosion-proof electric valve actuators linked by a Profi bus network. These have improved the speed, fl exibility and safety of fl ammable liquids transfer at the terminal (Figure 4). SIL requirements Often, the designers of a tank farm will carry out a formal functional safety assessment based on the principles of safety instrumented systems (SISs) as defi ned by the IEC 61511 and IEC 61508 standards. The safety functions relevant to electric actuators in these circumstances include Safe ESD and Safe Stop. Individual actuators are available with certifi cation up to safety integrity level 2 (SIL 2), typically based on a separate ESD input controlled by a dedicated safety PLC (Figure 5). For applications requiring even higher reliability, redundant setups can achieve SIL 3. Fail safe solutions A special safety case concerns the risk of power failures. Critical valves have to be able to open or close in an emergency even without electrical power. Actuators with Figure 6. AUMA's anti-corrosion coating complies with the requirements for the highest corrosivity categories C5-M certification according to ISO 12944-6. Without high-quality sealing and corrosion protection, actuators in harsh conditions are likely to fail prematurely. Figure 5. AUMA offers TÜV-certified electric actuators suitable for safety-related applications up to SIL 2/SIL 3. Figure 4. 500 AUMA actuators with separate ESD inputs have improved the speed, flexibility and safety of flammable liquids transfer at the Koole Tankstorage Minerals terminal in Rotterdam, the Netherlands.

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