More than 30 companies are located in the Marl Chemical Park. Yokogawa, the process control service provider, recently installed its CS3000 Process Control System there in association with the Ethernet-supported Visunet visualisation platform. This platform allows data to be visualised directly in the hazardous area and provides a network topology that simultaneously increases the availability of the plant set-up. Decentralised control stations with additional functionality ensure that plant operators will in future be able to safeguard their processes even more efficiently.
Andreas Grimsehl
Between them, the companies in the Marl Chemical Park operate around 100 production facilities housed in some 900 individual buildings. Practically all the plants are linked in terms of process materials and power. 1200 km of pipelines, 55 km of roadway and 100 km of rails make up the infrastructure of this business park and clearly illustrate the size of the facility. As a rule, the main plant sections are monitored and controlled from central stations as well as a large number of decentralised stations. The aim of the envisaged concept, developed by Yokogawa, is to increase operational efficiency through faster reaction times in the event of deviations from steady operation in combination with shorter control paths for plant operators.
Centum CS3000 from Yokogawa functions as the process control system. This application is located in the field control station (FCS), which accepts the measured data previously acquired by means of sensors. The data is processed in accordance with logic or control algorithms and then re-output to actuators.
Operator control and monitoring of the process take place via the human interface station (HIS). The computer on which the HMI is installed requires Windows XP or Vista. Other components are optionally available to make the plant process even safer and more effective, such as an integrated, safety-aligned control system (ProSafe), a process information management system (Exaquantum) to determine key indicators and an asset management system (PRM), which improves the efficiency of process plant maintenance.
Star-shaped network topology
The operator-oriented HIS, PIMS, ProSafe and PRM all communicate via a redundant 1 Gbit/s bus system (Vnet/IP). Part of the bandwidth in this system is reserved for the Ethernet protocol, so that all stations which support the TCP/IP protocol can be integrated. The stations are redundantly connected to a layer 2 switch. This star-shaped topology significantly increases the availability of the complete system compared to the previous line topology. Additional hardware can be connected via the switches. This need not necessarily be applications of the Yokogawa process control system and can even be external components, providing these conform to the Ethernet standard according to IEEE 802.3. The hardware to be connected must simply have an IP address from an approved range. Data security is guaranteed by isolating the IP address ranges and reserving a dedicated range for external hardware. Connections to other networks are secured via a firewall if desired. Thomas Bergsch, System Engineer IA Systems at Yokogawa, sees a decisive advantage in this open system philosophy: “General standards, pro-ven in many areas, can be used. Experience shows that there are no interface problems and the situation remains very flexible.“
Requirements for the visualisation platform
The platform that is used to represent process data in the field must comply with all technical and environmental conditions and constraints. Owing to the open architecture of the process control system, Ethernet based communication is an indispensable criterion for the visualisation component. The system must also be capable of withstanding ambient conditions that are often extremely harsh: severe fluctuations in temperature, relative humidity and the level of chemicals in the air, mechanical stresses due to machinery-induced vibration and the load to which the plant is subjected during cleaning with high-pressure systems are all factors that impact the closed housing of the visualisation platform.
Yokogawa opted for the Visunet visualisation platform from Pepperl+Fuchs in order to satisfy these requirements. Visunet is the first platform for the process industry to operate on the basis of Ethernet and the TCP/IP protocol, and in so doing completely dispenses with proprietary structures. The distance between the monitor, keyboard and mouse on the one hand and the host PC on the other can measure up to two kilometres. And when it comes to commissioning, an important feature is leveraged: Visunet has an onboard fault monitor, which records communication errors and documents lost data packages, for example. The system is available as a Visunet RM (Remote Monitor) solution as well as a Visunet PC. The latter comprises a panel PC with a monitor, keyboard and mouse. It can be used as a non-Ex solution but is also approved in accordance with Atex and IEC, categories II 2 G (Zone 1 Gas) and II 2 D (Zone 21 Dust).
Perfect view into the system from the plant area
“The Visunet platform gives us a perfect view into the system from the plant area. It lets the plant operator take care of supplementary tasks during his rounds and if the machinery is started up manually, he has access to all process schematics and data“, says Thomas Bergsch summing up. Thanks to the use of fibre optic technology, cable lengths of 400 to 500 m can be achieved and operated without any problems. In addition to its functional advantages, Visunet is also resistant to extreme ambient conditions and the closed VA housing is a robust and easily cleaned component.
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