Network infrastructure in large, integrated control systems

Modern integrated control systems have become a blend of traditional process automation and functions that have in the past only been found in IT departments. Today's control systems have become faster and more flexible than ever before. Many different types of systems can be blended together to form one integrated whole. Scan rates and refresh times move at speeds that allow changes at an ever-increasing pace. The size and speed of these integrated systems demand increased attention to the infrastructure of the network they rely on. Without a strong enough network backbone, the control system as a sum of all parts will not be able to sustain itself, giving way to communication losses and loss of process control. In order to design and maintain a stable, secure control system, special attention must be given to the network and automation engineers must get in touch with their inner IT professional. This paper describes many of the challenges and lessons learned during the commissioning and startup of the control system at the Holcim Ste Genevieve plant. The central control system consists of 18 primary Rockwell Control Logic PLCs and RSView SE HMI containing about 150,000 data connections. Including all sub-systems, there are around 50 PLCs throughout the plant and around 200,000 data connection points when including local touch panels. The commissioning of individual areas and startup of the plant as a whole was very successful, but during the first few months there were many challenges with communication losses and system stability, some leading to plant downtime. Some of these challenges were due to both weak points in the network infrastructure and the size of the system pushing limitations of hardware and software. Among the specific problematic areas was the selection and design of network switches, the Microsoft Active Directory governing the central control system domain authentication, and the application of user code and communication at the PLC level. Six months after startup, flaws were exposed in network security and the control system was lost for 3 days due to a dormant virus that became active. Much effort from Holcim and Rockwell was needed to strengthen the network infrastructure to achieve a stable, secure control system.