Measurement of real-time aspects of Simatic/spl reg/ PLC operation in the context of physics experiments

Today, most slow control systems for physics experiments at Forschungszentrum Ju/spl uml/lich are implemented with Programmable Logic Controller (PLC) technology and fieldbus systems. In many cases, even deterministic response is required from the PLCs. This raises the question about the real-time performance that can be expected from a PLC. Response-time measurements of Simatic/spl reg/ PLCs-manufactured by the world market leader Siemens-are presented. Influence of program structure and hardware configuration on performance and deterministic behavior of a PLC is discussed.