The work in this thesis successfully presents a way to implement the control of a mech-atronic system as a network of intelligent remote terminal units. Furthermore, it highlights the need for safety in such systems, and presents an implementation that successfully integrates control logic of the industrial system with its safety logic – a functionally safe system. It also clearly shows that controlling a production system as a network of physi-cally separate devices (controllers and RTUs) depends heavily on the underlying network protocols linking the devices. For an industrial control system, fieldbus protocols are well established for interconnecting controllers and field devices, although their dominance is now being challenged by the increasing adoption of industrial ethernet protocols. As a result, the body of this work also focusses considerably on the unique characteristics that make these protocols suitable for industrial control functionalities.
Although this implementation uses a centralized control architecture in a network of de-centralized intelligent devices as a way of keeping up with the topic of this thesis, it is certainly not the best architecture for a system that is composed of several RTUs, pos-sibly with hundreds or thousands of I/O addresses. While centralized control may not present any specific challenges for a small system, controller response times are ad-versely affected by the large bandwidth requirements of a network of many devices com-municating cyclically with a central controller. Apart from this, the complexity that results from centralized control of large networks is making control engineers follow the trend of decentralized automation and control networks. This complexity can be as a result of the trouble of debugging a large program on the central controller, for example. Therefore, a complete implementation of the control of the Festo system (Appendix F.1) as a net-work of intelligent RTUs can benefit from a decentralized architecture too. A way of im-plementing this is presented in Appendix E.2. The proposed hierarchical architecture reduces the bandwidth requirement on every communication link in the network. Further-more, the many decision-making nodes in a decentralized control architecture represent a better way to utilize the computing resources distributed throughout network. This the-sis is essentially a precursor to implementing a full scale profinet-IO system in the Festo network.
By incorporating monitoring devices at each level of the proposed architecture, this thesis can serve as a basis for a PLC-based low-cost SCADA system. An example of such a system is presented in [65]. While selecting the right technology is the first task in any migration project, the biggest justification for a new system is its superior business value
proposition [66]. In the 21st century, environmental concerns have also impacted corpo-rate objectives and the choice of technology in many industrial systems.
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APPENDIX A: RTU CONFIGURATION
APPENDIX B: SYMBOL TABLES
B.1 RTU symbol table
B.2 Controller symbol table (standard I/O)
B.3 Controller symbol table (safety I/O)
B.4 Controller symbol table (remote I/O & bit memory)
B.5 Controller F-DB (safety data block)
B.6 RTU F-DB (safety data block)
APPENDIX C: RTU PROGRAM
C.1 Standard Program
C.2 Safety Program
APPENDIX D: CONTROLLER PROGRAM
D.1 Standard Program
D.2 Safety Program
D.3 hand1 (Function Block)
D.4 hand2 (Function Block)
APPENDIX E: THE FESTO NETWORK
E.1 THE PHYSICAL LAYOUT
E.2 PROPOSED DECENTRALIZED CONTROL ARCHITECTURE WITH PNIO