There are some key issues in the PLC design according to the control systems that have to be addressed. The PLC design based control system is distinguished by long development and uncertainty time. Improbability comes out from the huge value of specific requirements, for example hazard analysis requirements, quality of software, and the hardware specifications obliged from the system of mechanical to be controlled. More than 50% of the operator assigned for the design of control system is scheduled for debugging and testing in order to cope with uncertainty. The long design lead-time is an effect of a severity sequential of process design in industrial practice, in case system developers do concern a methodology of system at all. In many cases the mechanical manufacturing design or transport system and the control system are surpassed on to different subcontractors with no or less communication.
A main problem, pushing the need for a methodology of systematic design, is the rising software difficulty in major projects alongside with the enduringly rising part of software life-cycle cost. An ordinary application of PLC has frequently to handle complicated systems with over 10,000 control nodes. 80-90% of the costs are going into software debugging, maintenance, expansion, and adaptation to meet changing customer requirements in industrial automation. The improved demand for re-configurability of manufacturing systems in fast response-markets forces an additional requirement on control systems. The increasing speed of changes in the manufacturing systems needs frequent adjustments of control programs. A main challenge is consequently to supply enabling technologies that can cost-effectively reconfigure control systems of manufacturing in reaction to changing new opportunities and needs.
Therefore, the requirement to struggle for higher quality of software, to manage with enlarged complexity, and to allow the economical and quick manufacturing control reconfiguration systems need advanced recent organize technologies, simultaneous design concepts, and design tools and new modeling of computer-aided. This article describes a design approach to plan PLC based control systems in order to lessen the reservations in managing the development of control software, rising the systems flexibility, and facilitating the simulation technology use for systems validation. The design advance comprises formal top-down modeling methods that are well known in control research real-time, but less known in industrial practice. A moved ahead methodology of design also implies incorporated the control system and the manufacturing system modeling. The manufacturing system modeling facilitates off-line testing and the control system simulation and should not cause extra cost although it may further require design time.