1、 1 1、 PLC design criteria A systematic approach to designing PLC software can overcome deficiencies in the traditional way of programming manufacturing control systems, and can have wide ramifications in several industrial applications. Automation control systems are modeled by formal languages or,
2、equivalently, by state machines. Formal representations provide a high-level description of the behavior of the system to be controlled. State machines can be analytically evaluated as to whether or not they meet the desired goals. Secondly, a state machine description provides a structured represen
3、tation to convey the logical requirements and constraints such as detailed safety rules. Thirdly, well-defined control systems design outcomes are conducive to automatic code generation- An ability to produce control software executable on commercial distinct logic controllers can reduce programming
4、 lead-time and labor cost. In particular, the thesis is relevant with respect to the following aspects. In modern manufacturing, systems are characterized by product and process innovation, become customer-driven and thus have to respond quickly to changing system requirements. A major challenge is
5、therefore to provide enabling technologies that can economically reconfigure automation control systems in response to changing needs and new opportunities. Design and operational knowledge can be reused in real-time, therefore, giving a significant competitive edge in industrial practice. Studies h
6、ave shown that programming methodologies in automation systems have not been able to match rapid increase in use of computing resources. For instance, the programming of PLCs still relies on a conventional programming style with ladder logic diagrams. As a result, the delays and resources in program
7、ming are a major stumbling stone for the progress of manufacturing industry. Testing and debugging may consume over 50% of the manpower allocated for the PLC program design. Standards IEC 60848, 1999； 2 IEC-61131-3, 1993； IEC 61499, 1998； ISO 15745-1, 1999 have been formed to fix and disseminate sta
8、te-of-the-art design methods, but they normally cannot participate in advancing the knowledge of efficient program and system design. A systematic approach will increase the level of design automation through reusing existing software components, and will provide methods to make large-scale system d
9、esign manageable. Likewise, it will improve software quality and reliability and will be relevant to systems high security standards, especially those having hazardous impact on the environment such as airport control, and public railroads. The software industry is regarded as a performance destruct
10、or and complexity generator. Steadily shrinking hardware prices spoils the need for software performance in terms of code optimization and efficiency. The result is that massive and less efficient software code on one hand outpaces the gains in hardware performance on the other hand. Secondly, softw
11、are proliferates into complexity of unmanageable dimensions； software redesign and maintenance-essential in modern automation systems-becomes nearly impossible. Particularly, PLC programs have evolved from a couple lines of code 25 years ago to thousands of lines of code with a similar number of 1/O
12、 points. Increased safety, for instance new policies on fire protection, and the flexibility of modern automation systems add complexity to the program design process. Consequently, the life-cycle cost of software is a permanently growing fraction of the total cost. 80-90% of these costs are going i
13、nto software maintenance, debugging, adaptation and expansion to meet changing needs. Today, the primary focus of most design research is based on mechanical or electrical products. One of the by-products of this proposed research is to enhance our fundamental understanding of design theory and meth
14、odology by 3 extending it to the field of engineering systems design. A system design theory for large-scale and complex system is not yet fully developed. Particularly, the question of how to simplify a complicated or complex design task has not been tackled in a scientific way. Furthermore, buildi
15、ng a bridge between design theory and the latest epistemological outcomes of formal representations in computer sciences and operations research, such as discrete event system modeling, can advance future development in engineering design. From a logical perspective, PLC software design is similar t
16、o the hardware design of integrated circuits. Modern VLSI designs are extremely complex with several million parts and a product development time of 3 years Whitney, 1996. The design process is normally separated into a component design and a system design stage. At component design stage, single fu
17、nctions are designed and verified. At system design stage, components are aggregated and the whole system behavior and functionality is tested through simulation. In general, a complete verification is impossible. Hence, a systematic approach as exemplified for the PLC program design may impact the
18、logical hardware design. 2、 SIEMENS PLC SIMATIC S7-300 series PLC applied to all walks of life and various occasions in the detection, monitoring and control of automation, its power to both the independent operation of, or connected to a network able to achieve complex control. The photoelectric pr
19、oducts with isolation, high electromagnetic compatibility； have high industrial applicability, allowing the ambient temperature of 60 ； has strong anti-jamming and anti-vibration and impact resistance, so in a harsh working environment has been widely Applications. I also mean freedom of communication S7-300 type PLC s a very unique feature, which allows S7-300-PLC can deal openly with any other
