Description
The mechanical structure of PLC is mainly shell and bottom plate. Not only the connection and fixation of internal circuit board, communication interface and terminal, but also the heat dissipation of PLC, the prevention of external dust, water vapor and impact, and the shielding of oscillation and even electromagnetic interference should be considered. In addition, structure planning is the primary manifestation of product appearance. Therefore, product structure planning not only needs to understand all kinds of electrical and mechanical knowledge, but also needs to consider the usage habits of on-site users, and also needs to have enough artistic accomplishment. Software, from the perspective of development, to complete all the functions of PLC has been a very huge system engineering, and some of these jobs in the entire PLC system software planning and programming, originally only a small part of all the workload. Others, mostly around the reliability aspect, software planning and programming. Software reliability planning, first of all to think about PLC in normal operation of various possible emergencies, to carry out fault-tolerant planning. Because PLC directly deals with all kinds of hardware, including CPU address, data, register, cache, and external input and output control, and many hardware will have different changes due to various influences. Therefore, the internal fault-tolerant processing is already a large workload, and there are no certain rules and precedents to follow in these aspects of programming, It all depends on experience. In addition, there are some external environmental impacts, such as electromagnetic interference, temperature change, signal fault, communication fault, overrun change of all kinds of signals, and human operation faults, such as programming fault, wiring fault and operation fault; We must carry out the necessary fault-tolerant planning, which depends on the accumulation of experience.
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