PLC的机械结构主要是外壳和底板。不仅要考虑内部电路板、通信接口和端子的连接和固定，还要考虑PLC的散热、防止外部灰尘、水汽和冲击，以及对振荡甚至电磁干扰的屏蔽。此外，结构规划是产品外观的主要表现形式。因此，产品结构规划不仅需要了解各种机电知识，还需要考虑现场用户的使用习惯，还需要有足够的艺术修养。
软件方面，从开发的角度来看，完成PLC的所有功能一直是一项非常庞大的系统工程，而其中一些工作在整个PLC系统的软件规划和编程中，原本只是全部工作量的一小部分。其他，主要围绕可靠性方面，软件规划和编程。软件可靠性规划，首先要考虑PLC在正常运行中可能出现的各种紧急情况，进行容错规划。因为PLC直接处理各种硬件，包括CPU地址、数据、寄存器、缓存和外部输入输出控制，许多硬件会因各种影响而发生不同的变化。因此，内部容错处理的工作量已经很大，在编程的这些方面没有一定的规则和先例可以遵循，这一切都取决于经验。此外，还有一些外部环境影响，如电磁干扰、温度变化、信号故障、通信故障、各种信号的超限变化，以及人为操作故障，如编程故障、接线故障和操作故障；我们必须进行必要的容错规划，这取决于经验的积累。
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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