从计算能力来看，计算机早已超越人脑，但这不意味着计算机有智慧——迄今为止，各种类型的计算机都仍只是人脑部分功能（主要是记忆与运算）的延展。在可编程逻辑控制器系统设计时，首先应确定控制方案，下一步工作就是可编程逻辑控制器工程设计选型。工艺流程的特点和应用要求是设计选型的主要依据。可编程逻辑控制器及有关设备应是集成的、标准的，按照易于与工业控制系统形成一个整体，易于扩充其功能的原则选型所选用可编程逻辑控制器应是在相关工业领域有投运业绩、成熟可靠的系统，可编程逻辑控制器的系统硬件、软件配置及功能应与装置规模和控制要求相适应。熟悉可编程序控制器、功能表图及有关的编程语言有利于缩短编程时间，因此，工程设计选型和估算时，应详细分析工艺过程的特点、控制要求，明确控制任务和范围确定所需的操作和动作，然后根据控制要求，估算输入输出点数、所需存储器容量、确定可编程逻辑控制器的功能、外部设备特性等，后选择有较高性能价格比的可编程逻辑控制器和设计相应的控制系统。 点数估算I/O点数估算时应考虑适当的余量，通常根据统计的输入输出点数，再增加10%～20%的可扩展余量后，作为输入输出点数估算数据。实际订货时，还需根据制造厂商可编程逻辑控制器的产品特点，对输入输出点数进行圆整。 
In terms of computing power, computers have already surpassed human brain, but this does not mean that computers are intelligent - so far, all types of computers are still only an extension of some functions of human brain (mainly memory and operation).
In the design of PLC system, the control scheme should be determined first, and the next step is the engineering design and selection of PLC. The characteristics and application requirements of the process flow are the main basis for design and selection. The programmable logic controller and related equipment shall be integrated and standard. According to the principle of easy integration with the industrial control system and easy expansion of its functions, the selected programmable logic controller shall be a mature and reliable system with operation performance in relevant industrial fields. The system hardware, software configuration and functions of the programmable logic controller shall be compatible with the device scale and control requirements. Being familiar with programmable controllers, function charts and related programming languages is conducive to shortening programming time. Therefore, when selecting and estimating engineering design, it is necessary to analyze the characteristics and control requirements of the process in detail, clarify the control tasks and scope, and determine the required operations and actions. Then, according to the control requirements, estimate the input and output points, the required memory capacity, determine the functions of the programmable logic controller, the characteristics of external equipment, etc, Then choose the programmable logic controller with high performance price ratio and design the corresponding control system. 
Appropriate margin should be considered in the estimation of i/o points. Usually, according to the statistical input and output points, an additional 10% - 20% expandable margin is added as the input and output point estimation data. When actually ordering, it is also necessary to round the input and output points according to the product characteristics of the manufacturer's PLC.