There has never been a single answer to the question of how we program control systems. This is because people write control programs that are designed to run on processors which are programmed by other people. Invariably personal preferences and subjective evaluations of what is important, what is necessary, what is preferable in the creation of these intermediate levels of control code, all become part of the final solution.
Not until the second attempt at standardization of Programmable Logic Controller code, IEC 61131 in 2003, was sufficient progress made to allow serious commonality of programming languages. Yet with all the work that has gone into the standardization, the industry has only been able to narrow things down to 5 languages.
Ladder diagramming is a set of symbols derived from electrical relay diagramming that has a very long and well established history. The fact that relay diagramming formed the basis for early automation systems is the reason for its existence and the reason that it grew into the standard means of describing control applications. The universality of ladder diagram is based in part on its history.
不幸的是阶梯图没有设计to incorporate more complex control elements. Really, any analog input signal was treated as a digital input with a threshold value that represented an “on” or “off” state. For many years, PID controllers for analog instrumentation, were their own specialized form of controller. Complex process controls were created using the PID controller as a building block and cascading signals in order to model in the hardware of the time, the needed control architecture for a given application.
因此，普遍性的问题是语言。我们可以在人类层面表示任何控制应用程序的描述性语言，然后在二进制处理器上托管该控制应用程序，以给出所需的结果？
简短答案？没有一个。
The reason is that there are many layers of abstraction required to reach the binary executable solution so that it reliably executes the desired scheme. In the ISO model of the computer, there are many layers between the CPU hardware and the user control code. Operating Systems, internal bus architectures, memory mapping, I/O subsystems all have to be designed to get signals from the real world to interface to the binary processor at the bottom layer of the system.
基于Linux的PLC多年来一直在开发，希望通用计算机成为成本最低和最大复杂性的最终解决方案。但是，嵌入式处理器和其他技术不断改变竞争环境。
控制体系结构的最基本层是现场可编程门数组。在过去的20年中，FPGA发展为利用硅和解决控制应用的最有力方法之一。国家仪器（National Instruments）可能是应用FPGA及其主要供应商Xilinx时最具侵略性的控制供应商，它一次又一次地迁移了该技术。
如今，FPGA正在进入PLC领域，而且过去的情况正常，很可能会永远改变控制的成本性能。
提交以下：机甲提示，，，，机电学
