本文主要讲述的是PLC的优点，可编程逻辑控制器(plc)广泛应用于制造业、石油天然气等行业。PLC系统由硬件和编程软件组成。硬件包括PLC模块本身、电源模块、数字输入输出(I/O)卡、模拟I/O模块、人机接口(HMI)等。所有的I/O模块和PLC都安装在一个背板上，允许PLC和I/O模块之间进行通信。除指令表外，还有四种常用的编程语言。它们分别是梯形图(LD)、顺序功能图(SFC)、功能方框图(FBD)和结构化文本(ST)。本篇assignment代写文章由美国论文人EducationRen教育网整理，供大家参考阅读。
Programmable Logic Controllers (PLCs) are widely used in various industry such as manufacturing industry and oil and gas industry. A PLC system consists of hardware and programming software. Hardware includes PLC module itself, power supply module, digital input and output (I/O) cards, analogue I/O modules, Human Machine Interface (HMI) and so on. All the I/O modules and PLC are installed on a backplane which allows communication between the PLC and I/O modules. There are four common used programming languages except for Instruction List. They are Ladder diagram (LD), Sequential Function Charts (SFC), Function Block Diagram (FBD) and Structured Text (ST).
A programmer can choose any of the languages to program. Whenever a programmer had finished programming, he/she can download the program into the PLC. A HMI is the interface between an operator and the PLC which allows an operator to control the operation of the PLC, input some parameters to the PLC and display some quantities.
PLC has many advantages. The main advantages are as follows:
Reliability
Since there is no mechanical connection between control relays, there is no failure due to mechanical malfunction.
Flexibility
PLC is reprogrammable. If a programmer want to overwrite a PLC, he/she only needs to write programs using programming software on a computer and download it to the PLC.
Smaller Physical Size
In some industrial applications, physical size is very critical. And also smaller size means lower power consumption and easy installation.
For this project we decided to use the PID control method to control the water supply system. This method can be realized by an individual PID controller or integrated into a PLC. PID stands for proportional integral derivative controller or control method. The PID control is mostly used to reduce error by adjusting the control variable over time. Here is some detailed explanations of the proportional, integral, and derivative sides of the control method.
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