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:
Since there is no mechanical connection between control relays, there is no failure due to mechanical malfunction.
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.