In my view, a PLC is essentially a small computer, an industrial computer specifically designed for electrical control. Its structure is quite similar to a computer, mainly consisting of five components:
1. Power supply
The PLC uses a 220V power supply.
There are both AC and 24V DC options available, depending on your needs. In fact, the AC power supply is ultimately converted to DC through a rectifier circuit inside the PLC.
2. CPU
The central processing unit (CPU) is the control center of a PLC and its core component; its performance determines the PLC's overall performance. It's like the PLC's brain; all control algorithms and logical operations are performed within the CPU, much like a computer's CPU, ultimately determining the device's performance.
3. Memory
It's similar to a computer's hard drive, used to store system programs, user programs, logical variables, and other information. The system program controls the PL/Plugin.
The C program that implements various functions is written by the PLC manufacturer and stored in a read-only memory (ROM), which cannot be accessed by the user.
4. Input
The input ports of various devices to the PLC, including digital and analog inputs, serve as bridges for signals to enter the PLC, much like the mouse and keyboard of a computer, providing input ports for the computer.
5. Output
PLCs control the output ports of various devices, which can output switch signals, analog signals, etc. The outputs are also divided into many types, such as relay outputs, transistor outputs, and thyristor outputs.
The above five main parts constitute a PLC device. Of course, there are many other corresponding modules, such as network modules, weighing modules, analog input/output modules, digital input/output modules, and so on. A PLC can be expanded with many modules according to its own characteristics.
There are many PLC brands on the market. The following are common equipment classifications.
Japan: Panasonic, Mitsubishi, Omron, Fuji, Hitachi, Toshiba, Keyence
United States: Rockwell Automation, ABB, Schneider Electric, GE, Honeywell
Germany: Siemens
Taiwanese brands: Delta Electronics, Yung-Hung
Mainland Chinese brands: Hollysys, Xida Supcon
There are so many brands now, and technology is developing rapidly. PLC technology has also advanced by leaps and bounds, so there are now more and more PLC brands, and they are becoming easier and easier to use.
So the question is, how do you learn to use so many PLC brands and master so many PLC usage skills?
I learned PLC technology on my own. First, you should be able to read and understand electrical diagrams, primary wiring diagrams, and secondary wiring diagrams. This is essential because if you can't read diagrams, you won't have the control logic in your mind. Let alone learning PLC, even a regular electrician might not know where to start. So, the first step in learning PLC is to learn the necessary electrical knowledge. This is the foundation.
Once you have a basic understanding of electrical knowledge, you can start learning PLCs. When I first encountered PLCs, the first one I used was the Siemens S7-200. Siemens PLCs have a high market share. There are many tutorials online that you can follow. Start from the basics and learn all the commands, understanding the function of each command and its application. After learning the commands, learn various communication techniques. Once you've mastered all of these, you can try writing some small programs, such as motor start-stop circuits, running lights, traffic lights, etc., gradually increasing the difficulty.
Once you've learned all this knowledge, try writing programs according to the control requirements. Don't be confined to one programming style; there are many ways to achieve the same result. Write programs according to your own established programming style, and once you achieve the desired control result, that's a good program, that's a correct program.
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