Ideas and methods for learning PLC programming

Electric workers will come into contact with PLC in their actual work. With the development of industrial automation and intelligent technology, PLC has replaced complex relay control cabinets and contactor control cabinets in many complex occasions and has been widely used. PLC is not only simple to wire, easy to wire and control, but more importantly, PLC troubleshooting is very convenient, eliminating the trouble of tedious wire management and circuit management. Therefore, PLC has been widely used in industrial automation and intelligence!

How to learn PLC

Some requirements for learning PLC

First, there is the circuit foundation

Only then can we understand the essence of the problem, discover errors and solve problems.

Second practical

It is necessary to learn and operate with real objects to improve the combination of real objects and theory, and better master knowledge points and practical application capabilities.

The third one is interested

Only in this way can you persist. Interest is the driving force that drives you to persevere. When you encounter problems and difficulties, ask if you don’t understand, check more information and use your brain more.

First, you must have a basic understanding of circuits. It is enough to be able to understand ordinary circuits. It would be best if you have maintenance experience, because programming mostly relies on logical thinking. There are skills, but not many, because human thinking is diverse.

It can be said that for the same set of movements, a hundred people may come up with a hundred different programs, but the movements they produce will all be the same.

Second, practice, which is the best way to learn. If you have a physical object, you will know how the soft component works, which is many times better than reading a book. If someone asks me which PLC is good to learn, I will say that I should choose one of Mitsubishi and Siemens to start learning. Siemens is more comprehensive and has more forum information. Mitsubishi is not weak either. Why do I recommend these two models? First, the programming ideas are more prominent. Basically, these two categories are imitated in China. For example, Delta, Fengwei, Yonghong, and Xinjie are basically copies of Mitsubishi. These have their own software. There are also many that are directly put on a shell, affixed with a trademark, and can be used directly with Mitsubishi GX Developer software. For example, Huichuan, although it also has its own software, it can also directly use Mitsubishi's software. In some cases, they do not have their own software and directly use Mitsubishi's software.

No matter which PLC it is, they all seem to be similar to me, except for a different programming method, and the principles are almost the same.

In order to enable everyone to master the basic PLC applications in the shortest possible time, we have compiled a list of ideas and methods about PLC programming for those who are new to PLC. From the most basic to the most complex, we have extracted the essence to make a leap forward in your understanding of PLC. We hope that this material will be helpful to everyone in learning PLC.

1. Understand the basic hardware knowledge of PLC

From a hardware perspective, PLC is mainly composed of a central processing unit (CPU), memory (ROM/RAM), input and output interfaces, power supply, expansion interface, and external device interfaces such as programmers.

2. Understand the software programming language of PLC

1. Ladder Diagram (LD): The most commonly used programming language in PLC programming. It is a programming language similar to relay circuits.

2. Instruction List (IL): A mnemonic programming language similar to assembly language, which consists of opcodes and operands like assembly language.

3. Functional Block Diagram (FBD): A PLC programming language similar to digital logic circuits. It uses a functional block diagram to represent the functions of a module. Different functional blocks have different functions.

4. Sequential Function Flowchart (SFC): A programming language designed to meet sequential logic control.

5. Structured Text (ST): A programming language that uses structured description text to describe programs. It is mainly used for user program compilation that is difficult to implement in other programming languages.

3. Combined with practical operation

When most people first learn PLC, they will choose to buy a related book, and then think about small projects based on what they have learned from the book, and then do PLC projects on their own after implementing some small functions. In the self-study stage of reading books, it will be relatively easy to get started with special guidance or further study. Everyone has different habits and characteristics when programming. Although we cannot force them to be consistent, good habits are still worth following.

4. Understand the process flow

PLC programming requires understanding the on-site process requirements, what signals to read, how to control the on-site equipment, and how to achieve the best control effect. The entire control process is controlled and executed according to the program designed in advance according to the process requirements, so the core content is to understand the process requirements.

5. Good programming habits

Everyone has different habits and characteristics when programming. Although we cannot force them to be consistent, good habits are still worth following.

1. Reasonable allocation of main program, subroutine and interrupt program

2. Sort out the programming logic relationship, timing relationship, and compile program flowcharts

3. Reasonably allocate registers and compile register symbol tables

After reading the summary of the above methods, do you feel that you have a general plan for learning PLC?