PLC technology is a highly practical skill; if you want to master it, you must practice. Some beginners spend a lot of time on theory, but after six months they still haven't understood PLC. The truth is, they simply lack practical experience. By practicing ladder diagram writing, program downloading, and debugging, they can develop a more intuitive understanding of PLCs and quickly master this technology. In the beginning, it's advisable to learn one brand of PLC first, as the principles of all PLCs are similar. Once you've mastered one, you can easily learn others by referring to the manual.
Learning PLC is a long and arduous process, and I personally believe that the following conditions are necessary:
1. Strong perseverance and sufficient patience
Some people see programming as a long and tedious job; others see it as a fun intellectual game. If you're the former, I strongly suggest you stay away from this job. After all, programming is a challenge to one's perseverance and patience.
2. Confidence to put things into practice
Many beginners are confused about PLCs, often out of fear of damaging the equipment. There's no need to worry about problems in your program affecting the PLC's normal operation. Whether there are problems in the program can only be discovered by running the PLC. And discovering and solving problems is how you improve your skills. Putting aside hardware operation, I've never encountered a PLC being damaged due to software issues. I suggest that when encountering unfamiliar instructions, write a small program and run it on the PLC. Then, modify the conditions one by one and observe the results (MicroWin provides excellent monitoring tools). Then, review the manual's descriptions. This will give you a very intuitive understanding of the instructions' functions and usage. Therefore, bold practice is essential for PLC programming. Of course, bold practice doesn't mean reckless operation; it must follow necessary guidelines. Another important point is to never connect a load before the program's reliability has been verified, to avoid unnecessary damage. Digital outputs are displayed with LEDs; analog signal processing can be handled using hardware or software simulation methods.
3. Requires meticulous logical thinking.
Programming itself is a logical thinking process. In high-level languages, the most frequently used conditional statements are `ifthenelse` and `select`, which represent causal relationships in logic. PLC programs are composed of these causal relationships: determining whether a condition is true or false, and then deciding to execute the corresponding instruction. Early PLCs were designed to replace relay logic circuits, thus inheriting the relay circuit's description method using contacts as trigger conditions. In PLCs, virtual contacts replace the metal contacts of relays, but the logical relationships expressed by the relay circuits are still fully preserved. Even with the introduction of numerical processing procedures that relay circuits struggle with, PLCs fundamentally still execute causal relationships. Therefore, clarifying the logical relationships between various events of an object is a crucial preparatory step before programming. Upon receiving a task, the first thing to do is to create a logic diagram, discuss it repeatedly with the user, and obtain their approval before truly beginning the program writing process.
4. Essential related knowledge
PLC programs directly operate on the specific technological processes of the target object, making an understanding of these processes crucial. Two areas of knowledge are indispensable: first, hardware knowledge of process instrumentation, including sensors, transmitters (secondary instruments), and the PLC itself—this forms the foundation for building a control system; second, process control theory, including the principles and applications of various control models, with two-position control and PID control models being the most important. PID control is currently the most widely used process control method and is highly versatile. The best way to learn PID is through reading. Almost all books on process control include content on PID, and reading relevant books is very beneficial for understanding it. We shouldn't blame schools for not teaching this content; instead, we should focus on how we learn this knowledge ourselves.
5. Develop good programming habits
Everyone has different programming habits and characteristics, and uniformity cannot be forced. However, some good habits should be followed by most people. First, clarify logical and timing relationships and create a program flowchart; second, allocate the main program, subroutines, and interrupt routines reasonably; third, allocate registers reasonably and create a register symbol table. PLC programming is closer to microcontroller programming, or rather, a PLC is a modular microcontroller. Therefore, many PLC operations directly target registers. If there is unreasonable register address overlap in the program, unpredictable consequences will inevitably occur. Creating a register symbol table can not only avoid the above problems (MicroWin will provide problem warnings), but also make the program more readable.
Finally, PLCs offer a wealth of instructions and modules, making them much more convenient than microcontrollers. However, beginners should try to use simple instructions to achieve their goals first. Although it may seem a bit rudimentary, it's a good way to get started and will help you understand more complex instructions. After gaining some experience, you should consider mastering the application of complex instructions and program optimization.
