Learn to know the PLC
Have a digital circuit / electrical foundation
1. Find the selection sample of PLC (mainly understand the hardware composition of PLC, do not need to understand the hardware parameters)
2. Install the PLC programming software (this can not find the manual, the current programming software in addition to GE's PLC, other homes have Chinese)
3. Look for the PLC manual and look at the PLC memory type. This is very important, and the basis of the digital circuit is used.
4. Find a project that someone else does, without looking at the logic, just look at the instruction usage and programming structure.
5. PLC has Mitsubishi and Siemens, different brands of PLC programming tools and methods are different, online not only programming software, but also simulation software, while reading, while programming on the programmer, compiled and then in the simulator Running in.
How to learn PLC well
First of all, we must have perseverance and confidence to dare to challenge, because learning PLC is a relatively boring process, the worst result is system collapse, it doesn't matter, the system is redone, come again; as long as the computer is not smashed, how can it do.
Run these instructions on the PLC continuously and observe the results of the operation to understand the role of the PLC instructions. Many beginners are confused about PLC's face, often because of fear and damage to equipment. And there is no reason for these fears. It is very important to read the manual carefully, but reading alone is not an engineer. What's more, the contents of the manual are not exhaustive. When I came into contact with unfamiliar instructions, I like to program a small program to let the PLC run. Then modify the conditions one by one, observe the results of the operation (MicroWin provides users with very good monitoring methods), and then re-understand the description of the manual, so that you can understand the role and use of these instructions very intuitively. Don't worry about any problems with the program you write, it will affect the normal operation of the PLC. There is no problem with the program, only the PLC can be found to run. Finding problems and solving problems is an improvement in one's ability. Regardless of the hardware operation, in terms of software alone, I have never encountered any damage to the PLC due to software problems. There is no need to worry about the possible consequences of the wrong connection of the relay circuit. Therefore, bold practice is the only way to PLC programming.
Programming itself is a logical thinking process. In high-level languages, the most used are conditional statements such as if then else and select. This is the causal relationship in logic. The PLC program is composed of these causal relationships: whether the condition is established, and then decides to execute the corresponding instruction. The original PLC was used to replace the relay logic circuit, so it inherits the description of the relay circuit with the contact as the trigger condition. In the PLC, the metal contacts of the relay are replaced by virtual contacts, and the logic relationship expressed by the relay circuit is completely preserved. Even if a numerical process that is difficult for the relay circuit is introduced, the PLC is fundamentally performing a causal relationship. Therefore, the logical relationship between the various events of the object is a preparation that must be carefully prepared before programming. After I received a task, the first thing was to sort out a logical relationship diagram, repeatedly discuss with the user, get the user's approval, and then actually enter the process of writing the program.
The PLC program is a specific process directly acting on the object, so the understanding of the specific process of the object is very important. In the process of communication with the user, I will use the knowledge of Unit OperaTIon that I have mastered to analyze the user's process, assist the user to organize the various logical relationships in the process control, and even include the configuration of various instruments and hardware. This is due to the profession I have studied. Of course, you can't ask all engineers who work on PLC programs to have my experience. But there are two kinds of knowledge that are indispensable: First, the hardware knowledge of process instrumentation, including sensors, transmitters (secondary instruments) and PLC itself, which is the basis for building control systems; second, process control theory, including The principles and applications of various control models, the most important of which are the two-position adjustment and PID adjustment models. PID regulation is currently the most widely used process control method, and it is highly variable. The best way to learn PID is to read. Almost all books that explain process control have content about PIDs. Reading more basic related books is very useful for understanding PID. I found that many netizens lacked this knowledge when they entered the PLC field. This is not terrible; the terrible thing is that the perpetrators cannot calm down to make up for the shortcomings of knowledge. We should not blame the school for not teaching the content, but to pay attention to how to learn this knowledge. Many of the problems encountered in the work are not mentioned in the school. This cannot be the reason for our refusal to work. We should respond to these issues with a positive attitude. My experience is that the knowledge that is learned to solve problems at work is easier to remember than the things that go to school.
to sum up
1, look at other people's procedures, take the essence.
2, more than your own contact, from simple to complex!
3, more to expand their knowledge (because PLC's function is more powerful, not only control but also communication!)
4, see more information!
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