How to learn PLC? Should I learn Siemens or Mitsubishi?

工控老司机

How to learn PLC? Should I learn Siemens or Mitsubishi? [Copy link]

LearningPLCThere are actually three main ways to get started:

UnderstandingPLC

Programmable logic controller, which uses a type of programmable memory for its internal storage program, executes user-oriented instructions such as logical operations, sequential control, timing, counting and arithmetic operations, and controls various types of machinery or production processes through digital or analog input/output.

Be familiar with the basic steps

The main contents of system design:

Draft technical requirements for control system design. Technical conditions are generally determined in the form of a design task book, which is the basis of the entire design;

Select the electrical transmission form and actuators such as motors and solenoid valves;

Select the PLC model;

Prepare the PLC input/output allocation table or draw the input/output terminal wiring diagram;

Write the software specification manual according to the requirements of the system design, and then use the corresponding programming language (commonly used ladder diagram) for program design;

Understand and follow user cognitive psychology, attach importance to the design of the human-machine interface, and enhance the friendly relationship between man and machine;

left]Design operating tables, electrical cabinets and non-standard electrical components;

Write design instructions and user manuals; The above contents may be adjusted appropriately according to specific tasks.

Basic steps of system design ：

The main steps of programmable controller application system design and debugging are shown in Figure 1.

Figure 1 Main steps in designing and debugging programmable controller application systems

1, deeply understand and analyze the process conditions and control requirements of the controlled object.

a. The controlled object is the controlled machinery, electrical equipment, production line or production process.

b. Control requirements mainly refer to the basic control mode, the actions to be completed, the composition of the automatic working cycle, necessary protection and interlocking, etc. For more complex control systems, the control tasks can also be divided into several independent parts, which can simplify the complex and facilitate programming and debugging.

2, determine I/O devices According to the functional requirements of the controlled object for the PLC control system, determine the user input and output devices required by the system. Common input devices include buttons, selection switches, travel switches, sensors, etc. Common output devices include relays, contactors, indicator lights, solenoid valves, etc.

3, select the appropriate PLC type:

According to the determined user I/O devices, count the number of input and output signals required, and select the appropriate PLC type, including the selection of model, capacity, and I/O Module selection, power module selection, etc. 4. Assign I/O points Assign PLC input and output points, compile an input/output assignment table or draw a wiring diagram of the input/output terminals. Then you can design the PLC program, and at the same time design and construct the control cabinet or operating table on site.

5、Design the ladder diagram program of the application systemDesign the ladder diagram according to the work function chart or state flow chart, that is, programming. This step is the most core work of the entire application system design, and it is also a relatively difficult step. To design a good ladder diagram, you must first be very familiar with the control requirements and have certain practical experience in electrical design.

6、Enter the program into the PLC When using a simple programmer to enter the program into the PLC , you need to convert the ladder diagram into instruction mnemonics for input first. When using the auxiliary programming software of the programmable controller to program on the computer, the program can be downloaded to the PLC through the connecting cable between the upper and lower computers. 7. After the software test program is input into the PLC, the test work should be carried out first. Because in the process of program design, there will inevitably be omissions. Therefore, before connecting the PLC to the field equipment, software testing must be carried out to eliminate errors in the program, and at the same time lay a good foundation for overall debugging and shorten the overall debugging cycle."]8、Application system overall debuggingAfter the PLC hardware and software design and control cabinet and on-site construction are completed, the entire system can be debugged online. If the control system is composed of several parts, local debugging should be carried out first, and then overall debugging; if the control program has many steps, it can be debugged in sections first, and then connected for overall debugging. Problems found during debugging should be eliminated one by one until debugging is successful.

9、Prepare technical documentsSystem technical documents include manuals, electrical schematics, electrical layout diagrams, electrical component lists, and PLC ladder diagrams.

PLC Selection of models

It is necessary to use PLC control when the control system has complex logical relationships (requiring a large number of intermediate relays, time relays, counters, etc.), when the process and product modifications are frequent, when data processing and information management are required (data calculation, analog control, PID adjustment, etc.), when the system requires high reliability and stability, and when preparing to realize factory automation networking.

In addition to learning some basic programming knowledge and concepts, learning PLC should also learn the ideas of each manufacturer to solve problems. At present, many manufacturers at home and abroad provide a variety of PLC products with different functions, but the different ways of thinking lead to different ideas for dealing with problems in each series of PLCs. Therefore, it is best for beginners to understand the differences between PLCs of various brands, so that they can have obvious solutions to the problems that arise during learning. I will describe in detail the similarities and differences between Siemens and Mitsubishi PLCs.

Different people have different views on the same problem, not to mention the two PLCs with such great regional differences. During use, you can experience how these two types of PLCs solve the same problem? Why do they solve it this way? What are the benefits of this solution? Which of the two solutions do you prefer (or which is more convenient)? Only by learning to think can you make progress faster! !

1. Different programming concepts

MitsubishiPLC is a Japanese brand. Its programming is intuitive and easy to understand. It is easy to learn, but it has more instructions. SiemensPLC is a German brand. Its instructions are more abstract and more difficult to learn, but it has fewer instructions. Therefore, the learning cycle of Mitsubishi and Siemens is the same.

I personally think that the software of Mitsubishi (a mid-to-high-end Japanese brand) PLC is at least 5 years behind that of Siemens. Let's not talk about large and medium-sized ones. Let's compare Mitsubishi's relatively advantageous minicomputer FX series with Siemens S7-200 series. Siemens has the following advantages:

1. Mitsubishi's programming software has evolved from the early FXGPWIN to the recent GX Developer 8.8, like all Japanese brands, the programming idea of this software is a single vertical structure from top to bottom, while Siemens' Micro-WIN is a structure that combines vertical and horizontal structures, and the subroutines support local variables. The same function only needs to be programmed once, which greatly reduces the difficulty and time of development.

2. S7-200 has always supported powerful floating-point operations, and the programming software directly supports decimal point input and output. Mitsubishi did not have this function until the FX3U series launched in recent years. The floating-point function of the previous FX2N series was fake.

3. The analog input and output program of S7-200 is very simple and convenient. AD and DA values can be directly accessed without programming. Mitsubishi's FX2N and its previous series all require very cumbersome FROM TO instructions. FX3U now supports this function, but it is five years or more late.

4. Of course, Mitsubishi's FX2N series also has its own advantages. First, the high-speed counter instruction is more convenient than S7-200, and second, the 422 port is more durable than Siemens' PPI port (because the PPI port of the 200 series is not photoelectrically isolated, non-standard operation and counterfeit programming cables may cause damage to the serial port).

The above comparison is only for small computers. As for Siemens' 300 and 400 series and the larger TDC series, there is no need to say more. Learning PLC, Mitsubishi is very easy to get started with, because the straightforward thinking is simple, but from the perspective of learning, Siemens is definitely better.

I personally think that it is relatively easier for beginners to learn Siemens, especially for beginners with poor foundation. It is not easy to get started with Mitsubishi. Siemens programming software is user-friendly and there are many kinds of information on the Internet. If you need video materials, you can add WeChat PLCJSZC or QQ596953709 to provide it to everyone for free. Second, the chips are different. This is mainly reflected in the capacity and computing speed. The program capacity of Siemens CPU226 is 20K, and the data capacity is 14K; while the Mitsubishi FX2N has only 8K in total, and the later 3U has made some improvements.

Siemens CPU226 and CPU224XP are equipped with two 485 ports, namely PPI ports, with a maximum communication speed of 187.5K; while all series before Mitsubishi FX3U have one 422 port, and the speed is 9.6K. If you need to connect an intelligent instrument or something, you must purchase special modules such as FX2N0-485BD. Moreover, the two communication ports can be connected to the download data cable and the touch screen for debugging the program. Otherwise, you have to unplug the touch screen data cable and then connect the touch screen data cable. It is very troublesome to adjust the program back and forth.

As mentioned above, the PPI port of the 200 series is not photoelectrically isolated. Non-standard operation and counterfeit programming cables may cause damage to the serial port. Please pay attention to this when using it. It is best not to plug or unplug it while it is powered on. The communication port of S7-200 is really very delicate, and it is definitely not as tough as Mitsubishi.

3. Different strengths of control

Siemens' strengths are process control and communication control. Siemens' analog modules are cheap and simple to program, while Mitsubishi's analog modules are expensive and complex to program. Siemens also makes communication easy and simple to program, while Mitsubishi is weaker in this area.

Mitsubishi's strengths are discrete control and motion control. Mitsubishi has rich instructions and dedicated positioning instructions. It is easy to control servo and stepper motors. It is also Mitsubishi's strength to achieve certain complex motion control, while Siemens is weaker in this area. There are no dedicated instructions. It is not impossible to achieve servo or stepper motor positioning control, but the program is complex and the control accuracy is not high.

For example, if a certain device only has some motion control, such as a robot, you can choose Mitsubishi's PLC. If a certain device has servo or stepper motors and needs to be positioned, you can also choose Mitsubishi's PLC. For central air conditioning, sewage treatment, temperature control and other applications where there are many analog quantities to be processed, Siemens PLC is more suitable. For a certain device site where there are many instruments whose data needs to be collected through communication, Siemens PLC is a good choice.

Therefore, for different equipment and different control methods, we must reasonably select PLC, use its strengths and avoid its weaknesses.

utuo2006

Thanks for sharing. Thank you.

pdaboy

Siemens is very good and has a high market share. But it is a little more difficult to learn. If you live in a small city, it is recommended to learn Mitsubishi first, because small local industries do not use Siemens much, and Mitsubishi has advantages in employment.