I. Different Programming Philosophies
Mitsubishi PLCs are a Japanese brand, and their programming is intuitive and easy to understand, making them relatively easy to learn, but they have a large number of instructions. Siemens PLCs, on the other hand, are a German brand, and their instructions are more abstract, making them more difficult to learn, but they have fewer instructions. Therefore, the learning time for Mitsubishi and Siemens PLCs is roughly the same.
In my opinion, Mitsubishi (a mid-to-high-end Japanese brand) PLC software lags behind Siemens by at least 5 years. Leaving aside large and medium-sized PLCs, even comparing Mitsubishi's relatively strong small PLC FX series with Siemens' S7-200 series, Siemens has the following advantages:
1. Mitsubishi's programming software, from the early FXGPWIN to the recent GX8.0 (the latest one I know of), is like all Japanese brands. The programming approach of this software is a single vertical structure from top to bottom. Siemens' MicroWIN, on the other hand, has a structure that combines vertical and horizontal programming. Moreover, subroutines support local variables, and the same function only needs to be programmed once, which greatly reduces the difficulty and time of development.
2. The S7-200 has always supported powerful floating-point operations, and the programming software directly supports decimal point input and output. Mitsubishi only had this function in the FX3U series launched in recent years. The floating-point function of the previous FX2N series was fake.
3. The analog input/output program of the S7-200 is very simple and convenient. AD and DA values can be directly accessed without programming. Mitsubishi's FX2N and earlier series required the very cumbersome FROMTO instruction. The 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 instructions are more convenient than those of S7-200. Second, the 422 port is more robust than Siemens' PPI port (because the PPI port of the 200 series is not opto-isolated, and non-standard operation and counterfeit programming cables may cause damage to the serial port).
The above comparison only applies to small-sized machines. As for Siemens' 300 and 400 series, as well as the larger TDC series, there is no need to elaborate here.
When learning PLC, Mitsubishi is easy to get started with because its logic is straightforward and simple, but from a learning perspective, Siemens is definitely better.
II. Different Chips
This is mainly reflected in capacity and processing speed. The Siemens CPU226 has a program capacity of 20K and a data capacity of 14K; while the Mitsubishi FX2N only has a total of 8K, although the later 3U has made some improvements.
Siemens CPU226 and CPU224XP come standard with two 485 ports (PPI ports) with a maximum communication speed of 187.5Kbps; while all Mitsubishi FX3U and earlier series have only one 422 port with a speed of 9.6Kbps. If you need to connect to a smart instrument or similar device, you must purchase a special module such as the FX2N0-485BD. Furthermore, you can use one communication port to connect a data download cable and the other to the touchscreen for program debugging; otherwise, you have to unplug and reconnect the touchscreen data cable, which is very cumbersome for adjusting the program.
Third, their strengths in control differ.
Siemens excels in process control and communication control. Siemens' analog modules are inexpensive and have simple programming, while Mitsubishi's analog modules are expensive and have complex programming. Siemens also excels in communication control with simple programming, while Mitsubishi is weaker in this area. (Today's forwarding code is: Yiwei Quality Assurance: 6-month replacement, 5-year warranty, lifetime maintenance)
Mitsubishi's strength lies in discrete control and motion control. Mitsubishi has a rich set of instructions, including dedicated positioning instructions, making it easy to control servo and stepper motors. It is also a strong point of Mitsubishi to achieve certain complex motion control. Siemens, on the other hand, is weaker in this area. It does not have dedicated instructions. While it is not impossible to perform servo or stepper positioning control, the program is complex and the control accuracy is not high.
For example, if a device only requires motion control, such as a robotic arm, a Mitsubishi PLC is a good choice. If a device has servo or stepper motors that need positioning control, a Mitsubishi PLC is also a good option. For devices like central air conditioning, sewage treatment, and temperature control that require processing many analog signals, a Siemens PLC is more suitable. If a device has many instruments on-site that require data acquisition via communication, a Siemens PLC is a good choice for better control.
Therefore, we should choose PLCs appropriately for different equipment and different control methods, making use of their strengths and avoiding their weaknesses.
