What are the differences between Mitsubishi PLCs and Siemens PLCs? What are their respective advantages and disadvantages? How should one choose which brand to learn?
Firstly, their programming philosophies differ. Mitsubishi PLCs are Japanese brands, and their programming is intuitive and easy to understand, making them relatively easy to learn. Siemens PLCs, on the other hand, are German brands, and their instructions are more abstract, making them more difficult to learn, although they have fewer instructions. Mitsubishi PLCs, however, have more instructions, so the learning time for Mitsubishi and Siemens PLCs is the same.
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.
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. Therefore, we must choose the appropriate PLC for different equipment and control methods, utilizing its strengths and avoiding its weaknesses. For example, if a device only requires motion control, such as a robotic arm, a Mitsubishi PLC is suitable. If a device requires positioning control with servo or stepper motors, a Mitsubishi PLC is also a good choice. For applications like central air conditioning, wastewater treatment, and temperature control, which involve processing many analog signals, a Siemens PLC is more appropriate. If a device requires data acquisition from numerous instruments via communication, a Siemens PLC is better suited for its ease of control. The differences are significant. The chips are certainly different (in terms of capacity and processing speed), but the biggest difference lies in the programming software's approach and structure.
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, let's compare Mitsubishi's relatively strong small PLC FX series with Siemens' S7-200 series.
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. The CPU226 and CPU224XP come standard with two 485 ports (PPI ports) and a maximum communication speed of 187.5Kbps. All previous Mitsubishi FX3U series only had a single 422 port with a speed of 9.6Kbps. If you need to connect to a smart meter or similar device, you must purchase a special module such as the FX2N0-485BD separately.
5. The CPU226 has a program size of 20KB and a data size of 14KB, while the FX2N only has 8KB in total. Later 3U models did show some improvement.
However, Mitsubishi's FX2N series has two advantages: first, its high-speed counter instructions are more convenient than those of the S7-200; second, its 422 port is more robust than Siemens' PPI port (because the 200 series PPI port is not opto-isolated, making it more susceptible to non-standard operation and...).
(Imitation of programming cables may damage the serial port.) Siemens' recently launched S7-1200 series directly supports Ethernet interfaces, and due to its integrated counting and measurement, closed-loop control, and motion control technology, the FX3U is once again far surpassed by Siemens. The above comparison is only for small-scale machines. As for Siemens' 300 and 400 series, as well as the larger TDC series, there's no need to elaborate here; in short, those who use it know its capabilities. Siemens' PCS7 software is absolutely profound and sophisticated, leaving all Japanese brands far behind.
Learning PLCs is easy with Mitsubishi, because the logic is straightforward and simple. From a learning perspective, Siemens is definitely better. But as I said before, after using PCS7, I realized how rubbish Japanese software is.
Siemens PLCs have two communication ports, while Mitsubishi PLCs have one. You can use one port to connect a data cable for downloading and the other to connect a touchscreen for debugging. Otherwise, you'll have to unplug and replug the touchscreen data cable to adjust the program, which is very troublesome.
