From “Dialects” to “Common Language”: The Translation Code Between PLC Brands
Do you remember the awkward moment when I first switched from a Siemens project to a Mitsubishi project? Standing in front of the control cabinet, holding the program list, my mind was filled with the S7-300 instruction format, yet I had to understand the ladder diagram of the FX3U in front of me. It felt like being thrown into a foreign country, only able to say “Hello” and “Thank you.”
Different brands of PLCs are like different dialects; although the core ideas are similar, the expressions are unique to each. Over the past fifteen years, I have traveled between these “dialect regions” and finally compiled a “multilingual translation manual.” Today, I would like to share it with my new colleagues!
Basic Instructions: The “Common Words” of Four Major Brands
No matter which PLC you use, these basic instructions are indispensable. Just like cooking rice requires both rice and water, these are essential elements for building automation programs:
| Function | Siemens (S7) | Mitsubishi | Omron | Rockwell (AB) |
| Normally Open Contact | —[ ]— | —[ ]— | —[ ]— | —[ ]— |
| Normally Closed Contact | —[/]— | —[/]— | —[/]— | —[/]— |
| Coil Output | —( )— | —( )— | —( )— | —( )— |
| Set | S | SET | KEEP(11) | L |
| Reset | R | RST | KEEP(10) | U |
Last year, while troubleshooting a filling machine at a beverage factory with the maintenance foreman, we discovered that the issue was with the reset instruction in the program. “Look, Siemens uses R, Mitsubishi uses RST, Omron uses KEEP(10); different brands have different notations, but they all do the same thing—reset the signal.” The foreman suddenly understood, “No wonder I always mixed them up after changing jobs!”
Timers and Counters: The Many Faces of Time Management
Timers are the time management experts of industrial automation, while counters are the faithful recorders of quantity. However, their “appearances” can vary greatly across different PLCs:
| Function | Siemens (S7) | Mitsubishi | Omron | Rockwell (AB) |
| On-Delay Timer | TON | OUT T□ K□ | TIM □ #□ | TON |
| Off-Delay Timer | TOF | — | — | TOF |
| Counter Up | CTU | OUT C□ K□ | CNT □ #□ | CTU |
| Counter Down | CTD | — | — | CTD |
Interestingly, during a renovation project, I directly “translated” Siemens’ TOF timer to a Mitsubishi PLC, only to find that Mitsubishi did not have a ready-made off-delay function. In the end, I used a standard timer with a little trick to achieve the same functionality.Engineers not only need to recognize these “words” but also understand the grammatical structures behind them.
Data Processing: Various Expressions of Logical Operations
I often tell interns,PLC programming is like building complex machines with blocks; data processing instructions are those uniquely shaped blocks, allowing your structure to be more sophisticated:
| Function | Siemens (S7) | Mitsubishi | Omron | Rockwell (AB) |
| Data Transfer | MOVE | MOV | MOV | MOV |
| Addition | ADD | ADD | + | ADD |
| Subtraction | SUB | SUB | – | SUB |
| Comparison | CMP | CMP | CMP | CMP |
| Logical AND | AND | WAND | AND | AND |
| Logical OR | OR | WOR | OR | OR |
Last summer, I worked until three in the morning on a fully automated production line, troubleshooting a production calculation error. The problem stemmed from the different ways PLC brands handle data types.Remember, although the instruction names are similar, data types, storage methods, and byte orders can vary completely between brands!
Communication Instructions: Letting PLCs “Socialize”
In modern factories, isolated operation of equipment is outdated.Facilitating smooth “conversations” between different devices is an essential skill in the era of Industry 4.0:
| Function | Siemens (S7) | Mitsubishi | Omron | Rockwell (AB) |
| Read Remote Data | RDREC | FROM | RXDU | MSG |
| Write Remote Data | WRREC | TO | TXDU | MSG |
| Network Communication | TCON/TDISCON | SOCOPEN | PMCR | MSG |
I remember once at an automotive parts factory, the client requested to integrate three originally independent production lines into one monitoring system. The three lines were using Siemens, Mitsubishi, and Rockwell PLCs respectively. That week, I practically lived in the factory, ultimately building this “Babel communication tower.” The client jokingly called me the “PLC United Nations Translator.”
Advanced Learning Suggestions
If you are transitioning from one brand of PLC to another,I recommend first clarifying the core logic before looking for corresponding instructions. Just like learning a foreign language, once you master the grammatical structure, the vocabulary will naturally follow.
All brands’ programming software have detailed instruction help; that is your best dictionary. When encountering difficult problems, don’t forget to consult the official manuals, where you will find the most authoritative explanations.
The most important thing is: Practice leads to true knowledge. Knowledge gained from books is often superficial; true understanding comes from hands-on experience. Building a small experimental environment to personally test the differences in various instructions is the fastest way to learn.
The world of industrial automation is fascinating, and I hope this “multilingual translation table” will help you switch seamlessly between different PLC platforms and become a true automation “polyglot!”