Introduction
Last week, the new electrical engineer at the company was frustrated again. Faced with a production line failure, he stared blankly at the PLC ladder diagram on his computer screen for half an hour, finally admitting with a red face: “I don’t understand this logic…” This was already the third time this month.
The harsh truth is: the company pays you to solve problems, not to pay for your education. A veteran engineer with 20 years of experience warns you that stepping on any of these PLC programming taboos can lead to being scolded by your boss or, in the worst case, paralyze the production line and lead to bankruptcy!
1. The Most Fatal Misconceptions for Beginners
PLC programming is not like doing experiments in school where mistakes can be corrected. A certain automotive factory once suffered a loss of 2 million due to a novice programmer neglecting sensor fault handling, resulting in a robotic arm malfunctioning. Remember these three painful lessons:
1. There is no trial-and-error cost in a company: A one-minute production line stoppage can cost thousands of yuan; your “learning process” is the company’s real money.
2. Experience is more important than theory: Knowing the MOV instruction and being able to handle on-site interference are two different things; 90% of the problems cannot be found in manuals.
3. System thinking determines life and death: The most painful case I have seen is when a programmer only focused on a single device, resulting in a material blockage on the entire production line for 36 hours.
2. The Top Ten Taboos That Senior Engineers Will Never Tell You
Taboo 1: Variable names that look like passwords
Counterexample: In a wastewater treatment plant, the program was filled with names like X0, Y1, and three years later, when the equipment was modified, the team spent 72 hours clarifying the variable relationships.
Correct approach: Use a three-layer naming method of “Device_Function_Status” (e.g., Mixer1_Speed_High).
Taboo 2: Treating PLCs like personal computers
Painful lesson: A programmer at a food factory used 32-bit floating-point numbers for cumulative calculations, resulting in PLC memory overflow and all batch records being cleared.
Hardware rules:
▶️ Always reserve 20% memory margin.
▶️ Use BOOL type for switch quantities first.
▶️ Assign timer numbers from low to high.
Taboo 3: Not testing boundary conditions
Classic accident: A photovoltaic panel cleaning system did not test for -30℃ conditions, resulting in the entire control system freezing in winter, with repair costs exceeding 800,000 yuan.
Testing checklist:
✅ Voltage fluctuation test (±15%).
✅ Extreme temperature test.
✅ Full load continuous operation test.
3. Programming Languages Are a Toolbox, Not Decoration
A food packaging machinery factory once suffered delays of two weeks in a complete line renovation because the electrical engineer overly relied on ladder diagrams and could not implement complex PID algorithm control.
In the Yangtze River Delta manufacturing cluster, electricians who master mid-to-advanced PLC programming skills like TIA Portal and CODESYS generally earn over 15,000 yuan per month, while operators with only low-voltage electrician certificates linger around the 6,000 yuan mark.
4. Control System Design is the Ultimate Test
The essential difference between an excellent PLC programmer and an ordinary technician lies in system thinking.
A wastewater treatment plant’s aeration control system failed to consider the lag characteristics of the DO sensor, leading to PID parameter tuning failure and ultimately causing the death of the microbial community in the biochemical pool.
This warns us: we must thoroughly understand the principles of feedback control, feedforward compensation, and understand the necessity of redundant designs like safety relays and emergency stop circuits.
5. Project Practice is the Only Sharpening Stone
In a steel group’s continuous casting machine project, a young engineer’s perfectly simulated program in the lab failed to consider on-site electromagnetic interference, leading to abnormal encoder signals.
This 2 million yuan lesson illustrates that only through the tempering of real projects can one understand the significance of having a grounding resistance of less than 4Ω and the necessity of using twisted shielded cables near inverters.
It is recommended that practitioners start with small equipment modifications and gradually challenge complex scenarios such as multi-axis synchronous control and high-speed signal acquisition, using a fault log to accumulate every abnormal code and build a moat of professional capability.
Feel free to leave comments and engage in discussions!