With over 10 years in the non-standard automation industry and having handled hundreds of PLC projects, ranging from standalone devices to complete line integration, and from simple logic to complex algorithms, I can reflect on the fact that the highest technical barrier is indeed programming—ladder diagrams, structured text, and function blocks, each requiring a solid foundation.
However, after completing many projects, one realizes that programming only accounts for 20% of the overall project difficulty; the remaining 80% of challenges lie outside of programming.
Programming is indeed fundamental, but not the bottleneck
Let’s start with programming. Whether it’s Siemens TIA Portal, Allen-Bradley’s Studio 5000, or Mitsubishi GX Works, the programming languages and development environments are quite mature. Experienced engineers can quickly build a program framework after receiving the process requirements:
- Main program loop: initialization → automatic operation → fault handling → manual debugging
- Modular design: IO mapping table, alarm handling, motion control, communication interfaces
- Standardized programming: variable naming conventions, complete comments, version control
An engineer with 3-5 years of experience can usually complete the main logic of a moderately complex device program in 1-2 weeks.
The problem is that finishing the program is just the beginning.
The real difficulty: requirements are always changing
1. The “dynamic balance” of customer requirements
Case Study: A packaging line renovation project
Initial requirement: 4-station turntable, cycle time of 18 seconds, simple labeling function.
Changes in requirements during project execution:
- Week 2: Request to add visual inspection to eliminate defective products
- Week 4: Cycle time requirement increased to 12 seconds
- Week 6: Added data traceability function, requiring barcode association
- Week 8: Temporarily added a new product specification, requiring quick change functionality
Each change seems simple, but it actually impacts the entire system architecture.Visual inspection requires a redesign of the layout, the increased cycle time necessitates optimization of all action sequences, data traceability involves MES interface development, and the quick change function directly overturns the original product positioning method.
Solutions:
- Spend sufficient time on requirement research at the project start; do not rely solely on the technical leader’s description
- Must visit the site to observe the actual process flow and understand the operators’ habits
- Design with 30% expansion space reserved; consider future additions in IO points and program structure
- Establish a requirement change process; evaluate the impact and cost of each change
2. The “unforeseen” in on-site debugging
Programming is done in the office, but the equipment must run on-site.The gap between the on-site environment and the ideal state often exceeds expectations.
Case Study: An automotive parts inspection line
Theoretically, the workpiece is positioned by standard fixtures, sensors detect, and the PLC determines compliance. However, during actual debugging, the following issues were discovered:
- On-site vibrations were greater than expected, affecting the stability of precision detection
- Poor power quality led to frequent interference faults reported by the frequency converter
- Operators did not follow SOPs, frequently intervening manually in the process
- Environmental temperature changes caused instability in cylinder action times
These issues can never be discovered during program simulation.
Solution strategies:
- Reserve ample time for on-site debugging, typically 1.5-2 times the program development time
- Understand the on-site environment in advance: power quality, grounding conditions, distribution of interference sources
- Add fault tolerance mechanisms in the program: sensor signal filtering, action timeout protection, abnormal state recovery
- Establish comprehensive logging for easier problem tracing
3. The “barrel effect” of system integration
Non-standard projects rarely involve a single device; they usually require the integration of multiple subsystems.The performance of the entire system depends on the weakest link.
Typical integration challenges:
Communication protocol compatibility
- Old devices use Modbus RTU, while new devices support EtherNet/IP
- PLC communication with the upper computer, OPC servers are often unstable
- Clock synchronization issues between different brand devices
Timing coordination issues
- Device A takes 25 seconds to complete processing, while device B has a waiting time of only 20 seconds
- How to optimize the overall cycle time when multiple devices work in parallel
- Device interlock shutdown in abnormal states
Solutions:
- Conduct detailed communication tests before integration to confirm protocol compatibility
- Establish unified device status management for transparency of all device statuses
- Design a flexible timing configuration mechanism that can be adjusted on-site according to actual conditions
Project Management: A Required Course Beyond Technology
The Art of Balancing Cost Control
Customers always hope for stronger functionality, lower prices, and faster delivery.
In reality, only two out of the three can be achieved.
Cost composition analysis:
- Hardware costs: 35-40%
- Software development: 20-25%
- On-site debugging: 15-20%
- Project management: 10-15%
- Risk reserve: 10%
Experienced project managers consider these factors during the quoting phase, rather than simply adding a markup to hardware costs.
Key Nodes for Schedule Control
Standard PLC project milestones:
- Requirement confirmation (15%): the most important yet often overlooked
- Solution design (30%): determining the technical route, affecting all subsequent work
- Hardware arrival (50%): concentrated reflection of supply chain risks
- Program debugging (70%): the key phase of technical implementation
- On-site acceptance (90%): the final reflection of customer satisfaction
- Project delivery (100%): document handover, training completion
Each node can potentially be delayed; the key is to have contingency plans in place.
After-Sales Support: The “Long Tail Effect” of Projects
Delivering equipment does not mark the end of the project, but rather the beginning of another phase.
Common after-sales issues:
Insufficient training for operators
- Theoretical training is easy, but practical experience takes time to accumulate
- Staff turnover leads to new employees being unfamiliar with equipment operation
- Inadequate ability to handle exceptions, where small issues escalate into major failures
Chaotic spare parts management
- Insufficient inventory of critical spare parts leads to equipment downtime
- Long procurement cycles for non-standard parts affect repair efficiency
- Incomplete spare parts lists make it difficult to find alternatives during repairs
Remote support capabilities
- On-site problem descriptions are unclear, making remote diagnosis difficult
- Network environment limitations prevent stable remote connections
- Time zone differences affect response speed
Solutions:
- Establish a standardized training system and assessment mechanism
- Provide detailed fault diagnosis manuals and video tutorials
- Design remote monitoring functions to proactively identify potential issues
- Establish a rapid response spare parts supply system
Summary of Experience: Key Elements for Successful PLC Projects
1. In-depth preliminary research
Do not settle for the customer’s one-sided account; it is essential to:
- Conduct on-site investigations of existing process flows
- Understand the skill levels and habits of operators
- Analyze the impact of the on-site environment on equipment
- Assess interface requirements with other systems
2. Forward-looking design
- Leave room in hardware selection, reserving 20-30% of IO points
- Program architecture should support functional expansion
- Communication interfaces should consider future integration needs
- Human-machine interface design should facilitate maintenance
3. Systematic debugging
- Single machine debugging → online debugging → system debugging, step by step
- Establish complete test cases covering various working conditions
- Record detailed debugging logs for easier problem tracing
- Develop emergency plans to handle unexpected situations
4. Standardized delivery
- Technical documentation must be complete: electrical schematics, program lists, operation manuals
- Training must be thorough: theory + practice, ensuring operators are proficient
- Spare parts lists must be detailed: specifications, supplier information, alternative solutions
- After-sales processes must be clear: response times, handling procedures, responsibility definitions
In Conclusion
PLC programming is a technical barrier, but the key to project success lies in engineering implementation capabilities.
Programming skills can be quickly improved through learning and practice, but abilities such as understanding requirements, on-site debugging, and project management require extensive practical experience.
A true technical expert is not just someone who can write good programs, but an engineer who can successfully execute projects and satisfy clients.
Technology is the foundation, but engineering capability is the core competitive advantage.
This article is based on years of practical experience in non-standard automation projects, and I welcome discussions and exchanges with peers.