Before selecting a DCS system, it is essential to clearly define the application goals and functional requirements. The size of the system must be determined through discussions among instrument automation professionals, process engineers, computer experts, and design institutes. This ensures that the system meets the production and operational needs as effectively as possible.
1. Application Objectives of DCS
(1) Enhance Production and Management Levels
Improving production efficiency, reducing costs, saving energy, enhancing product quality, increasing flexibility in production changes, improving equipment management, enabling scientific fault analysis, and standardizing production management can significantly boost labor competition and uncover production potential.
(2) Improve Equipment Control Level
Realizing stable control, operation optimization, advanced control, sequence logic control, equipment fault diagnosis, interlock protection, and optimal control for local or full equipment systems enhances both production and management levels. This contributes to achieving safe, stable, long-lasting, efficient, and high-quality production with significant economic and social benefits.
These goals can be implemented in stages, gradually expanding the system to reach the ultimate objective.
2. System Function Requirements
(1) Data Acquisition and Storage
This includes analog and digital signal scanning times, historical data storage types (such as adjustment trends and historical trends), number of points, period, and input signal processing functions.
(2) Control Functions
The system should have complete monitoring, adjustment, and sequence control capabilities, along with equipment operation monitoring, interlock protection, and feedback control functions. It should support process control languages like ST, FORTRAN, BASIC, C, or other control languages and advanced control software.
(3) Display Functions
Features include CRT size, color, screen refresh time, screen type, and quantity. Displays should include general diagrams, flow charts, control groups, adjustment screens, trend displays, alarm screens, status screens, operation logs, and history queries. The system should also support window stretching, overlapping, Chinese character display, and touch screen functionality.
(4) Alarm Functions
Alarms should cover analog/digital signals, instrument deactivation, and system component faults. Features such as alarm filtering, grouping, prioritization, and suppression are essential for effective management.
(5) Report and Screen Copy Functions
Support for real-time and scheduled reports (daily, monthly, annual), alarm summaries, operation records, and screen printing is crucial for comprehensive documentation.
(6) Operational Safety
Includes password-based access, operator key functions, disturbance-free switching between manual, automatic, and cascade modes, and redundancy measures to ensure secure operations.
(7) System Flexibility
The system should be reliable, scalable, and compatible with existing systems. Open communication interfaces and backward compatibility are important for future expansion.
System function requirements should be tailored to specific project needs. For example:
a. Fast scan speed and sequence control execution cycle must align with process specifications. A case where a DCS failed to meet process requirements led to the need for an additional PLC, increasing investment.
b. Advanced control software development should focus on control functions and development tools.
2. Selection of DCS
1. Model Selection Principles
Selecting the right DCS model is critical. With rapid technological advancements, the market has evolved from foreign monopolies to a mix of domestic and international manufacturers. Users typically evaluate 3–5 models through bidding, considering factors like reliability, stability, scalability, cost-performance, and after-sales support. Choosing a model that matches the company’s maintenance and management capabilities is ideal.
2. Evaluation Content of the Model
Evaluation includes hardware configuration, I/O card capabilities, communication functions, host computer interface, software features, technical services, application tools, and pricing. Each aspect should be compared to ensure the best fit for the project.
3. Lessons Learned
End users should make decisions based on their own conditions, using patent and design institute recommendations as guidance. Over-reliance on powerful models may lead to unnecessary costs and maintenance issues. A successful case involved a user choosing a more cost-effective model that improved performance and reduced expenses by over one-third.
3. DCS System Configuration
1. Work Content of System Configuration
DCS configuration involves determining I/O points, control stations, monitoring stations, operation stations, auxiliary consoles, communication systems, power supplies, and spare parts. The goal is to minimize hardware while ensuring efficiency and leaving room for future expansion.
2. Experience and Lessons
Over-configuring or under-configuring hardware can lead to inefficiencies or operational delays. Redundancy should be adjusted based on whether the system is new or upgraded. Operators should not be overloaded with too many stations, but neither should they be insufficient, especially in large-scale projects.
4. Establishment of the System Use Environment
1. Work Content
Creating a proper environment for DCS is vital. This includes setting up the control room, ensuring proper lighting, temperature, grounding, and avoiding interference. Standards like GB2887-82 and manufacturer guidelines should be followed.
2. Experience and Lessons
Environmental conditions directly impact DCS performance. High temperatures, dust, and poor grounding can cause failures. Proper air conditioning, dust prevention, and clean rooms are essential. Avoid adding heating systems or plumbing in the control room to prevent water damage.
5. Staff Training
1. Work Content
Training is crucial after system setup. It includes training for system engineers, configuration designers, hardware and software engineers, and operators. Proper training ensures smooth operation and future system improvements.
2. Experience and Lessons
Training should focus on practical skills rather than theoretical knowledge. For foreign DCS systems, language barriers and unclear abbreviations can hinder usage. Comprehensive training helps operators understand and use the system effectively.
6. System Configuration and Generation
1. Work Content
System configuration involves both hardware and software setup. Key steps include designing configurations, understanding DCS functions, and consulting with process engineers to ensure practicality and usability.
2. Experience and Lessons
End-user involvement in configuration leads to better results. Poorly configured systems often fail to meet actual needs. Successful cases show that combining theory with practice yields the best outcomes.
7. Installation and Commissioning
1. Installation Work Content
Installation requires a clean, well-lit, and properly grounded environment. All components must be installed according to manufacturer guidelines, with careful attention to voltage, temperature, and wiring.
2. Debugging Work Content
Debugging involves checking hardware, testing system functions, and verifying joint operations with field devices. Proper planning and documentation are essential to ensure a smooth commissioning process.
3. Experience and Lessons
Proper installation and debugging prevent costly errors. Ensuring correct voltage, grounding, and signal connections is critical. Regular checks and backups help avoid data loss during testing.
8. Commissioning and Assessment
1. System Operation
Commissioning requires the system to be fully tested, with trained personnel and backup parts ready. The system must meet all technical standards before being put into operation.
2. System Assessment
A 72-hour evaluation period is recommended to assess system reliability and performance. Metrics like operating rate and fault tolerance are key indicators of success.
3. Experience and Lessons
Proper preparation before commissioning ensures a smooth transition. Post-commissioning assessments help identify areas for improvement. Effective management and maintenance are essential for long-term success.
9. System Maintenance
1. Maintenance Work
Maintenance involves regular health checks, parameter updates, and handling faults. Keeping detailed records and maintaining spare parts is crucial for system reliability.
2. Continued Application Development
Application software development should evolve alongside the system. Regular updates, advanced control features, and integration with MES systems enhance system performance and economic benefits.
In conclusion, implementing a DCS system successfully requires thorough planning, proper selection, accurate configuration, and continuous maintenance. When done correctly, DCS becomes a cornerstone for achieving stable, efficient, and profitable operations within an enterprise. It also lays the foundation for modern management information systems and integrated production control.
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