DCS fault prevention and maintenance measures
Selection, design, and debugging of DCS
Whether building new units or upgrading DCS, the configuration of systems and controllers should focus on reliability and load rate (including redundancy) indicators. The design of communication bus load rate must be controlled within a reasonable range, and the load rate of the controller should be balanced as much as possible to avoid the occurrence of "high load" problems that affect the safe operation of the system due to insufficient funds caused by large-scale involvement.
(1) The allocation of system control logic should not be overly concentrated on a single controller, and the main controller should adopt redundant configuration.
(2) The power supply design must be reasonable and reliable. One is to emphasize the load factor of power supply design; Secondly, it is important to emphasize the redundant configuration of the power supply, while ensuring the independence of the two power sources.
(3) We should pay attention to the reliability measures of DCS system interfaces. Emphasize the redundancy of important interfaces and the selection of interface methods, mainly focusing on reliability and real-time performance.
(4) For DCS system grounding, it is necessary to follow the manufacturer's requirements to avoid grounding problems that may cause widespread system failures. Attention should be paid to considering the anti-interference measures, self diagnosis, and self recovery capabilities of the system, and isolation measures should be emphasized for I/O channels. The quality and shielding issues of cables must also be highly valued, and computer specific shielded cables should be used for important signals and controls.
(5) To fully consider the controllability of the main and auxiliary equipment, operator stations and backup manual control devices should be configured according to the operating characteristics of the equipment and the requirements for handling emergency faults of the unit under various working conditions. The emergency stop button configuration should use a separate operating circuit from the DCS. At the same time, we cannot blindly pursue the "simplification" of human-machine interface, and system configuration should also prioritize meeting safety production requirements. Special emergency intervention operations related to safety cannot be entirely based on the integrity of DCS.
(6) When designing and configuring peripheral equipment such as actuators and valves related to unit safety, it is necessary to ensure that these critical devices can move in a safe direction or remain in place in the event of power loss, gas loss, signal loss, or DCS system failure.
(7) For the protection system, the multiplex signal acquisition method should be adopted, and the blocking conditions should be used reasonably to make the signal circuit have logical judgment ability.
(8) During the debugging period, test all logic, circuits, and operating conditions according to the debugging outline and specific methods.
The system should undergo passive maintenance after a malfunction, mainly including the following tasks:
(1) In daily work, it is necessary to carefully follow the 25 countermeasures requirements, fully prepare for various accident scenarios including DPU (CPU) crashes and network communication breakdowns, and compile emergency handling measures, safety measures, technical measures, and maintenance steps into a book to ensure the safe operation of the unit.
(2) Handle DCS faults according to the requirements in the manufacturer's application manual. Before replacement, confirm that the card module model, address (ensuring no conflict with other equipment addresses), jumper wires, etc. are consistent with the replaced card and strictly follow the online replacement procedure.
(3) Passive maintenance of faults should also strictly follow the work order system to avoid hasty repairs. Detailed analysis should be conducted based on specific fault manifestations. Based on the self diagnosis alarm and fault phenomenon judgment of the DCS system, identify the fault point and verify the maintenance results by eliminating the alarm. For example, poor contact of communication connectors can cause communication failures. After confirming poor contact of communication connectors, use tools to redo the connectors; Communication lines that are damaged should be replaced in a timely manner. The fault light of a certain card flashing or all data on the card being zero may be due to incorrect configuration information, the card being in standby mode with redundant terminal connection wires not connected, a fault in the card itself, or the lack of configuration information in that slot. When a production status is abnormal or an alarm occurs, you can first find the instrument that reflects this status, and then use the instrument to check the correctness of the signal one by one along the direction of signal transmission until the fault is identified.
(4) Work tickets must be issued for on-site equipment troubleshooting, and DCS mandatory and isolation measures must be taken. When repairing valves, bypass valves should be activated. After the maintenance is completed, promptly notify the centralized control operation personnel for inspection, and the operators should switch the automatic control circuit to manual mode.
(5) When there is a large-scale hardware failure, unexplained failure, or failure beyond the technical level of our maintenance personnel, in addition to emergency spare parts replacement work at that time, we should promptly contact the manufacturer and have their professional technical support engineers further confirm and troubleshoot the problem.
DCS should be managed comprehensively from design, construction, commissioning, to operation. As system maintenance personnel, they should develop scientific, reasonable, and feasible maintenance strategies and methods based on system configuration and production equipment control, achieve close coordination between preventive maintenance and daily maintenance, and carry out systematic, planned, and regular maintenance. For various faults that occur during operation, specific problems should be analyzed. The key to reducing DCS failures is to prioritize prevention and ensure that the system operates well in the required environment for a long time.
Reprinted from official account: Industrial Control E Station