What is a DCS system?
DCS, or Distributed Control System, is also known as a centralized control system in the domestic automation industry. It is a multi-level computer system composed of process control and process monitoring levels, linked by a communication network. It integrates computer, communication, display (CRT), and control technologies. Its basic ideas are decentralized control, centralized operation, hierarchical management, flexible configuration, and convenient configuration.
I/O in DCS control system
Control systems need to establish input and output channels for signals; this is called I/O. In a DCS, I/O is typically modular, with one or more I/O channels on a single I/O module used to connect sensors and actuators (control valves).
DCS control unit: A process control station consists of several racks, each rack can hold a certain number of modules. The rack where the CPU is located is called the CPU unit. There can only be one CPU unit in the same process station. The other racks used to hold I/O modules are called I/O units. The I/O units are connected to the CPU via a fieldbus.
Commonly used I/O signals are generally divided into: AI – analog input signal; AO – analog output signal; DI – digital input signal; DO – digital output signal.
DCS system selection, design, and debugging
1. System and controller configuration should prioritize reliability and load factor (including redundancy). Communication load factor must be kept within a reasonable range, and controller load factor should be balanced as much as possible to avoid "high load" problems.
2. The allocation of system control logic should not be overly concentrated on a single controller; the main controller should be configured with redundancy.
3. The power supply design must be reasonable and reliable. Pay attention to the load rate and redundancy configuration of the power supply design, and ensure two independent power supplies.
4. Pay attention to the reliability of DCS system interfaces, and be mindful of the interface methods and redundancy of important interfaces.
5. DCS system grounding should be performed according to the manufacturer's requirements to avoid widespread system failures caused by grounding issues. Special attention should be paid to system anti-interference measures, and isolation measures should be emphasized for I/O channels. Cable quality and shielding are crucial; dedicated computer communication shielded cables should be used for important signals and control functions.
6. Based on the equipment's operating characteristics and the requirements for handling emergency faults under various operating conditions, configure operator stations and backup manual control devices. Emergency shutdown/furnace shutdown buttons should be configured with a separate operating circuit independent of the DCS.
7. For protection systems, a multiplexed signal acquisition method is adopted. Interlocking conditions are used appropriately to enable the signal loop to have logical judgment capabilities.
8. During the commissioning period, all logic, circuits, and operating conditions shall be tested in accordance with the commissioning outline and procedures to ensure that all parameters are set correctly and reasonably.
