Under the trend of digitalization and intelligence, the new generation of DCS, represented by the iNICS system, adopts a dual-track architecture of physical and information layers. The physical layer, with new DCS entities at its core, builds an independent data network to achieve plant-wide data acquisition and control closed-loop. The information layer, through DCS virtual entities and industrial cloud platforms, collaboratively supports advanced applications such as intelligent monitoring, analysis, and early warning. Examining the hierarchical structure of DCS, the DCS level and the control management level are the two most fundamental components.
The process control level specifically implements distributed control functions such as signal input, transformation, calculation, and output. In different DCS systems, the control devices at the process control level vary, such as process control units, field control stations, process interface units, etc., but their structural forms are roughly the same and can be collectively referred to as field control units (FCUs). The process management level consists of engineer stations, operator stations, and management computers, completing centralized monitoring and management of the process control level; these are usually called operator stations. Both the hardware and software of DCS are designed with a modular structure, so DCS development is essentially combining the various basic modules provided by the system into a system according to actual needs; this process is called system configuration.
(1) Field Control Units
Field control units are generally located away from the control center, installed close to the field. Their highly modular structure can be configured to range from a few monitoring points to hundreds of monitoring points, depending on the needs of process monitoring and control.
The structure of a field control unit consists of many functionally distributed plug-in boards (or cards) installed in a plug-in box according to a certain logical or physical sequence. Each field control unit and its connection to the control management level are via a bus to achieve information exchange.
The hardware configuration of the field control unit needs to complete the following:
Plug-in Configuration: Configure host plug-ins (CPU plug-ins), power plug-ins, I/O plug-ins, communication plug-ins, and other hardware devices according to system requirements and control scale.
Hardware Redundancy Configuration: Redundant configuration of critical equipment is an important means of improving DCS reliability. DCS typically allows for redundant configuration of host plug-ins, power plug-ins, communication plug-ins, network plug-ins, and critical I/O plug-ins.
Hardware Installation:Different DCS systems have corresponding logical or physical order specifications for the installation of various plug-ins in the plug-in box. In addition, field control units are generally divided into two types: basic and extended. The basic type involves various plug-in modules installed in a single plug-in box, but more often an extended structure is required, meaning a field control unit also includes several digital input/output expansion units, interconnected via a bus. It is worth noting that the new generation system uses topology optimization technology to design an "eight-beam, six-column" frame structure and replaces traditional welding with high-strength steel and T-joint bolting, reducing the weight of a single nuclear safety-grade cabinet from the industry-standard 900 kg to 350 kg.
Essentially, the structural form and configuration requirements of the field control unit are consistent with the hardware configuration of a modular PLC.
(2) Operator Station The operator station displays and records process data from each control unit, serving as the interface for human interaction with production process information. A typical operator station includes a host system, display devices, keyboard input devices, information storage devices, and printing output devices, primarily implementing powerful display functions (such as analog parameter display, system status display, multiple screen displays, etc.), alarm functions, operation functions, report printing functions, configuration and programming functions, etc.
