GE SR489-P5-HI-A20-E DCS Hierarchy – DCS Process Control – DCS Control Management

Examining the hierarchical structure of DCS, the process control level and control management level are the two most basic components that make up DCS.
The process control level specifically implements decentralized control functions such as signal input, transformation, operation, and output. In different DCS, the control devices at the process control level are different, such as process control units, on-site control stations, process interface units, etc., but their structural forms are roughly the same and can be collectively referred to as on-site control units (FCUs). The process management level is composed of an engineer station, an operator station, a management computer, etc., which completes centralized monitoring and management of the process control level, commonly known as an operation station. The hardware and software of DCS are designed according to a modular structure, so the development of DCS is actually to combine various basic modules provided by the system according to actual needs into a system. This process is called system configuration.
(1) Field control unit
The on-site control unit is generally located far from the control center and installed near the site. Its highly modular structure can be configured into process control units with varying scales from several monitoring points to hundreds of monitoring points according to the needs of process monitoring and control.
The structure of the on-site control unit is composed of many functionally dispersed plug-in boards (or cards) installed in a certain logical or physical order in the plug-in box. Each on-site control unit and its connection with the control management level are connected by bus to achieve information exchange.
The hardware configuration of the on-site control unit needs to complete the following tasks:
Configure hardware devices such as host plugins (CPU plugins), power plugins, I/O plugins, communication plugins, etc. based on system requirements and control scale;
Hardware redundancy configuration is an important means to improve the reliability of DCS by configuring critical equipment with redundancy. DCS can usually achieve redundancy configuration for host plugins, power plugins, communication plugins, and network and critical I/O plugins.
Different DCS hardware installations have corresponding regulations in logical or physical order for the installation of various plugins in the plugin box. In addition, on-site control units are usually divided into two types: basic and extended. The so-called basic type refers to the installation of various plugins in a plug-in box, but more often, an expandable structural form is required. That is, a on-site control unit also includes several digital input/output expansion units, which are connected to each other through a bus.
Essentially, the structural form and configuration requirements of the on-site control unit are consistent with the hardware configuration of the modular PLC.