Difference and connection of DCS/PLC system

The integration of PLC and DCS is the development trend in the control field. In the future, a large number of PLCs will be integrated into industrial distributed control systems. With the continuous improvement of the internal compatibility, replaceability and stability of the system, the classic control system will be replaced by the DCS integrated configuration system. From the perspective of usage, the average time between failures of the PLC control system is about 40,000 to 60,000 hours. DCS Distributed Control System DCS, also known as Distributed Control System, is a complex industrial system used for centralized control or classified parallel control of the production process. It belongs to a comprehensive equipment control device. The emergence of DCS is that with the continuous improvement of modern large-scale industrial production automation, the requirements for the system in the production process become increasingly complex. At this time, an industrial system that can perform parallel centralized control is needed to take a comprehensive view of the overall situation, so DCS came into being. , it can combine the communication network with the automatic control system, which has a high level of efficiency improvement for industrial production. The classic DCS system generally consists of three parts: centralized management system, decentralized control device and communication network connection module. Workflow analysis of DCS system: DCS can use configuration software to set up and manipulate hardware and program modules according to actual process control requirements, such as selecting control circuits, control schemes and generating trend screens after configuration. The DC generates a series of configuration files prior to startup, which can be loaded into the process control unit and operator station based on various file properties before the system is operational. Then the process control unit finds the corresponding control algorithm from the function module library solidified in the EPROM, and starts the process according to the content of the configuration information file. The difference between DCS and PLC: DCS control system is an artificial system developed by instrument manufacturers on the overall disc-shaped control device. It can analyze relevant analog quantities through on-site monitoring data, thereby providing correct information to the control personnel. DCS system manufacturers can use different communication protocols, but the network transmission platform generally adopts Ethernet, and provides a convenient external expansion interface for future function expansion, which provides great convenience for future function expansion. The PLC system is generally a curing device. After the system is installed and started, the demand for function expansion is very small, so it is difficult to carry out related function expansion and compatibility investigation. The DCS control system can use redundant control units to ensure the stability of the overall system, which can provide the function of non-disruptive switching to the standby module in the event of a major failure of the system and cannot continue, and ensure that the system operating state is not lost . However, although the PLC device uses a cyclic sequential scanning method with high control accuracy, there is no redundant control program for hot-swappable modules, and the entire system must be maintained and replaced after the system is stopped. DCS control systems usually have a complete system database, each link in the database system provides real-time references to relevant data, and supports other links flexibly and conveniently. At the same time, in the PLC configuration equipment of DCS, each link has a corresponding data link, which can be applied in real time when dynamically called to ensure the normal operation of the system.