Regarding the issue of communication between the lower-level and upper-level machines in a DCS system
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Dear experts, please give some guidance. A DCS system collects data from the field using various cards, processes it through controllers, and then uses those cards to carry out control functions. As for communication, the upper-level computer reads the registers of the lower-level computer via predefined protocols; the DCS serves as the medium for communication between the lower-level and upper-level computers. How is it achieved? What’s the principle behind it? I don’t understand this; maybe my description isn’t accurate. I earnestly ask experienced experts to kindly provide guidance
What you said does indeed have a problem. When the DCS communicates with other systems, it isn’t considered a slave station; nor are those other systems considered master stations. The DCS system acts as a slave station, while the other systems are the master stations. But what you said isn’t quite in line with the standard practices; generally, the DCS system serves as the master station and functions as the process control system for the entire factory, while other systems such as PLCs and frequency converters act as slave stations, all of which are monitored by the DCS system
In normal process control, DCS and PLCs belong to the control layer; communication between the DCS and subsystems takes place within the same layer. The control layer typically uses bus protocols such as Profibus-DP and VNet； The concept of a host computer generally refers to the data processing layer above the control layer; it typically reads data via OPC and stores it in SQL, from where the data is retrieved for further processing, usually using protocols such as TCP/IP.
Well, I checked some information. To be precise, it should involve setting up an OPC server in the DCS system to provide data to third parties
Yes, as you said, the DCS provides data to third parties through OPC. To do this, does one need to create a database first, read the DCS data into that database, and then transfer it to the third parties? . .
Databases are mostly built using SQL to store and retrieve data values; they typically require a large amount of disk space for storage. Such databases are managed by third-party software. Normally, OPC software installs an independent OPC server to fetch real-time data from DCS systems, which is then sent to the SQL server managed by the third party.