How to integrate PLC with DCS
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It’s my own process; I’d like to ask those familiar with automatic control: the main workshop uses Zhejiang University’s ZHKW DCS, while one set of auxiliary equipment is controlled by a Siemens PLC, forming its own separate system. The two are about 200 meters apart. Now, the data from the PLC needs to be sent to the DCS for display, but not for control. How should they be connected? Or what does Party A need to buy?
It’s done via communication, but there should be a delay as shown by the DCS.
It is necessary to install communication cards from Zhejiang University’s Zhongkong system, connect them to the PLC communication interface, and then complete the configuration on the DCS. Modbus communication protocol is generally used for this purpose!
For serial communication, a serial server needs to be purchased. Connect the PLC’s communication cable to the serial server (the DCS must support serial servers; configure the serial server on the DCS), then connect the serial server to the DCS switch using an Ethernet cable. Configure the communication points on the DCS, and the data from the PLC points will be displayed.
The information you provided isn’t comprehensive enough. Siemens PLCs are available in 200/300/400 series; those in the 200 series usually come with a serial port built-in ； For 300/400, a CP341 is generally required to enable Modub communication. The commonly used DCS systems for central control are JX-300XP and ECS700. If it is ECS700, it is necessary to check whether the serial communication module COM741-S and the base are available on site ； If it is 300XP, it is necessary to check whether there are an XP248 card set and an XP526 terminal board on site
If there is a host computer available, the simplest and most direct approach is to use OPC for access
Use the Modbus module for communication; you should ask the supplier of the complete set of equipment, as their automation specialists will inform you.
Modbus communication, fiber optic converter, communication cable, CP341, cable
Modbus (485) or Profibus DP is recommended. If the CPU of the Siemens PLC comes equipped with a DP port (such as 315-2DP), then Profibus DP offers better cost-effectiveness compared to Modbus
In our plant’s flare system, the S7-200 units use Modbus communication to transmit data from port 1; this data is sent to the host computer in the gas holder control room, which is located over 200 meters away. Two-core shielded computer cables are used for this connection. The gas holder control system is part of the plant’s SCADA system, and the host computer has interfaces that support such communication; by using addressing techniques, it is possible to read and write data to the remote PLCs. What needs to be purchased is a data converter; we use the MOXA 232-485 model. Additionally, you need to know the variable addresses in the program of the external PLC that you want to read from and write to.