Solving a problem in PLC and DCS communication
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Now, a compressor manufacturer has its own PLC, and it needs to transmit certain signals to my DCS via communication. After this communication, do these signals still need to pass through a safety barrier or relay before connecting to the I/O cards in order to reach the DCS? If not, how do these signals get into the DCS? How should one draw a circuit diagram? Thank you all.
Using fiber optics for communication between PLC and DCS achieves electrical isolation!
These signals are transmitted over a single wire; they are digital signals, similar to Ethernet signals. Your DCS must have communication ports, and it needs to be configured according to the communication protocols provided by the air compressor manufacturer. Generally, this involves RS485 interfaces, as well as MODBUS or PROFIBUS communication protocols. Therefore, safety barriers and relay isolation are not required. Drawing a circuit diagram should simply involve one line branching into multiple lines for representation.
It is usually an RS485 interface, with MODBUS or PROFIBUS communication
First, check what communication protocols are available for the PLC. The simplest approach is to see if the DCS upper-level software has a communication driver for that PLC; if it does, a connection can be established directly through that driver, without the need to install anything globally on the DCS, which also makes maintenance easier in the future
Communicate with the DCS using PROFIBUS-DP.
First, check what communication protocols the PLC supports, and then see if the DCS is compatible with those protocols. If it is to be used only for monitoring rather than for control or interlocking, the suggestion from Section 5 can be adopted. However, generally, when a DCS supports third-party protocols, an additional fee is required as a license must be purchased. Generally, RS232 or RS485 communication, MODBUS or PROFIBUS communication, and TCP/IP communication are used; as a result, it is sometimes necessary to add communication hardware to the DCS and PLC.
Are there PLCs that support the Hart protocol? This allows direct communication with our plant’s DCS
PLCs do not use the HART protocol; the HART protocol is used for field instruments!
There are dedicated communication card modules available, which allow for direct communication without the need to go through a safety barrier.
Our HC900 unit and the infrared analysis instrument use the 485 communication method; the infrared analysis instrument only needs to provide a device address
The most important thing is that your DCS monitoring software must be compatible with the PLC’s communication protocol; our factory uses RS485 communication, and one communication cable is sufficient for that purpose!
For ESD and DCS communication in our factory, communication cables are used; the communication card used by the DCS is the ACM12 with an RS485 interface, and no safety barriers are required
Communication is generally done using RS485/232, without the need for a safety barrier; both the PLC and the DCS side require dedicated communication cards, which can be configured as needed.