The issue of displaying and controlling PLC data on a DCS
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I’m seeking advice from experts in control systems. I have a set of equipment that is controlled by a PLC, and now I want to transfer the data to an existing DCS system for monitoring and control. Do I need to purchase cards with the appropriate number of inputs/outputs for this? Can it still be controlled through some communication protocol? Similarly, for two sets of DCS to control each other, is it sufficient to use some kind of communication protocol? No need for double card slots?
1. Add corresponding communication modules to the PLC and DCS, such as those that support the Modbus protocol, Modbus TCP protocol, and Profibus protocol. Typically, the DCS acts as the master, while the PLC acts as the slave. You still need to exercise control over this; it is recommended to use a redundant configuration for the communication module. 2. Generally, your PLC is equipped with a host computer; you can configure this host computer as an OPC SERVER, while the DCS stations act as OPC CLIENTS. Honeywell DCS is more convenient and advantageous for implementing this solution; other brands are somewhat more complicated or do not support it at all as a CLIENT. This may require purchasing licenses and software.
Thank you, expert. I have another question: the number of control points that this PLC needs to handle is unknown. Will this affect the selection of the communication module? To put it plainly, if I have 10 or 100 PLC control points, is the additional hardware the same in both cases?
First of all, you haven’t specified what model of PLC or DCS it is, so it’s difficult to give you an exact answer; I can only provide a rough estimate
Then what’s the need for a PLC? Just put everything back into the DCS
For the mainstream DCS/PLCs available on the market today, a communication cost of three to four hundred points (WORD) is completely acceptable. A BOOL digital value can be packaged into a WORD, so that 16 digital values actually occupy 1 communication slot.
If communication interfaces have been reserved during the system design phase, there is no need to add additional communication cards. If there are other important points that need to be controlled in addition to monitoring, hard wiring is advisable. Naturally, if the number of reserved points on the existing circuit boards is insufficient, it should be increased accordingly.
Transfer the data communication from the PLC to the DCS; use the DCS interface for the displays, and retrieve the data by utilizing the communication module of the DCS. OPC is not involved for now