How to integrate the control and power distribution of complete sets of equipment into the DCS, and achieve control within the DCS?

The first issue is that the manufacturer provides the control scheme and instructions; this ensures that control functions can be implemented on the DCS side without problems. Almost everything that can be done with a PLC can also be achieved using a DCS, and it is easier to carry out unified maintenance and management once things are deployed on the DCS. Only issues with control within the warranty period might lead to disputes with the manufacturer. In our factory, everything that can be integrated into the DCS has been integrated there, in order to minimize the use of separate PLCs for independent control

My current project is facing similar issues. There are two provisional solutions: one is, as mentioned above, to integrate the functions of the PLC into the DCS； Another approach involves retaining the on-site PLC and communicating with it via a DCS; both the DCS and the PLC can be used for control. If a SIS is involved, separate wired connections must be established to ensure system stability. The communication protocol used in this project is Modbus RTU. I hope this will be helpful to you; it is for reference only.

So, which is higher in cost, implementing DCS or using on-site PLCs?

We need to figure out how to carry out our project now, to facilitate future operations. Personally, I prefer to go with DCS for easier management.

There are two options: one is to use a complete set of equipment controlled by a PLC, with communication to the DCS； Secondly, the complete sets of equipment can be connected directly to the DCS system; in this case, factors such as whether the backup channels of the existing DCS are sufficient need to be considered. Generally speaking, connecting them directly to the DCS system may be cheaper, but it will increase the load on the system.

Does Modbus-RTU cause severe delays when there is a large amount of field data?

First of all, there is a problem with the design: how to integrate the control and power distribution of the complete set of equipment into the DCS in order to enable control within it. You should know that the power distribution for complete sets of equipment is handled by electrical systems; whether it’s done through a PLC or without a PLC, it makes no difference from an electrical perspective – it’s still the electrical systems that handle the power distribution. At most, there might be a relay placed somewhere in that setup. Now, to answer your question: 1. As for whether to use a PLC or a DCS, each has its own advantages. Using a PLC offers the benefit of integrated equipment control and solutions provided by the equipment manufacturer; since the manufacturer has a good understanding of its own equipment, it is possible to utilize it effectively, and this also saves on costs related to customization and maintenance. However, the downside is that a black box situation can occur from time to time; generally, communication is used to transmit a large number of data points to the DCS, but a certain degree of black box behavior remains inevitable. If you want to switch to DCS control, first you need to understand the drawings provided by the equipment manufacturer, as well as all the details related to the logical control mechanisms, and then ask the manufacturer to assist you with the configuration process. This is a rather challenging process, as your knowledge of the equipment is not sufficient, and it takes time to get started. The advantage is that the entire set of equipment is no longer a black box; in case of any faults, it’s possible to identify them directly through the DCS, eliminating the hassle of having to contact the manufacturer when things are unclear. However, this also means that more maintenance work is required for the DCS. As for the cost issue, it really depends on what kind of DCS you use. If you use an imported DCS, such as one from Honeywell, then for a slightly larger device with hundreds of safety gates and cards, the cost will be enormous. Not to mention that if you have multiple devices, you’ll need additional controllers as well, which will definitely drive you crazy. If you are using a domestic DCS, such as those from Zhejiang University Zhongkong, it will definitely be more expensive than PLCs, but the price increase won’t be excessive. 2. The problem here is strange – are you using a bus meter? Why use a bus protocol? Isn’t communication between complete sets of equipment done using communication protocols? It is usually the Modbus communication protocol.

It’s best for the manufacturer to install the RTU on-site for complete systems; operation should be avoided as much as possible, and monitoring is sufficient. If there are set values, they can be adjusted remotely, while all other functions are handled by the RTU. This applies to things like heating furnaces, electric heaters, refrigeration equipment, and dew point control devices – the responsibilities are clear. That’s my suggestion!

Communication data is generally not recommended for control, unless it can be ensured that the communication is extremely stable.