Is it better for the desalination water pump in the chemical desalination system to be controlled by the chemical water treatment PLC station or by the plant-wide DCS?

It is more reasonable and convenient to use a PLC station to control the chemical desalination water pumps. This is because the chemical demineralized water system already has a complete PLC station that was specifically designed and optimized for this system. By keeping the demineralized water pump under PLC control, it is possible to leverage the PLC’s specialized regulatory capabilities for specific systems, thereby ensuring the stability and efficiency of system operation. Moreover, maintenance and troubleshooting will also be more centralized and convenient. .

Either one is fine; it depends on which system your factory is more familiar with, PLC or DCS. In our factory, there are very few people who understand PLCs, while there are many who are familiar with Zhejiang University’s DCS system. When a PLC system breaks down, it causes a lot of trouble for the staff, as no one knows how to deal with it; even installing WINCC presents difficulties, let alone using TIA Portal for programming. Relatively speaking, DCS is suitable for processes that are not very sensitive to time, and it is particularly well-suited for the large-scale processing of analog signals. It’s fine to open a valve half a second late. PLCs are well-suited for applications involving a large number of digital signals; for instance, in controlling stepper servo motors, interrupts can be used to enable immediate response. If chemical demineralization isn’t time-sensitive, DCS can be used as a replacement; having them in one system makes maintenance easier. If a PLC is used, it’s also possible to transmit the status remotely to the DCS via communication; furthermore, control can be exercised from the DCS as well

Mainly, the system needs to stop when the liquid level in the tank in front of the water pump is low; this definitely needs to be taken into account in the PLC； However, all the equipment and instruments on the water side fall within the scope of DCS control; thus, it seems like each has its own responsibilities to manage, but it’s not clear what the best approach would be. Should we consider the supply side or the demand side?

You are speaking from a maintenance perspective, and that’s fine. In our current design, we’ve clearly taken this into account within the PLC logic. Essentially, if the DCS needs to control the demineralized water pump, hardwiring must be used instead of communication-based control. Therefore, during the design phase, we must think this through carefully; otherwise, it might not be possible to make corrections later on

It can be resolved through communication; whether it’s a PLC or a DCS, both support PROFIBUS, and a dedicated data area can be created for interaction.

If you’re afraid of the hassle, use DCS; it’s easier as everything is integrated within one system. That is, you have to use the DCS automatic control program to replace the previous PLC automatic control program.

If the equipment isn’t yet available, it’s advisable to use DCS instead. If the manufacturer provides you with PLC equipment, then using it would be a waste. Using DCS configuration is much more convenient than using PLCs; moreover, the entire plant can be integrated as one unit. In our factory, there are also many sets of equipment that use PLCs. The workers here don’t understand how they work; it’s quite troublesome to make any modifications in the future. Whenever something breaks down, we have to call the manufacturer for repairs. Especially when it comes to equipment used in pilot and lab-scale tests, making any changes is even more troublesome.

This newsletter is simple; you can add whatever you want, whenever you like. But here, since it involves control and interconnections, the use of communication is completely prohibited; only hardwiring is allowed.