Feasibility of constructing a simple \"distributed system\" using Siemens S7-300
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With a new project upcoming for the company, there are disagreements internally regarding whether to introduce a DCS, and I personally am against it. I am mainly considering the company’s current technical capabilities and engineering experience (I certainly don’t look down on my other colleagues; I’m just aware of my own limitations). Implementing a DCS system is practically as difficult as reaching the sky ； Moreover, DCS undoubtedly increases costs. The engineering background is as follows: Our company has been contracted to undertake the construction of 3 workshops at a solid waste environmental protection facility. The initial phase of the work focused on one workshop, where two processes required automated control for continuous operation; the pumps and valves in other areas of the workshop could be operated manually (remotely). At first glance, this seems like a case that would require a distributed control system (in my opinion). However, an issue arises: Is it feasible to reject the use of a DCS and instead use 300 PLCs to connect all the control variables in the workshop to a central control room, with a host computer used for control? What communication devices are involved? Is there anyone who can give some guidance on the specific usage of the CP5611 card?~
The last edit to this post was made by huio1983 on 2012-2-28 at 08:21. The boundaries between PLCs and DCS systems are becoming increasingly blurred; functions can be implemented using the appropriate cards. I don’t understand why it is said that DCS systems are expensive. Both PLCs and some DCS systems can communicate with higher-level computers through OPC, unless there are special requirements
In fact, Siemens’ DCS uses the architecture of the PLC S7 combined with a host computer! I still recommend DCS; in my opinion, the difference between the two is not significant, as the technical requirements are the same.
It can be achieved using a 300PLC. It depends on the specific number and type of signal points, as well as the communication distance. If you use a CP5611 card in your host computer, then the PROFIBUS communication protocol can be employed. PROFIBUS communication uses the RS485 physical structure; its theoretical communication distance is 1200 meters. When the distance exceeds 1000 meters, it is recommended to use an RS485 repeater. The farther the distance, the more the signal attenuates, and the lower the communication rate. PLCs are more suitable for logical operations, while DCS focuses on system operation, monitoring, and management. However, the gap between PLCs and DCS is becoming smaller and smaller. The hardware for the controller in Siemens PCS7 DCS systems is the 400 series PLC. Attached are the technical specifications for CP5611; I hope it will be helpful. http://www.ad.siemens.com.cn/download/searchResult.aspx?searchText=A0028
I think it’s fine to use a PLC for two-position cut-off control; using a PLC for PID control is rather complicated and not conducive to future maintenance and modifications. In more complex control systems, it becomes even more troublesome, and the historical data tracking functionality isn’t as user-friendly as that of a DCS – it’s not as convenient to view and track data with a DCS.