Is Siemens’ S7-400 considered a DCS control system?
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For a 10,000 capacity air separation unit, a DCS system is required for the control system and related process equipment; among the recommended systems, Siemens’ S7-400 product is listed. Does this count as a DCS system? Online searches indicate that it is considered a PLC.
The S7-400 can be used as either a DCS system or an SIS system.
A S7-417H in redundant configuration will do
Siemens’ DCS is called PCS7 internally. The hardware consists of an S7-400 CPU + EM200M + 300 IO modules. To be honest, the DCS he added is really awkward to use. If you go with DCS, for a 10,000-unit air separation unit, both domestic control systems and Hilscher’s systems are viable options; I highly recommend using the domestic control system.
The S7-400 is a PLC as well as a DCS system. There is no significant difference in performance between large-scale PLCs and DCS at present.
Today’s PLCs are moving in the direction of DCS systems; DCS control can be achieved as long as there are AI/AO modules available, but further improvements are needed in terms of software. Personally, I think DCS is still the better choice for process control. As far as I know, all AP air separation plants use S7-400 for their DCS.
DCS is a system composed of various hardware components and several software systems. A PLC is a programmable logic controller; it is merely hardware, equivalent to the CPU part of a DCS. By using the S7-400 series of PLCs and configuring various hardware components along with appropriate software managers, it is still possible to create a DCS system.
The PLC program uses a polling structure and does not execute CPU interrupt instructions; it still simulates the current flow in the hardware circuit, which means there is still a difference between it and a DCS. Therefore, it is inaccurate to say that PLC is a hardware foundation of DCS. However, as the analog calculation capabilities of PLCs continue to improve, it is now possible to do so without affecting performance.
How is the concept and structural composition of DCS described? What kind of system is considered a DCS? What is the understanding of narrow-sense DCS and broad-sense DCS?
It can be understood literally. PLC, or Programmable Logic Control System, is primarily used for digital control; certainly, it has made significant improvements in terms of analog control as well, but it still lags behind DCS in many aspects. DCS, or Distributed Control System, is mainly used for analog control and is typically applied in medium to large-scale process control applications. Hardware is one aspect, while the corresponding programs have different focuses.
Discussing these things is putting the cart before the horse, or it serves some purpose. When getting a system, the first thing to check is its usability and whether it suits my needs. This system is good value for money, reliable, and easy to use, right? This is the main approach to thinking about this matter.