Differences between DCS control systems and conventional instrument control systems
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When looking at standard 20505, it can be seen that there are differences between DCS control systems and conventional instrument control systems. Since I’m not familiar with these two concepts, let’s use an example to illustrate: What category does the scenario where a PT100 signal is fed into a PLC control cabinet fall under? The flow meter signal is fed back to the PLC, which then uses this signal to control the control valve. What kind of system is this?
The DCS control system, also known as a distributed control system, implies decentralized control with centralized management. Individual decentralized control systems are usually regular instrument control systems; by bringing them together for unified management, we obtain the DCS control system.
What does centralized management mean? Just as in the example I gave, all the signals from the entire system are fed back to the PLC, which is used for control via a computer – isn’t that considered a DCS control system?
It’s not this kind of awareness; control via a computer constitutes a computer-based control system. In a DCS, each system is controlled independently, with the computer serving only as a tool for management and monitoring. When the computer fails, it does not affect the normal operation of individual systems.
This post was last edited by A fierce tiger in the heart on 2016-9-8 at 14:47. Just tell me, as in the example I gave, how to draw graphic symbols. . Is it a circle, or a rectangle, or a hexagon? Should there be horizontal lines inside? :Lol: What I meant by controlling it on a computer is controlling things like pumps and valve switches.
In automation engineering, detection devices (various sensors and transmitters) and actuators (control valves are commonly used in the petrochemical industry) are referred to as primary instruments, while control, computing, display, indication, alarm functions, etc., are called secondary instruments. Secondary instruments can be various actual meters, or they can be virtual ‘meters’ (control tools such as DCS, FCS, PLC, IPC, etc., which are based on computers and networks). The primary instruments that make up Basic Process Control Systems (BPCS) and Safety Instrument Systems (SIS) are various sensors and transmitters that collect information on the production process; these instruments then use control valves or solenoid valves to intervene in the production process ； However, there are two possibilities for secondary instruments: one is to use conventional instruments (such as YS series, S series, I series, EK series instruments), and the other is to use control tools based on computers and networks such as DCS, FCS, PLC, IPC, etc. Therefore, HG/T20505 -2014 uses different symbols to distinguish between these two situations.
This post was last edited by Xin You Meng Hu on 2016-9-9 08:34. It was explained very well – clear and straightforward! Do you think my understanding is correct? I first draw a circle around the primary instrument (sensor), and then add one with a box around it to represent the secondary instrument (virtual instrument PLC). Also, the YS series, S series, I series, and EK series of instruments you mentioned refer to actual physical devices, right?
In conventional instrument control systems, also known as panel-mounted instrument control systems, these instruments are generally installed in front of control panels. The S-series and I-series instruments mentioned on the sixth floor are examples of such devices; they use individual instruments to carry out various control functions. For instance, alarms display warning information, regulators control the circuits, operators are used to manually open and close valves, and recorders are instruments that display data along with historical trends. The DCS systems we use today replace these panel-mounted instruments with control cabinets and operator stations – the control cabinets handle logical operations while the operator stations are responsible for displaying information. What category does the setup mentioned by the poster, where PT100 signals are fed into a PLC control cabinet, fall under? The flow meter signal is fed back to the PLC, which then uses this signal to control the control valve. What kind of system is this? This should be called a computer control system; it simply uses a PLC, an editable logic controller, instead of a DCS to carry out the logic control functions. It can also be referred to as a distributed control system