What is a DCS system?
DCS stands for Distributed Control System – This is a system where control is not centralized in one place, but it is distributed, dividing control to each scene, each branch in the system. system.
DCS . system monitoring room
Compared with PLC control system, DCS system is a more complete solution. These include hardware, software, and system-wide communications.
What does the DCS system do?
The advantage of the DCS system is that it is capable of handling analog signals and performing complex computational processing sequences. Not only that, they are also easy to integrate or extend.
Today, production systems, whether large or small, have the appearance of control devices, communication networks and operating system software that support the integration of distributed control capabilities. These systems can handle from a few hundred to several thousand in/out points.
A DCS system can simultaneously perform many adjustment loops, multi-stage control, run modern control algorithms such as: predictive model control (MPC), Fuzzy, Neural, quality control ( QCS)… Thanks to the same hardware and software structure.
Along with the development of the DCS system, the control systems until now support a variety of communication methods (Profibus, Ethernet, Foundation FieldBus) from local to management level.
Always appreciated for research and improvement. Current DCS systems have very high reliability and double redundancy in all branches in the system (controller, I/O module, communication bus), program changeability, structure change system, adding and removing components without interrupting, without restarting the process (online changes).
All of the above characteristics show that DCS systems completely meet the requirements of a total integrated automation solution.
How is the DCS system classified?
Currently, DCS systems are classified based on their operating background, specifically they are divided into 3 types that we can understand as follows:
The DCS system runs on the PC platform
In recent years, it has become much more common to boldly experiment and use a personal computer (PC) directly as a control device. If compared with PLC controllers and specialized DCS controllers, this solution has advantages such as:
- Open feature
- Free Programmability
- High computing performance
- Multifunction
- High economy
The development of computer technology, software industry and fieldbus technology are the strong factors that confirm the competitiveness of PC in industrial control.
DCS-PC . System
The PC-based DCS system is a relatively new solution, for example: PCS7 (Siemens, Slot-PLC solution), 4Control (Softing), Stardom (Yokogawa)…
DCS system works on PLC
Programmable logic controllers (PLCs, programmable logic controllers) can be considered as a type of specialized control computer.
With flexible in/out coupling structure, simple working principle, ability to program and store programs in memory without direct hardware intervention, etc., that’s why PLC is compatible high with DCS system.
Some typical PLC-based DCS systems are SattLine (ABB), Process Logix (Rockwell), PCS7 (Siemens), …
Old-fashioned DCS system
These systems are essentially control modules that are developed and embedded by the machine manufacturer. They are usually a closed system, not following today’s industry communication standards, the controllers used are often only for process control, so a combination of PLCs must be used for control problems. logic control and sequence control.
Later new systems also feature better openness, some with hybrid control capabilities. Responsible for both process control, sequence control and logic control (hybrid controller).
Today, with the great development of DCS systems, these old systems are also gradually replaced and renovated to suit the system control needs of business owners.
Components of a DCS . Distributed Control System
In a DCS system there are many different components involved. But overall, we can weight, divide them into 4 main parts as below for easy learning and operation.
The ingredients include:
Local control station
It is the place to perform all control functions for a stage. Local control stations are often scattered near the production site area.
Controlling the DCS . system
The functions performed by the local control station are as follows:
- Process control: Control of closed loop circuits (temperature, pressure, flow, …)
- Sequence control
- Logic control
- Set the output signals to a safe state in the event of a system failure
- Temporary storage of processing signals in the event of loss of communication with the operator station
- Identify cases where threshold values are exceeded and generate alarm messages
Regardless of the type of equipment used, a local control station must meet important technical requirements such as:
- Real-time feature
- Reliability and Availability
- Convenient programming, allowing to use/install advanced algorithms
- Hybrid control capabilities (continuous, sequence and logic)
DCS . system operating station
The operating stations are under supervisory control level, these stations are located in the central control room. Operator stations can operate in parallel and independently of each other. People often arrange each operating station corresponding to a segment or a workshop for convenient control.
However, the software running on all stations is exactly the same, so in case of necessity each station can replace the function of the other stations.
Typical functions of an operator station include:
- Displays standard images (overall images, circuit images, sequence control images, real-time graphs, etc.)
- Display freehand graphics (technology flowcharts, control keys)
- Create and manage control formulas
- Handling events and incidents
- Data storage and management
- System diagnostics, operator support and system maintenance
- Automated reporting support
DCS . system development-engineering station
Technical station is the place to install DCS system development tools, allowing to configure, create and monitor control application programs and man-machine interfaces, etc. for the system.
Technical station- DCS . system
Some typical features of technical station development tools are:
- Development does not require DCS hardware in place
- The most common programming languages are function block diagrams (FBD-Function Block Diagram, or CFC-Continuous Function Chart).
In some systems, people do not distinguish between the operator station and the technical station, but use a keypad with a key to switch between the two operating and development modes.
Communication system
When using a distributed in/out structure, local control stations will be supplemented with bus interface modules to connect to remote in/out stations and some smart field devices.
Fieldbuses typically have to satisfy requirements such as:
- Real-time feature
- Simplicity and low cost
For flammable and explosive environments; and other special technical requirements on transmission standards, cable materials and electrical properties of network components, transmission cables, etc.
The most strongly supported media fieldbus types are Profibus-DP, Foundation Fieldbus, DeviceNet and AS-I. In environments requiring fire safety, Profibus-PA and Foundation Fieldbus are the two most commonly used systems.
Learn the functions of the DCS . system
The main and most important function of DCS; is to control all technological processes in the factory. Control functions are assumed by control devices, located in the central control room or in control stations.
Control function
The DCS performs all the basic control functions of a plant. Components that perform basic control functions in DCS are called “Function Blocks”. Each function block represents the smallest part of the control problem. The implementation of the control function design is essentially a combination; function blocks together to match.
– Function to perform automatic tuning algorithms: Automatically perform feedback adjustment for loops of continuous processes. The main components involved in the auto tuning function are the PID blocks; in/out data format conversion function blocks and math function blocks
– Sequence control algorithm implementation function: Performed for some work stages in sequence of events in the factory. This function both controls each stage independently; simultaneously manage the entire chain of events occurring in the system.
Controlling the DCS . system
– Function to perform complex algorithms: DCS system is an application control system for large-scale factories; Modern and complex technology. Therefore, it is necessary to have advanced algorithms to solve optimization problems and save materials.
System operation and monitoring functions
- The DCS system allows us to represent all the processes; plant equipment visually and vividly, providing operating and monitoring interfaces.
- The DCS system has divided, sorted and represented the parameters; state in various forms to maximize operator convenience. Process variables in addition to being directly viewable. We can also monitor through graphs. Allows us to compare, evaluate control quality and make control decisions.
- Besides the control functions, status monitoring; the giving of operator warnings and handling suggestions; is also an indispensable requirement for any DCS system. The alarms in the system are divided into several different levels:
Warning (Warrning)
Alarm (Alarm
Error Reporting (Failure) - To support monitoring and management; DCS provides reports for each process variable; critical areas periodically or on demand. In addition, regular performance reports are available to:
Collect, display and print information about the operating status of the system
Reports of alarms, I/O and statuses
Report on working history, errors, events occurring in the system
Security function (Security) To prevent operating errors and ensure system safety. DCS provides the ability to split access to the granular system to each device and function block. Various levels of security can be set from the level of zones; to each device in the factory. Each operator has only authority and responsibility in a certain area.
The content of the article has provided us with the most overview of the DCS system. To understand how the system actually works; we need to have models or directly participate in exploiting DCS system; in factories to master them.
Articles I have references from many sources; so there will definitely be errors in the content implementation process. We look forward to receiving your comments to make the article more and more complete!
Source: https://huphaco.vn/he-thong-dcs/
Part 3: Source: https://cncvina.com.vn/category-product/day-chuyen-tu-dong/
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