Distributed Control Systems, DCS. • Individual Controllers communicating to a central computers acting as workstations. • Communication accomplished by. A distributed control system (DCS) is a computerised control system for a process or plant .. Print/export. Create a book · Download as PDF · Printable version. Distributed control systems (DCSs) are computer-software packages communicating with control hardware and providing a centralized human– machine.
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PDF | This paper addresses intelligent communication among device entities to solve aspects of the Distributed Control System (DCS) for process control in an . Distributed control system used to control complex distributed industrial functions. Find about 4 basic elements and 7 features. Have a basic knowledge of, and be able to define, what a Distributed. Control System is. ➢ Understand the general benefits of Distributed Control Systems.
Distributed Control System is a specially designed control system used to control complex, large and geographically distributed applications in industrial processes. In this, controllers are distributed throughout the entire plant area. These distributed controllers are connected to both field devices and operating PCs through high speed communication networks as shown in figure. Discrete Field devices such as sensors and actuators are directly connected to input and output controller modules through communication bus.
Controllers are distributed geographically in various section of control area and are connected to operating and engineering stations which are used for data monitoring, data logging, alarming and controlling purpose via another high speed communication bus. DCS provides information to multiple displays for user interface. Distributed Control System continuously interacts with the processes in process control applications ones it gets instruction from the operator.
It also facilitates to variable set points and opening and closing of valves for manual control by the operator. Its human machine interface HMI , face plates and trend display gives the effective monitoring of industrial processes.
This controller is the supervisory controller over all the distributed processing controllers. Control algorithms and configuration of various devices are executed in this controller.
Network communication between processing and engineering PC can be implemented by simplex or redundant configurations. It can be placed near to field devices sensors and actuators or certain location where these field devices are connected via communication link. It receives the instructions from the engineering station like set point and other parameters and directly controls field devices. These modules are extendable according to the number of inputs and outputs.
It collects the information from discrete field devices and sends this information to operating and engineering stations. In above figure AC F and AC Fcontrollers acts as communication interface between field devices and engineering station. Most of the cases these act as local control for field instruments. It is used to monitor entire plant parameters graphically and to log the data in plant database systems. Trend display of various process parameters provides the effective display and easy monitoring.
These can also be configured to have control capabilities. Communication media consists of transmission cables to transmit the data such as coaxial cables, copper wires, fiber optic cables and sometimes it might be wireless.
Communication protocols selected depends on the number of devices to be connected to this network. For example, RS supports only for 2 devices and Profibus for devices or nodes. In DCS, two or more communication protocols are used in between two or more areas such as between field control devices and distributed controllers and other one between distributed controllers and supervisory control stations such as operating and engineering stations. In factory automation structure, PLC-Programming Logic Controller is used to control and monitor the process parameters at high speed requirements.
These are used in manufacturing processes where designing of multiple products are in multiple procedures such as batch process control. DCS facilitates system availability when needed by redundant feature at every level.
Resuming of the steady state operation after any outages, whether planned or unplanned is somewhat better compared to other automation control devices. Redundancy raises the system reliability by maintaining system operation continuously even in some abnormalities while system is in operation. DCS offers many algorithms, more standard application libraries, pre-tested and pre-defined functions to deal with large complex systems.
This makes programming to control various applications being easy and consuming less time to program and control. It provides more number of programming languages like ladder, function block, sequential, etc for creating the custom programming based on user interest.
But this type of industrial control system covers large geographical areas whereas DCS covers confined area. DCS completely takes the entire process plant to control room as a PC window. Powerful alarming system of DCS helps operators to respond more quickly to the plant conditions. Access to control various processes leads to plant safety. DCS design offers perfect secured system to handle system functions for better factory automation control. Security is also provided at different levels such as engineer level, entrepreneur level, operator level, etc.
DCS system can be implemented in a simple application like load management using network of microcontrollers. Here the input is given from a keypad to a microcontroller, which communicates with the other two microcontrollers.
The operators are seated as they can view and control any part of the process from their screens, whilst retaining a plant overview. Evolution of process control operations[ edit ] Process control of large industrial plants has evolved through many stages. Initially, control would be from panels local to the process plant.
However this required a large manpower resource to attend to these dispersed panels, and there was no overall view of the process. The next logical development was the transmission of all plant measurements to a permanently-manned central control room. Effectively this was the centralisation of all the localised panels, with the advantages of lower manning levels and easier overview of the process.
Often the controllers were behind the control room panels, and all automatic and manual control outputs were transmitted back to plant. However, whilst providing a central control focus, this arrangement was inflexible as each control loop had its own controller hardware, and continual operator movement within the control room was required to view different parts of the process. These could be distributed around plant, and communicate with the graphic display in the control room or rooms.
The distributed control system was born. The introduction of DCSs allowed easy interconnection and re-configuration of plant controls such as cascaded loops and interlocks, and easy interfacing with other production computer systems.
It enabled sophisticated alarm handling, introduced automatic event logging, removed the need for physical records such as chart recorders, allowed the control racks to be networked and thereby located locally to plant to reduce cabling runs, and provided high level overviews of plant status and production levels. Origins[ edit ] Early minicomputers were used in the control of industrial processes since the beginning of the s.
The DCS largely came about due to the increased availability of microcomputers and the proliferation of microprocessors in the world of process control.
Computers had already been applied to process automation for some time in the form of both direct digital control DDC and setpoint control. Sophisticated for the time continuous as well as batch control was implemented in this way.
A more conservative approach was setpoint control, where process computers supervised clusters of analog process controllers. A workstation provided visibility into the process using text and crude character graphics. Availability of a fully functional graphical user interface was a way away.
Development[ edit ] Central to the DCS model was the inclusion of control function blocks. One of the first embodiments of object-oriented software, function blocks were self-contained "blocks" of code that emulated analog hardware control components and performed tasks that were essential to process control, such as execution of PID algorithms. Function blocks continue to endure as the predominant method of control for DCS suppliers, and are supported by key technologies such as Foundation Fieldbus  today.
Midac Systems, of Sydney, Australia, developed an objected-oriented distributed direct digital control system in The central system ran 11 microprocessors sharing tasks and common memory and connected to a serial communication network of distributed controllers each running two Z80s. The system was installed at the University of Melbourne. Attention was duly focused on the networks, which provided the all-important lines of communication that, for process applications, had to incorporate specific functions such as determinism and redundancy.
As a result, many suppliers embraced the IEEE This decision set the stage for the wave of migrations necessary when information technology moved into process automation and IEEE The network-centric era of the s[ edit ] In the s, users began to look at DCSs as more than just basic process control. The system installed at the University of Melbourne used a serial communications network, connecting campus buildings back to a control room "front end".
Each remote unit ran two Z80 microprocessors, while the front end ran eleven Z80s in a parallel processing configuration with paged common memory to share tasks and that could run up to 20, concurrent control objects.