What is DCS Distributed Control System

What is DCS ?(Distributed Control

 A distributed control system
(DCS) is a control system for a process or plant, wherein control elements are
distributed throughout the system. This is in contrast to non-distributed systems,
which use a single controller at a central location. In a DCS, a hierarchy of
controllers is connected by communications networks for command and monitoring.

                                                                                       Figure 1 DCS plant architecture

So as per the above diagram
different components are distributed over the plant, now we will see the
component of DCS system.
stations (ES)
stations (OS)
station (MS)
Station (AS)
Bus & Plant Bus
1.      Engineering Station: Its
PC systems where you can configure hardware & program for all other
distributed station. There are multiple engineering station where all required
engineering software’s are installed for configuration. It can also use for
creating new projects, new IO logics, modifying CFC & SFC logics and
preparing documentations.
Figure 2 Engineering Station
2.      The operator station is
used to operate and monitor the DCS system in process mode.
connect the operator station to the plant bus to enable the required data
communication with the automation system. Operator stations are PCs on which
the DCS OS software is installed.

operator station can be designed as a single-station system for smaller plants
and less stringent requirements. In larger plants with more stringent
requirements, the OS can be designed as a multiple-station system with OS
servers and OS clients. PC station with human-machine interface for operating
and monitoring of your PCS 7 plant in process mode. The operator station can be
designed as a single-station system or multiple-station system.

                                                                                              Figure 3 Operating Stations

3.      Maintenance Station :
maintenance station is based on an operator station (OS). This OS focuses on
Plant Asset
and enables diagnostics and maintenance of the plant. When the diagnostics
structure is created in the plant hierarchy, an OS is assigned the functions
for asset management. The OS functions can be supplemented with diagnostics
functions and program packages for a specific plant. The Engineering Station is
used as a Maintenance Client. PC station for diagnostics of all DCS components.
The diagnostic status is represented by hierarchically structured diagnostic
pictures and communicated to the user in diagnostic messages. The maintenance
station can be designed as a single-station or multiple-station system. The
maintenance station (in the single station) or the MS client (multiple-station
system) is preferably operated on an engineering station.

4.      Automation Station :
automation station carries out the following tasks:
registers and processes process variables from the connected central and
distributed I/O and outputs control information and set points to the process.
It supplies the operator station with the data for visualization.  It registers actions on the operator station
and forwards them to the process.
                                                  Figure 4 Automation Station
OS Server and OS Client
server is connected to the automation systems and receives the process data. An
OS server can have operator control and monitoring functionality only if a
maximum of four OS clients access this OS server. By using more than one OS
server, you have the option of distributing data over multiple OS servers. For
example, for a large plant, you can store a plant unit on each OS server.
OS clients are
used in process mode for operator control and monitoring. OS clients access the
data of the OS server, visualize this data and allow operators to control the
process. Data from several OS servers is displayed in a process picture that is
displayed on the OS client. You can connect up to four process monitors to OS clients.
This requires the use of multi-VGA cards
Distributed IO: It
can be placed near to field devices (Sensors & Actuators) or certain
location where these field devices are connected via communication link. It
receives instructions from the engineering station like set point and other
parameters and directly controls field devices.

Field Bus & Plant Bus: Its
communication bus which works in potential explosive area. Its communicating
field device or sensor to device coupler in field. Where plant bus is
communication bus from device coupler to automation station or operating
station for supervisory level control. 

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