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What is DCS ?(Distributed Control System)

 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.

·         Engineering stations (ES)
·         Operator stations (OS)
·         Maintenance station (MS)
·         Automation Station (AS)
·         Field 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.
You 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.

The 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 :
The maintenance station is based on an operator station (OS). This OS focuses on Plant Asset
Management" 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 :
The automation station carries out the following tasks:
It 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
An OS 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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