The Architecture of Distributed Control System (DCS)

A type of automated control system that is distributed throughout a machine to provide instructions to different parts of the machine. Instead of having a centrally located device controlling all machines, each section of a machine has its own computer that controls the operation. For instance, there may be one machine with a section that controls dry elements of cake frosting and another section controlling the liquid elements, but each section is individually managed by a distributed control system. A DCS is commonly used in manufacturing equipment and utilizes input and output protocols to control the machine.

Structure of DCS:

As DCS contains the distribution of the control processing around nodes in the system, the complete system is reliable and mitigates a single processor failure. It will affect one section of the plant process; if a processor fails and the whole process will be affected when the central computer fails. This distribution of computing power to the field Input / Output (I/O) field connection racks also ensures fast controller processing times by removing possible network and central processing delays.

The architecture of DCS:

Distribution Control Systems (DCS) consists of three major qualities.

1) Various control functions can be distributed into small sets of subsystems that are of semiautonomous. These are interconnected by a high-speed communication bus and their functions include data presentation, data acquisition, process control, process supervision, reporting information, storing and retrieval of information.

2) The second characteristic is the automation of manufacturing process by integrating advanced control strategies.

3) The third characteristic is arranging the things as a system.

The organizing of the entire control structure as a single automation system can be done with DCS as it unites sub-systems through a proper command structure and information flow. DCS is included with basic elements such as engineering workstation, operating station or HMI, process control unit, smart devices, and communication system.

Features:

Distribution Control Systems (DCS) can be used in various control applications with more number of I/O’s with dedicated controllers. These systems are used in manufacturing processes where designing of multiple products in multiple procedures such a batch process control.

Features of DCS are:

•    System redundancy
•    More sophisticated HMI
•    Scalable platform
•    System security

Applications:

Distributed control systems (DCS) are majorly used in manufacturing processes that are continuous or batch-oriented.

Applications of DCS include:

•    Chemical plants
•    Petrochemical (oil) and refineries
•    Pulp and Paper Mills
•    Boiler controls and power plant systems
•    Nuclear power plants
•    Environmental control systems
•    Water management systems
•    Water treatment plants
•    Sewage treatment plants
•    Food and food processing
•    Agrochemical and fertilizer
•    Metal and mines
•    Automobile manufacturing
•    Metallurgical process plants
•    Pharmaceutical manufacturing
•    Sugar refining plants
•    Agriculture Applications

Benefits of DCS:

Benefits of using DCS include:

•    It requires minimal troubleshooting
•    It contains HMI graphics and faceplates
•    Alarms
•    Lends itself to better organization and consistency than a PLC/HMI combo
•    Batch management is possible
•    OPC server
•    Reduced engineering time
•    Redundant operator system servers

How is DCS different from PLC?

To perform advanced regulatory control on a plant-wide scale, DCSs contain the built-in infrastructure. Slower processes typically require coordination across various production units. Superior speed makes PLCs a better choice for applications involving fast production startup using discrete I/O. They also offer range in I/O granularity and maintainability.

At the same time, the distributed control system is hybridized to incorporate PLCs and PCs to control certain functions and to provide reporting services.

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