Distributed Control System

What is DCS?

• Centralised

• Decentralised

Centralized• Single Master - Slave(s)

system

• All Stations depend on single central controller to sent and receive information

• No direct contact between stations

Centralized• Disadvantages :

• Reliability .

• Wiring and installation costs.

• The complexity is high for a system handling very large number of variables simultaneously.

Decentralized• Hierarchical Control

Distribution

• Central Controller >Local Controller > Stations

• Different Local Controllers might not be connected together

• Also known as Layered or Hierarchical system

Decentralized• Advantages :

• Lower implementation and upgrading cost

• More reliable, flexible

• Less complex

• Lower cost of interfacing

Distributed Control System

• Customizable Decentralized System

• Hierarchy of Controllers are connected by Communication channels

• Generally designed with redundancy to handle safety-critical processes

DCS vs PLC vs SCADA• More Expensive• Control Continues

Process

• Critical Applications

• Process Oriented

• Maintains Constant Stream of Data for control

• High Speed Machine Control

• Data Gathering Oriented

• Maintains speed by Storing values and data for use during outrages

Direct Digital Control

Digital Control => Use of Computers

Direct Digital Control - A digital computer generates control signals which directly operate the control devices

Supervisory Control - A digital computer generates control signals used as reference values for conventional analog controllers

Distributed Process Control

Distributed Process Control System

i) Central Control Station

ii) Controlling portions

• Central Control Station

- Human Machine Interface

Display, Storage, I/O Devices, Control s/w• Controlling Area

- Measurement of analog & digital signals

- Generation of output to actuators• Communication: By individual channels or

shared data highways