THE DISTRBUTED CONTROL SYSTEMS ( DCS)

The distributed control systems ( DCS ) are the product of the control industry, the DCS was developed in 1970 as a replacement of single loop digital and analog controllers as control computer systems. Analog  digital controls ( ADCs) typically consist of unit controllers which could handle multiple loop, multiplexer unit to handle a large amount of I and O operator and engineering interface workstation, a historian foreign device gateways and advance control  in a system box or computer, All these are fully integrated and usually connected via communication network ( Bryan,1997).
The digital control systems (DCS) suppliers have traditionally the approach of welding technology and application expertise to solve specific problems. The programming method is called the function block programming which allow a developer to programme the system by mimicking the actual process and data flow The digital control system (DCS) allow reliable communication and control within process and takes hierachical to control with the majority of the intelligence housed in a centralized computer.(Somogyl,2004).
A good analogy for the (DCS) is the main frame computer and desktop computers. In time past it was unheard of,  for computer to based their cooperate computing on anything  order than a mainframe computer, but due to advancement of technology in PC hardware and software, many components now use a network of powerful desktop computer to run their information system. This architecture gives then more power in a flexible user friendly network environment, and at a fraction of the cost of maintenance likewise DCS systems are more distributed than in the past.
The digital control systems are generally used in application where the proposition of analog to digital I and O is higher than 60 and 40 ratio and the control function are more sophisticated .The digital control system DCS are ideal for industries where the process is continuous ,has a high analog system and is distributed across a large geographical region, It is also suited for application;s where down time is very expensive, such as oil processing and refining, industrial pulp and paper including chemical production etc ( Somogyl, 2004 ) .