The structure of a DCS is often referred to as its architecture. In terms of functional modules, DCS’s from various vendors have lot in same. The image below gives the architecture of generalized DCS. The following major inter connected technologies have been used for distributed control.

1.    Shared bus

2.    Ring and

3.    Hierarchical.

In shared bus systems the connected processors communicated over a common channel using time-sharing, thus allowing attached computers to transmit information in short-duration, high speed bursts.

A ring system consists of high speed, unidirectional digital communication channel (e.g. fiber optics link, twisted-wire pair, etc.) which’s arranged as a closed loop or ring microcomputers are attached to the ring by ring – interface units.

A hierarchical system consists of number of minicomputers or microcomputers interconnected in a tree structure.

The data collection and direct – control activities are handled at the lowest level, whereas data processing, summary processing and coordination are performed at higher levels.

The proper selection of architecture including software and type of processors greatly influences the performance of the distributed control system. Variations in the architecture are determined by several factors, such as memory size and rate, data paths between computers, usage flow control and error checking and recovery.

In the next post, I will discuss about the distributed control system architecture in depth.