Distributed Control System:

Distributed Control System – Since the beginning of process control in late 1970s, it has made great progress in every control activity. Similar to the other electronic equipment, its size is decreasing and its power is increasing. The conventional instrumentation is now outdated. The speedy development in the field of electronics has left the instruments working on mechanical lever, bellows and pointers far behind. The so-called miniature instruments of the size of 6″x3″ are no longer miniature as compared to CRT console which is capable of handling hundreds of loops. The concept of control room has been totally changed.

Instrumentation is no longer limited to the measurement of temperature, pressure, flow, level, etc. parameters etc parameter, as an independent paramter using individual controller for each parameter. This process of using individual controller is known as parallel control concept. The instrument system has now been enhanced to complex high speed machinery data, integrating control of various plants data presentation for the management, etc. through the concept of distributed control in which the controllers are distributed around the plant graphically and also functionally.

Since instrumentation is a highly responsible task nowadays, the system should be quite sufficient, reliable and supported with effective subsystem for carrying the task.

With the introduction of microprocessor, the process control has become a window to the process enhancement and invaluable data generated as a byproduct has widened the field of process control to include process optimization and computer integrated manufacture.

The present trend in process control is to evolve a complete system with process control as basic function over which the interactive operator interface, process optimization, production planning and control can be built to suit the market needs. Distributed control systems open the gateway to better realization of process design with host computers and process models gainfully utilizing the data collected by the DCS. A distributed control system can briefly be defined as a control system with communication capabilities and it is a powerful and sophisticated tool in the hands of process control engineers.

The utilization of digital computer to start with and development of control strategy based on microprocessor embedded distributed control system for the plant makes it interesting development in process control. The latest trend is distributed control systems with intelligent control station physically distributed over the plant tropology.

Advantages (Added facilities) in DCS technique:

Following are the advantages or the added facilities as a result of the DCS:

1. Data presentation is in a systematic format enabling easy comparison of various parameters and taking decision by a printer.
2. Logging of data is done by a printer thereby eliminating human error.
3. It is possible to control through dynamic graphic.
4. Operator’s action can be logged, thereby eliminating confusion.
5. The alarm system can be regrouped.
6. Complex computations, analysis, etc. can be carried out easily.
7. Management information can be generated at regular intervals.
8. The super-imposed trends helps in the analysis of plant parameters and
9. Hardcopy gives the actual dynamic printout at a particular instant.
10. The controlling software used is very simple and the application is readily The software changed in one unit has no impact on other units and hence the system becomes very flexible. User’s risk in software is minimum.

Disadvantage of DCS Technique:

1. All information and data though presented in a systematic format is hidden behind the CRT. Hence, it requires a skilled operator.
2. In an emergency, decisions have to be taken single handedly, as few operators are there in the control room.
3. 3. Failure of one controller effects more than one loop. Hence it calls for very high MTBF (Mean Time Between Failures) and high degree of redundancy.