07/27/2012 | Autor / Editor: PRASANTA KUMAR CHATTERJEE / Dominik Stephan
Although PLC and DCS are both used in the automation systems, there were completely different purposes behind their creation, and up to a certain time their functionalities were quite different. Today, advanced automation solutions can even over-perform both of them. Recently, in an exclusive discussion with PROCESS India team, A. Bhaduri, General Manager-Process Solutions, Rockwell Automation (India), explained the origin, evolution, convergence and next level of these two technologies. An excerpt...
The challenge that today Rockwell is facing in the Indian market is – when we position our PlantPAx, we hear, “Look guys you are from the PLC (Programmable Logic Controller) arena what will you do in the DCS (Distributed Control System) arena?” But this architecture is all about how you design it. The controller can do both. Ask a DCS manufacturer, if they can work in a sequential logic or a PLC space – they cannot. But Rockwell Automation can always go to the other side.
That is the beauty of our system. Now, before going into the details of this technology, let us peep into the growth and development of both PLCs and DCSs.
In the early 1990s, automotive manufacturers (General Motors in particular) thought that in their manufacturing processes, they needed an automated system to take care of certain sequential operations.
Those sequential operations could be repetitive, periodic, or at times those could have multiple repetitive functions – that get repeated after gaps. That means one periodicity will get spaced between another one. That is the basis of Programmable Logic Controller. It is programmable because a sequence of functions are created or programmed in it. There is a logic, which determines what each of these sequences should consist of. That brought in the era of PLCs accompanied with Ladder Logic, which is the basic programming used in PLCs.
Rockwell automation has been catering to automation needs of the Indian Oil & Gas (O&G) sector, for more than 60 years. After several major accidents in the O&G industry in the past few years, today the sector is under huge regulatory pressure for maintaining safety and sustainability of operations with stringent concern for preventing environmental damages. Rockwell is all set to address this immediate need through its latest safety PLC – the AADvance... More in our interview: Automation From the Conceptual Stage on Leads to Cost Saving
While looking at the DCS space, it takes us to a refinery of Exxon Mobil in Texas. There were three different crudes. They had certain crude distillation units followed by fractionating columns, followed by distillation to get primarily two types of end products – Gasoline and Kerosene.
So, what they were looking for was a control and monitoring mechanism of those fractionating columns or distillation columns, which subsequently came to be known as crackers / hydro crackers – under the influence of a particular temperature and pressure, as well a catalyst to accelerate or decelerate the process – depending on the process technology involved.
So, when they wanted to monitor the progress of their operations, that involved analog values. A pressure or a temperature cannot be determined by a digital ON/OFF or 0/1 kind of sequence, it is determined by analog values only.
With distributed control systems underway, a sythesis of both technologies seemed more or less unevitable - read more about how these systems evolved on poage 2!
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