Distributed Control System (DCS)
Since the beginning of automation the biggest threat was failure of control system processor. Initially microprocessors were very sophisticated and its failure rate was also very high. To solve this problem many solution came in to existence. One of them was the concept of Distributed control System (DCS).
Distributed Control System is nothing but it is a control system with many controllers. Here each and every group of controller is designated for handling a segment of process. In modern Distributed Controller System (DCS) each group has its own redundant working controller.
How Distributed Control System (DCS) came to existence
Actually Distributed control system is not an invention; it is an evolution of automation. Before Distributed Control System (DCS) automation was handled by a single micro-controller or mini-computer. This system was not a perfect fail proof design because all process control was depend on a single controller or computer.
Decade of Industrial Minicomputer control
For Automation industry 1950 was a revolutionary decade because Industrialization was started in 1950s. At that time IBM 1800 was the first computer which was used to process sensors signal. In 1959 “RW-300” was first Industrial computer which was developed by “Ramo-Wooldridge” Company and used in a refinery “Texaco Port” These minicomputers were the turning point of process industry. Because from these computers operator can monitor plant parameter from remote location and accordingly operator can take action.
Related article: Feedback Control
The Race begin
After a successful trial of mini industrial computer many companies were ready to invest for future. Many electronic companies introduce his control system no doubt it was starting of today’s “Distributed Control System (DCS)”.
In 1975 “CENTUM” was first Distributed Control System (DCS) which was developed by Japanese Company “Yokogawa”. It same year (1975) “TDC-2000” introduced by “Honeywell” and “UCS-3000” universal controller introduced by US-based company “Bristol”. After it in 1978 Valmet DCS system (Name: Damatic, now Valmet-DNA) came in to market. After it in 1980 Bailey (now ABB) introduced his Distributed Control System (DCS). Its name was Network-90, it was first network oriented control system with many other facilities which was not available in other DCS system. At the same time “Fisher Control” (now Emerson) introduced “PROVoX” and “Fisher & Porter” introduced DCI-4000.
Era of network Control
After 1980s many control system was available in market. At the same time companies want to add new features in DCS and that feature was network compatibility. Developers were trying to add LAN supportable configuration in DCS. So attention was only LAN or Peer to Peer communication with DCS. Z-80 microprocessor was the perfect example of early days. It was known as first serial communication network in DCS. At that time full TCP/IP standard was not implemented. But in 1987 Foxboro was first DCS with Ethernet support.
From network to internet control
After the implementation of “OLE for Process Control” by Microsoft, users were demanding this feature in DCS and it was fulfilled by DCS manufacturers. Late 1987s most of DCS is supporting internet connectivity. With the help of OPC communication, Data transfer became very easy between different devices. OPC was an open platform so after some time a lot of software was available in Market and theses software were capable to fetch data from Process to internet.
Distributed Control System (DCS) Architecture
Basic feature of DCS
“Feature is other name of requirement……..”
The basic feature of DCS is to provide robust and fail proof control algorithm with proven control mechanism.
Redundancy is important feature for any Distributed control system. It should be in all level of Hardware component. Means It should be field Level instrument and in Input & output card level and must be in Processor or controller level component. After it, It should also be in Extended Network level. Basic aim of redundancy is to avoid Hardware level failure.
If we consider its engineering station, so for development of logic there should be a pre define object oriented library because it makes things easy and error free for any developer. Also pre build equipment templates are very good for fast development of any project. Now in DCS some manufactures are also providing “Bulk Configuration Tools”. By this “Bulk Configuration Tools” developer can easily change logic for many drives or section in project
On the other hand operator console is a very important segment for any distributed Control System (DCS). A standard display Library with highest ASME compliance is required so it becomes an important feature. Dynamic Alarm management is also required from a distributed Control System. So we can say Alarm Management is also basic feature of DCS.
Network Layout of DCS
In any DCS system we can categorize two types of networks. It is Controller to controller network and second one is network of operator console. It is also called Ethernet network. Controller to controller network is called node network because it is based on node id of processor. In some DCS processors are also IP configured so at that placed Ethernet network is used between controller to controller. These networks can be change. It depends on manufacture to manufacture but it will be available in all DCS. Simplest network architecture
What makes Distributed Control System (DCS) better
Robust control is a type of fail proof control and it can be achieve by distributed control architecture. Here one set of processor is designated for a particular task or a part of system. In the worst condition if that set of processor goes fail then only that part of system will not work and it can be overcome by other part of system.
Concept of redundancy
In any control system processor plays very important role. In fact we can’t imagine a control system without processor. Here in Distributed Control System each node of processor unit consist one set of processor one of them is working and other is in Standby condition. Its standby mode is called redundancy and this standby processor is called redundant processor. In modern Distributed control system Redundancy expands to Input & Output cards level.
Compatibility with other devices
After the development of OPC (OLE process control) users were demanding to monitor all plant data in to central control room. It was a valid requirement in 1980s. Now it becomes a common feature of Distributed control system (DCS) and this feature makes DCS better than other control system. After using OPC platform, compatibility of DCS is increasing day by day. Almost all devices are compatible with DCS.