The process control engineer wants to unify his view of alarms and trends across sites, but does not want to compromise the localised functionality of the scada system at each of those sites. The operations manager wants to reduce the number of control rooms and associated staff at remote locations without compromising the close-to-process monitoring that his operations demand. Senior management would like to see process control server costs brought down without compromising redundancy or reliability.
Delivering on these expectations in a conventional process control configuration is challenging. To help address these challenges it is necessary to adopt a total systems perspective that looks beyond the features, availability or price of specific components of the system and instead looks at the network architecture itself as an opportunity for gains to be made. This is where the concept of clustering can make a difference.
Clustering is the grouping or organisation of process elements such that the association between elements of the same cluster is strong and that between elements of different clusters is weak.
Clustering yields benefits
In a process control environment, an operation with a number of production lines for example, might have a pair of servers for each production line (one primary and one standby server on each line). With clustering, one centralised server can act as standby for all production lines servers. This means clustering retains redundancy without the need for standby servers on each line or machine.
Through clustering, organisations can reduce costs of staffing at remote locations/lines/sites, reduce the number of control rooms and reduce the hardware cost for redundant servers at each location/site/line.
In a clustered system, functionality can be extended when scaling up, without the high costs of upgrading or replacing pairs of servers.
Clustering helps to streamline project management and system maintenance through improved consistency, data integrity and standardisation across projects (since the centralisation of clustering enables a change made in one place to be replicated across the system without the need for changes being made in each individual system).
Using clustering
The traditional application of clustering is in combining sites or systems. By creating a single unified list of alarms across systems and a single view of trends across systems, the operator is able to act on any incidents or exceptions across systems.
Clustering can be used to split a system or systems to create reliable sub-systems maintained through a centralised set of servers. This approach can be used when there is a need to increase overall system capacity or spread system load while still ensuring that system functionality is close-to-process.
With a clustering approach, organisations also have the ability to utilise the same configuration for a project multiple times and have the configuration automatically duplicate for each cluster. This ensures simpler and faster replication of systems. Once one project has been tested, duplication of this project ensures roll-out of any number of systems with reduced testing requirements for the duplicate systems. For such replicated systems the operator can view one display page on-screen driven by variables from different clusters at different times based on the operator's command.
The key is for potential users to understand how best to quantify the potential benefits - not just from the dollar savings, but also from the hard-to-quantify benefits of improving centralisation without compromising localisation of process control.
For more information contact Niconette du Toit, Citect, +27 (0)11 699 6600, [email protected], www.citect.com
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