Collecting the right data, at the right time, in the right place.
Historically scada systems were designed to have a centralised server with remote connections to the controllers in the field. Typically the centralised server would be connected to the controllers by a slow bandwidth link and the servers would be required to dial-up the controllers on a schedule to retrieve time-stamped data. However, in today's environment where decisions need to be made in realtime, this style of architecture is no longer the preferred option. The quality and timeliness of data is now more important than ever and this necessitates the need to accurately log high quality data as close to the process as possible. Although the data is logged in these remote locations it must be available to be analysed from a central location without compromising the system integrity.
One of the benefits of localised data-logging is that it is as close to the process as possible which means that there is a reduced risk of losing data. It also means that the quality of the data is improved, the quantity of data stored can be increased, and operations can be carried out either locally or remotely.
One of the reasons against having data-logging at the remote locations is the high cost. For example, if the application was critical it would need redundant servers at each of the remote locations, rather than a single pair of redundant servers and simply a client at each remote location. This significantly increased the costs of the system implementation and maintenance. One option was of course to compromise the reliability or availability of the system by not having localised redundancy, but this is not ideal or recommended. What is termed reliability clustering is the solution.
Clustering provides the ability to realise the benefits of localised data-logging, without the high cost of implementing and maintaining the system. So what is clustering? Clustering is combining multiple scada systems to provide a single unified operator interface. You can cluster I/O, alarms and trends such that multiple systems that were once monitored by multiple operators can now be viewed and monitored by one operator across those systems.
So what is reliable clustering? Reliable clustering is a proposition unique to CitectSCADA. It enables a single server to be a redundant pair to many remote servers. It should be used in applications where the customer has separate control systems scattered around their plant and would like to have a redundant system (but not a redundant system at each local control centre as this is expensive), or sites where the customer has a centralised server but is worried about particular processes and would like to have them monitored through a local server with full alarm, trend and report functionality (eg stackers, remote stations, cranes).
Consider the following scenario:
A control system made up of a number of different process areas over a wide area needs to run 24/7. Some of the process areas require operators full time, other process areas may only need local operators at certain times of the day while the remainder of the time it can be monitored and controlled centrally. In terms of clustering, this means one can design the system such that at each remote location you may have a single server (and clients for local monitoring and control), while at a central location you have a server that is the standby of the different remote locations as well as centralised clients that can monitor and control all the remote locations. Data from all the remote locations can then be viewed on graphic displays, alarm displays or on the Process Analyst.
Data-logging as close to the process as possible provides a number of advantages in terms of the amount and quality of data that can be logged. It can also reduce operational costs through reduced staffing at remote locations. Further, through innovative implementation of clustering technology, reliability can be assured while at the same time reducing computer hardware costs. So now it is possible to collect all your data, at the right time, in the right place.
For more information contact Quintin McCutcheon, Citect Africa, +27 (0)11 699 6600, [email protected], www.citect.com
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