DATA LOGGING

A SCADA solution is usually capable of storing large quantities of events in a time sequence.
This is a very useful and powerful tool. The basis of it is to log whatever the system setup has decided to register.
These are some of the most common types of data that we can log :
– Any change of state of any digital variable, input or output
– For analog values, any variable can be set to be logged at a fixed sample interval. This allows for later retrieval of this data to be plotted against time variable. Fine logging of variables can create unnecessary large amounts of log data.
– All alarm changes of state are usually logged.
– Internal system actions may be logged and become important in debugging situations. These include communication errors, remote units that lose or regain contact, some operator actions, and the management of the log itself.

Log files can be exported, as almost any type of data in a SCADA system, and used for data processing or archiving offline.
There is always a limit to the amount of data that a system can log before needing to let go of some of it, caused by lack of storage space. This can be handled by human intervention but it can also exist as a safety measure if no action is taken by an operator.