Specifies with tag should be data logged for Historical Trending. A file will be created on the SCADA node hard drive to record data for this tag. Fastest record rate is once/second. A Data Log Deadband is applied before writing to file. If the change in the Tag's value from last record exceeds deadband, then a new record is written (record-by-exception).
Data can be viewed in a Data Log Trend Group Display, up to 12 tags per Data Log Trend Group Display. A file is created for each tag allowing tags to be added or removed from Data Log Trends without loosing historical data.
It is highly recommended to use a Data Log deadband to reduce Disk Access. This will reduce the size of the Data Log Trend files and time used to write to the Hard Drive. The Hard Drive is usually the bottle neck in Data Logging. An IDE Hard Drive at 7200 rpm can handle about 800 Tags per second of Data Logging. Using Disable Data Log Seconds recording can also greatly reduce Disk Space and system throughput if one-second data is not needed.
Log Data Maintenance should also be used to delete and, optionally Archive, Data Log Trend files. A large number of files in the Data Log Folder will reduce Disk Access time and slow you system greatly. You should also Defragment your hard drive frequently (once per day is the Microsoft recommendation) if you are data logging
See also:
3.2.23.1 Disable Data Log Seconds recording
6.2.3 Add Data Log Trend Group