Deadband used with Data Logging to the SCADA Node Hard Drive. These appear in the Data Log Trend displays. A Data Log Deadband is applied before writing to file (for one-second data. If the change in the Tag's value from last record exceeds this deadband, then a new record is written (record-by-exception).
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.
Log Data must be YES for logging to occur. This deadband applies to one-second data. Minute, Hourly and Daily records are not affected by this deadband.
DATA LOG Deadband is in percent of SPAN (% of SPANHI - SPANLO).
See also:
4.2.15 Log Data