Record tag values

While an InTouch application is running, its tag values can be logged and permanently saved. You can use this log data to create historical trend graphs that show some aspect of your plant processes over time.

Note: You should use Historian Server to save historical InTouch data for large applications, or when you want to create detailed reports. Refer to Historian Server documentation for details about configuring historical logging.

The following figure shows tag data from a pump saved to historical log files and/or Historian Server database. The InTouch Historical Logger writes a log entry each time a tag’s value changes more than its specified log deadband range.

When storing data to historical log files, the InTouch HMI creates two log files. One file contains logged data stored in a proprietary format. The other file is an index to the data.

Names are assigned to the two log files with the following format:

YYMMDD00.LGH and YYMMDD00.IDX

where:

A daily logging cycle begins and ends at midnight. The Historical Logger writes the last entries to the active log files at midnight and archives them. Two new files are created for the next day and data is logged to them.

Log files are saved for a specified number of days. Log files that are older than the retention period are deleted. For more information about setting the number of days to retain log files, see Configure general logging properties of the historical log file.