Logger Tags

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Logger tags are used to control when data is to be logged. They are required only for tags such as the Analog Input and Digital Input, which do not have logging built-in.

The Logger tag must be linked to an Historian tag, which will perform the actual recording of the data. The Logger's only job is to define when the value from the source tag is to be recorded.

Note that many tags have built-in logging through a connection to the Historian. As a general rule, the built-in logging is preferred when available. If you attempt to attach a logger to a tag that has its own historian connection, a warning will be displayed to discourage you from proceeding.

Logger tags themselves have no values and cannot be drawn on a page

Logger properties Conditions tab

The Conditions tab for the Logger tag properties folder consists of the attributes used to identify the tag whose value should be recorded and the logging mode to use when logging the tag's data. The logging mode can be a time period or for whenever the monitored tag's value changes.

Log Data From

Select the tag whose values will be passed to an Historian by this Logger tag.

The Log Data From field can be used to associate this tag with a new or existing tag using the … button. The … button opens the Tag Browser, which displays only the existing tags for your application, and enables you to create a new tag using its New button. (Information on using the Tag Browser can be found in "Tag Browser").

The Log Data From field can be cleared using the X button to its right.

Right-clicking the name of the tag that has been selected in the Log Data From field opens the tag properties folder for the selected tag.

Log On Change As Well As Time

If the Log On Change As Well As Time check box is selected, data will be logged when the value of the tag being monitored changes as well as every defined interval as defined in the Log Rate tab. Note that this feature does not apply a deadband to filter out miniscule changes.

Enable

Enable or disable the logging of tag data by this logger using a constant value (either a 0, or a 1), an expression, or the value of a second tag.

If the Constant check box beneath the Enable field is selected:

  • Enter a 1 to enable the logging of the data for the tag being monitored.
  • Enter a 0 to disable the logging of the data for the tag being monitored.

Any expression or tag that returns either a 0 or 1 (or non-zero) can also be used. Please see Constant, Expression or Tag for help selecting which option to use.

Logger properties Log Rate tab

The Log Rate tab of the Logger tag properties folder is used to identify the rate at which the data is recorded for the monitored tag. Intervals start at midnight. An interval of 86400 (seconds in a day) would write a value once at the end of each day.

Logger properties Historian tab

Historian

If an Historian tag is selected, this tag's run-time values will be saved for use in reports and the Historical Data Viewer. Historian configuration and advanced logging options are described in the discussion of the Historian Tags.

There are consequences if you change the selected Historian tag after you have begun collecting data. If you switch to a new Historian (perhaps for organizational or load sharing purposes), the data collected for this tag by the previous Historian will become inaccessible. Historian selection and configuration should be done during the project design stage.