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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
Optimize Your Configuration - Avoid problems when logging data
Logger properties ID tab
The ID tab of every tag includes the same common elements: Name, Area, Description, and Help ID.
Name:
Uniquely identifies each tag in the application. If the tag is a child of another, the parent names will be displayed in a separate area before the name field.
You may right-click on the tag's name to add or remove a conditional start expression.
Area
The area field is used to group similar tags together. By defining an area, you make it possible to:
- Filter for particular tag groups when searching in the tag browser
- Link dial-out alarm rosters to Alarm tags having a particular area
- Limit the number of tags loaded upon startup.
- Filter the alarm display to show only certain areas.
- Filter tag selection by area when building reports
When working with Parent-Child tag structures, the area property of all child tags will automatically match the configured area of a parent. Naturally, you can change any tag's area as required. In the case of a child tag, the field background will turn yellow to indicate that you have applied an override. (Orange in the case of user-defined types. Refer to Configuration Field Colors)
To use the area field effectively, you might consider setting the same Area for each I/O driver and its related I/O tags to group all the tags representing the equipment processes installed at each I/O device. You might also consider naming the Area property for the physical location of the tag (i.e. a station or name of a landmark near the location of the I/O device). For serial port or Roster tags, you might configure the Area property according to the purpose of each tag, such as System or Communications.
You may define as many areas as you wish and you may leave the area blank for some tags (note that for Modem tags that are to be used with the Alarm Notification System, it is actually required that the area field be left blank).
To define a new area, type the name in the field. It will immediately be added. To use an existing area, use the drop-down list feature. Re-typing an existing area name is not recommended since a typo or misspelling will result in a second area being created.
There is no tool to remove an area name from VTScada since such a tool is unnecessary. An area definition will exist as long as any tag uses it and will stop existing when no tag uses it (following the next re-start).
Description
Tag names tend to be brief. The description field provides a way to give each tag a human-friendly note describing its purpose. While not mandatory, the description is highly recommended.
Tag descriptions are displayed in the tag browser, in the list of tags to be selected for a report and also on-screen when the operator holds the pointer over the tag’s widget. For installations that use the Alarm Notification System, the description will be spoken when identifying the tag that caused the alarm.
The description field will store up to 65,500 characters, but this will exceed the practical limits of what can be displayed on-screen.
This note is relevant only to those with a multilingual user interface:
When editing any textual parameter (description, area, engineering units...) always work in the phrase editor. Any changes made directly to the textual parameter will result in a new phrase being created rather than the existing phrase being changed.
In a unilingual application this makes no difference, but in a multilingual application it is regarded as poor practice.
Help Search Key
Used only by those who have created their own CHM-format context sensitive help files to accompany their application.
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.
