National Instruments BridgeVIEW

Chapter 6 Historical Data Logging and Extraction

If the Citadel Path is empty, the File Dialog function is executed. This

brings up a File dialog box that lets the operator select the directory

containing the historical data files.

The example then uses the tag list returned by the Get Historical Tag

List VI to set up a list of names in the front panel Tag List listbox, found by

selecting List & Ring»Single Selection Listbox from the controls palette.

It uses the first timestamp output to initialize the Start Timestamp

control on the front panel. By default, the example displays the first

60 seconds worth of data on the historical data display. Historical data is

displayed using the XY Graph indicator named Historical Trend Display.

The Read Historical Trends VI returns historical data from Start

Timestamp to Stop Timestamp for the tags that are selected in the Tag

List listbox and returns data in a form that can be wired directly to an

XY Graph.

The shift register in the while loop is used to detect user input changes on

the operator interface by remembering the previous Start Timestamp,

Stop Timestamp, and the selected tag list. If any of these controls are

changed, historical data is retrieved for the new settings and the XY Graph

indicator is updated.