National Instruments BridgeVIEW User Manual

Page 156

Chapter 6

Historical Data Logging and Extraction

6-5

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

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.