National Instruments BridgeVIEW 用户手册

Chapter 6

Historical Data Logging and Extraction

© National Instruments Corporation

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

 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.