A trend is a graph display of shared variable values over time. With the LabVIEW Datalogging and Supervisory Control (DSC) Module, you have several options for displaying trends for real-time and historical data.

Displaying Real-Time Trends

A real-time trend is a display of shared variable values as they are collected in real time over a relatively short period of time. You can use the Distributed System Manager to display a real-time trend or use the Real-Time Trend Express VI to display a real-time trend in an application.

Because the Real-Time Trend Express VI waits for the specified time interval, place this Express VI in its own While Loop to control the execution rate of this Express VI. To run other VIs at the same rate that the real-time trend updates, place these VIs in the same While Loop.

The Real-Time Trend Express VI updates the value for each shared variable every time the Shared Variable Engine writes to the waveform chart indicator of this Express VI. If a VI using this indicator runs several times, the real-time trend continues to display previously acquired data. The manufacturer recommends that you configure this Express VI before the While Loop begins executing. You must specify the Shared Variable List to use this Express VI.

Displaying Historical Trends

A historical trend is a display of project values that have been logged to the Citadel historical database, usually over a relatively long period of time. If you configure an application to log values, you can display a historical trend in several ways.