# About data logging

Use data logging and the trend graphic object to chart how tag values change over time.

At run time, when the operator opens a graphic display containing a trend, the trend displays values from the data log file for the data log model that is running. The data log model specifies the data to collect in the data log file.

Use these editors to set up data logging:

- Data Log Model - set up a data log model that specifies how many log values to store, the conditions that trigger data logging, and which tags to monitor.
- Startup - turn on data logging by selecting the Data logging check box. Also use this editor to specify the data log model to use at run time.
- Graphics - create a graphic display containing a trend graphic object, and set up the trend to display values from the data log model. Specify what the trend object looks like, which tag values to display, the start time, the time span for the data, and the name of the data log model.

As soon as the project starts running, it begins logging values to the data log file. When the file is full, the oldest data is deleted to make room for new data. The application supplies data from the log file to the trend object for the specified tags and time span.

Tip: | The data log file is retained when an application is restarted after a shutdown or power loss. You can delete the log file from the run-time computer at project startup.

## See also

The Data Log Model editor

Configure startup settings

The Graphics editor

Set up data logging (Setup tab)

Set up data logging (Paths tab)

Keywords: data logging, model