Is historical data logging enabled by default?

Yes on Analog & Digital Status tags, though you can modify the historian configuration or turn it off if desired. The default set-up is to log on data change with a default 0.25% dead-band setting so you will not be filling your hard drive inadvertently.

Loggers can be added to any tag and logging will occur on tags without loggers if you are viewing them in the HDV.

To this point, watch the deadband on the historian tab of the status tag. If you are logging something that has large scaling, you may not actually log any data at all. Think totalizers coming from the PLC.

The default is set for .25% of the scaling to prevent overloading the drive. You should always adjust it to something appropriate for the tag.

And, also remember that the tag drawn on the screen represnts live data from the device. When you trend it, it is data retrieved from the data logs. So, if you have an inappropriate deadband, it might be changing on the screen but never writing to the log.