The trends by default are live data only. Nothing historical is included. The data starts plotting from the time you opened that display, and then that data is discarded when you navigate away from the display.
In order to keep that data, as Phrog30 mentions, you need to create a datalog. Create a new datalog and then in that datalog add all of the tags you will want to be stored for use with your trends. Anything that you want to go on any of your trends needs to be in that datalog. You only get one, so everything must go in there.
After you have the datalog setup, you will need to go back to your trend configuration and tell it that you are using a datalog. That way it knows to grab historical data and show that data on your trend.
Then go to your startup folder and check the box for datalog and make sure the one you created is selected. This will make sure that whenever the application is started, it will also start logging data to the datalog.
Be careful not to log more than you actually need and log it faster than you really need it. The datalog has a maximum number of records that it can store. Older PV terminals had a max of 300,000 records. So if I was storing 50 tags once every 0.5 seconds that would be 6,000 every minute and it would be full in 50 minutes. At that point old data gets removed to allow new data to be stored. Newer terminals I believe store 1M records. So just be smart about what you are logging and how often in gets logged.
When you are watching a trend that is using a datalog, it will show you data from the datalog, plus it will include live data from when you opened the display. So if you log the data once every ten seconds but your trend is sampling once per second then as you watch the display it will show you the historical data and also update every second with live data. But if you navigate away from that window and then reopen it, the live data starts over. That can be surprising sometimes.
OG
