Does Trend Display Aspect gets data from Log Configuration?
Voted best answer
Trend display will not get data from log configuration unless until we configure it to do so.
If you link the log configuration to the variable which needs to be plotted in trend then the trend will show the history value of variable along with real time value otherwise, the trend will plot, only real time value of the variable as long as trend display kept opened.
The log configuration can be added for properties/ variables of a particular object in the required level (for ex: Control structure)
If you want to find out on which log configuration the variable is using then just enable "Log name" column the trend display (or in the trend template).
I dont think you can select log configuration for a trend display as whole.
Hope this answers your question.
A trend display configured for Log="SEAMLESS" and Treatment="Time Average" will automatically choose the best fitting log or set of logs for the given time scope and sample interval.
By choosing a log other than SEAMLESS, the trend is forced to only read that particular log from the historian.
By choosing another treatment than SEAMLESS, e.g. Maximum will limit the set of logs included in the SEAMLESS algorithm.
By selecting Treatment=ExtMomentary ONLY primary logs will be considered and ALL data points are returned. This will paint a "vidid" trend curve for the expense of having to read all points from the hard disk (rather than reading from a better fitting secondary log). The Momenatary treatment (without Ext prefix) should be avoided since it reads ALL points and transfers ALL points to the trend, even if it can not paint all of them. ExtMomentary gives same visual result, but to much less network bandwidth usage - thus it is faster and leaner.
No trend request may exceed 86400 points at any time, that is why a 7 day scope of a 1 second sampling log will only paint one day when using Momentary treatment.
The ExtMomentary treatment will paint more than one day (since it intelligently compresses the data during network transfer), but only enable reading from primary (raw) logs. If primary log stores 5 days and secondary (averaged) log 31 days, ExtMomentary will only paint 5 days when choosing a 7 day scope.
The default trend treatment should therefore be set to Time Average (and SEAMLESS).
The historical data in the trend display is bound to the the logs in the log configuration aspect. The mentioned "Log Name" column allows you to select between "seamless", "trim", and the primary and hierarchical logs defined in the log configuration. Seamless option will basically combine data from all logs defined and is used commonly, whereas trim will result in real time data only.
Now, where do the logs come from?... Generally, primary logs are kept in Connectivity Servers and hierarchical ones are either from connectivity servers or dedicated historian servers, if there are any.