How to
Creating a Trend Log from a Value
You create a log when you want to track changes of an object.
The interval trend log collects data at a specific time interval. Each logged value is stored as a record in the trend log. Use this trend log when the logging interval is less than 1 hour.
You create interval trend logs using WorkStation or WebStation. In WorkStation, you configure the properties of the interval trend log to meet the specific needs of your site.
For example, in the figure below, the interval trend log records a variable every minute. The records are printed in a trend chart. The interval trend log does not record the values between the intervals.
Interval trend log schematic.
The interval of the interval trend log is aligned with the activation time of the trend. For example, if the activation time is 09:01:00 and the interval is 15 minutes, the trend will log at 09:16:00, 09:31:00, 09:46:00, and so on.
An interval trend log with delta can reduce the storage of similar records, and may not fill up the storage capacity as quickly as an interval trend log with no delta.
An interval trend log with delta checks the monitored value at each interval and records the new value if it differs from the previously recorded value by more than the delta. Delta is the difference between the current variable value and the last log value. To log a variable according to the time interval, use a delta of zero.
For example, in the figure below, the interval trend log records a variable every minute but only if the variable exceeds or falls below the delta of 3. The records are printed in a trend chart. Notice that the interval trend log with delta does not record the values between the intervals, or on intervals where the variable is within the delta.
To log a variable only according to the time interval, set Delta to zero.
Interval trend log with delta schematic.
If an interval trend log has a delta and a calculation method that uses periods, make sure the period contains the required amount of records to generate a correct calculation. If the value does not differ from the previously logged value by more than the delta within the period, then none or too few values are recorded for the calculation.
Adapt the period so it contains the required amount of records to generate a correct calculation.
If a calculation method is connected to an interval trend log with delta, make sure that the period and delta are adapted for the calculation.
In WebStation, in the System Tree pane, right-click the value you want to log.
Point to Open trend log and then click New .
Refresh the web browser to see the trend log in the System tree pane.
Building Operation gives the trend log a name that cannot be changed.
Interval Trend Logs
Context Menu
Context Menu – Open Trend Log Submenu