How to
Configuring an Interval Trend Log
You configure the properties of an interval trend log to meet the unique needs of your site.
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.
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.
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 WorkStation, in the System Tree pane, click the interval trend log you want to configure.
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Edit the properties:
Table: Interval Trend Log Properties - Basic Tab
Property
Description
Status
Displays the status of the trend log.
Enabled
Displays True if the trend log is enabled.
Logged variable
Enter the variable you want to log.
Delta
Select the minimum value change that triggers a new record.
For more information, see Interval Trend Log Delta .
Activation variable
Enter the variable that makes the trend log start recording values when the variable is True .
For more information, see Trend Log Activation .
Activation time
Specify the time when the trend log is to start recording values.
For more information, see Trend Log Activation .
Interval
Type how often to log the variable. The interval defines the time between two log records.
Log size
Select the number of records to store before old records are overwritten, including internal records generated by the trend log.
For more information, see Log Record Storage .
Clear when enabled
Select True to clear the trend log when it is enabled.
Click the Save button
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Interval Trend Logs
Interval Trend Log Properties
Configure Dialog Box – Configuration Tab
Interval Trend Log Delta
Trend Log Activation
Configure Dialog Box – Operation Tab
Log Record Storage
Editing the Interval of an Interval Trend Log
Editing the Delta in an Interval Trend Log
Trend Log Does Not Start Record Due to the Start Condition