How to
Creating a Change of Value Trend Log
You create a change of value trend log to record the changes of a variable.
The change of value trend log records the variable each time the difference between the current value and the last log value exceeds the delta. Use the change of value trend log to, for example, record a variable that has an unequal oscillation.
The change of value trend log is limited to 10 records per second.
Do not set the delta too small since this can quickly fill up the trend log.
For example, in the figure below, the change of value trend log records a variable every time the variable exceeds or falls below the delta of 3. The records are printed in a trend chart. Notice that the change of value trend log records the values without any time perspective between the records.
Change of value trend log schematic.
The change of value trend log, which is not a variable triggered trend log, has the function to start log records according to a given start condition. For more information, see Trend Log Activation .
You can configure the maximum log interval in a change of value trend log. The maximum log interval is the maximum time that can elapse between two recordings regardless of whether the value has changed or not. The maximum log interval is calculated from the last actual recording. When the maximum log interval is configured, it bypasses the delta and the recording is triggered when the configured time period has elapsed.
In WorkStation, in the System Tree pane, select the folder or SmartStruxure server where you want to create the trend log.
On the File menu, point to New , and then click Trend .
In the object type list, select Change of Value Trend Log .
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In the Name box, type a name for the trend log.
In the Description box, type a description for the trend log.
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Click Next .
In the Logged variable box, enter the variable you want to log.
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In the Delta box, enter the minimum value change that triggers a new record.
Click the Set unit button
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Select a unit for the trend log values.
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In the Prefix box, select the prefix of the unit.
Click Select .
In the Activation variable box, enter the variable that is to make the trend log start recording values when the variable is true
In the Activation time box, specify the time when the trend log is to start recording values.
In the Maximum log interval box, select the maximum time that can pass between two recordings regardless of whether the delta value has been exceeded or not.
In the Log size box, enter the number of records to be stored before old records are overwritten.
In the Available trend storage box, check that the available number of records is not exceeded.
In the Clear when enabled box, select True to clear the trend log every time the trend log is enabled.
Click Next .
In the Extended Trend Log box, click the browse button
to create an extended trend log and connect it to the trend log.action_zoom_plus_stroke 
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In the Trend Log List box, click the browse button
to create a trend log list and connect it to the trend log.action_zoom_plus_stroke
In the Trend Chart box, click the browse button
to either create a new trend chart or connect the trend log to an existing trend chart.action_zoom_plus_stroke
Click Create .
Change of Value Trend Logs
Trend Units
Trend Log Activation
Log Record Storage
Creating an Extended Trend Log
Creating a Trend Chart that Monitors a Trend Log Series
Creating a Trend Log List
Create Object Wizard – Naming the Object Page
Create Trend Log Wizard – Configure Change of Value Trend Log Page
Create Trend Log Wizard – Connect Objects to the Trend Log Page