# Set up data logging (Log Triggers tab)

In the Log Triggers tab you specify when to log tag values. Choose whether logging takes place at regular intervals or when tag values change. The default is Periodic/10 seconds, which means values are logged every ten seconds.

## Options

- Periodic
  - Interval

    To log tag values periodically, choose Periodic. In the Interval box, type a time and select a time unit to specify how often tag values are logged. All tags in the model are logged each time this interval expires.

- On Change

  Use the On Change trigger to log tag values once a value has changed by a certain percentage. The percentage is based on the tag's minimum and maximum values as configured in the Tags editor. Only tags that change by the specified percentage are logged. For example, specifying 10 means a tag's value must change by 10 percent to be logged. FactoryTalk View only attempts to read minimum and maximum values for tags with a percentage change other than 0.

  If you are logging a tag that does not have a minimum or maximum attribute, for instance, a direct reference data item (a non-HMI tag), or a data server tag in Logix 5000, the percentage calculation does not work, and any change in the tag's value is logged.

- Maximum update rate

  Specify the maximum rate at which data servers will send data to the tags in the data log model. The update rate applies to all the data log model tags. The default update rate is 1 second.

  At run time, all tags are updated immediately when the data log model is started, regardless of the update rate.

- Change Percentage

  Type the percentage a tag value has to change to trigger logging. To log all changes, type 0. The percentage can contain decimals.

- Heartbeat

  Type a time and select a time unit to specify how often tag values are logged even if no change has occurred. The heartbeat ensures that the data in the log file is current.

  Specify 0 for the heartbeat if you do not want to use it. All tag values are logged whenever they change.

  Tip: | The heartbeat value must not be less than the maximum update rate. However, if you specify a heartbeat rate of 0 (heartbeat not used), this will not conflict with any update rate.

## See also

About data logging

Set up data logging (Setup tab)

Set up data logging (Paths tab)

Set up data logging (Tags In Model tab)

The Data Log Model editor

The Tags editor

Configuration of a CSVDataLog or a DataStorePlus ActivewX control