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Using Exception Triggers to Log Data with a Boolean Tag as a Trigger


Last Update: 11/7/2018

In OPC, a Boolean Tag is a value of 0 when False or Off and a value of -1 when True or On. The most effective way to use a Boolean Tag as a trigger is to use the "Item value is equal to OPC True (non-zero)" and "Item value is equal to OPC False (zero)" options. For an example of how to set a condition where a log group is triggered when a tag value is True, refer to the instructions below.

  1. Create an exception-based trigger for the log group. Then, specify whether the data will be logged via static interval, data change, or both.
  2. Once finished, click Next.
  3. Configure the stop and start conditions. Select the Start tab, and use the search button to browse the server for the tag that will be used as a trigger for the log group.
  4. Set the rate at which the trigger tag should be polled and evaluated. This rate should be faster than the rate at which the data is expected to change.
  5. Set the condition to "Item value is equal to OPC True (non-zero)."
  6. Select the Stop tab, and use the search button to browse the server for the tag that will be used as a trigger for the log group.
  7. Set the rate at which the trigger tag should be polled and evaluated. This rate should be faster than the rate at which the data is expected to change.
  8. Set the condition to "Item value is equal to OPC False (zero)."
  9. Click Next | Finish to complete the log group.

With this configuration, when the tag's value is True, the log group will enter a triggered state and logging will start. When the tag's value is False, the log group will no longer be triggered and logging will stop.

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