Kepware Knowledge Base: Solution
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.
- Create an exception-based trigger for the log group. Then, specify whether the data will be logged via static interval, data change, or both.
- Once finished, click Next.
- 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.
- 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.
- Set the condition to "Item value is equal to OPC True (non-zero)."
- 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.
- 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.
- Set the condition to "Item value is equal to OPC False (zero)."
- 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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