Bad Quality Suppresses alarm

I am using v7.7.2. I have a user-defined data type for an alarm that includes an OPC tag for a Boolean alarm from a PLC, a memory Boolean tag for a test alarm and an expression alarm tag that goes true if either the OPC or memory tags is true. This expression tag is used for alarming. The setup works well for testing displays, notification pipelines, etc.

However, I do run into trouble when I am working offline, with no connection to the PLC. In that case, the OPC and expression tags get marked with Config Error. The logic still works, i.e., the expression alarm tag still goes true if I set the test memory tag. However, since one part of the expression can’t be resolved (probably returns null), the quality is shown as Config Error. The alarm does not appear in the alert table. I presume alarm events are not fired if the quality is bad. The alarm itself is configured as a equal to 1 condition. I have also tried a configuration of not equal to 0 without success. I’d like to be able to test alarms even when not connected to a PLC.


You might have to add some logic to look at the quality.

I think the general behavior of all the drivers is to report a null value along with bad qualities, which may explain why your comparisons are failing.

The thing that I find odd is that the value of the alarmed tag is being set to true. Animations and other functions work correctly, but the alarming does not.


Is this still an issue you’re experiencing? Were you able to add logic to bypass the bad quality issue?