800xA alarm shelving - cannot shelve alarm
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- Is this "tag" - or rather Object - a Library Type or a single control module ?
- Is it a standard ABB block or your own site specific function ?
- If it is a Library Type ( ie used in many places ) are any other objects showing the same problem.
- If it is a single control module or function block then have you used 2 separate "Alarm Cond" blocks to generate each alarm message ? Have you verified the message texts on these AlarmCond blocks ?
- Are there any other changes to the Alarm Handling aspects for this object eg. Alarm Expression, Alarm hiding configuration etc ?
Very strange behavior. I never face this kind of problem. Well, I can suggest you a workaround.
Create another Tag of same object type (say Analog Input) with similar Name and connect the same signal to this newly created Tag. Check for alarm shelving.
Delete this particular Tag from the controller and then recreate another with the same name, and connect the Real signal to this newly created Tag. Configure Alarm shelving and check. Hopefully, problem will not repeat.
** Before deleting the Tag, be very much sure that there shall no negative impact on your system or plant.
The problem was the CondNameLL value in the SignalInReal function block. Instead of the default ||SL_LL value I found that 'Low Low' had been hardcoded to this pin in the Function Diagram. The pin was hidden so it wasn't noticeable.
I deleted the hardcoded text and set the value to ||SL_LL. I had to restart the alarm managers to restore the shelving functionality.