Is there anyway or a tool to fix the chattering alarms?
A) Put an On Delay on the alarm – that will delay triggering the alarm until the condition has been true for a set number of seconds (this requires Conditional Alarming to be enabled for that function block).
B) Increase the Alarm Hysteresis for that alarm if warranted – perhaps the value is set too low.
C) Verify and justify the alarm limit – perhaps the process is being expected to run too close to the alarm limit.
D) Validate the alarm itself – if operators are getting a frequent alarm on this point, but they have no expected action to take other than acknowledgement, then maybe there is no need for an alarm at all.
In reply to Steve Elves:
thank you Steve.
Yes what I meant is alarms that come in and go out frequently. I’m going to try the first option which is putting the alarm On Delay.
In reply to SAM:
is there a way to enable the Conditional Alarming at the same time to more than function block?
Could you provide some additional explanation of what you are trying to accomplish? Typically alarms based on limits are only done in one block on a module.
Gareld Butler
Yes Steve.
In reply to Maarten van der Waal:
I agree with Maarten that you should first verify the Alarm Hysteresis (deadband) is appropriately set, and follow that by the alarm trip limit. Is the alarm really needed? Is there an operator action and time to respond defined? Is there excessive noise in the signal, or is the control unstable?
The ON delay will prevent the nuisance alarm from appearing at all, and if it does, the alarm timestamp will be offset from the time the process crossed the limit. If there is no action to be taken by the operator on a short deviation beyond the limit, then an ON Delay keeps the alarm from needlessly reporting. If the chattering condition is to be treated as an alarm, and the operator is to respond, then an OFF delay is needed.
The danger is in using the delays to mask an underlying propblem, maybe a sticky valve, or poorly designed installation or inadequate control, etc. Similar to placing a heavy filter on the PV so the process looks stable. masking the problem may be needed short term, but I'd strongly recommend a fix closest to the propblem.
Andre Dicaire