So this has been an issue I'm trying to tackle for a good part of the year, and one I've tried a few solutions for but ultimately none of which I've been completely satisfied with yet. So I'm asking for some guidance from those of you more experienced than I am.
Basically I'm looking to implement persistence on point state alarms from analog points. For example, if I have a well level reported by a SCADAPack (ranged 0-100%) and it has an alarm on the '1 Low' state of say 30% with an Enabled Unsolicited RTU event. I want to be able to set a persistence time on it for say 5 minutes. This means if the well level goes from 33% to 28% and does not rise back up past 30% within the next 5 minutes, I want ClearSCADA to raise an alarm. However, if the well level goes from 33%->28%->32% within the span of say 2 minutes, I don't want ClearSCADA to raise an alarm on that point at all.
Some solutions I have explored:
Setting Persistence Into Alarm
My understanding is this delays the RTU from generating an event for the point state change from 'Normal' to '1 Low' and if the point returns to the normal state within the persistence delay, it does not even generate the point state change event at all.
My experience with this is that it seems to work great for binary points (after getting some forum help) but not so much for analog points. The reason is the change in analog value that triggers the alarm is usually large enough to surpass the event deviation. So the RTU will generate an unsolicited event regardless, not for the actual state change but for the value change. ClearSCADA processes this value change event and updates the point value, immediately raising an alarm despite the delay on 'Persistence Into Alarm'.
I've abandoned this approach for now but if there is a way to make it work, I'm all ears.
Implement persistence as RTU code and the actual alarm as a separate binary point
Probably the most robust solution, however I am concerned about the increase in point count as this would mean every analog point will need to be accompanied by one or multiple digital points to store each alarm. If it is to be integrated in a SCADA template, it would mean a lot of extra digital points that need to be created for each possible alarm that could appear on the analog.
Using 'pending severities' and alarm redirection
This is currently where I'm at. I've made some dummy 'pending alarm' severities and used alarm redirection to escalate them (after a delay) to actual alarm severities that the operators can visibly see and act upon.
The main issue with this is the pending alarm needs to be somehow acknowledged if it doesn't get escalated into an actual alarm, otherwise the point will just stay in an unack-cleared state. The only way I can see to fix this is to write some logic that's called via redirection on alarm clear to auto-acknowledge that pending alarm.
However, my roadblock here is that there does not appear to be an easy way to selectively acknowledge alarms on a CAlarmObject. So if I call the Accept() method via logic, it will acknowledge every alarm on that point rather than only the pending alarm. I think setting a dedicated alarm condition for the pending alarm might be the way to fix this?
However I just want to check if this whole approach is really recommended for what I'm trying to achieve here before I put more effort into refining it.
... View more
