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10/09/2017
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Hello.
In the event notification, is there a standard way (in the event filter – Select clauses) to obtain the actual process value that exceeded the limit?
Let’s say for a LimitAlarmType (https://reference.opcfoundatio…..t9/5.8.11/ ) – I can see properties that contain the various limits, such as HighLimit. But, it is not clear to me whether the event will also contain the value value that has triggered the alarm, and where.
Or, maybe I do not understand the concept very well.
Please help
05/30/2017
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If you have a limit of 40 and you know it was exceeded. Do you really care that it was actually 40.0001?
Remember the alarm is triggered when the threshold was crossed so even if the value continued to rise, the value captured at the instant that the alarm was triggered would likely be very close to the limit.
If you need the current value the InputNode allows you to read the current value.
10/09/2017
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Thank you Randy.
What I take from your answer is that the alarms defined in the UA spec do not allow for that, but it would be doable with a custom EventType derived from one of them, is that correct?
Apparently, my customer cares about the actual value, at least for logging/auditing purposes. It also does not have to be that close to the limit, if it is obtained on a slow rate or changes unexpectedly fast. There are all kinds of reasons.
Reading InputNode would have to be done after the event is received, right? So it’s not going to be the same as including its value with the event.
05/30/2017
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Sometimes customers have requirements that do not make sense.
Large spikes can be captured with Hi and HiHi alarm.
The value that triggered the alarm can be part of the message.
You can also add subtype or a well known property that can be added to any instance of the existing alarm types.
You can also subscribe to the possible inputs so you have a recent history when an alarm is produced.
The well known property is likely the easiest to sell to your customer.
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