Examples (Informative) – OPC Unified Architecture

Annex B Examples (Informative)

B.1 Examples for Event sequences from Condition instances

B.1.1 Overview

The following examples show the Event flow for typical Alarm situations. The tables list the value of state Variables for each Event Notification.

B.1.2 Server maintains current state only

This example is for Servers that do not support previous states and therefore do not create and maintain Branches of a single Condition.

Figure B.1 shows an Alarm as it becomes active and then inactive and also the acknowledgement and confirmation cycles. Table B.1 lists the values of the state Variables. All Events are coming from the same Condition instance and therefore have the same ConditionId.

Table B.1 – Example of a Condition that only keeps the latest state

EventId	BranchId	Active	Acked	Confirmed	Retain	Description
-*)	NULL	False	True	True	False	Initial state of Condition.
1	NULL	True	False	True	True	Alarm goes active.
2	NULL	True	True	False	True	Condition acknowledged Confirm required
3	NULL	False	True	False	True	Alarm goes inactive.
4	NULL	False	True	True	False	Condition confirmed
5	NULL	True	False	True	True	Alarm goes active.
6	NULL	False	False	True	True	Alarm goes inactive.
7	NULL	False	True	False	True	Condition acknowledged, Confirm required.
8	NULL	False	True	True	False	Condition confirmed.
) The first row is included to illustrate the initial state of the Condition. This state will not be reported by an Event*.

B.1.3 Server maintains previous states

This example is for Servers that are able to maintain previous states of a Condition and therefore create and maintain Branches of a single Condition.

Figure B.2 illustrates the use of branches by a Server requiring acknowledgement of all transitions into Active state, not just the most recent transition. In this example no acknowledgement is required on a transition into an inactive state. Table B.2 lists the values of the state Variables. All Events are coming from the same Condition instance and have therefore the same ConditionId.

Table B.2 – Example of a Condition that maintains previous states via branches

EventId	BranchId	Active	Acked	Confirmed	Retain	Description
^a)	NULL	False	True	True	False	Initial state of Condition.
1	NULL	True	False	True	True	Alarm goes active.
2^b)	NULL	True	True	True	True	Condition acknowledged requires Confirm
3	NULL	False	True	False	True	Alarm goes inactive.
4	NULL	False	True	True	False	Confirmed
5	NULL	True	False	True	True	Alarm goes active.
6^b)	NULL	False	True	True	True	Alarm goes inactive.
7^b)	1	True	False	True	True ^e)	Prior state needs acknowledgment. Branch #1 created.
8	NULL	True	False	True	True	Alarm goes active again.
9^c)	1	True	True	False	True	Prior state acknowledged, Confirm required.
10	NULL	False	True	True	True ^e)	Alarm goes inactive again.
11^d)	2	True	False	True	True	Prior state needs acknowledgment. Branch #2 created.
12^c)	1	True	True	True	False	Prior state confirmed. Branch #1 deleted.
13	2	True	True	True	False	Prior state acknowledged, Auto Confirmed by system Branch #2 deleted. ^f)
14	NULL	False	True	True	False	No longer of interest.
a) The first row is included to illustrate the initial state of the Condition. This state will not be reported by an Event. b) If the current state of the Condition is acknowledged then the Acked flag is set and the new state is reported (Event #2). If the Condition state changes before it can be acknowledged (Event #6) then a branch state is reported (Event #7). Timestamps for the Events #6 and #7 is identical. c) The branch state can be updated several times (Events #9) before it is cleared (Event #12). d) A single Condition can have many branch states active (Events #11) e) It is recommended as in this table to leave Retain=True as long as there exist previous states (branches). f) The system Auto confirms this event, since a confirmation is that the operator has taken some action. The confirmation of the previous state (line 12) indicates that the operator has taken an action and this transition does not require a separate confirmation.

B.1.4 Server current-State Model with Suppression

This example adds additional fields to the model illustrated in B.1.2. This example does not use acknowledge or confirm – it assumes that the alarm is automatically acknowledged (and does not support confirm). It does add OutOfServiceState and SuppressedState.

Figure B.3 shows an Alarm as it becomes active, is suppressed or is placed out of service and then inactive. Table B.3 lists the values of the state Variables. All Events are coming from the same Condition instance and therefore have the same ConditionId. The Client subscription includes an event filter that excludes suppressed or out of service conditions (i.e. SuppressedState = True or OutOfServiceState = True). The events shown in green are delivered to the Client. The Retain column indicates the global value of the Retain flag. The “Retain sent” column indicates the overridden value sent in a notification if SupportsFilteredRetain is True. If SupportsFilteredRetain is False the value from the Retain column is sent.

Figure B.3 – SuppressedState and OutOfServiceState example

Table B.3 – Example of a Condition that is Suppressed / OutOfService

EventId	Active	Suppressed State	OutOf Service State	Retain	Retain sent	Event Deliver with Filter	Description
-*)	False	False	False	False	False	-	Initial state of Condition.
1	True	False	False	True	True	Yes	Alarm goes active.
2	True	False	True	True	False	Yes	Placed OutOfService
3	True	True	True	True	False	No	Alarm Suppressed; No event since OutOfService
4	False	True	True	False	False	No	Alarm goes inactive; No event since OutOfService
5	False	False	True	False	False	No	Alarm not Suppressed; No event since not active
6	True	False	True	True	False	No	Alarm goes active; No event since OutOfService
7	True	False	False	True	True	Yes	Alarm no longer OutOfService; Event generated
8	False	False	False	False	False	Yes	Alarm goes inactive
9	False	True	False	False	False	No	Alarm Suppressed; No event since not active
10	True	True	False	True	False	No	Alarm goes active; No event since Suppressed
11	False	True	False	False	False	No	Alarm goes inactive; No event since Suppressed
12	False	False	False	False	False	No	Alarm no longer Suppressed
13	False	False	True	False	False	No	Placed OutOfService
14	True	False	True	True	False	No	Alarm goes active; No event since OutOfService
15	False	False	True	False	False	No	Alarm goes inactive; No event since OutOfService
16	False	False	False	False	False	No	Alarm no longer OutOfService

This behaviour occurs when the implementation supports SupportsFilteredRetain flag subscription.

B.1.5 Example for On-Delay, Off Delay and ReAlarmTime

This example illustrates how on-delay, off-delay and alarm dead bands can be used to reduce the number of alarms that are generated / reported (see 5.8). It also illustrates how ReAlarmTime is used to bring an alarm back up to an active state (see Figure B.4).

Some process values may have sudden jumps that are very brief and do not constitute an alarm. For example, a motor on start draws a large current, but quickly come back down. This is a normal motor current load, and should not be alarmed, but a sustained current load is a problem and should be alarmed, by configuring a OnDelay time, the momentary spike will not generate an alarm, since the value has to be above the alarm threshold for the duration of OnDelay.

An AlarmDeadband is used to keep a noise signal from generating multiple Alarm activations a signal once it crosses an alarm limit will not return to norm unless it drops below the limit by the amount of the deadband specified. In the example the process value is jumping up and down around the limit, but the alarm just remains in the same active or acknowledged state. The Alarm can have a deadband for each limit (High vs HighHigh) and these deadbands can be different.

The OffDelay can also be used, much as the OnDelay, except it will keep a Value in alarm even if it drops below a limit, but only very briefly. Again, this setting is used to limit the number of alarms that occur in a system.

The ReAlarmTime is used to ensure that actions are taken to correct the issue that generated an alarm. Some alarms are configured to generate a new alarm if they have been in an active state for the ReAlarmTime period. The Alarm, goes back to an Unacknowledged state, as if it had just occurred.

Figure B.4 - Alarm example - On Delay, Off Delay, ReAlarmTime

B.2 AddressSpace examples

This Clause provides additional examples for the use of HasNotifier, HasEventSource and HasCondition References to expose the organization of areas and sources with their associated Conditions. This hierarchy is additional to a hierarchy provided with Organizes and Aggregates References.

Figure B.5 illustrates the use of the HasCondition Reference with Condition instances.

Figure B.5 – HasCondition used with Condition instances

In systems where Conditions are not available as instances, the ConditionSource can reference the ConditionTypes instead. This is illustrated with the example in Figure B.6.

Figure B.6 – HasCondition reference to a Condition type

Figure B.7 provides an example where the HasCondition Reference is already defined in the Type system. The Reference can point to a Condition Type or to an instance. Both variants are shown in this example. A Reference to a Condition Type in the Type system will result in a Reference to the same Type Node in the instance.