Alarms are always configured on a Tag, excluding Vision client tags. Every time a Tag with a configured alarm receives an updated value, the configured alarm will examine the new value. If the new value on the Tag meets some criteria, as defined by the alarms mode settings, then the alarm generates a new alarm event.
Alarms are monitored by the gateway, and are considered gateway scoped. However, some module features and functions can be used to monitor the live status of alarm events.
Each alarm event contains several attributes that store metadata about the source Tag at the time the alarm event was created. Alarm events are effectively a "snapshot" of several parameters when the alarm went active. Tags can have multiple alarms configured on them, meaning that it's possible for multiple alarm events to be created from a single value change on a Tag.
Alarm Events and Their States
The state of an alarm event is determined by two conditions
Determines if the alarm is active, or "live".
All alarm events start with an Active condition, and then move to a Cleared condition. Alarm events never transition from Cleared to Active. Instead, a new alarm event would be created should the value on a tag meet the setpoint criteria.
- Active - The alarm event is still active. Meaning, the value on the source tag still meets the setpoint configured on the alarm. If the alarm is used to signal that there's a problem, then the active condition means the problem is still active.
- Cleared - The alarm event is no longer active. The value on the source tag no longer meets the setpoint configured on the alarm.
Alarms feature an Acknowledgement functionality. Acknowledgement is simply a flag that can be marked on an alarm event. Commonly the acknowledged condition is used as a way for users to signal to other users that an alarm is being handled.
Imagine a scenario where multiple operators are monitoring any alarm events that occur. Acknowledgement allows an operator to "claim" an alarm, signaling to the others that the event is being handled by someone.
Alarm event acknowledgement is generally handled by either the Vision or Perspective Alarm Status Table components, or the system.alarm.acknowledge function.
- Unacknowledged (Unacked) - The alarm event has not yet been flagged as "acknowledged".
- Acknowledged (Acked) - The alarm event has been flagged as "acknowledged".
Alarm Event States
The two conditions above are combined form the state of an event. The four possible states are:
- Active and Unacknowledged
- Active and Acknowledged
- Cleared and Unacknowledged
- Cleared and Acknowledged