Overrides and Effective State

An alarm can be in two basic states:

• "Active": Timely operator action required (actively alarming / annunciating)
• "Normal": No operator action required

In an ideal world alarm producers are sophisticated and aware of the machine program and nuisance alarms are non-existent. Nuisance alarms are alarms which are in the Active state incorrectly - there really isn't any operator action required despite the alarm producer indicating there is. In practice, nuisance alarms are very common and quickly undermine the value of an alarm system. Overrides are one way for operators to deal with nuisance alarms by adding a layer of indirection from alarm producers and allowing effective alarm state to differ from actual alarm state. Multiple overrides are possible simultaneously and precedence determines effective override state, which is factored into effective alarm state.

Override Table

Precedence	Name	Trigger	Duration	Note
1	Disabled	Manual Operator Command	Indefinite	A broken alarm can be flagged as out-of-service
2	Filtered	Manual Operator Command of filterable alarm	Indefinite	An alarm can be "suppressed by design" - generally a group of alarms are filtered out when not needed for the current machine program. The Filter Processor helps operators filter multiple alarms with simple grouping commands (like by area).
3	Masked	Automatic upon activtation of both maskable alarm and parent alarm	Only while parent alarm is active	An alarm can be suppressed by a parent alarm to minimize confusion during an alarm flood and build an alarm hierarchy
4	OnDelayed	Automatic upon activation of on-delayable alarm	Short with expiration	An alarm with an on-delay is temporarily suppressed upon activation to minimize fleeting/chattering
5	Shelved	Manual Operator Command	Short with expiration	An alarm can be temporarily suppressed via manual operator command
6	OffDelayed†	Automatic upon de-activation of off-delayable alarm	Short with expiration	An alarm with an off-delay is temporarily incited upon de-activation to minimize fleeting/chattering
7	Latched†	Automatic upon activation of latchable alarm	Until Operator Ack	A fleeting alarm (one that toggles between active and not active too quickly) can be configured to require acknowledgement by operators - the alarm is latched once active and won't clear to Normal (or Active) until acknowledged

† Incited alarm override (Others are suppressed override)

Operator Initiated

• Disable and Undisable
• Shelve and Unshelve
• Filter and Unfilter
• Unlatch (acknowledge)

Automated

• On-Delay and Un-On-Delay
• Off-Delay and Un-Off-Delay
• Latch (unacknowledge)
• Mask and Unmask
• Unshelve (timer expiration or one-shot active encountered)