Figure 4.5
Alarm processing states (excluding state G, H and I)
State A
Normal
Auto
acknowledge
?
No
Yes
State C
Acknowledged
alarm
State B
Unacknowledged
alarm
State E
Unacknowledged
latched alarm
Alarm
condition
clears?
Alarm condition
occurs
Latched
alarm?
State D
Return to normal
Unacknowledged
alarm
No
Yes
Yes
No
Alarm
condition
reoccurs?
Alarm
condition
clears?
Yes
No
Latched
alarm?
Yes
No
State F
Acknowledged
latched alarm
Alarm
condition
reoccurs?
Yes
No
Yes
No
Alarm
condition
reoccurs?
Yes
No
Operator action
Automatic action
Reset (unlatch)
alarm
Acknowledge
alarm
Acknowledge
alarm
Acknowledge
alarm
Active alarm condition
Active alarm
Inactive alarm condition
Active alarm
INFO
For alarms configured with a
Latch
, the alarm remains
Active
even if the
Alarm condition
has become
Inactive
. The alarm
requires acknowledgement and resetting (unlatch) by the operator before the alarm can be cleared and return to normal.
This provides an additional layer of protection.
Table 4.5
Alarm states
Alarm state
Description
Alarm condition*
Alarm**
A
Normal operating condition
No
Inactive
B
Unacknowledged alarm
Yes
Active
C
Acknowledged alarm
Yes
Active
D
Unacknowledged alarm
No
Inactive
DESIGNER'S HANDBOOK 4189340911K UK
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