4.4.1 Behavior of Alarms after a Power Cycle

The response of an alarm after a power cycle depends upon the latching type, whether it has been configured to be a blocking alarm, the state of the alarm and the acknowledge status of the alarm.

 

The response of active alarms after a power cycle is as follows:

 

For a non-latching alarm, blocking, if configured, will be re-instated. If blocking is not configured the active alarm will remain active. If the alarm condition has gone safe during the down time the alarm will return inactive.

 

For an auto-latching alarm, blocking, if configured, will be re-instated, only if the alarm had been acknowledged prior to the power cycle. If blocking is not configured or the alarm had not been acknowledged the active alarm will remain active. If the alarm condition has gone safe during the downtime the alarm will return inactive if it had been acknowledged prior to the power cycle else it will return safe but not acknowledged. If the alarm was safe but not acknowledged prior to the power cycle the alarm will return safe but not acknowledged.

 

For a manual-latching alarm, blocking will not be re-instated and the active alarm will remain active. If the alarm condition has gone safe during the downtime the alarm will return safe but not acknowledged. If the alarm was safe but not acknowledged prior to the power cycle the alarm will return safe but not acknowledged.

 

The following examples show graphically the behavior under different conditions:-

 

Example 1

Alarm configured as Low; Blocking: No Latching

 

Example 2

Alarm configured as Low; Blocking; Manual Latching

Example 3

Alarm configured as Low; Blocking: Auto Latching