4.3.5 Alarm Latching
Alarm latching is used to hold the alarm condition active once an alarm has been detected. Alarm Latching is configured using ‘P’ codes, P22 (Alarm 1), P25 (Alarm 2) – (only Manual latching is available in FM approved controllers - 816L, 808L, 804L), P28 (Alarm 3), P33 (CT Alarm) as:-
| none | Non latching | A non latching alarm will reset itself when the alarm condition is removed. If it is still present when acknowledged the ALM beacon illuminates constantly, the flashing alarm messages remain and the output remains active. | |
| Auto | Automatic |
An auto latching alarm requires acknowledgement before it is reset. The acknowledgement can occur BEFORE the condition causing the alarm is removed. An example of the action for Alarm 1 attached to OP4 is described below: |
|
| Alarm 1 occurs | ALM and AL1 flash. 4 is ON. | ||
| Acknowledge (the alarm is still present) |
ALM is constant. AL1 remains flashing, 4 is ON |
||
| Alarm 1 condition is removed | All conditions are reset | ||
| Alarm 1 occurs | ALM and AL1 flash. 4 is ON. | ||
| Alarm 1 condition is removed | ALM and AL1 flash. 4 is ON. | ||
| Acknowledge (the alarm condition has been removed) | The alarm indication and output are reset. | ||
| Nan | Manual |
The alarm continues to be active until both the alarm indication is removed AND the alarm is acknowledged. The acknowledgment can only occur AFTER the condition causing the alarm is removed. An example of the action for Alarm 1 attached to OP4 is described below. |
|
| Alarm 1 occurs | ALM and the alarm number flash. 4 is ON. | ||
| Acknowledge (the alarm is still present) | The alarm indication and output continue to show alarm. | ||
| Alarm 1 condition is removed | The alarm indication and output continue to show alarm. | ||
| Acknowledge (the alarm condition has been removed) | The alarm indication and output are reset. | ||
| No.AL | No alarm |
No alarm indication and no latching An example of the action for Alarm 1 attached to OP4 is descibed below. |
|
| Alarm 1 occurs | 4 is ON. | ||
| Acknowledge (the alarm is still present) | 4 is ON | ||
| Alarm 1 condition is removed | 4 is OFF | ||
| Alarm 1 occurs momentarily | 4 is ON but reset as soon as Alarm 1 condition is removed. | ||
By default alarms are configured as non-latching, de-energised in alarm.
It is possible to mix alarms between any of the latching types listed above. Each alarm so configured will behave independently.
☻ ‘P’ codes are found in section 5.2.