Latching alarms

Latching alarms are alarms that continue to report for a period of time even after the condition clears.

Alarm conditions are logged in non-volatile memory once they are detected. The stored status of all possible latching alarm conditions reports in the "35-day alarms" field of the alarm message.

Latching alarms report in the alarm message even if the alarm condition clears. How long the latching alarm reports depends on the Meter Sample Rate (MSR). This is called the persistence period. For a typical MSR of one hour, the alarm reports for thirty-five days after the condition clears. If the condition occurs again during the 35 day period, the alarm continues reporting and the 35 day count restarts the next time the condition clears. This means that when a SmartPoint alarm reports, it indicates that either the condition is currently occurring or has occurred within the past 35 days. When the alarm no longer reports, that indicates the condition has not been present for the past 35 days.

Specifically, the SmartPoint module retains the alarm state from the previous 840 MSR meter readings, thus the expiration interval varies with MSR. One of the main purposes for the thirty-five day history is for SmartPoint modules operating in a walk-by/drive-by only environment where the module is read monthly; the 35 day history ensures the alarms will be observed even if they are a month old.

For example, a water SmartPoint module is configured for an hourly reading (the MSR is one hour). The module then detects a water leak. The leak alarm condition is logged, and alarm messages transmit. The water leak is then repaired. The SmartPoint module will continue to show a leak condition for the next 35 days (840 readings / 1 hour MSR = 35 days). After 35 days the alarm expires and clears.