Alarm Filter

An alarm limit has a parameter called Alarm Filter. If the filter is 0, then the first reading beyond the limit activates an alarm. If it is set to 1, then two consequtive readings beyond the limi are needed to trigger an alarm.

The Alarm Filter can be defined as a number of consecutive readings beyond a limit, that must be registered before the alarm detection will be activated.

If the detection is activated then the next consecutive reading beyond a limit will activate the alarm.

The charts below present the way the alarm is activated depending on the alarm filter value when there are 3 consecutive readings above the limit.

The counter of the readings beyond a limit is set back to the Alarm Filter value, if a reading is within the allowed range. In the case below the counter started with 2 and was decreased to 1 after reading number 1 was received. It was then reset to 2 when reading number 2 was received and then reading number 3 decreased it to 1 but the next reading was below the limit which reset it to 2 again.

The the alarm was not triggered because there was never a situation where the value was beyond the limit while the counter was equal 0.

If an active (not signed) alarm exists and any next reading was back within the limits, the next alarming sequence will generate another active alarm.

If there is an active alarm and the readings are still beyond the limits, no new alarm will be activated. On the other hand, if the readings are still outside the limits, and an active alarm is signed, it will be generated again as soon as the alarm filter conditions are met.