Alarm filter

An alarm limit has a parameter called Alarm Filter.

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 armed.

To trigger an alarm, the system uses an internal counter C which:

• is initially equal to the Alarm Filter value,

• is decreased by 1 after a reading outside the limits is registered,

• is set back to the Alarm Filter value when a reading is within the limits,

• is set back to the Alarm Filter value when the alarm for the MP is signed.

If C = 0 then alarm detection is armed and the next reading outside the limits will trigger an alarm.

Below there are some examples showing the alarm triggering for different Alarm Filter values.

Example 1

Alarm Filter = 0, initial C = 0, alarm detection is always armed.

Alarm is triggered at the first reading outside the limits.

Example 2

Alarm Filter = 2, initial C = 2, alarm detection is armed after 2 readings outside the limits.

Alarm is triggered at the third consecutive reading outside the limits.

Example 3

Alarm Filter = 2, initial C = 2, alarm detection is armed after 2 readings outside the limits.

Alarm is not triggered because the reading registered when C = 0 is within the limits which sets the counter C back to 2.

This method has the following consequences:

• 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.

The Alarm Filter is used to properly handle the real life scenarios where we want to observe a parameter frequently but the alarms shall only be activated if multiple readings are outside the limits.