Alarm Definition

In the alarm management in CODESYS, the definition of an alarm consists of the following components:

General description (ID, observation type, message text, etc.)
Description of the cause of the alarm (expression to be observed, limits, min. pending time, etc.)
Description of the alarm effects (notification actions, acknowledgment method, display options, etc.).

Parts of the alarm definition are grouped in the form of alarm classes. A single alarm is typified in its definition within an alarm group with one of the classes. Parts of the definition are located in the alarm group and apply to all alarms of this group.

Below you see an overview of which parameters and properties of an alarm are defined in which object of the alarm configuration:

Alarm Class	Priority Archiving yes/no Acknowledgment method Single acknowledgement yes/no Notification actions on alarm state transition Representation in the visualization
Alarm Group	Text list for message texts Archiving object Deactivation variable
Single alarm within the alarm group	ID Observation type and expression to be observed Individual deactivation variable Alarm Class Message text Pending time Latch variables (for example to display additional variable values in the message text or to be able to filter the alarms in online mode) Higher Prio. Alarm Whose triggering acknowledges the alarm defined here

Acknowledgment method, individual acknowledgment:

For each alarm class, you define an acknowledgement method and one or more notification actions to make sure that the user has taken note of an alarm. The acknowledgement method specifies which states and state transitions are processed for acknowledgement when an alarm occurs.

You use the notification actions to define which actions should be executed for a state transition. As soon as the user has acknowledged an occurring alarm, it is removed from the current alarm list. The different acknowledgment methods are described in diagrams which are available as a tooltip of the Acknowledgment method in the dialog of the alarm class configuration.

Alarm condition:

When defining an alarm, in the observation type the alarm condition is defined for which the fulfillment triggers the alarm. Depending on the observation type, you need to specify a suitable alarm condition in the Details column. Different input fields are available depending on the observation type.

Observation type: Digital, Upper limit, Lower limit, Outside range, Inside range, Change, Event

Example of observation type Digital: PLC_PRG.xAlarm1 = TRUE

Alarm event:

An alarm event is assigned to an alarm condition. While an alarm condition can exist over a longer period of time, the alarm event describes the current occurrence of a change. For example, the transition from the normal state to the alarm state.

In the CODESYS alarm configuration, the same names are used for the three types of events and the respective alarm states.

Event types: Active, ACK, Inactive

Messages are not saved as a copy in the history.

Effect: If you make a small change to a message (for example, correcting a typing error), then this change has an effect on the history because the corrected message is now displayed there. However, if you completely reconfigure the alarm (change status or condition and update the message), then all previous alarms which were recorded due to the outdated configuration will get the new message in the history. Check on a case-by-case basis whether it is not better to add a new alarm instead of upgrading the outdated alarm.