Glossary · HMI, SCADA and operations
Message class
Also known as: Alarm class
German: Meldeklasse
In HMI and SCADA systems, a message class is a category of messages with common properties, such as whether acknowledgment is required, display colors, audible signal and logging, for example error, warning, system or operating messages.
- HMI and SCADA
In one sentence
A message class groups HMI messages with shared properties such as acknowledgment, colors, sound and logging, for example errors or warnings.
Example
In the HMI project, the message class "Error" requires acknowledgment and shows red, while the class "Operation" only logs operator actions without display.
How it applies
- Engineering: Message classes define behavior centrally, so every message of a class behaves the same. Align them with the alarm philosophy: priorities and classes are related but not identical concepts.
- Operation: Operators learn the meaning of colors and symbols per class. Using a class inconsistently, for example routine information as "Error", undermines that learning.
- Documentation: Explain each message class with its color, symbol and required action in the operating manual. Define the classes in the terminology database in both languages, since class names appear in the HMI.
Message class vs. alarm priority
A message class groups messages by type and handling. An alarm priority ranks alarms by urgency and consequence. A system may have one class "Alarm" with several priorities.