Glossary · Maintenance and diagnostics
Event log
Also known as: Event history, Event journal
German: Ereignisprotokoll
In industrial automation and IT, an event log is a chronological record of events in a system, such as alarms, operator actions, state changes, logins and configuration changes, each stored with a timestamp and a source.
- Maintenance
In one sentence
An event log is a timestamped, chronological record of alarms, operator actions, state changes and system events in a control or IT system.
Example
The HMI's event log shows that an operator changed the oven set point at 14:02, three minutes before the over-temperature alarm.
How it applies
- Engineering: Decide which events are logged, with which attributes (time, source, user, old and new value) and for how long. Synchronized clocks are essential if logs from several devices are compared.
- Operation: Operators and shift leaders use the log to understand what happened during a shift and to hand over open issues.
- Security and compliance: Logs of logins and configuration changes support incident analysis under IEC 62443. In regulated industries, logs may have to meet data integrity requirements.
- Documentation: The manual should explain where the log is found, what the columns mean, how to filter and export it, and how long entries are kept. Retention and deletion rules belong in the operating documentation.
Event log vs. audit trail
An event log records what happened in the system in general. An Audit trail is a secure, computer-generated record that shows who created, changed or deleted which record and when, so that changes can be reconstructed. An event log becomes an audit trail only if it is protected and complete enough for that purpose.