Glossary · Maintenance and diagnostics
Online diagnosis
Also known as: Online diagnostics, Runtime diagnostics
German: Online-Diagnose
In automation and maintenance, online diagnosis is fault detection and diagnosis carried out while the system is in normal operation, for example through continuous self-tests, device diagnostics over the fieldbus or live access to controller data with the engineering tool.
- Maintenance
In one sentence
Online diagnosis detects and diagnoses faults while a system runs, using self-tests, device diagnostics and live access to controller data.
Example
The engineering tool connected online shows that one IO-Link sensor reports a contaminated lens while the line keeps running.
How it applies
- Engineering: Devices and controllers provide diagnostic data during operation; fieldbus and IO-Link devices can report detailed status without interrupting the process.
- Operation: Online diagnosis enables early warnings and Condition-based maintenance because degradation becomes visible before a failure stops production.
- Security: Online access with an engineering tool, especially over a remote connection, must follow the plant's access rules; see Remote access. Online changes to running programs need a controlled procedure.
- Documentation: Manuals should explain which diagnostics are available during operation, how to access them and which actions are allowed without stopping the machine. Read-only diagnosis and online program changes should be described as clearly different tasks.
Online vs. offline diagnosis
Online diagnosis works during operation and is limited to non-intrusive checks. Offline diagnosis requires the system or device to be out of operation and allows deeper tests.