Glossary · Automation fundamentals, platforms and components
Online mode
Also known as: Online connection, Monitoring mode
German: Online-Modus
In PLC engineering, online mode is the state in which the engineering tool is connected to a running controller and can monitor variables, compare programs, force values or download changes.
- Automation components
In one sentence
Online mode connects the engineering tool to a running controller to monitor values, compare programs or download changes.
Example
In online mode, the technician watches the status of the conveyor interlock in the ladder diagram and sees which condition is missing.
How it applies
- Commissioning: Online mode is essential for testing and troubleshooting. Changes made online take effect in the running machine.
- Safety: Forcing values or downloading changes online can cause unexpected movement. Access should be restricted and procedures should require a safe machine state or appropriate precautions.
- Documentation: Maintenance procedures should say when online changes are allowed, who may make them and how they are recorded. Online edits that are not saved back to the project are a common source of configuration drift; include a check in the procedure.
Online vs. offline mode
In offline mode, the engineer edits the project without a connection to the controller. Only after download does it affect the machine. Comparing online and offline versions reveals undocumented changes.