Glossary · Automation software engineering and architecture
Soft real time
Also known as: Soft real-time
German: Weiche Echtzeit
In real-time systems, soft real time describes timing requirements where missing a deadline degrades the quality or value of the result but does not constitute a system failure.
- Software engineering
In one sentence
Soft real time describes timing requirements where missed deadlines reduce result quality but do not count as a system failure.
Example
The trend display on the HMI should refresh every 500 ms; an occasional delay makes the curve less smooth but does not affect the machine.
How it applies
- Engineering: Soft real-time tasks such as visualization, logging and cloud communication can run on general-purpose operating systems and at lower priority than control tasks.
- Requirements: Soft real time still needs measurable requirements, often statistical, for example 95 percent of updates within 200 ms.
- Documentation: Clarify in the technical data which functions are hard and which are soft real time. Users should not rely on HMI or cloud functions for time-critical or safety-related purposes.
Soft vs. hard real time
In Hard real time, every deadline must be met, and a miss is a failure. In soft real time, occasional misses are acceptable. Firm real time lies between: a late result is useless, but occasional misses are tolerated.