Glossary · Engineering, integration and validation
Software-in-the-loop (SIL)
Also known as: SiL, SIL testing
German: Software-in-the-Loop (SIL)
In control engineering, software-in-the-loop (SIL) is a test method in which the control software runs on a PC, virtual controller or emulator and is connected to a simulation of the machine or process, without the real control hardware.
- Validation
In one sentence
Software-in-the-loop (SIL) tests control software on a PC or virtual controller against a simulated machine, without real control hardware.
Example
Every night, the PLC program runs on a virtual controller against a model of the sorter, and 300 automated test cases check the sorting logic.
How it applies
- Engineering: SIL tests can start as soon as software exists, without hardware. They are fast to set up and easy to automate in Continuous integration (CI) pipelines.
- Testing: Logic, sequences and error handling can be tested reproducibly, including rare scenarios.
- Commissioning: SIL is often the first stage of Virtual commissioning, followed by Hardware-in-the-loop (HIL) tests with real controllers.
- Documentation: The documentation team records the controller emulation and model versions used; results obtained on emulated controllers may differ in timing from the real hardware.
Software-in-the-loop vs. Safety Integrity Level
Both are abbreviated SIL. Software-in-the-loop is a test method; Safety Integrity Level (SIL) is a measure of the required integrity of a safety function under IEC 61508 and IEC 61511. Write the term out on first use or use "SiL" for the test method to avoid confusion, especially in safety documentation.