What is Hardware-in-the-loop (HIL) Testing?

What is HIL or Hardware-in-the-loop Testing? When is this used? Why do we use it?

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- everything RF

Apr 13, 2021

Hardware-in-the-loop (HIL) testing is an alternative to standard testing methods for embedded systems, IC based components, controllers etc. In HIL these components are tested using simulation techniques instead of standard tests that involve physically embedding these components in a larger mechanical or electronic system. In HIL the component being tested is tricked to work as if it is part of the final assembled product. This allows developers to run through thousands of possible scenarios to test the component without spending the time and cost associated with actual physical testing.

HIL testing requires powerful simulation software running on computers with hardware modified to have ports so that the interfaces of the component to be tested can be connected to the computer. A HIL test software places the component in a simulated version of the machine/device it is a part of and interacts with its real I/O as though the physical machine/device is present. As the software can be updated, changes in the device/machine’s electronic architecture and software can be quickly incorporated. This allows a wide breadth of relevant scenarios and expansion of test coverage as needed to comprehensively test without risk to a physical, costly system.

Though the long-term goal of HIL is to prevent a costly mistake in an expensive program, it’s also a design tool that engineers can use to iteratively test and tweak their designs. This improves product quality before formal testing even begins. Additionally, engineers can conceive of and test new ideas quickly, which helps them maximize innovation through timely feedback.

Choice of hardware and software to be used for HIL testing is the most important factor that will affect maximum test coverage and time spent on system setup and usability. In addition to the quality of the simulation software, the hardware it is paired with should not only account for system specifications such as connector type and I/O but also for fault insertion and the ability to test real-world scenarios. To keep pace with rapidly changing market requirements, finding a solution that addresses not only current tests but also future ones is important, thus necessitating a need for testers that are customizable and future-proof.

Originally used in automotive and aerospace industries the use of HIL has expanded to several other industries over the years such as electronics, semiconductors, wireless, energy, industrial machinery etc.

Advantages of HIL Testing

Reduced Cost to Test: The high cost to execute tests on components of complex and huge machinery like huge aircraft sub-systems, industrial machines etc. justifies the substantial investment in HIL. HIL can be used complementarity to field testing, reducing the resources spent on field testing to a large extent.

Reduce Risks Associated with Failure: With complex machines, control system malfunction can lead to catastrophic failure, destroying equipment or presenting safety hazards. HIL can be used to validate components before running physical equipment. Throughout development, HIL can be used to reduce the chances of software changes to the controller introducing new failure modes. This is also referred to as regression testing. Both uses reduce the likelihood of encountering unexpected failure modes on physical hardware in the future.

Concurrent development of components of the control system: In many development projects, certain components like controllers, MCU etc. may be available long before other parts of the same machine/device like a power converter, plant, and feedback sensors etc. are available. Using HIL, testing on the controller can begin before the other components are ready. This reduces overall development time for engineers.

Testing in many simulated variations of the same device/machine: Machines often have several models with slight variations in their specifications, and testing samples of each variation can be expensive. Using HIL, testing from a subset of the available variations can be leveraged. For example, field execution of some tests could be carried out on a few variations like the largest, smallest, and a few other models. Then HIL testing could be used for some functions of the intermediate models.

Testing fault modes: HIL allows more robust testing of fault modes. Often thorough testing of fault modes is impractical when relying wholly on physical systems. With HIL, faults can be induced through software and can be synchronized with a wide range of conditions. For faults that arise from mechanical failure, inducing faults over such a wide range of conditions on a physical machine/device is highly impractical.