System Integration Labs (SIL) redefining the verification process: Aversan
Mississauga, Ont. - Traditionally many of the aircraft systems and controls were electrical, mechanical or pneumatic in nature, and the electronic control provided augmented functionality for increased efficiency or performance. To this end, the means of verification was done via a system rig with the real physical components present, applying real pressures/temperatures/forces in order to have the mechanical components respond as if they were on aircraft.
Aircraft systems are now becoming more complex with more and more digital control to achieve efficiency, and failure tolerance in order to meet minimum dispatch requirements and maximize in-service time. The majority of the system complexity and control has shifted from the electrical/mechanical/pneumatic realm to the digital realm, hence the traditional approach to system testing must follow.
The system test rigs, although using the real mechanical components in the loop, and representative aircraft components, still have limitations. The main limitation is the operating envelope; the system rig is not at altitude and consequently the corresponding environmental conditions cannot be replicated. A large portion of the operating envelope can be simulated to some degree by increased capabilities of the facility control and adjusting operating conditions to achieve similar performance points (i.e. homologue), however all of this comes at a cost. The greater the operating range of the facility, the greater the cost of the facility – both initial investment and hourly operating cost. For example, the operating cost for a pneumatic rig for an environmental control system could be in excess of $1000/hour, whereas a controller system integration lab only needs electrical power for the controllers and computers, and operation is only several dollars per hour (10kW @ $0.15/kWH)
Verification planning, although intended to be driven by coverage, is inevitably constrained by project costs, and thus needs to find a more cost-effective means to achieve its end. With the vast majority of system functionality and complexity now in the digital controllers, the high cost of system rig makes it prohibitive as the sole means of system verification.
A system integration lab (SIL) is the solution to achieve the necessary verification coverage in a cost-effective manner. The SIL contains electronic controllers running in real time with real-time validated simulation models closing the loop. With this type of venue in our arsenal, the majority of verification activities that would normally take place on the system rig can be covered in the SIL at a fraction of the cost. With a SIL as part of the project plan, one can also reduce the complexity, capabilities, and cost associated with a system rig.
On a recent project we realized over 90% of the systems requirement verification in the SIL environment. The system rig was only used for verification of particular operating points and requirements associated with performance and dynamics. The availability of the SIL allowed us to simplify the system rig by eliminating the controller hierarchy in this setup, which in turn reduced dependencies for operating the system rig and allowed for more direct control of the system under test. The integration of the controllers and their interactions were covered in the SIL.
The SIL also provides fully automated execution allowing for 24/7 unattended operation; whereas system test rigs have safety considerations and require attended operation. Although the automated testing does require more initial cost to develop the automated procedures, typically the return on investment is achieved after 2 or 3 test campaigns. Unfortunately, even now, many project plans are highly success-oriented, assuming only one or two test campaigns at most, with NO problems. For this reason projects typically do not buy into the automated solution, and by the time they run into their second or third test campaign – it’s already too late.
With increasing system complexities, strategies for verification must be re-aligned and cost-effective alternatives identified. A SIL is a flexible alternative to meet this goal.