One of the factors making the test bench so flexible is its modular design. A test rig is made up of six subracks with one channel per subrack. This means that six control units can be tested at the same time. Other than sharing the PC for starting the test and for data visualisation and having the same power supply, the six units operate completely independently of one another.
Each subrack is a separate functional unit with an internal ARM9-based process computer, running a Linux operating system with a realtime patch. This has proven to be extremely reliable, even in endurance tests lasting more than 5,000 hours. The Smart "MCM Process Realtime" application with integrated Lua script interpreter runs on the realtime-compatible operating system. It is therefore possible to create test sequences with the relatively simple Lua scripting language – a platform-independent interpreter language -, which does not require a compiler but is rather translated into machine language at runtime.
The process computer is also provided with an integrated buffer memory for storage of all measurement data. Once the test parameters have been set, the test procedure can thus be performed independently of an external computer.
Independent subracks offer several advantages. For example, a problem with one subrack does not lead to the loss of a complete test run for all six control units. "All we then have to do is to replace the one subrack, and there is no disruption of the other tests in progress," says Stefan Siefert-Gäde, who is responsible for the Test Equipment of the Active & Passive Safety Technology division at ZF.
Subrack configuration away from the test bench
The fact that the individual subracks can be simply removed from the test bench and then configured saves yet more time. For this purpose, the modules are fitted in a mobile desktop enclosure which can be connected to a PC separate from the test bench. This enables the test engineers to configure the subracks for the next planned test while the current test is still in progress on the test bench. Opon completion of this test, all that has to be done is to exchange the subracks and connect up the new units under test.