Being in effect a separate, independent test bench, each subrack can be configured and also operated away from the test rig. They can therefore be used to accompany the development process, and the scripts written at this stage can later be directly employed in testing. When actually working on the test bench, this independent operation permits the parallel and asynchronous execution of different test scripts for each unit under test.
Separation of communication and measuring equipment adds to flexibility
A further step towards greater flexibility is the strict separation of the communication level from the test controller together with the associated measurement hardware. "The test sequences for a particular control unit and the measuring equipment employed tend not to differ much from one vehicle manufacturer to another," explains Siefert-Gäde. "But communication certainly does."
Upon request from ZF, Smart Testsolutions implemented separation by integrating a VN8900 modular communication interface from Vector Informatik with a VN8970 module into each subrack. The network interface supports bus systems such as CAN, FlexRay, LIN and K-Line and, like the measurement equipment, is an embedded system which can be configured from a PC via USB or Ethernet. It handles all communication with the control unit and communicates with the test controller from Smart Testsolutions via LAN. "The reason for choosing the Vector solution was that our Development departments work with the Vector simulation tool CANoe," says Siefert-Gäde. Thus, test developers can incorporate the CANoe residual bus simulations from the Development departments into their tests with very little modification.
Originally, the LAN connection between the communication box and process computer used the Ethernet protocol UDP. This protocol transmits data packets but does not check that they have been transmitted in full and is therefore somewhat unreliable. Messages not transmitted on account of an electrical fault or EMC interference are irretrievably lost. ZF therefore requested Smart Testsolutions to further develop their test controller software MCM Process Realtime to support the reliable TCP/IP protocol.