The primary purpose of the DAS is to simulate a vehicle environment for an ECU to test under lab conditions where it is impractical or impossible to use the actual vehicle or engine. This requires the DAS to generate and monitor complex timed signals such as CAM and crank with nanosecond resolution.
Typical ECU modules have a complex I/O layout. The ECU signals are defined in an Excel worksheet to identify any changes to existing signals. With this worksheet, users can outline the signal names, tolerances, and unit as well as signal conversion or scaling using the DAS multistage math functions. Users can easily add or remove typical signals without any system software changes.
Due to tight tolerances, the ECU signals require the DAS to easily adapt to slight differences in production-built modules as well as variations in test setups. In response, DAS baselining records all ECU outputs over a specified time to dynamically adjust the user’s tolerances to match the current ECU outputs. With the baseline information, the user can now detect minute deviations during testing.
Because the system monitors at such a high rate, recording every reading produces a large amount of data. To manage the data, the DAS produces a report that shows the nominal readings in the recorded baseline and any reading that exceeds the user-defined tolerances. Now the DAS can spend more time monitoring the ECU for anomalies. Using our LabVIEW logfile tool, the user can quickly generate a detailed report that shows module performance broken down by individual tests.
During the test procedure, the DAS can function as a master or slave for EMC testing, a benchtop HIL simulator, a functional tester, or with Ethernet control for simple integration with existing test control software.
Features of the high-speed DAS include the following:
- 192 digital I/O lines
- 16 analog I/O lines
- Arbitrary waveform generator
- Two CAN ports
- Easily definable measurement criteria in an Excel spreadsheet (signal type, parameters, tolerance, and more)
- Remote command interface over Ethernet for test automation
- Automatic module baselines for all signals for more accurate detection of system anomalies
- Data logfile creation
- Data reports, summaries, and graphs in Excel using a logfile tool developed with LabVIEW
- Timing signal display
High-Speed Data Acquisition Using the NI PXI Platform
National Instruments products are the heart of our system. NI provides all of the I/O for our DAS system including complex signal generation, high-speed acquisition, and vehicle bus simulation and monitoring. We developed both the DAS and logfile tool solely using LabVIEW, and our system relies entirely on the speed and accuracy of NI products. We could not use our standard capture cards for our application due to the precision timing involved with the ECU signals. Instead, we chose to use NI R Series intelligent DAQ field-programmable gate array (FPGA) modules to provide the complex-timed waveforms and simulated-sensor outputs. The NI PXI- R Series intelligent DAQ modules also gave us the ability to capture and properly time the ECU output signals at the higher acquisition rates.
DAS data processing was another problem we faced. Our solution was to develop a logfile tool in LabVIEW using inherent parallel processing and generate a multicore application that processed our data using the host computer’s complete power.
Benefits of Using the National Instruments Platform
With the available tools to conduct testing in normal lab environments instead of special full-vehicle chambers, the DAS system greatly reduced our customer’s costs. Because the DAS could monitor and control all of the ECU signals, we completed the testing in a single pass instead of multiple passes, which was previously necessary due to the limited number of channels available on our customer’s old acquisition system. Now customers can complete test profiles in as little as three weeks rather than three months with older acquisition systems.
Thomas J.. Mangliers