Dillon Glissmann, DISTek Integration, Inc.
Developing a flexible, automated test fixture to independently and jointly test a vehicle’s system of electronic control units (ECUs) while users create and maintain collections.
Customizing NI TestStand software by using the NI LabVIEW graphical programming environment to control a modular, PXI-based test system.
A worldwide supplier of agricultural, construction, and forestry equipment continues to strive to improve its overall efficiency and effectiveness. To achieve this, a test system to assist engineers with the validation and verification of new and existing products was required. The new system needed the power to test a range of requirements and the flexibility to adapt to hardware changes and future systems. DISTek Integration Inc. was tasked to design, prototype, and deploy an advanced test system that would meet these requirements.
NI TestStand software and PXI hardware from National Instruments were selected to develop a solution to house numerous technologies that effectively interact with the ECUs. In a complete system, the ECUs communicate across a controller area network (CAN) bus using the SAE J1939 protocol. The test system simulates this bus communication using the NI PXI CAN DeviceNet module and a custom LabVIEW application. This LabVIEW application serves as a J1939 CAN engine for receiving and simulating messages from other ECUs.
The diversity of ECU I/O is handled by a combination of multiple NI PXI-659 data acquisition boards, NI PXI-6527 module, NI PXI R Series module with FPGA, and NI cRIO-9474 and NI cRio-9477 modules . The data acquisition hardware measures various control outputs from the system. The NI FPGA hardware is used for hard, real-time generation of frequency-based signals such as those produced from Hall-effect sensors. Also included is an NI PXI-2569 general purpose relay switch module to simulate the operator control switch matrices.
In addition to satisfying the I/O requirements of the units under test, NI TestStand also maintains and controls the power to the system, ECUs, and I/O channels using a combination of data acquisition devices, GPIB, and a software-controlled fault bus. Adjusting the overall system power simulates the variable voltage supplied by onboard batteries. Switching power at the ECU level means any combination of units can be active simultaneously, while switching at the I/O level allows for the controlled faulting of channels.
With the expandable and adaptable test system, hardware can be reconfigured and built upon as new products are developed. The test system is divided into functional chassis for each of the ECU test bays. Each chassis contains numerous spare terminals, I/O for system reconfiguration, and open external connectors. With the power of the FPGAs that control the discrete outputs of the system, channels can also be reconfigured to serve more complex purposes, such as simulating encoders, pulse-width modulation (PWM) signals, or other digital devices that might interface with an ECU. If the unit under test changes channel name, scales and terminals can easily be modified when an operator updates documentation contained within Microsoft Excel spreadsheets. The data are then parsed using a LabVIEW application accessible through the system-user interface.
Custom step types created in LabVIEW and added to the NI TestStand Sequence Editor facilitate writing tests for the system. These high-level step types allow the operator to interact with the test system on a simplified, user-friendly level. The updated arrangement of the development menus brings these new custom steps to a more prominent position without removing the more complex native operations within NI TestStand. This limits the time spent navigating windows, allowing for faster creation of tests.
Using a simplified user interface developed in LabVIEW, a user can organize a series of tests, save the list for later use, and execute the list of tests while monitoring the system and generating reports. Monitoring analog inputs and CAN messaging can be done any time during test execution with user-changeable indicators. Reports are filed and organized for later reference based on pass/fail status.
Serving as a standalone test fixture capable of testing an entire system of ECUs, the system can serve as a companion to in-the-field testing. Not only is repeated testing with the automated test system more reliable than using a manual test system, but it is also safer, because it permits testing of safety interlocks that can be difficult or dangerous for an operator to effectively test in the field.
The overall flexibility of the test system gives users an adaptable and easy-to-use system for creating and executing tests. NI TestStand provided an out-of-the-box solution that reduced development time by supplying a number of key features, while LabVIEW contained the native functionality for controlling the necessary test system hardware.
DISTek Integration, Inc.