Focus Software, Inc. teamed up with ET&B, a joint venture company formed by Exemplar Manufacturing and Thomas & Betts, to design and implement a test procedure for intelligent power modules used in the production of automobiles. The tester is required to test the entire functionality of the module including testing for short and open circuits in less than 20 seconds per module. National Instruments LabVIEW with PXI and SCXI was selected based on its flexibility, availability, and robustness.
The test system requires cycling the module relays and testing over 60 circuits for open or short conditions. To |properly test the module, the system is required to have 72 analog inputs, 16 electromechanical relays, 16 digital outputs, 16 digital inputs, and SAE J-1850 bus communication capability. A PXI system was selected based on its ability to combine a robust industrial computer with the power and flexibility of SCXI. The PXI-1010 chassis was used as well as an SCXI-1001 12-slot chassis to provide the capacity for the large signal count required. The PXI-8156/233 and corresponding modules are required to perform module control and tests as well as communicate with several supporting test instruments. Several relays on the IPM require SAE J-1850 vehicle bus protocol communication. To accomplish this communication, a J-1850 bus communication instrument called SenseNET was selected. This instrument is manufactured by Netlynx and was selected based on its powerful architecture as well as the flexibility provided by the accompanying LabVIEW drivers. An RS-232 serial port is used to communicate to the SenseNET device.
The test software was written using LabVIEW. The software is required to run continuously without user intervention during the testing cycles. The software uses an advanced state machine with digital I/O communication with the test stand hardware to accomplish the unattended testing. Several utilities are built in to the software to provide maintenance, self-testing, and backup capability.
When the system boots, it automatically runs a self-test diagnostic to ensure the tester is functioning properly. The self-test consists of checking all DAQ input channels, configuring and reading the SenseNET hardware, setting up GPIB power supplies and load banks, and testing communication with the test stand. The system provides feedback to the user to help diagnose any possible problems.
With the system editor, which is a setup utility, users can customize their system options. With a key feature of the system, the user puts the test into debug mode. This mode helps diagnose specific wiring harness issues or problems with the IPM. Single stepping through a test will pause the system after each test step. Pausing stops the test sequence, but does not stop the data acquisition so the operator can inspect the voltage readings to determine problem areas in the system. The system editor also provides a very simple method of program updates. If an update to the software becomes available, the user can update the program by simply clicking on the update button. The software will then launch an update utility and close the test program. When the update program completes, the system will reboot to the updated program.
While operating in normal mode, the run test is simply a status box indicating the test step being executed and the pass/fail result. If the user places the tester in debug mode, then the software displays all analog, digital and J-1850 status. The screen shot to the left shows the screen during debug mode. The testing sequence performs more than 50 separate steps when running the test sequence. Steps that check for open and shorted circuits perform checks on more than 70 analog input voltage levels. Timing is very closely controlled so each step takes only as much time as it needs before continuing. If the module passes the tests, a label is printed and applied to the part by the test stand. If a failure occurred, an error code is generated to indicate the type of failure. The test stand then prints the error code on a label and places the module in a failure bin.
The software tracks all failures by part number in a daily log file. The log file tracks failure codes, date, time, and part numbers. The log file is then used later to retrieve bad modules from the failure bin for analysis. The file is then printed and backed up by the user at the end of the shift.
The system provides a utility for printing, backing up, and deleting daily log files. This utility also provides file size as well as hard drive free space. To print, back up, or delete log files, the user simply selects the proper log files and performs the desired function. The software performs very extensive error checking to help prevent the user from making mistakes.
Focus Software developed the intelligent power module test system, a production test system for end-of-line testing for a power distribution module used in Chrysler mini-vans. The module consists of dozens of solid state and mechanical relays that control the vehicle power distribution for systems such as ignition, headlamps, wipers, and horns. The end-of- line tester is a robust enough system to test production modules for functionality, short circuits, and open circuits. Using LabVIEW with PXI and SCXI, the testing system performs the rigorous test procedure in less than the production requirement time of 20 seconds per piece.
For more information, contact:
Focus Software, Inc.
6111 Jackson Rd., Suite 117
Ann Arbor, MI 48103
Tel: (734) 994-1505
Fax: (734) 994-1506