|PXI TestStation expansion board. |
The flexibility and affordability of modifying test stations equipped with PXI expansion boards was experienced recently by a manufacturer of high-volume automotive dashboard electronic units when they replaced a functional test system with a standard in-circuit tester (ICT) with PXI modules. The benefits of the change included 60 percent lower acquisition costs, higher test coverage, faster test throughput, reduced equipment floor space, and lower operational costs.
This particular manufacturer needed to update the company's test strategy to keep pace with increasing demands for its automotive dashboard systems. The existing test strategy consisted of a comprehensive functional test running on a commercial test system. The test system, which had been discontinued by its manufacturer, was becoming increasingly difficult to support. The goal was to find an alternative test solution with equivalent or better test coverage, faster test throughput, and lower operational costs.
The manufacturer's electronic system to be tested, a dashboard controller, is a medium-complexity circuit board with 500 components, including 100 light-emitting diodes (LEDs), passive analog components, stepper motors, push buttons, an audio speaker, phototransistors, electrically erasable programmable read-only memories (EEPROMs), multiplexer (mux), and liquid-crystal-display (LCD) drivers. The basic test requirements for the automotive dashboard specify that a solution can ensure that all components have been properly placed and that the board is free of short- and open-circuit defects. Functional test requirements include communication with the controller-area-network (CAN) bus after power up, upload of dedicated firmware to the FLASH memory to perform self-test procedures, storage of calibration data in EEPROM, simulation of loads, measurement of very precise time intervals, verification of audio levels, and measurement of LED colors and intensity.
The dashboard controller's manufacturer examined three options for satisfying its test requirements:
- Replicate the current functional test strategy as best as possible by integrating off-the-shelf PXI instruments in a custom functional rack system.
- Deploy a two-stage test strategy, where the first stage performs traditional ICT testing and the second stage performs defined functional testing.
- Replace the existing functional test system with an ICT system that could be extended to support functional test requirements in a single test stage.
The first option offered the benefit of most closely matching the manufacturer's current test strategy and allowing for direct transfer of existing tests in the fastest time possible. However, this option also came with the same weaknesses as the existing test solution, including high support costs, indeterminate fault coverage, limited diagnostic accuracy, and slow throughput. By adding traditional ICT to the mix, the second option would improve fault coverage and diagnostic accuracy, as well as simplify functional test requirements. However, it would also increase both acquisition and operating costs because it would require two test systems, two test fixtures, and additional product handling. The third option was perceived as ideal since it would eliminate the weaknesses associated with the first two options. The challenge was to find an ICT solution that could be extended to best support the company's functional test requirements.
After researching various solutions in the market, the manufacturer selected Teradyne's TestStation LH tester as the best solution for its test requirements. In addition to its high-performance ICT capabilities, the TestStation's PXI functional expansion board capabilities were found to be unique among all ICT systems researched. The functional expansion board supports the installation of PXI instruments in a chassis attached to a low-profile board that plugs directly into an accessory slot of the TestStation backplane. The innovative and compact design simplifies addition of functional test capabilities to the system without expanding equipment floor space or complicating fixture tooling.
|Teradyne test station. |
The bottom of the board supports the addition of four industry-standard 3U PXI instruments, while the top half of the board is a signal distribution hub that supports routing of the PXI instrument signals directly to the unit under test (UUT), to external GPIB instrument ports, or to the system analog bus (where they can be further routed to any pin in the system). Additional signals are provided to connect the TestStation's arbitrary waveform generator (AWG) and to synchronize the PXI instruments with the tester's standard digital-multimeter (DMM) instrument.
Application programs to communicate and control the PXI instruments can be developed using popular and intuitive graphical programming environments such as Labview, LabWindows/CVI, or Visual Studio. Once created, PXI functional test procedures can be tightly integrated with an ICT program using TestStation's Dynamic Programming Extension feature. This feature provides a mechanism to link the tester run-time executable directly with external dynamic-link-library (DLL) routines. Program status and measurement variables can be easily passed between the tester and external software applications, providing maximum flexibility for test program developers.
The process for implementing the combined TestStation ICT/functional test solution for the dashboard controller board involved five steps:
Generating the ICT. This was completed in a matter of hours using TestStation device library models and automatic test generators. The ICTs provide certainty that structural and assembly faults in the dashboard controller will be detected quickly and accurately. The original test solution relied on more complex functional tests to detect these defects.
Identifying required functional tests. This step involved reviewing the existing functional tests and identifying those that were still required. Any functional tests that provided overlapping test coverage with the in-circuit tests were targeted for removal while those that provided supplemental coverage were targeted for integration with the in-circuit tests. Many of the existing functional tests could be migrated easily and re-used because of TestStation software support for external program DLL routines and the built-in hardware support for the industry standard PXI and GPIB instrumentation buses.
Installing required functional instruments. Once the functional tests were identified, the dashboard controller manufacturer could select the instruments that would be needed to execute these tests. It was determined that three PXI instruments (a CAN communication controller, a high-density resistor simulator card, and a high-accuracy counter/timer) would provide the test functionality needed for the dashboard controller application.
Fabricating the test fixture. This step involved communicating fixture requirements for both the ICT and functional portions of the test program to the fixture fabricator. The ICT fixture wiring instructions were automatically generated as part of the ICT program development. However, additional instructions had to be created by the manufacturer to account for the addition of an optical camera box for measuring LED luminosity and intensity, pneumatic pushers to test switches, a microphone to measure audio, and a printed-circuit-board (PCB) marker.
Integrating and debugging ICT and functional tests. This last step included qualification of the program and the fixture and verifying that the tests were reliable and repeatable for production testing. This step also provided the dashboard controller manufacturer the opportunity to compare and contrast the new combined ICT/functional test solution with the original functional test solution.
The benefits of the combined approach won out easily in the eyes of the manufacturer because it significantly lowered both the acquisition and operational costs. Lower acquisition costs were achieved because the TestStation solution cost 20 percent less than the original functional test system and was twice as fast. Calculations showed that the manufacturer saved 60 percent ($300,000) for every two functional test systems replaced with a single TestStation system. Those savings were achieved without sacrificing any reduction in test capacity.
Lower operational costs were achieved from less expensive fixture kit pricing, reduced factory floor space, faster program development times, less defect escapes, faster repair times (due to more accurate ICT diagnostics), and lower support costs.
Contact: Teradyne, Inc., Systems Test Group, 600 Riverpark Drive, MS-NR-7001-1, North Reading, MA 01864 978-370-6238 E-mail: firstname.lastname@example.org Web: http://www.teradyne.com