Customer Solutions

Improving Maintenance and Extensive Functionality of an Automotive Tester with PXI and TestStand

Author(s):

Michael Hansson, M. Hansson Consulting

Industry:

Automotive

Product:

Data Acquisition, LabWindows/CVI, NI TestStand, PXI/CompactPCI

The Challenge:

Developing a flexible and easy-to-maintain automated production test system that requires frequent model change-overs, lengthy test sequences, 40 A currents, and more than 370 relays and 110 loads in a single 19 in. rack.

The Solution:

Manufacturing an automated test system using a combination of PXI components, customized load cards and relay cards, standard bench equipment, pneumatics, interchangeable test adapters, and a software environment based on NI TestStand and NI LabWindows/CVI.

At M. Hansson Consulting, we were contracted by TEMIC Automotive (Philippines), Inc. to develop an automated test solution that combines functional and final testing to handle multiple models on a new production line. The proposed tester needed to combine a number of testers into one, as well as allow for rapid model change-overs and high currents typical of automotive applications. A prior R&D-oriented test system was deemed less suitable for use in a production environment because of its limited coverage, its large size, and its relative complexity.

Achieving a Rugged, Reliable Solution with PXI
The PXI platform was an easy choice because of its rugged reliability and its compatibility with the customer’s existing PC-based systems, and because we could incorporate a variety of hardware functionality in a single easy-to-maintain chassis. We selected the PXI-1006 chassis for its large number of slots. We selected the PXI-8175 embedded controller, with its 866 MHz CPU, to control the tester under Windows 2000. We used a PXI-GPIB card to communicate with the external bench equipment using IEEE 488.2, while a PXI-8221 carrier held the customer-specified CAN card. A PXI-8420/2 serial interface card expanded the number of serial ports for use with barcode readers.

We connected three PXI-2503 multiplexer cards to the PXI-6025E 12-bit multifunction data acquisition card to perform signal acquisition. The convenient analog plugs included with the TB-2605 terminal blocks made it easy to have the three multiplexer cards function as a single 144-channel 1-wire multiplexer. Because the input signals from the device under test (DUT) exceeded +10 V, we used an SCC-A10 attenuator mounted in an SC-2345 module carrier to attenuate the input signal. We used the PXI-6527 isolated digital I/O card to interface with the pneumatics, the proximity switches, and other external peripherals. Finally, after adding nine high-current and high-density switching cards, the 18-slot PXI chassis was left with only one empty slot remaining.

We mounted a programmable electronic load, a programmable power supply, and a digital multimeter at the bottom of the rack. We also mounted a receiver from TTI Testron to the front of the rack, where we could plug in a variety of interchangeable test adapters (ITAs), depending on the model being produced.

We wanted to avoid the cost and the size of using PXI-standard relay cards for all the required switching of the application. We did not want to develop custom printed circuit boards (PCBs) due to their maintenance and impracticality for high currents. Therefore, we mounted nine customized aluminum cards, each 3 mm thick, vertically in a 6 U tall rack case mounted in the rack and behind the receiver. We bolted more than 60 automotive power relays from Tyco Electronics to these cards using off-the-shelf mounting brackets. The relays are rated for on the order of 10 million cycles and for currents exceeding 60 A. We wired all relay terminals to DIN 41612 high current connectors embedded in card-mounted front panels. In turn, we connected these connectors to the receiver, to the PXI chassis, or to load cards using a wiring harness inside the front of the rack. Similarly, we mounted more than 110 loads to aluminum cards or to perforated Eurocard PCBs placed in a 3 U tall rack case. We can easily unplug and pull out all relay and load cards. We used only high-quality tinned stranded copper wire with all terminals isolated using heat-shrinkable tubing and all wires bundled using flexible braided sleeves and held in place using cable ties and open-slot trunking.

We used a custom bracket assembly to mount the LCD panel monitor in a hinged manner with the pneumatic components and the load rack hidden behind. Similarly, we used a drawer-style keyboard and a customized cover panels to provide the tester a cohesive, smooth appearance.

We connected sensors and pneumatic actuators to each ITA, which had two custom jigs and beds-of-nails. With the resulting easy-to-use automated fixture, the production operator could simply plug in a unit, close the cover, and testing would begin. While one unit was being tested, the operator could load a unit into the other bay.

Using TestStand and LabWindows/CVI to Provide Intuitive User Interface
The software posed a unique challenge all by itself. We needed an environment that presented an uncluttered, intuitive user-interface to the production operators and allowed support engineers to easily and quickly implement and test changes to the test sequence and the test limits.

NI TestStand was more than up to the task. We developed a software environment so that a custom "shell" written in NI LabWindows/CVI handles the customized user interface (UI) and calls the TestStand engine to perform the test sequences. The TestStand engine then calls routines in dynamic link libraries (DLLs) that we developed using LabWindows/CVI. These DLLs handle all low-level actions, such as opening and closing relays and programming the power supply.

When debugging test sequences and fine-tuning test limits, the support engineers may simply bypass the UI "shell" and open the test sequences directly from TestStand. The support engineers can then take full advantage of the debugging features of TestStand’s Sequence Editor to, for example, single-step through a test sequence. We also used the built-in database support and report generation features of TestStand to minimize the amount of code we had to write.

We handled CAN communication with a third-party CAN library, which we called from within one of our LabWindows/CVI DLLs. The software also needed to periodically transmit diagnostic CAN messages to keep the DUT in an active state. We accomplished this by having each TestStand sequence spawn a second thread, running in parallel with the main sequence but at lower priority.

We developed twelve different test sequences -- one for each model and type of test. Each sequence contains between 300 and 900 individual test steps, and each sequence executes between 55 and 130 seconds.

Delivering an Easy-to-Maintain, Small Automotive Tester with PXI
Without PXI technology, this tester would have been substantially larger and harder to maintain than it is currently. In addition, NI TestStand provided the flexibility that the customer’s application requires. The test engineering manager at TEMIC Automotive (Philippines), Inc., said that the PXI test system makes it easier to achieve a universal test system for the various families of electronic products. Not only is it flexible, it is also comparably faster than previous systems in terms of execution of test steps.

For more information, contact:
Michael Hansson
General Manager
M. Hansson Consulting
107 M. Alvarez Ave.,
Talon, Las Pinas City, Philippines 1704
Tel: +63(2) 801-3097
Fax: +63(2) 800-5797
mhansson@mhconsulting.com.ph