Let the sunshine in
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 12/1/2003
A control module for power sunroofs in passenger vehicles. The module controls motors that open and close the sunroof, and it monitors vehicle speeds for controlling a louver.
THE CHALLENGEExercise the control module's hardware by simulating input signals and output loads. The system must measure current supplied to the DUT and measure DUT temperature. It also must simultaneously test four DUTs. The customer required easy changing among DUTs with different electrical connectors.
THE TOOLS- Condor GLC50-5, a 5-V, 8-A DC power supply. www.condorpower.com.
- National Instruments, PXI-1011 chassis with NI-8176 embedded controller; PXI-6040E data-acquisition card,
- PXI-6602 32-bit counter-timer card; SCXI-1125 signal-conditioning module; SCXI-1112 thermocouple module; SCXI-1162HV digital input module; SCXI-1163R digital output module; and LabView software development environment. www.ni.com.
- Xantrex XFR20-20, a 20-V, 60-A DC power supply (4 pcs.), www.xantrex.com.
- Resistors, relays, line drivers, connectors, and other discrete components.
When Aisin World Corp. of America (Plymouth, MI; www.aisinusa.com), a manufacturer of automotive components, needed an automated test station that controls vehicle sunroofs, it turned to system integrator VI Engineering (Farmington, Hills, MI; www.viengineering.com). The test station had to simulate control signals from the vehicle and supply 13 VDC at up to 20 A to the DUT, and then verify that the sunroof operated properly.
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The customer wanted the test station to test four controllers at once, measure the current that each DUT draws, and measure the DUT's temperature. The test system also needed to include extra I/O lines for future expansion. Engineers from VI Engineering, headed by team leader Mark Williams, designed a system that met those requirements. |
The system consists of a PXI chassis with an embedded PC, a data-acquisition card, and a counter-timer card. Because the DUT required voltages that exceed the input range of the data-acquisition card, VI's engineers added signal-conditioning cards that adjust the voltages and provide electrical isolation.
An analog signal-conditioning module connects to four shunt resistors—each connected to one of four power supplies—to measure start-up and continuous current from each supply. Test limits in the software determine if each DUT's current consumption meets specifications. Four more analog channels carry signals from thermocouples that engineers use to measure temperatures on the DUTs. Excessive heat indicates that a DUT might fail prematurely.
The counter-timer generates a pulse train that the DUT interprets as wind speed. When the frequency reaches a simulated 50 mph, the controller must activate a louver that deflects the wind away from the passengers.
A custom interface board takes simulated digital control signals from the tester and drives four relays that connect each power supply to its appropriate DUT. A fifth power supply provides 5 V to drive the relays.
All signals connect to the board through ribbon cables. A custom cable assembly called a "pigtail' contains a circular connector that plugs into a mating connector on the cables that connect the power supplies to the interface board. At the other end of the pigtail, a connector inserts into the DUT. With the pigtail design, users can easily change DUTs by simply replacing the pigtail assembly.
RESULTSThe test stand lets the user test four DUTs at once. Operators can run tests either automatically or under manual control through the user interface.
Because VI Engineering used a modular approach to its software design, the company was able to reuse much of its LabView code when developing a similar tester for another client. In addition, the pigtail cables let engineers connect any DUT to the test system. Thus, changing DUTs requires a simple exchange of a cable assembly. By using the modular design, VI Engineering was able to develop the tester for another client in just three weeks.
