Lights Go On, Lights Go Off

Author(s):
Alan Gleichman - Hella Electronics, Inc.

Industry:
Automotive

Products:
LabVIEW, PXI/CompactPCI

The Challenge:
Produce two automated testers capable of research and development testing, design validation and product validation for automotive signal light flasher modules. Use common software on both testers to reduce cost.

The Solution:
Use the rapid application development power of LabVIEW along with National Instruments signal conditioning and data acquisition equipment to make a 6 unit and a 15 unit tester.

Abstract
Hella Electronics Corp. produces electronic modules and systems for the automotive industry. In order to respond quickly to new designs, the Product Development and Engineering Laboratory has standardized on LabVIEW software, PCI-MIO data acquisition boards, and SCXI signal conditioning. This paper examines the system and software design techniques used on a pair of flasher module test systems. Fully automated testers were created to meet the specifications of the automotive OEM. One tester is dedicated to endurance testing, while the other tester performs parametric and short-term tests.

System Design
The design goals for the test systems are stated below:

• Standard components that are LabVIEW compatible.
• Robust actuation of the test pieces.
• Acquisition of data that is accurate and repeatable.

A computer with a PCI-MIO-16E-4 controls a SCXI chassis, a 1 kW power supply, and an environmental chamber. The flasher’s input lines are controlled by SCXI-1160 Switch/Relay boards. On the 15-unit tester, measurement lines are connected to an SCXI-1104 multiplexer board. On the 6-unit tester, measurement lines are connected to SCXI-1120 isolated multiplexer boards.

The pneumatic hazard button actuators on the 15-unit tester are controlled by a SCXI-1160 board. The power supply is controlled by an analog output from the PCI-MIO-16E-4 and a contact from a SCXI-1160 board. The environmental chamber is controlled via RS-232 communication.

Custom loads of actual vehicle lamps were created for these testers. Each flasher uses a load of 4 lamps. This equates to 60 lamps for the 15-unit tester and 24 lamps for the 6-unit tester. These custom loads add many challenges to the project including large inrush currents, heat, and very bright flashes of light.

The high channel count and 42 volt inputs of the SCXI-1104 made it ideal for this application. However, the 2 Hz filter removed the high frequency data needed for analysis. Fortunately, the local National Instruments representative was able to put me in touch with a SCXI application engineer. The application engineer gave instructions on removing the SMD filter capacitors from the SCXI-1104, which allowed it two distribute unfiltered data to the PCI-MIO-16E-4 board.

Software Design
The software was created with the following main menu choices:

• Run a Test
• Create a Report
• System Diagnostics
• Software Configuration

From this screen the operator can set limit values, enable/disable which flashers are tested and monitor test data and system status.To provide accurate control and reliable data acquisition a threaded architecture was used. One thread provides control of the SCXI-1160 Relay boards and the analog output. This loop operates independently of the other threads with a delay of 10 milliseconds. The system status is sent to the user interface thread and the data acquisition thread via LabVIEW 2 style global variables. Data is acquired in a separate loop with a 50-millisecond delay so that there is little risk in overrunning the FIFO buffer of the data acquisition board. The analog data is placed into LabVIEW 2 style global variables. The user interface thread reads these buffers and performs the data analysis, updates the screen, and outputs the data to a file.
A demo mode was added to the data acquisition and the control threads. In the demo mode, simulated data is passed through the same buffers to the user interface thread. This allows off line debugging of analysis and control portions of the software.

Reports are generated by reading back data files and sending selected data to a Microsoft Word document via ActiveX. This method was used so that the report formats could be changed without making software modifications. Figure 3 shows the system diagnostic screen. The diagnostic screen allows direct access to all of the test stands I/O. This allows analysis of any system anomalies that may occur.A software configuration screen sets many of the system parameters that need to be modified occasionally. These settings include the following:

• Test information fields
• Demo mode On/Off
• 15-Unit Tester/6-Unit Tester
• Test Profile
• Report Template
• Data Acquisition Rate
• Data columns to be stored in the data files

These settings are stored in a Windows style ini (configuration) file.

Conclusion
Basing these testers on LabVIEW and National Instruments hardware lead to significant timesaving. An important source of this timesaving was the ability to run the same software on both testers. Since the development of these test systems, additional savings have been realized by reusing portions of the software on other testers.

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