Captronic Builds Automotive Electronic Cluster System with ...

[Pages:3]Captronic Builds Automotive Electronic Cluster System with NI Compact FieldPoint and LabVIEW

By: Anu Kalidas M., Captronic Systems Mondeep Duarah, Captronic Systems

Category: Automotive

NI Products Used: Compact FieldPoint Network Controller, Analog Input, and Digital I/O; DAQ card; PCI-6013 Multifunction DAQ; LabVIEW 7.0; LabVIEW Database Connectivity Toolset

Pull quote: The test system blended properly with the production flow because of the highly reliable NI hardware and the user-friendly test software.

The Challenge: Developing a test system for the end-of-line functional testing of automotive electronic clusters.

The Solution: Using the flexibility and ruggedness of National Instruments Compact FieldPoint modules and the graphical features of NI LabVIEW to build a configurable, expandable functional test bench, which minimizes testing time and maximizes productivity.

Testing Electronic Clusters Cluster assembly in an automobile includes a speedometer, tachometer, fuel gauge, temperature gauge, odometer, and a set of telltale lamps. Conventional clusters have mechanical parts, which, in addition to being cumbersome, give erroneous results. In contrast, electronic clusters have less weight and longer life, and they provide more accurate results. We developed a test system to be developed was for the end-of-line functional testing of electronic clusters. Major requirements for the test setup included:

? Measuring voltage and current ? Turning on and off sinking and sourcing LEDs ? Driving electromechanical relays ? Generating the square waves of variable frequencies ? Providing compactness, ruggedness, and reliability ? Storing test data on a database ? Generating reports from test data ? Simulating test sequence in software ? Offering provisions for future expansion

The NI Compact FieldPoint distributed I/O system supported all the above functionalities. We used Compact FieldPoint analog input modules to measure both voltage and current. We used

sinking and sourcing digital output modules to activate LEDs and drive relays. Because required frequency resolution was high, we used the NI DAQ card to generate square waves. Also, the modularity of Compact FieldPoint provided us with the scope for future expansion. We developed the test software was developed using LabVIEW 7.0, which has excellent graphical capabilities that came in handy while creating the user interface and conducting test simulations. We used the LabVIEW Database Connectivity Toolkit to log the test data and store test configurations on a Microsoft Access database.

During the end-of-line functional testing of electronic clusters, we simulated various conditions like speed, engine RPM, and fuel-tank level through hardware. Then we applied the conditions to the respective pins of the cluster and noted its behavior in response to these inputs. The speedometer and tachometer required frequency inputs while the fuel and temperature gauge required resistance inputs. We performed tests that included sweeping the speedometer and tachometer from minimum to maximum and back; applying square waves of frequencies equivalent to known speed and RPM; testing whether indicated values in the speedometer and tachometer were within acceptable limits; checking fuel and temperature gauge indications by applying corresponding resistance inputs; measuring telltale lamp currents; and switching telltale lamps to check for light leakage.

Each cluster included a speedometer, tachometer, temperature gauge, fuel gauge, and 22 telltale lamps. There were five cluster variants, and the number of telltale lamps was different for each variant. In addition, the maximum ranges of speedometers and tachometers varied depending on the clusters selected. During the test, a set of pneumatically actuated clamps held the cluster assembly stationary. Also, we mounted the entire test hardware, including power supplies and pneumatics, in a suitable rack.

Designing a Reliable, Rugged System Taking into account the different types of I/O required for the test setup; the reliability, ruggedness, and modularity required; and the space constraint, we chose Compact FieldPoint modules for the test system. We also chose LabVIEW 7.0 for developing the test software due to its rich GUI features and seamless integration with Compact FieldPoint hardware, which helped in reducing development time. For square-wave generation, we used NI DAQ hardware because of the high frequency resolution required. The application software ran on a touch screen panel PC that communicates with the NI cFP-2000 controller through Ethernet.

There were two types of telltales: sourcing LEDs and sinking LEDs. To activate sourcing LEDs, we used the NI cFP-DO-401, and to activate sinking LEDs, we used the NI cFP-DO-403. We implemented the fuel and temperature gauge resistance switching using electromechanical relays. We started these relays and solenoids for activating the pneumatic cylinders in the cluster-holding assembly with the help of another cFP-DO-401 module. We used NI cFP-AI-110 modules to measure telltale currents. A limit switch ensured that the female connector in the test fixture mated properly with male connector in the cluster. Also, we used a pressure switch to ensure that air pressure stayed above six bars. The user could abort a test and unclamp the cluster by bypassing the test software through an emergency switch. We monitored the states of the limit switch, the pressure switch, and the emergency switch through the NI cFP-DI-301 module.

To test a cluster, we had to insert it into the test fixture and press the "start test" switch. This activated the pneumatic cylinders, which held the cluster in its position, and powered on the cluster to start the test. At the completion of the entire test sequence, if the cluster had passed the tests, the software generated a unique serial number and printed a bar code. If a cluster failed the test, then the software generated a sticker with a fault identification code.

Implementing a Configurable Solution We tested five variants with the test system. Each variant differed in the number of telltale lamps, speedometer and tachometer ranges, and the number of checkpoints required. The information for each cluster was stored in a cluster database. Based on the variant we selected, the system retrieved the corresponding information from the database.

Based on the cluster variant we selected, a master cluster showing the expected behavior displayed on the screen, which helped us compare the expected behavior and actual behavior. The results of the test were stored in a results database also known as a Microsoft Access database. The Compact FieldPoint item tags and channel information were stored in the `IO_Config' database. We implemented all the database operations using the LabVIEW Database Connectivity Toolkit.

We could divide the test software into three basic parts. First was the configuration part, which took care of cluster information as well as I/O configuration information. The functions involved selected cluster-information extraction from the cluster database and I/O-detail extraction from the `IO_Config' database. Based on the first-stage inputs, the second or testing stage determined the number of test sequence and various test parameters. We sequenced the tests in such a way that the entire test took the minimum amount of time.

At the end of the entire sequence, the results were stored in the results database and, depending on whether the cluster passed the test, the system printed the bar code or fault identification code. was printed. During the third stage, or report generation, stage, the user took the report of previous tests, which were in the database. Because all the data was available in a database, the report featured the parameters necessary for statistical process control, including the number of clusters failed and the number of failures under different categories.

The test system blended properly with the production flow because of the highly reliable NI hardware and the user-friendly test software. The customers were not only able to speed up the testing process and bring down defective clusters shipped to zero, but they were also able to use the data from the test bench to fine-tune the production process. All this was possible at onefourth of the cost of a ready-to-use tester because of the configurable solution offered through the virtual instrumentation approach.

For more information, contact: Anu Kalidas or Mondeep Duarah Captronic Systems, India

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