Wiring Harness News WHN Sept-Oct 2020 WHN Sep-Oct 2020 - Page 54

54 SEPTEMBER/OCTOBER 2020 Wiring Harness News INDUSTRIAL INFO-TAINMENT Wire Harness Testing Evolution and the Advent of Test Fixtures Continued from page 52 ____________ of positions and the spring pressure involved will usually necessitate the incorporation of a clamp and a mechanical slide to assist the operator with engagement. While no approach may catch every instance of an unseated terminal these will work toward the mitigation of these errors. Connector Housings that Accept Male and Female Terminals Some connector housings are designed to accept both male and female terminals. This can present special challenges for the manufacturer in insuring that the proper sexed terminal is delivered to the customer. In some cases, special probes that have an insulator set either in the center or around the outside can be used to read a male terminal only or to read a female terminal only. Locking and Marking In order to prevent bad harnesses from being passed on to the customers, manufacturers may choose to add a locking feature to one of the fixtures used to test the harness. Once engaged and locked in place, the operator is unable to remove the wire harness (Fig. 8). When the testing process is complete and the unit has passed, an accept signal is sent from the circuit analyzer to a solenoid or to an air cylinder to trigger the release of the connector. Circuit analyzers typically have ports or are used in conjunction with relay modules to Figure 8. Locking & Marking Fixture control such devices. A supervisor typically has control to release a bad harness from the fixture. Additionally, marking devices can be incorporated into the test fixture to apply a mark upon successful completion of a test. This is typically done using an electric scribe that etches a mark in the connector housing, or a solenoid or air cylinder that punches a mark. Some ink marking mechanisms are also designed for such applications. These provide another layer of certainty that the product was tested and that it passed. Many circuit analyzer systems will print a label for application to the product for this same purpose. Test Station vs Build & Test There are generally two schools of thought when it comes to production and testing of wire harness. One is to build the harness off line and then bring completed wire harnesses to a test station. The other is to test concurrently while building. Those that choose to build off line will frequently use fixtures without spring probes to hold connectors in place while they are plugged. Completed harnesses are then taken to a test station where fixtures are either mounted or hang as pigtails and moved to engage the connector on the harness. Figure 9. Build-Test Boards Fixtures that are used on build/ test boards are constructed in such a way as to hold empty connector housings in the fixture to allow them to be plugged with terminated wires (Fig. 9). Connectors with front locks may need to be removed to allow the lock to be closed. Depending upon the fixture design, connectors may be plugged while in hand and then engaged into the test fixture which will force the secondary locks closed. Circuit analyzers may signal proper connections during this process or stop the process to allow trouble shooting if an error occurs. Hipot Testing and 4 Wire Kelvin Testing Delrin and polyurethane offer good dielectric qualities for the construction of Hipot and Kelvin test fixtures. These tests are often run at high voltage levels and require special attention to insulation between spring probes to prevent arcing and false failures. This is done by burying the probe/sleeve assemblies in the material or insulating with heat shrink. It is also important to keep the fixtures debris free as this can lead to false failures as well. Special precautions should always be taken to shield operators from electrical shock. A basic continuity test fixture can easily be modified to perform a 4 wire Kelvin test by simply attaching a second wire lead as near the spring probe sleeve assembly as possible. Figure 10. Functional Test Applications 2 Functional Testing Spring probe style test fixtures are used heavily across automotive and other applications because durability and serviceability is a necessity when thousands of tests are involved. These fixtures will typically be designed to be hand held and incorporate robust strain reliefs and jacketed cable to endure continuous movement. In many instances these fixtures may be suspended from tool balancers, positioned to allow operators to quickly grab and engage into connectors on seat assemblies, dash assemblies, door panels, sun roofs or front and rear end assemblies. Cameras have become prevalent in vehicles and special coax probes have been developed to carry images across these connections as part of testing (Fig. 10). Similar fixtures will be used in automated assembly and test applications where the device is attached to an actuator and moved in and out of the connector without operator intervention. These fixtures will frequently incorporate quick disconnect interface connectors to expedite change out for servicing. Spring probes with high current ratings will be incorporated if power will be applied as part of the test process. Figure 11. Control Module Test Fixture Spring probe style fixtures are increasingly used for burn-in testing, and programming of ECUs, and testing of circuit boards because of their durability and serviceability (Fig. 11). The Future of Testing Increasing quality and speed demands will lead to continuous innovation on the testing front. Look for incorporation of proximity switches for additional checks and increasing demand for pressure/vacuum testing to catch damaged seals and other leaks in sealed harness systems. The development of smaller connection systems with smaller terminals will likely drive greater demand for spring probe testing style as mating terminals may not offer needed durability and present greater risk of damage. About ECC Electrical Continuity & Components (ECC) has been assisting the global wire harness manufacturing base with testing issues for over thirty years including basic continuity, terminal seating, functional and burnin test applications. ECC’s focus has been to save their customers time and money while improving the quality of wire harnesses and cable assembles worldwide. For more information, contact ECC at 614-409-9104, find them online at www.eccco.com; and visit them at the Wire Processing Expo or the Assembly Show in Rosemont. You can email Mark directly at mdmolnar@eccco.com Many Thanks to Mark Molnar for his diligent work on this article!