Testing a single wire may be simple, but testing a complex assembly of wires is not. There’s more required to test involved wire harnesses than purchasing a cable tester—this actually could be the simplest part. You need a systematic process to develop and implement the test solution in production. Data management is key to this process.
Many cables use simple pin-to-pin wiring and can be easily tested. Even with slightly more complex interconnections, the task is manageable. Most cable harness testers can automatically learn the interconnections and create a test program with little or no programming effort.
However, the larger and more complicated the UUT such as aircraft, radar systems, or satellites, the more sophisticated the tools must be to manage the process. For example, a typical aircraft may range from 10,000 to 40,000 terminations in the wiring through hundreds of connectors. The wire list may detail more than 15,000 connections and include components such as resistors, relays, circuit breakers, diodes, and switches in addition to splices and terminal blocks. And, there could be more than 100 pages of schematics.
Without tools designed to manage the data and generate the required engineering documentation, development and implementation tasks are very complicated. It could require six to 12 months of engineering development time.
For example, a software tool cut development time by one third for a huge aircraft modernization program at one Boeing facility. The project, under the direction of Test Engineer Robert Reynolds, needed to develop test files and adapters for 18,000 test points. According to Mr. Reynolds, if attempted manually, this project would have taken three people six months. Instead, he did it alone in the same amount of time.
Streamlining engineering and programming also can represent a significant cost advantage. Users realize fast payback on the investment thanks primarily to the considerable improvements in efficiency.
Software tools that support design and analysis lay the foundation for an efficient process with high-quality results. First, a comprehensive engineering design package provides a robust environment to create testing solutions for complex wired assemblies. Once the cable assemblies are in production, a data-capture tool establishes a database that can be used for detailed analysis.
The combination of design and data analysis tools, such as TestAssistant® II and TestStats® from DIT-MCO International, creates an engineering environment for manufacturers and end users testing complex products. In addition, Boeing is discovering that the software package can improve its capability to react to change orders and execute new test programs and adapters.
Test Development Process
During the early stages of test development, many engineers focus on the features and functionality of the automated tester. However, as soon as possible, the test engineer must determine requirements to implement a test solution, beginning by answering several key questions:
• What testing specifications must be satisfied?
• When will complete wire and parts lists be ready?
• How fast must the testing cycle be completed?
• How many products will be tested over the life cycle?
• Does the test solution need to be portable?
• Will tests be conducted in a workshop setting or in an assembly line?
• When is the first article test scheduled?
• What milestones in the project management plan impact test engineering?
The answers to these questions dictate what must happen next.
If you have a high volume or fast test cycle requirement, consider integrating additional tooling to facilitate test setup, making it easier, faster, and more ergonomically sound for the test technician. Tooling might consist of support stands, booms, or lifts for the interface cables to position the cables next to the required connection point.
However, there is a potential trade-off: You achieve faster, more efficient setups, but dedicated tooling adds to the overall cost of the testing. Nonetheless, high-volume or particularly complex tests may justify the extra cost.
With TestAssistant, the software imports the wire and parts lists for an individual assembly. Initially, the software compiles data from each source and identifies which terminations are end points that require a connection to the tester.
For the large military transport aircraft modification program, the Boeing test engineer was able to download wire and parts lists for hundreds of harnesses and assemblies. The data was entered into a spreadsheet and uploaded to a database in TestAssistant. This served as the foundation for test programs and adapter design.
TestAssistant helps improve test accuracy during development. Its analysis and reporting tools flag potential problems with the data itself, making it possible to resolve problems and quickly regenerate test programs.
Adapter Cables and Connectors
For a complex product’s final assembly test, users often dedicate both the tester and the adapters to the product, requiring the development of new custom adapters. For subassembly tests in a typical workshop environment, adapters frequently are taken from the shop’s generic stock.
TestAssistant supports data management for both scenarios:
• The software maintains a database of all existing test adapters.
• Once the product’s end points are found, TestAssistant searches the database to find candidates with the appropriate mating connectors.
• Details about each possible adapter are presented to the engineer, who decides which of the possible adapters are appropriate.
• If new adapters are required, TestAssistant automatically designs them, generating a bill of material and a wire list for each one.
• The software creates a unique part number in the user’s standard format.
There are several discrete steps, but even when only new adapters are created, the entire process can be completed quickly. TestAssistant determines the best fit of the end-point connectors to the test system to avoid using overly complex adapters. The software can even design clip adapters for loose wires the product may contain.
Once the test adapters have been selected from the library or design documents generated for new adapters, TestAssistant defines the connection of each adapter to the product. The screen displays a graphical image of the test system.
The specified test adapter is dragged on-screen to a connector on the test system. Once the adapter is assigned to the test system in the software, the view of the specific connector on the tester changes, indicating that it is mated and no longer available for use elsewhere.
To change the test-point location of any adapter, it is dragged to another available connector. As a result, software has made a traditionally tedious process straightforward and simple.
Test Program Generation
The software now knows how the product will be connected to the tester. Then TestAssistant automatically generates the test sequences that the user has selected, which may include low-voltage safety test, high-voltage leakage and continuity testing, continuity through passive components, and complex component testing including activation of relays in the product.
At this point, new adapters could be built per design documents generated by the software, or existing adapters would be pulled from inventory. Once all the adapters are in hand and the product is ready, the next step is verifying the test solution.
Commissioning and Verification
With the test system, test adapters, the test program, and the test product on-site, it might appear that the first production unit is ready to test. There actually are interim steps that will improve the process.
For numerous reasons, test engineers prematurely jump to testing. They may plug in everything from the tester to the UUT and start running test programs. They soon experience a high volume of errors with no easy way to determine why or where the errors occurred. The errors could lie in the test program, the adapter cables, or wiring in the UUT. The engineer now faces the huge, frustrating task of isolating the source of the problem.
Rather than proceeding directly to production testing, best practices dictate setting up and commissioning the entire system. The goal here is to install and configure the test system so that when production actually begins, electrical testing identifies only real faults in the UUT.
A methodical diagnostics process accomplishes this goal in a predictable, controlled manner. TestAssistant generates specialized diagnostic test programs specifically for this phase of the development.
Probe tests, the first of two diagnostics, verify adapter cable construction and the connection of each in the test system. TestAssistant generates a program to manually probe each of the test adapters. This accomplishes two things: It verifies the wiring of each adapter against its design, and it proves that the test system is correctly addressing the adapter through the test software. If wiring errors are found in the adapters, the adapter’s wiring can be changed in the TestAssistant database and the tests regenerated in a few minutes, avoiding actually reworking the test adapters.
On the surface, it may seem a slow, tedious process to manually probe each adapter. However, the time saved by achieving a 100% verified test setup will simplify subsequent steps and shorten the time required to complete the test of the first production unit.
The adapters are connected to the UUT to test the first article. TestAssistant generates a specialized diagnostic to assist this process. When technicians hook up the adapters to the product, the software systematically looks at every connector on the product and selects one pin on each connector to test.
The software searches through all the internal wiring, then chooses the ground circuit when possible and tests it for continuity. One-pin testing proves that each test adapter is connected to the corresponding location on the product and, because only a single pin is checked on each connector, the test runs very quickly.
One-pin tests may uncover an issue in the engineering data such as drawings not updated to reflect an engineering change order (ECO) or other design update. If that’s the case, then Test Assistant can quickly regenerate the entire test program in a few minutes.
With commissioning and verification completed, you can proceed to production knowing that any faults exist either in the product wiring or in the accuracy of the original. With this process, you can feel confident that you are dealing with real faults that need to be resolved in the UUT.
One military aircraft manufacturer explained it this way: If you bypass a systematic diagnostic process, you frequently underestimate time requirements. In turn, this may delay production, increase costs, increase staffing, and risk the capability to respond to the customer as promised. In other words, working on the fly rarely produces desired outcomes.
For most projects, production testing is just the start of the ongoing process of responding to ECOs. TestAssistant accommodates ECOs by importing the wiring changes necessary to implement a change order into the database through a series of add and delete instructions.
If new test adapters are required to support the ECO, the process is identical to the initial design task. Test adapters can be automatically designed and visually placed on-screen on any available test connector. Alternatively, if no product connector changes, the test data is quickly recompiled, eliminating hours or weeks of engineering time.
Best practices during production suggest monitoring and storing test results rather than deleting them when the product is 100% error-free. An application such as TestStats automatically captures raw test data and provides a way to add detail related to the cause and location of each test failure.
For example, the technician can enter the cause of a fault as well as the amount of time spent fixing it. Investing a little extra time filling out fault information ultimately pays off by reducing test time.
TestStats identifies the most common and most time-consuming faults to repair. If the same fault continually appears, for example, you can isolate the cause and correct the problem.
Why use development and implementation software tools such as Test Assistant and TestStats? Quite simply, they improve test efficiency and test operation productivity, particularly for complex assemblies. Once production testing is underway, they provide the foundation for a process to monitor and analyze the data, leading to further process improvements, cost reductions, and faster cycle times.
More specifically, using these tools in tandem:
• Helps establish a methodical, sustainable process for the entire cycle of testing.
• Simplifies and automates testing complex components.
• Simplifies, automates, and manages adapter cables and test interfaces that often are more difficult to develop than the actual test program.
• Provides a comprehensive design tool that reduces design and development time from months to days.
With the right software tools to support integrated data management and automated testing, test engineers are equipped to accomplish more with fewer resources, in less time, and at lower costs. This results in a faster payback on investment on software designed to leverage the capabilities of automated test equipment.
About the Author
Karl Sweers, the technical marketing manager at DIT-MCO International, has more than 25 years experience with advanced wire harness test solutions. With a background in electrical engineering, he specializes in developing customized applications. DIT-MCO International, 5612 Brighton Terrace, Kansas City, MO 64130-4530, 800-821-3487, e-mail: [email protected]