Don’t look for atomic-powered cable/harness testers. The present crop of testers isn’t quite that revolutionary, but they do incrementally improve upon those available a couple of years ago by increasing measurement range or adding capabilities and features such as an integral LRC bridge or fiber-optic testing.
In addition, most testers are further differentiated by the intended use. Some are more portable than others. A few are limited to only low voltages or high voltages. Yet others can handle any size test requirement including a complete military jet fighter.
Examples of application-oriented features include label printing, modularity that allows sections of the tester to be distributed across a large EUT, and extensibility that handles huge numbers of connections. In addition, a design’s physical ruggedness must be considered when addressing field, military, or large industrial testing.
On the added-intelligence side, guided assembly is a form of user-tester interaction that eliminates build errors. As a harness is being assembled, the operator is prompted to insert the connector contacts in the proper locations. In one approach, an LED illuminates the empty cavity. When the pin is inserted, the LED no longer is visible. After both ends of the wire have been inserted, a continuity test confirms correctness, and the program moves on to the next wire.
These and many other attributes are presented in the cable tester comparison chart that accompanies this article. Tester capabilities clearly affect the price. Nevertheless, the lowest overall cost of test results from the best match between feature mix and application. A few real-life examples illustrate a variety of ways in which this has been achieved.
Cable/Harness Comparison Chart
Click her to View Chart
Big Truck Harnesses
Stoneridge Electronics North America supplies switches, sensors, and wiring harnesses worldwide for many types of vehicles. For heavy-duty trucks, the harnesses are built into a modular dashboard assembly that contains the majority of the cab and dash wiring with provisions for body-builder options. There are approximately 300 to 400 leads.
According to Dennis Skiver, board tool and test engineer at Stoneridge, “All the harnesses are VIN specific; that is, option-based. As shown in Figure 1, the harnesses are assembled on conveyors of 4′ x 16′ build boards and connected to Dynalab NX Testers through connector holders, matrix cards, and ribbon cables.
“We currently use three expansion boxes per board for a capacity of 3,072 test points. Although a typical harness may only use 600 to 800 test points,” he explained, “the boards are set up for all possible combinations or options, necessitating different test points for each of the possible connector holders that may be used.
“A separate manifest is generated for each harness, which lists all the features required,” the Stoneridge engineer said. “At the conveyor entry station, the operator scans a bar code on the manifest with a wireless scanner. The information is compiled by the resident Dynalab compiler for downloading to the tester. The operator then scans a bar code that designates the board’s unique identification number, a parameter setting within the NX tester, and gives the station the address for the download. The compiled file is downloaded to the tester via a wireless network.
“The operator is prompted to start the test, and the harness is electrically tested for continuity at each of the subsequent stations. At a station, the tester displays the pick location that has been programmed in for each feature or group of wires,” he continued. “This tells the operator the rack and location of the wires needed for that station. At the end of the build, or at the last station on the conveyor, the complete harness is tested again for continuity and for shorts—any wire connected to the wrong place or any wires not needed for that job.
“At this stage, all ancillary devices such as resistors, diodes, relays, and splice caps are tested through specific routines contained in the master program. After all tests are complete, the tester sends a report back to the exit station, a bar-coded label is generated, and the harness is removed from the board for post operations. Through these processes,” he concluded, “we have traceability of each harness including the board it was built on and the date and time it was built.”
Cable Assembly Test
Cable harnesses usually are tested as subassemblies, but in this application, Design Concepts in Olathe, KS, uses a CAMI Research CableEye® Cable Tester while bonding flexible printed circuit (FPC) cables to clear touch panels. James Hudson, the company’s engineering manager, elaborated:
“The heat bonder we supply is an air-operated press that applies both constant heat and pressure. We currently are doing a job for a company that manufactures capacitive touch panels. With the heat bonder, we are attaching FPC cables to these panels using a Z-axis adhesive, one that is electrically conductive only in the Z axis when cured.
“The panels have circuit traces with a specific resistance, and we are using the tester both to check for shorts and to measure this specific resistance between connections of the FPC cable. Really, we are just testing a one-ended cable. The CableEye tester allows us to do a pass/fail test on the measured resistance values, and we can export the measurements from each cable to a spreadsheet for archiving.”
Surviving Sandstorms
It is obvious to anyone who has served in Iraq or Afghanistan that most cable testers aren’t going to work long in such dusty, sandy places. Enter Eclypse International’s environmentally sealed Model RTS Tester with optional explosion-proof chassis and mechanical high-voltage lockout switch. Not only is the tester rugged, but because of these safety features, it can be used for integrity testing on aircraft wire and cable harnesses in a preflight hanger (Figure 2).
The company’s Marketing Director Christopher Teal confirmed that being completely sealed contributed to the RTS-501 purchase by the U.S. Air Force and Navy in August 2008. However, the main requirement, as stated in a Defense Industry Daily article, was to improve what previously was a laborious, error-prone, manual troubleshooting procedure.
According to the article, …”[the RTS-501] offers a quick automated evaluation of the important characteristics of wiring, such as continuity, isolation, insulation, and distance to fault on all wiring circuits, from simple cables to complex printed circuit boards…. [The testers] can be stacked in a daisy chain to allow up to 128,000 points of switching and can handle 3,500 continuity tests per minute.”
The article also included firsthand reports of trials conducted by Navy, Air Force, and Marine personnel. In general, the system saved a great deal of time and in a few cases found faults or potential faults that had not previously been identified manually. “Setup, connection, and testing of 480 wires take about one hour with the analyzer compared to about 24 hours with an ohmmeter. In one instance, the analyzer found a mis-wire in the auto-pilot system and a burn-through in the flight control system that the aircraft’s maintenance team was unaware of.”1
A major factor always considered in military programs is future replacement costs. In this respect, the RTS-501 uses open architecture commercial components to make future parts replacements easier and lower cost. Also, the system can record and collect baseline test data for comparison to data from other similar systems, adding the benefit of proactive maintenance to already existing reactive capabilities.
Ranking Tester Features
In any cable tester application, a number of features are needed, many unrelated to the instrument’s basic electrical capabilities. Selecting the best tester for the job begins with a clear definition of requirements ranked by importance.
Enhanced Functionality
The Stoneridge example highlights integration of cable testing into the company’s manufacturing system. John Weinhardt, a Dynalab Test Systems sales engineer, said that with the correct options, NX testers connect to Ethernet networks. Also, with an extended version of the company’s NX Editor Software, users could define all possible harness options in a master program. A unique test program can be automatically compiled based on selection of the applicable feature codes.
Enhancing a tester’s functionality is an ongoing trend. With the advent of PC-based testers several years ago, programmability and connectivity greatly improved, making possible comprehensive manufacturing test environments such as those developed by Stoneridge.
Following the trend in a different direction, users long have been able to test cable harnesses that contained components such as resistors and capacitors, and many testers can power and test relays. DIT-MCO International’s Karl Sweers explained that the Model 2650 Wiring Analyzer with multiple bus architecture allows any point to be a switching point or an external energization point or both. This means that you can power and test relays, lights, and other active components that require energization.
Another feature that often is provided in a tester is four-wire or Kelvin ohms measurement. Although originally required for more accurate measurement of low-value resistances, Kelvin connections have additional benefits.
WEETECH’s North America Sales Manager Chuck Anderson said that the company has developed a built-in LCR measurement bridge. It handles RL and RC parallel/serial networks as well as simple R, C, and L measurements. Used with the tester’s guarding feature and four-wire Kelvin capability, the bridge provides increased measurement accuracy.
It’s not a large step conceptually from testing cables with embedded components to performing functional testing on a cable/harness assembly. WEETECH offers an optional functional test box that supports testing keys and switches and powered devices such as horns, signals, and brake lights. It can switch an external source up to 24 VDC.
Large test systems often must work with databases or allow construction of databases from test data. For example, Eclypse and NAVAIR have been working together for a number of years to develop an automated wire analysis program. Extensive software associated with the hardware tester supports the user from test generation to data collection.
Automatic test file generators are provided for basic tests as well as circuit breaker testing. Troubleshooting notes and hookup details also are generated as part of the test program. Repair actions can be recorded, and the software produces XML data for test and repair analysis. And, it’s possible to determine the location of a fault.
Large systems often are used to test many different types of EUTs, each with its own set of adapter cables. Simply maintaining and organizing these cables can be very difficult, and several testers include features to minimize the problem. For example, WEETECH testers support an adapter cable library.
According to Mr. Anderson, “Each adaptation cable can be equipped with an ID chip. The company’s CEETIS test interface solution first provides the user with the ID number of the required cable or cables. Then, it verifies that the correct adaptation cables have been inserted in acceptable positions, and it detects where they are inserted and adjusts the test program to test at those system addresses.”
DIT-MCO has similar capabilities but uses different terminology. The DIT-MCO 2650.MTA brochure states that with either a bar-code scan or a keyed code corresponding to each connector you can connect cables in any convenient order.
Nevertheless, versatility does not necessarily imply size, as evidenced by the Cirris Systems Signature Series Testers. With a maximum of 1,024 points, these instruments are limited to smaller cable/harness assemblies. Nevertheless, more than 250 standard adapter cards are available, catering for most common types of connectors. For the shop that works with a wide range of cables, this kind of flexibility saves time and money.
Targeted Specifications
As Figure 1 shows, although lots of variations are possible in a dashboard cable, the wiring to the tester remains fixed and attached to each build board. This situation is very different from the way in which military or large industrial test equipment is used.
In a field test application, the tester often has to be taken to the EUT. This implies a need for rugged construction as well as compactness and tolerance of more challenging environmental conditions. The DIT-MCO Model 2651 Wiring Analyzer features intrinsically safe operation and is certified to MIL-PRF-28800 Class 3 Shock & Vibration and Temperature & Humidity. Sealed covers guard against infiltration by dust, sand, and rain.
Of course, you may not need a fully MIL-speced analyzer, but you probably do want a long service life from your tester. DIT-MCO states that heavy-duty electromechanical dual form C relays are used in the 2650 master switching unit. Before buying a cable/harness tester, it’s worth asking what kinds of relays are used because they directly determine electrical accuracy as well as longevity.
You may just need a tester that tests, which is basically the requirement that Design Concepts had. On the other hand, a pass/fail indication was too simple for the heat-bonder application. It was necessary to accurately measure the bonded resistance because that data verified the quality of the FPC-to-touch panel connection and was archived in a spreadsheet.
Summary
Without looking at the broader picture, it’s tempting to consider the benefits that could be gained by using a tester with a few specialized capabilities. Dynalab’s Mr. Weinhardt commented on some easily overlooked but important features. “When a cable has passed all tests, a label is printed with the date, time, a part number, and the operator ID. This provides an excellent quality-control mechanism because only good cables receive labels. It’s also critical that the test program is secure, and the NX tester has a front-panel key slot for this purpose. Only authorized personnel can change or run the test program.”
CAMI Research’s Director of Marketing Christopher Strangio said that it also was necessary to make testers easier to use. With that in mind, the company has introduced improvements to the M3U Tester including synthetic speech reading of the pin number and wire color. Light-guided assembly uses the new Light Director System to ensure correct cable build, and an API now allows the CableEye software to be embedded in Visual Basic or other external control software.
Commenting on the Cirris Systems Pin Sight guided assembly feature, Brent Stringham, director of sales and marketing, explained that in addition to on-board guided harness assembly, the company also provided force sensing to verify contact retention. The easy-wire product line accommodates on-board guided assembly and in-process testing for harnesses with up to 32,000 points.
In the future, a completely new, commercially disruptive cable/harness test technique may make current equipment obsolete, but that isn’t happening today. In many ways, cable/harness testing is a mature business, so perhaps it’s not surprising that manufacturers have found innovative ways to differentiate their products.
The fact that they have represents both a challenge and an opportunity. There’s little doubt you can find a tester that meets your technical needs, whether that means a specialized fiber-optic test section or a straightforward continuity pass/fail capability. The challenge is in identifying all the supporting features that must be provided to create the optimum test solution.
Reference
June 2009