Remaining in the pack for a share of today’s cable/harness market gets tougher every day as customers request more varied and complex products. To remain competitive, cable/harness manufacturers must find new ways to trim production and test to the bare minimum. Some companies with low-volume cable/harness production are shifting their focus to a just-in-time (JIT) strategy to stay ahead of the pack and reduce overhead at the same time.
With JIT manufacturing, you make the product only when you need it. It sounds easy, but a JIT process really requires detailed planning to reduce defects and eliminate duplicate steps.
Automation is one possibility for reducing defects, but the immense variety of cables and harnesses makes implementation impractical. Consequently, companies must find other ways to improve the manual assembly process and the follow-up testing.
An effective cable/harness test when implemented in the production environment does not increase overall cost. The goal is to perform tests with no setup costs, no matter where in the process the testing occurs.
The JIT method requires a flexible work group and equipment that readily adapt to new situations. Software that takes advantage of the computational power and display capabilities of the PC also helps meet the changing requirements.
For example, an on-line data base that contains cable specifications from golden cables or wire lists saves time because the test information is accessed automatically, said Christopher Strangio of CAMI Research. “Total test time, including the data-base search, is typically <1 second for cables with <32 conductors and a maximum of 3 seconds for 96-conductor cables."Graphic wiring displays are important for work groups responsible for correcting cable errors, added Mr. Strangio. “The errors are highlighted on the screen to quickly guide the user to their location. This is especially helpful when the cables contain difficult-to-see internal jumpers. The graphic display can change the angle to a front view of the pins or a rear view of the termination end.”
Some units, such as the Horizon Harness Tester from Cabletest International, offer a graphical LCD with a touch screen to minimize setup and programming time and make file selection easy. The unit also allows you to change products by snapping in new adapters. The operator then points to the next product in the test queue and the appropriate adapter is automatically indicated.
An equally simple selection of tests is performed with the Dynlab Model 256, which stores 32 test programs. To automatically access the correct test, you can use the data base or scan a bar code on the cables.
JIT methodology progresses more smoothly if the test hardware is modular in design, agreed Joseph DeSanto, President of Invotronics. The system also should guide operators during assembly, and test the connections at the same time, he said.
Cables and harnesses fall into several categories, such as computer-related, microwave and RF, fiber-optic, industrial controls and sensors, power line and vehicle harnesses. To implement JIT testing, each category of cable and harness assembly requires a tester, a fixture jig-tooling adapter and a test program, said Eugene Sequeira of Computer Systems Technical Support. Manufacturing processes, quality-assurance methods and testing requirements also must be evaluated continuously to assure cost-effective solutions.
In many applications, low-volume cable manufacturers cannot afford to create a test program from a wire list because of the short turnaround requirements. In these cases, a known-good or golden unit helps create a test program using the self-learn mode.
Because their requirements are very stringent, military and aerospace users of cable testers must be careful when considering JIT methods, said David O’Brien, Chief Engineer at Chatsworth Data. “The testers must be able to perform valid insulation and dielectric withstand voltage tests that meet tougher military and aerospace standards.”
“Unfortunately, there is a tendency in the cable-test industry to increase test speed, reduce test voltages and substitute the insulation resistance test for the dielectric withstand voltage test. These are unacceptable shortcuts,” said Mr. O’Brien.
Customers should exercise caution when evaluating cable testers, said Mr. O’Brien. Units must perform a dielectric withstand voltage at a minimum of 1,500 VAC. Also, high-speed test algorithms and scanning techniques that only simulate “one point against all others” test violate safety and military standards.
Resistive and Capacitive Measurements
Most harness tests do not require capacitive measurements, said Dan Hardin of Cablescan. However, capacitance tests give an indication of shorts in long-length harnesses that are not apparent with resistive measurements, he added.
The combination of resistive and capacitive measurements determines the existence of crosstalk, said Mike Mathews of Cabletest International. They show the location of shorts and opens and help discern the difference between an open and a miswire failure.
Capacitive measurements are required to verify capacitors embedded in a product and to check continuity in an unterminated shield. For example, shielded cables for aircraft and satellites often are fed through bulkhead interfaces. The termination of a shield may not be connected at both ends. This makes continuity measurements impossible but helps avoid ground-loop problems.
Cable/harness products that use coaxial or twisted-pair cables must incorporate capacitive measurements to detect cross wiring, said C. H. Wu, President of ABC Digital Electronics. This technique can detect problems on cables because mutual capacitance in a twisted pair can be two or three times that of a crossed-line pair from two twisted pairs, he said.
“Capacitance measurements indicate a cable’s characteristic impedance,” observed Karl Sweers of DIT-MCO International. “This is important when you must use cables that provide high-frequency or digital interconnections because cables with excessive capacitance distort the signals, limiting the bandwidth. This produces the same effect as adding a low-pass filter to the signal.”
To determine the characteristic impedance, the system must measure small capacitance values without adding the effects of the test system and the interface capacitance, said Mr. Sweers. Some companies offer the instrumentation and software to detect product capacitance even when the test unit is attached to a capacitive interface connector.
Emerging markets, notably the data-communications industry, require clock rates of several hundred megahertz. Often these signals are distributed among several bays of equipment and spread over a large area, said Ed Cioli, Vice President of OmniTester.
These systems rely on the transmission properties of the interconnection cabling to maintain signal integrity. Signal delays, pulse spreading or crosstalk among adjacent signal paths can create testing nightmares, he added.
More companies verifying high-speed cables now test at their operating frequency. Performance at a lower frequency is not an accurate representation of how it will act at a higher speed. Capacitance measurements are the starting point to help emulate the demands a high-frequency system places on cables and harnesses.
Cable/Harness Products
System Performs
6,000 Tests/Min
The System PC-328 Cable/Harness Tester permits measurements between any two terminations, in any sequence, for up to 6,000 tests/min. It measures continuity, shorts and leakage resistance. Typical applications include computer-backplane wiring, telephone switching-assembly wiring, multilayer printed-circuit assemblies, aerospace harnesses and multiconductor telephone cables. The system is comprised of resistance, voltage and current modules, and continuity and leakage components. Options include four-wire resistance measurement, high-voltage insulation resistance and dielectric strength test facilities. $50,000 to $150,000. ABC Digital Electronics, Inc., (201) 666-6888.
Software Uses FDR Technique
For Testing Cables
An upgrade to the 2300-12 Distance-To-Fault Location Software uses a frequency domain reflectometry (FDR) technique for testing RF cables and antennas at their frequency of operation. The software also compensates for cable attenuation. The FDR technique is used when DC continuity checks performed by time-domain reflectometers do not provide a clear indication of equipment operation. $4,000. ANRITSU WILTRON Sales Co., (408) 778-2000.
Unit Features Continuity
Test/Assembly Aid
The Model 64 Cable/Harness Tester provides continuity testing, assembly aid features and multiple program storage for 8 locations, 16 with a removable EEPROM. Cable tests are self-learned or downloaded from a PC. The unit also identifies wires and displays point labels. Maximum interwire capacitance is 0.01 µF. Sensitivity to shorts is 1.0 k(ohm) for opens. Cablescan, (714) 998-1961.
Compact Wiring Analyzer
Features 1,500 VDC Hipot
The Horizon Wiring Analyzer offers 1,500-VDC and 1,000-VAC hipot testing capability. It has a 3″ x 5″ touch-screen display that allows file selection and tester use via a series of graphical menus. The analyzer is available with 32 to 128 test points and can be linked to an Ethernet for transfer of test programs and statistics. Test features include resistance checking with m(ohm) resolution, capacitance measurement and twisted-pair verification. Low voltage version–$2,900; high-voltage version–$16,000. Cabletest International Inc. (905) 475-2607.
PC-Based Cable Tester Offers
Expansion for 192 Test Points
The CableEyeTM System is a PC-based cable tester with a graphic wiring display, an internal cable data base and a label printer. It includes an expandable hardware test fixture that links to any MS DOS-based PC via a serial port. The system offers 192 test points for scanning cables with 96 conductors. Standard connectors include DB25, DB9, Centronics, DIN8 and Bellcore 6-position types. Software enables the user to view connector drawings and pin numbers, and display intermittent connections. $1,990. CAMI Research Inc., (617) 860-9137.
Cable Analyzer Tests
Continuity From 0.5 (ohm) to 2 k(ohm)
The Cablemaster 400 PC is an automated PC-controlled cable, harness and connector tester. It tests dielectric strength to 3,000 VAC or VDC, insulation resistance to 10 G(ohm), and continuity from 0.5 (ohm) to 2 k(ohm) at a maximum current of 3 A. Intermittent failures are analyzed by a sampling method which compares resistance value changes as cables are flexed. The 400- to 1,600-point unit tests military and aircraft cables to MIL-STD-202. $34,500. Chatsworth Data Corp., (818) 341-9200.
Cable Tester Checks
Capacitors and Twisted Pairs
The Model 1000H+ Cable Tester checks capacitors and twisted pairs, and identifies a defective end of a cable. Capacitor measurements range from 5 nF to 100 µF. The unit also offers hipot testing to 1,000 VDC, insulation resistance from 5 M(ohm) to 500 M(ohm), connection resistance measurements from 0.001 (ohm) to 100 k(ohm), and four-wire measurements from 0.001 (ohm) to 10 (ohm). The company’s CTLynx software package and test language for controlling the unit is included with the tester. $4,795 for 128 test points. Cirris Systems Corp., (800) 441-9910.
Circuit Analyzer Performs
3,000 Tests per Minute
The UCA-3000 Universal Circuit Analyzer performs 3,000 tests per minute. It checks cables, wiring harnesses and other wiring devices as well as backplanes and equipment racks. The system performs high-speed analysis on 65,536 points in increments of 500 points per expansion unit. It runs resistance and hipot tests with optional testing of inductance, capacitance, frequency and diodes. Program editing and the use of macros are accomplished via software. $29,500. Computer Systems Technical Support, Inc., (714) 777-2787.
Benchtop System Expands
To 50,000 Test Points
The Model 2115 High-Voltage Benchtop System tests 1,000 points per chassis and connects to additional chassis for a maximum of 50,000 test points. The unit can stand alone or be mounted in a 19″ rack. Standard capabilities include 1,500 VDC or 2-A test stimulus, resistance from 0.01 (ohm) to 1,000 M(ohm), and capacitance measurements from 10 nF to 1,000 µF. The system performs 3,000 continuity tests per min and 2,800 insulation tests per min. $50,000 to $100,000. DIT-MCO International, (800) 821-3487.
Circuit Analyzer
Stores 32 Programs
The Model 256 Circuit Analyzer stores 32 test programs and tests 128 to 256 test points. It checks diodes for shorts, opens and orientation. Resistors are tested with 5% accuracy between 5 k(ohm) and 50 k(ohm). Drive voltage ranges from 2 VDC to 12 VDC, and current extends from 1 mA to 10 mA. It has a four-line, 20-character backlighted LCD, and offers user-programmable alarm conditions. $965. Dynalab, Inc., (614) 866-9999.
Automatic Circuit Analyzer
Tests Cables and Panels
The SAC-512 Automatic Circuit Analyzer tests relay panels, cables, harnesses, subassemblies, and control and breaker panels. It operates on 60-Hz or 400-Hz aircraft power. The system provides four-wire measurements and the capability to test 488 switching points in 122-point increments. Programmable features include resistance from 0.01 (ohm) to 1,000 M(ohm), voltage from 0.25 VDC to 500 VDC, current from 0.005 A to 1.00 A, DC voltage measurements from 25 mV to 500 V, AC voltage measurements from 25 mV to 350 V, and capacitance measurements from 1 nF to 1,000 µF. $75,000. Eclypse International Corp., (800) 933-8839.
Universal Termination Module
Handles Variety of Connectors
The Universal Termination Module helps test connectors in cable and wire-harness assemblies. The module consists of a base unit, specific to the pin spacing and connector profile under test, and a front plate. The front plate holds the connector while pogo-pin fittings in the base contact the connector pins to provide continuity. The system allows the spring-loaded pins, LEDs and printed circuit cards to be reused. The terminator face plate can be changed without reconnection or back wiring. Starts at $35. Invotronics, Inc., (800) 521-3579.
Tester Translates Pin
Designations Automatically
The PC/DOS Tracer Cable/Harness Tester offers 256 test points. An EEPROM module stores both test and text files for translation tables. Translation tables link automatically with test files to provide matching pin designation and wire color-code displays. Tests are referenced using part numbers and revision levels of cables. Starts at $995. Noetic Technologies, (800) 780-6343.
Unit Tests For
Continuity, Insulation
The OmniScan-Series One performs integrity testing of cable and harness assemblies. It offers continuity, insulation and capacitance testing capabilities. A communications link downloads information for off-line programming. $1,850. OmniTester Corp., (800) 523-2283.
System Tests Cable Assemblies
Connected to Card Cages
The Model 405 D/C Manufacturing Defects Analyzer interfaces the tester’s switch electronics directly to the UUT. It identifies shorts, opens, solder bridges and missing, reversed, incorrect and defective components. The tester checks cable assemblies connected between card cages. It uses active electronic paddle cards that are plugged into the cardcages and only tests points directly associated with the cable assemblies. The system uses one cable connected in a daisy-chain arrangement between the electronic paddle cards. Applications include card-cage assemblies, cable-harness assemblies, back-wired harness boards, backplane assemblies and distributed modules. $50,000 to $100,000. Testronics, (214) 542-3111.
Copyright 1995 Nelson Publishing Inc.
April 1995