Our dependence on complex systems in modern manufacturing leaves us vulnerable to unexpected process failure that may have expensive consequences. While we cannot foresee the future, our awareness of failure modes should lead to simple preventve measures. Well taken precautions help avoid the silent panic following our realization that a preventable accident will extract a heavy cost in time and inconvenience to correct.

Any action which serves to impair or prevent normal operation of your cable harness tester may have expensive side effects on your business –

• Contract manufacturers may be unable to ship cable products without the required quality certification;
• OEM manufacturers may be unable to certify incoming cable or harness assemblies before commitment to inventory;
• Factory maintenance personnel may be prevented from diagnosing malfunctioning robotic, printing press, or other computer-controlled machinery, causing expensive delays in production.

Disruptive events include both temporary situations like voltage transients, and less easily corrected problems like equipment damage.

Test and quality control engineers may be proactive about preventing process failures by their awareness of potential problems, and development of procedures to prevent failure and speed equipment repair when failure occurs.

We summarize major causes of process failure and suggest actions you may take to minimize their effects.

1 – Attachment of a “Live” Cable to the Tester

Each of the one-hundred or more test points in a typical cable tester connects directly to an integrated circuit used in applying or measuring test signals. Although various means of overload protection can be built into each point, it becomes economically impractical to isolate the test points from more than a few volts higher than the maximum test voltage. Should the operator inadvertently connect a live cable to the tester, severe damage may ensue. If the overvoltage is considerably above the test voltage, breakdown of the affected IC may transmit the overvoltage through the power bus reaching many interconnected ICs and rendering the circuit board irreparable. ICs may actually explode leaving a blackened crater on the inside of the case as shown in the following photos.

Note: Testing a cable that is connected to a power supply will cause rapid destructive heating which will destroy electronics. Sensible precautions must be employed to prevent this scenario.

2 – Static Discharge into Test Point Terminals

Taking the usual precautions of working on a grounded workbench with dissipative mats, grounding the test equipment, and wearing a wrist strap may be insufficient to protect the tester from static damage. Charge may develop on the insulation of long cables as a result of frictional motion when the operator coils or uncoils the cable while moving it to the test bench. Charge on the insulation then attracts opposite charge on the copper conductors just under the insulation. This in turn forces charge to the cable endpoints where it remains trapped. Refer to the drawing below.

The properly grounded operator picks up the cable by its connector, which is insulated from the outer jacket and conductors, and unknowingly discharges the copper conductors into the test equipment at the moment the connector is attached. The volume of charge released may overload clamping diodes built into the tester’s ICs, causing damage to the circuitry. Generally, cables longer than 10 feet (three meters) pose increased risk, especially cables with rubber insulation.

Note: A sufficiently large discharge will overcome any static suppression circuitry that is embedded within the tester. Sensible precautions must be employed to prevent damage to the tester.

3 – Power Line Transients

A one second power interruption may disrupt batch testing and cause a loss of log data or batch reports, requiring involvement of a supervisor to restore normal operation, and possibly repeat testing. Power surges and switching noise risk damage to equipment as well as stored data.

2 – Conductive Debris

Wire clippings, metal punch-outs, metal dust, or spilled beverages may cause unintentional connections between test points, or work their way onto the circuit board and introduce shorts. Coffee and soda are highly conductive when liquid and leave conductive residue when dry, creating a difficult repair problem, especially for testers measuring isolation resistance above one Megohm.

1– Connector Wearout

Natural wear caused by the friction of inserting or removing connectors from mating sockets cannot be avoided. However, some simple precautions will prevent premature failure and quickly restore equipment to proper function.

2 – Defective Connectors

If the physical characteristics of connectors used on your cables are slightly out of specification, they may deform or in other ways damage the mating connector on your cable tester. For example, plastic RJ45 modular plugs sometimes have excess unremoved flashing from the mold, or sharp edges, which catch the wire pins on sockets. When unplugged from the tester, the wire pins may hang up on the flashing and become bent upon removal, permanently damaging the socket. Note that the same problem may damage your customer’s connectors and you may be held responsible.

3– Improper Insertion

Test technicians who apply excess force off-axis from insertion direction may bend the pins or shell of a mating connector.

4– Contamination

Liquid spillage, including glue, potting compound, or beverages, can permanently damage both the cable tester and device under test. Airborne dust can also build up and cause a tester fault.

Contaminated test fixtures will spread dirt, oils and conductive debris to the header connectors of the test equipment and vice versa. Contaminated test fixtures and/or header connectors could lead to false test results (false FAILs) of your product. Because of the risk of cross contamination, we recommend regular maintenance of your test fixtures and header pins following recommendations for protecting your cable tester.

5– Improper Storage and Packaging

Most cable testers use plug-in connector boards to accommodate many different connector styles. When boards are detached from the tester, connectors may be damaged if not properly stored. An example of recommended storage is shown in photo below (Fig. 4).

Testers that are inadequately packaged to survive the rigors of shipment to the factory for service will likely arrive damaged.

Component Failure

Under normal circumstances, equipment will ultimately fail given enough time and use. The “mean time between failure” statistically predicts how long you can expect normal operation, on average, before failure occurs. While end-of-life wearout cannot be avoided, we need not invite this outcome prematurely.

Software Failure

Inadvertent erasure of valuable data, malicious action, or internal hardware failure, may expunge critical programs, procedures, scripts, and log files. No other process failure yields as easily to correction, or risks such adverse consequences. As we increasingly rely on computer-controlled equipment, our procedures must reflect data backup as an essential action of no less importance than documentation, labeling, or inspection.

Our dependance on complex systems in modern manufacturing leaves us vulnerable to unexpected process failure that may have expensive consequences. While we cannot forsee the future, our awareness of failure modes should lead to simple preventive measures. Well taken precautions help avoid the silent panic following our realization that a preventable accident will extract a heavy cost in time and inconvenience to correct.

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