Effects of Repetitive End Cleaning on Multimode Plastic Fiber Optic Cable Performance

Periodic cleaning of the end faces of fiber optic cable links in aircraft avionics systems is undertaken as part of routine maintenance or when problems develop. Aeronautical Radio Incorporated (ARINC) has established guidelines for the installation and cleaning of fiber optic cables and components in its standards and a number of isopropyl alcohol based fiber optic cleaning kits are available on the commercial market. While these kits and techniques have proven successful in maintaining signal integrity over the short term, an industry standard as to the effects of repetitive cleaning operations has not been well established. The purpose of this study is to evaluate the effects of repeated end face cleaning on cable transmissivity and make this data available to the industry. It is anticipated the results will provide information useful to the overall determination of cable life cycles enhancing the safety and integrity of fiber optics usage in aircraft avionics systems. Introduction As part of a study recently undertaken at the Southern Illinois University Department of Aviation Technologies, effects of short term exposure to common aircraft chemicals and solvents on fiber optic cable transmissivity were evaluated to determine the level of degradation occurring due to chemical activity if any. Test groups of cables and controls were prepared, ST type connectors attached, and baseline values of cable transmissivity measured and recorded. Following short term exposure (1 week) to various solvents and chemicals, the cables were retested and the results recorded and evaluated. As part of the test regimen, the cable ends were cleaned using Aeronautical Radio Incorporated (ARINC) accepted methods following initial preparation and after exposure to the various test chemicals. In the control portion of the study, one set of cables was exposed to a typical isopropyl alcohol cleaning chemical for one week and subjected to the same standard regimen performed on all the test samples. No significant short term effects on the cleaning chemical control set were noted in the study (Hannon and Ramsundar, 2007). Since fiber optic cable ends in aerospace applications are cleaned prior to installation, at periodic maintenance intervals, or when problems arise, it is conceivable that the effects of repetitive cleaning may be detrimental to long term cable performance. The aerospace industry, through contacts with Boeing Aerospace in St. Louis, MO, desired information on the extent of these effects if any (Boeing, 2007). In order to satisfy this request, an evaluation of the long term effects of repetitive cable end cleaning was undertaken wherein cables were subjected to over 100 cleaning cycles over a seven and one half month period. Study Protocol This research consisted of evaluation of 10 meter lengths of polymethyl methacrylate (PMMA) plastic core fiber optic cable as may typically be used in aircraft installations. The cable specimens were cut to the specified lengths and categorized. Following initial preparation, ST type connectors were mounted on the cables and the end faces polished, cleaned, inspected, and initially tested to establish a baseline transmissivity level. Appropriate controls were run in parallel with the testing JAAER, Spring 2010 Page 4 1 41 Hannon: Effects of Repetitive End Cleaning on Multimode Plastic Fiber Opt Published by ERAU Scholarly Commons, 2010 Repetitive End Cleaning operation. Testing procedures followed the guidelines outlined in Aeronautical Radio Incorporated Project Paper 805: Fiber Optic Test Procedures and the repetitive cleanings were performed in accordance with ARINC Project Paper 806: Fiber Optic Installation and Maintenance Procedures (ARINC, 2005) and Cisco Systems brochure on inspection and cleaning procedures for fiber optic connections (Cisco Systems, 2006). The cable samples and controls were periodically subjected to the standardized cleaning regimen and transmissivity tests at intervals not exceeding once per day over a period of 7 112 months. A fiber optic transmissivity test set employing 650 qM wavelength red light was used for determination of cable performance. Source illumination of 650 qM is the wavelength normally employed for data transmission in 1 mm plastic fiber optic cable. An ambient temperature and relative humidity reading was also taken concurrently with each test cycle. Test, temperature, and relative humidity results were logged and documented in accordance with sound research practices and accepted scientific method. The step by step procedure for cleaning, inspection and testing of the cables was well documented and a checklist used to assure consistency and repeatability. Errors due to inadvertent mechanical abrasion or end compression were mitigated through careful handing of the cable samples and use of dust covers on the ST connector ends. Several transmissivity test readings were taken at each test interval and averaged to help alleviate any inherent test set measurement or interpretation errors. Cable transmissivity before and after cleaning at each test interval and over time was measured in microwatts and recorded. The data was then transferred to an Excel@ spreadsheet and graphed for documentation, study, and interpretation. Values representing the power transmitted through the cables prior to, after and throughout the successive cleaning regimens were recorded and statistical analyses conducted using both Excel@ and SPSSB where thought relevant. Materials Durable Materials: Fiber Optic Test Set; Manufacturer: Industrial Fiber Optics #IF-FOM Fiber Optic Microscope 100X; Manufacturer: Fiber Optics Instruments Sales, Inc Fiber Optic Tool Kit; Manufacturer: Industrial Fiber Optics #IF-TK4 Professional Fiber Cutter; Manufacturer: Industrial Fiber Optics #IF-FC 1 'ST' ferrule Polishing puck Glass Polishing Plate Fiber Optic1 Wire Stripper 766-A; Manufacturer: Fiber Optic Instruments Sales, Inc ST Connector Crimping Tool 4-oz Water Dispenser Consumables: ST (Straight Tip) Connectors PMMA 1 mm Fiber Optic Cable (see specifications, Appendix E) 99% Isopropyl Alcohol Bleached White Cotton Head Swabs Distilled Water Sanitary Cleaning Tissue 3 yM Polishing Film 2000-grit Polishing Paper KEEN Single-Edge Razor Blades Cleaning Methodology Thorough cleaning was performed consistently using the cotton swab and isopropyl alcohol method as described below: Dip cotton swab into bottle of 99% isopropyl alcohol. Vigorously shake off excess alcohol £tom the swab to prevent residue. Hold the fiber vertically so the fiber surface points upward and carefully place the base of the swab against the fiber optic surface. Drag the swab across the fiber optic surface in a single stroke. Do not drag the swab back and forth. Repeat £tom step 4, using the other side of the swab. Check fiber cable with fiberscope to ensure the fiber if fi-ee fi-om cleaning solvent residue and cotton fibers. Results Repetitive cable cleanings and transmissivity testing were conducted during the period of early September, 2007 through mid-April, 2008. Figure 1 depicts all the parameters examined including temperature and humidity of the testing environment over the 7 !h month testing period. While the relationship between the before and after cleaning tests and unaltered control appear fairly flat throughout the testing period, some interesting variances were noted. 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