Electronic Restoration >> How To Clean Smoke Damaged Electronic Circuits

Fiber termination and handling techniques greatly influence fiber optic system reliability.Missing or ineffective process controls can lead to failure. The user can easily introduce defects due to the mechanical limitations of optical cable. It is therefore critical for the to user institute proper harnessing and How To Clean Smoke Damaged Electronic Circuits  handling practices. 

Tests may have to be performed to verify that bending losses are not induced due to inadequate bend radiuses or that radial stress is not introduced to the cable as it passes through box walls or bulkheads.To minimize handling related failures, How To Clean Smoke Damaged Electronic Circuits installers and test personnel must be made aware that they are working in the vicinity of optical cable. 

Care should be taken to avoid undue stress to the cable or the connections. Connector mating and de-mating should be controlled. All terminations should be cleaned and How To Clean Smoke Damaged Electronic Circuits visually inspected prior to mating anyassemblies, even if only for testing.Cleanliness is critical when using fiber optics in space environments. 

Fiber opticconnectors often contain many microscopic particles, which need to be removed prior to use. Metallic shelled fiber optic connectors may also have a contaminant coating of oil or How To Clean Smoke Damaged Electronic Circuits film residue from machining processes. Connectors should be subjected to a thorough cleaning process to remove particles and contamination prior to being used on anassembly. 

The user is cautioned to use cleaning solvents and How To Clean Smoke Damaged Electronic Circuits procedures that will notattack the connector materials. Cleaning of the optical end faces of terminated connectorassemblies is typically performed with 2-propanol alcohol. Cleaning and visualinspection should be performed prior to mating assemblies at all stages of the test andintegration process.

VIBRATION Mission specific vibration levels are usually specified for a given component or box aswell as for the spacecraft. These levels must be doubled (g2/Hz) for validation of theoptical fiber assembly interconnection. Table 2 shows an How To Clean Smoke Damaged Electronic Circuits example of the typical randomvibration profile used to validate assemblies. 

This profile is used for 3 minutes duration on each of three axis directions—x, y, and z. These tests are done only on the cableinterconnect systems and not on the instrument systems. Optical cable assemblies are typically sensitive How To Clean Smoke Damaged Electronic Circuits to two significant thermally inducedeffects. One is the optical stability of a fiber optic cable configuration to a changing thermal environment. 

Performance can degrade due to stresses induced by the differingthermal expansion coefficients of the How To Clean Smoke Damaged Electronic Circuits constituent materials. The second effect is shrinkage of components due to thermal cycling. The shrinkage of the optical cable components is usually of more concern since it can lead to the catastrophic failure of anassembly. 

Both characteristics need to be tested to determine if a cable is suitable forspace flight. Performance of the cable during cycling is tested by monitoring optical power transmission for the How To Clean Smoke Damaged Electronic Circuits duration of the thermal cycle test sequence. The cable lengths usedfor characterization typically are based on the actual lengths that will be used in theapplication. 

The test cycle extremes are normally set to the survival temperature limitsfor the mission plus 10 ºC at each extreme. For example, How To Clean Smoke Damaged Electronic Circuits testing is to be performed overa -25 ºC to +70 ºC range when the mission specification requires a survival temperaturerange of -15 ºC to +60 ºC.

Shrinkage testing is conducted by making interim measurements over a specified numberof total How To Clean Smoke Damaged Electronic Circuits cycles. The cycling extremes should be determined from the manufacturer’sspecification. Cycling is divided into 4 to 8 cycle sessions and after each sessionmeasurements are made. The cycling ramp rate shall be 2ºC/min or less such that thecables are not shocked by the temperature change but cycled. 

Cable lengths shallrepresent the actual lengths required for the application. Thermal cycling shouldcontinue for at least 60 cycles or when the How To Clean Smoke Damaged Electronic Circuits shrinkage rate between measurements drops to less than 0.1%. Not only is this testing used to compare cables for thermal stability but itis also used to determine what preconditioning is required prior to terminating a flightcable. 

As an example, Figure 3 shows the shrinkage characteristics of several candidatecable assemblies. Thermal cycling is an effective method of identifying assembly failure modes that areassociated with the termination procedures used. If epoxy is incorrectly applied orconnector parts are not secured in compliance with How To Clean Smoke Damaged Electronic Circuits industry standard procedures, theinterconnection will fail at some point during the testing. 

Failure of a termination isdefined as pistoning (or pushing through) of the optical fiber into or out of the connector.If a fiber pistons through the connector and impacts with other side of the interconnection, How To Clean Smoke Damaged Electronic Circuits it can chip an end face. The chipping can result in cracks that canpropagate and leave the cable completely disabled. 

Thermal cycling of mated cables isrequired to characterize for pistoning. The optical transmission of the cables should bemonitored during the cycling. End face visual inspections at 200X should also beconducted prior to and How To Clean Smoke Damaged Electronic Circuits after testing to ensure no damage has occurred. RADIATION Optical fiber is susceptible to temporary and permanent damage from exposure to gammaradiation. 

Testing has shown that gamma radiation has a greater effect on optical fiberattenuation than does proton or neutron radiation [11]. Qualification tests and applicationprecautions should be based on the requirements of the application. Typically, How To Clean Smoke Damaged Electronic Circuits theperformance of optical fiber in a space radiation environment is significantly dependenton the wavelength of operation, the thermal environment, the dose rate and total dose, and the length of the fiber. 

Single mode fiber tends to outperform multimode due tosmaller amounts of dopants present in the silica material.In many cases, How To Clean Smoke Damaged Electronic Circuits the actual space flight environmental parameters of total dose and doserate are not used for characterization testing. Most background radiation dose rates arevery low but will add up to a considerable total dose after several years. 

Since thiscannot be duplicated in the laboratory, models are utilized to expedite testing. Forgermanium doped multimode optical fiber, a two-dose rate test is conducted and the datagathered is used to extrapolate to lower dose rates [10]. Additional How To Clean Smoke Damaged Electronic Circuits information concerning gamma radiation effects and radiation testing are presented in references 2 –4. 

An optical fiber radiation How To Clean Smoke Damaged Electronic Circuits database is available at http://nepp.nasa.gov/photonics. It contains all relevant gamma radiation data for the past decade that can be directly tracedto a part number and is presented in reference 5. In some cases extrapolation data is alsoavailable.

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