Electronic Restoration >> Troubleshoot An Electronic Circuit Board

Optical fiber cable assemblies consist of a combination of two or more of the following parts: optical fiber, cable, connectors, and assemblies. In most cases optical fiber is not used without some type of interconnection. Some of the test methods presented here have been developed at the GSFC Code 562 Technology Validation Assurance (TVA) Laboratory for Photonics Troubleshoot An Electronic Circuit Board and are noted as such. 

The TVA has developed these methods over the past 8 years to address the specific needs of space flight projects at GSFC and to address the failure modes that are common Troubleshoot An Electronic Circuit Board to Commercial-Off-the-Shelf (COTS) optical fiber devices. A references column is provided in Table 4 to provide insight into known failure modes and the test methods used to characterize them. 

All references cited hereare available at http://nepp.nasa.gov/photonics web site. It is important to note Troubleshoot An Electronic Circuit Board that military products cannot in general be assumed to be qualifiedfor space flight. Military specifications are not typically written to accommodate spaceflight requirements. The choice of military qualified fiber components is also verylimited. 

Therefore most of the parts and assemblies used for space flight are COTS.Many of the listed tests are common to commercial and space applications and can beconducted economically only by the manufacturer. In those cases, Troubleshoot An Electronic Circuit Board the manufacturer'scertified results are acceptable. Tests that are critical to determining the suitability ofproduct for space flight are either verified independently or performed in addition tomanufacturers' tests.

Table 3 summarizes the tests to be performed on optical fiber, optical fiber cable, opticalfiber connectors, and optical fiber assemblies that include either optical fiber terminatedto connectors or optical cable terminated by connectors. For each test and part type, a symbol letter is used to designate the entity by which the test is to be conducted: themanufacturer, Troubleshoot An Electronic Circuit Board end user, or both. 

A key is included at the bottom of the table.The Fiber Optic Test Procedures (FOTP-XXX) listed in Table 4 correlate directly to theEIA/TIA 455-XXX series. EIA/TIA 455 has been replaced by FOTP for brevity.Although more tests are done, Troubleshoot An Electronic Circuit Board those specified here are performed typically by the vendor. The tests presented here are required by NASA projects for validation purposes on allgrade levels (i.e., levels 1, 2, and 3). 

There are no distinctions in the validation andqualification of fiber optic components at this time between the grade levels. Testing offiber optics for space flight applications should be determined from the application andreliability requirements of the project. It is the responsibility of the user to specify detailed test conditions and Troubleshoot An Electronic Circuit Board pass/fail criteria for each test. 

These values shall be based on the nearestequivalent military specifications, manufacturer's specification, or the application, Troubleshoot An Electronic Circuit Board whichever is most severe.2/ The group 1A samples shall be subdivided as specified in the table for groups 2 to 6, inclusive. These minimum sample sizes are needed for qualification: Level 1 to 12 fuses Level 2 to 8 fuses Level 3 to 4 fuses3/ 

External visual examination required after testing to verify no evidence of mechanical damage.4/ The power supply shall have Troubleshoot An Electronic Circuit Board an open-circuit voltage not less than the specified voltage rating of the fuse under test.5/ Fuses rated < +125 °C shall be tested to condition A.6/ Materials listed in NASA Reference Publication 1124 that meet TML and CVCM limits are acceptable for use without further testing.7/ 

Not applicable for SMT fuses.8/ Not applicable for SMT fuses utilizing thick or Troubleshoot An Electronic Circuit Board thin film technologies. Hollow SMT fuses constructed with wire-in-air technology shall be subjected to the group 4 inspections. Fuses are specified to interrupt within a maximum of 5 seconds when driven at 200% of their rated current for nominal ratings up to and including 10 amperes. 

A fuse with a nominal rating of 15 amperes is specified to interrupt within a maximum of 10 seconds when driven at 200% of its rated current.The power supply shall be capable of delivering appropriate levels of current to achieve short fusing times.2/ In a space environment, Troubleshoot An Electronic Circuit Board the possible escape of air from inside the fuses reduces the filament cooling mechanism (heat transfer by conduction). 

Thislowers the blow current rating and decreases current capacity with time, making it necessary to derate current ratings on fuses used in space applications.3/ Fuses rated at 1/2 ampere or below are especially affected by loss of air; thus, Troubleshoot An Electronic Circuit Board their derating factors are larger.4/ Current derating factors are based on data from fuses mounted on printed circuit boards and conformally coated. 

Other types of mountings require Troubleshoot An Electronic Circuit Board project office approval. It should be noted that the lifetime of the fuses is controlled by two factors: cold resistance of the fuse and the heat sinkingprovided by the installer. The thermal resistance of the fuse to the thermal ground is very important, as is the case with power transistors and power diodes mounted on circuit boards.5/ 

Recent studies have shown the occurrence of enduring arcs in fuses rated at 125 volts when the applied voltage is greater than 50 volts. Therefore, Troubleshoot An Electronic Circuit Board the voltages on these fuses should be derated to 50 volts or less.6/ Electrical transients produce thermal cycling and mechanical fatigue that could affect the life of the fuse. 

For each application, Troubleshoot An Electronic Circuit Board the capability of the fuse to withstand the expected pulse conditions should be established by considering the pulse cycle withstanding capability for nominal I2t (energy letthrough the fuse) specified by the manufacturer. Any test that has been performed during screening on the samples selected for qualification tests need not be repeated.2/ 

Generic data may be used in lieu of testing as long as the data meets the following requirements:i) It is obtained on parts built to S-311-P-079 specifications using the same materials and Troubleshoot An Electronic Circuit Board similar construction and design, andbuilt in the same facility as the flight parts.ii) The data is less than 2 years old relative to the lot date code of the flight parts.3/ Samples for Groups 2, 3, and 4 should be selected from parts that have passed Group 1 tests.

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