Smoke Damage >> How To DIY How To Repair A House Damaged By Smoke

Effects on Smoke on Functional Circuits SNL also tested complete and functional circuit boards for their susceptibility to damage from smoke [18]. These boards contained five functional circuits that could be energized and How To DIY How To Repair A House Damaged By Smoke monitored during smoke exposure. Each circuit was present twice on each board, built with either surface-mount technology (SMT) or pin through hole (PTH) components. 

Half of the boards tested were How To DIY How To Repair A House Damaged By Smoke protected with a polyurethane conformal coating. The circuits included thefollowing: High-Voltage Low-Current (HVLC): This high-resistance series of capacitor-resistorpairs was subject to a 300 Vdc bias. The nominal current was 6 μA. Within the networkitself, the potential difference between any two adjacent copper traces was 60 Vdc. 

High-Current Low-Voltage (HCLV): This circuit contained a number of How To DIY How To Repair A House Damaged By Smoke resistors andcapacitors in parallel. A constant-current power supply adjusted the applied voltage tomaintain 1 A through the nominal 1.43 Ω. High-Speed Digital (HSD): This circuit simply connected a series of NAND logic gates.

While powered, a 5 V, 20 ns input pulse was applied to the first gate, and the output ofthe final gate was monitored. Increases in the rise, How To DIY How To Repair A House Damaged By Smoke fall and delay (relative to input) timesof the output square pulse all indicate degradation of a circuit. High-Frequency Low-Pass Filter (HFLPF): a system of inductors and capacitorsconfigured to attenuate high frequency input signals. 

Before and after exposure, thefilters were tested for signal attenuation from 50 MHz to 1 GHz. During exposure, theywere tested for: attenuation at 50 MHz, 250 MHz and How To DIY How To Repair A House Damaged By Smoke the frequencies at whichattenuation reached -3 and -40 dB. High-Frequency Transmission Line (HFTL): this circuit was two adjacent PCB coppertraces, designed to exhibit 50 Ω impedance. 

It is expected that a small amount of a signalon one line will be transmitted to the other. This behavior, How To DIY How To Repair A House Damaged By Smoke referred to as coupling, isfrequency dependent and is expected to increase with the conductivity between the lines.During exposure, coupling between the lines was measured at 50 MHz, 500 MHz and 1GHz. 

Pre- and post-exposure tests added measurements of coupling with the second lineconnected in a reversed configuration.In addition to the functional circuits, additional components on the board were tested for leakagecurrents before, during and How To DIY How To Repair A House Damaged By Smoke after exposure. Further leakage current measurements wereperformed using an interdigitated comb test board. 

Each board had four distinct comb patternsand during exposure, two were biased with 5 Vdc and the other two with 30 Vdc.The tests used the standard exposure method, How To DIY How To Repair A House Damaged By Smoke with fuel loads of 3 g/m3, 25 g/m3and 50 g/m3heated with 50 kW/m2 and 25 kW/m2. Soot deposition was measured with two quartz crystalmicrobalances (QCM), one oriented vertically and the other oriented horizontally. 

The quantitiesdeposited and fuel burned are listed below in Table 2. Note that the 25 kW/m2heat fluxexposures caused smoldering of the fuel while the 50 kW/m2flux caused flaming. No direct measurements of corrosion were performed, How To DIY How To Repair A House Damaged By Smoke but visual inspection of componentsshowed that components made of reactive metals (such as nickel) had corroded significantlyafter the test.

The HVLC circuit showed susceptibility to smoke exposure. Resistance decreased noticeablywith smoke density and recovered somewhat after venting of the chamber. Conformal coatings were very effective at preventing or limiting resistance losses for all fuel loads. In this particular circuit, How To DIY How To Repair A House Damaged By Smoke the PCB traces were the most vulnerable to damage because they carried the highestpotential differences and were more closely spaced than the leads of attached components.

Because this vulnerability was independent of the types of components attached, there was noobserved difference between PTH and SMT.The HCLV circuit was largely insensitive to smoke. Because the circuit had a very low initial resistance, How To DIY How To Repair A House Damaged By Smoke the addition of weakly conductive alternate paths would have little impact. 

Theexception was the case of the bare (having no conformal coating) SMT board. In all of the medium and high fuel load tests, How To DIY How To Repair A House Damaged By Smoke the resistance of these circuits increased measurably (0.9 % -1.7 %) and did not recover after venting. This change is attributed to corrosion of contacts or solder joints. None of the changes in these tests represented a significant effect on systemperformance.

The HSD circuit was tested for its response to a 20 ns, +5 Vdc pulse by measuring the output risetime, fall time and delay. Changes in signal degradation due to differences in cable length makedirect comparison between pre-test results and in situ measurements invalid. However, How To DIY How To Repair A House Damaged By Smoke none ofthe circuits showed significant change in response to changing fuel loads or the presence ofconformal coatings. 

Previous work indicates that the highest fuel load used would have causedfailure due to circuit bridging in complementary metal-oxide semiconductor (CMOS) chips, How To DIY How To Repair A House Damaged By Smoke but that advanced Schottky transistor to transistor logic (FAST TTL), such as those in the HSD, areless sensitive.The HFLPF did not show any response to smoke. 

However, How To DIY How To Repair A House Damaged By Smoke active measurement duringexposure was performed with an input frequency (250 MHz) that would not be impacted bychanges in system capacitance due to debris (the expected failure mode). Post-test measurements over a wider range of frequencies showed no change from the pre-test condition.

It was expected that the most severe changes in capacitance would occur during exposure, How To DIY How To Repair A House Damaged By Smoke when the testing method would be unable to measure those changes.The HFTL circuit was tested to determine coupling between two adjacent lines. Coated boardsshowed no change in coupling during or after exposure. 

The bare board experienced a large (from -52 dB to -17 dB) increase in coupling of 50 MHz signals during exposure. Coupling on the bare board returned to pre-test values quickly after venting of the test chamber. At high frequencies (500 MHz and 1 GHz) coupling on the bare board actually decreased during smoke exposure and How To DIY How To Repair A House Damaged By Smoke returned to pre-test values after venting. 

Leakage current data are presented only for the PTH boards and the interdigitated comb; leakage data for other components in the methodology section were not reported. Resistance on the bareboards dropped as fuel load increased and How To DIY How To Repair A House Damaged By Smoke recovered somewhat after venting. 

Changes in the interdigitated comb were less consistent, but surface resistance generally decreased with increasing fuel loads and How To DIY How To Repair A House Damaged By Smoke partially recovered after venting. Results in Table 4 are presented inthe change of Log10(R) between pre-test values and average during smoke exposure.


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