Environmental Management

Environmental Needs Maintain internal temp within operating temp of components Optics: 10 Mp cameras » -40 < 0 < 70 Electronics (all temps in  C) FPGA » 0 < T < 85 Connector Board » 0 < T < 70 D3 supplied OEM Board » -40 < T < 85 – Electronics Range 0  C < T < 70  C

Environmental Needs Allow for standard Environmental conditions as defined by MIL-STD-810G and DO-160 Temperature Range: -32C to 45 C (on ground) Humidity: 90%

Power Requirements of Devices Voltage Line (Volts) DSP (Amps) FPGA (Amps) SATA (Amps) DDR2 (Amps) INS (Amps) Cameras (Amps) SPI (Amps) Total Current/Voltage (Amps) TBD Total Current/Device (Amps) MAX POWER= W

Environmental Management: Heat Major sources of heat generation inside chassis – Hard drive about the half the heat produced comes from this – Voltage Regulator – FPGA – DSP Net Heat generated by system can be estimated using the net power input to the system

Environmental Management: Heat Transfer analysis Heat Transfer model: assuming a steady state Radiation – Least efficient mode – Model as black body From electronics to chassis From chassis to external environment – Model dependant primarily on surface area of components q rad T Chassis T Ambient

Environmental Management Heat Transfer: radiation model Treat enclosure as a black box radiating heat to the outside air – Neglect Convection Protected from moving air – Neglect Conduction Temperature at surface of chassis = temperature inside of chassis Heat radiating from chassis is 50% of heat radiating from boards (q c =.5q b ) Board stack Chassis wall q chassis q board T chassis T boards T ambient T chassis

Environmental Management Heat Transfer: radiation model Used a ‘double’ radiation model Radiation from electronics to chassis wall Radiation from chassis wall to outside environment – Combined the two models into one by assuming an efficiency between the heat transfer rate of the electronics and the chassis wall External environment Internal environment t  ground  C  P gen (w) T boards Final (°C)

Environmental Management Heat Transfer: radiation model ‘Safe zone’ between ~ 10 and ~ 30 W

Environmental Management : Humidity dew point: should we be concerned with condensation? Temperature at which water will condense on a surface – Function of ambient temperature and relative humidity – Used to determine whether additional steps should be taken to control temperature/ humidity inside the chassis. Conclusion: Condensation will not be a big problem – May run into trouble at very high humidities (above 80%) Dew point is very close to air temperatures environmental data dew point solution relative humidity (%) t  air  c  dew point ( C)

Environmental Management dew point: should we be concerned with condensation? Some environmental management techniques may be valuable to prevent condensation at high humidities – Main options: include a heating system to keep temperature inside the chassis above dew point reduce humidity inside the chassis to lower the dew point inside the chassis » a common method : silica gel packs condensation control selection matrix Heater system silica gel pack weightrankwith weightrankwith weight effective at reducing/preventing condensation52102 simplicity in manufacturing/implimentation3-313 reusability12222 allows for flexability as heat requirements change41428 allows for air/water tight enclosure22448 total: 17 27

Appendix: Radiation Assumptions: Treat enclosure as a black box Neglect Convection Neglect Conduction Temperature at surface of chassis = temperature inside of chassis All Power consumed by electronics is output as heat radiating out  =.89 q c =.5q b

Appendix: Humidity Dew point temperature is given as: – Constants defined as follows: Variables: – T d - Dew point (  C) – T - Ambient temperature (  C) – RH - Relative humidity (%) – m - Temperature range dependant constant (non- dimensional) – T n - Temperature range dependant constant (  C) constants temp range Tn (  C) m 0 to to