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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 • 0C < T < 70C
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)
12 0 0 4.5 0 0 0 0 4.5
5 0.5 0 4.5 0 0.42 0 0 5.42
3.3 0 0.5 4.5 0 0 0 0.104 5.104
2.5 0 TBD 0 0 0 0 0 TBD
1.8 0 1 0 0.276 0 0.71 0 1.986
1.2 0 1 0 0 0 0 0 1
Total Current/Device (Amps) 0.5 2.5 13.5 0.276 0.42 0.71 0.104 18.01
MAX POWER= 102.78W
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• TAmbient
Environmental ManagementHeat 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 (qc = .5qb)
Board stackBoard stack
Chassis wall
q chassis
q board
T chassis
T boards
T ambient
T chassis
Environmental ManagementHeat 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
tgroundC
Pgen (w) Tboards Final (°C)
-32 0 -51.93-32 5 -23.10-32 10 -1.78-32 20 30.04-32 25 42.79-32 50 90.74-32 70 118.75-32 100 152.0045 0 25.0645 5 38.4145 10 50.2345 20 70.6145 25 79.5745 50 116.4845 70 139.8845 100 168.90
Environmental ManagementHeat Transfer: radiation model
‘Safe zone’ between ~ 10 and ~ 30 W
Environmental Management : Humiditydew 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 (%)
tairc dew point ( C)
1 -51.7815 -83.236
40 -51.7815 -58.846
50 -51.7815 -57.167
80 -51.7815 -53.544
90 -51.7815 -52.617
1 25.21848 -34.858
40 25.21848 10.652
50 25.21848 14.052
80 25.21848 21.519
90 25.21848 23.459
Environmental Managementdew 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 packweight rank with weight rank with weight
effective at reducing/preventing condensation 5 2 10 2 10simplicity in manufacturing/implimentation 3 -1 -3 1 3reusability 1 2 2 2 2allows for flexability as heat requirements change 4 1 4 2 8allows for air/water tight enclosure 2 2 4 4 8total: 17 27
Appendix: RadiationAssumptions: Treat enclosure as a black box
Neglect ConvectionNeglect Conduction
Temperature at surface of chassis = temperature inside of chassisAll Power consumed by electronics is output as heat radiating out= .89 qc = .5qb
Appendix: Humidity
• Dew point temperature is given as:
– Constants defined as follows:
• Variables: – Td - Dew point (C)
– T - Ambient temperature (C)
– RH - Relative humidity (%)– m - Temperature range
dependant constant (non-dimensional)
– Tn - Temperature range dependant constant (C)
constants
temp range Tn (C) m
0 to 50 243.12 17.62
-40 to 0 272.62 22.46