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