wireless system for tps sensors presented by: tye reid and greg swanson
Post on 20-Dec-2015
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TRANSCRIPT
Outline
• Introduction• Motivation• Project Challenges• Prototype• Prototype Specs• Calibration• Testing• Results• Conclusion
Introduction
• Goal – to design and build a wireless system to transmit data gathered from sensors embedded into the TPS of atmospheric entry probes. Thermal Protection
System (TPS)
Forward Bay Cover
Backshell
Pressure Vessel
Motivation
• Reduction in Complexity (eliminates harnesses, wire routes, and wire holders)
• Easier and Safer Implementation (routing through safety barriers isn’t needed)
• Improved assembly efficiency
• Weight Savings
Project Challenges
• Transmission through RF non-transparent material
• Transmission through high interference environment
• Thermal protection of wires and circuits
• Size requirements associated with space flight
Prototype• Zigbee RF transmitters chosen for their
low power/bandwidth design
• Thermocouple voltage to temperature conversion chips for embedded thermocouple sensor readings
• Optimized PCB layout to minimize EMI
• Different antennas for signal strength testing
Prototype SpecsTransmission Type Radio Frequency
Data Rate 4 Hz
Data Transfer Real Time
Power Source 2 AA
System Life Power 8 days constant transmission
Temperature Resolution +/- 1% readout
Temperature Range 0 – 1128 degrees Celsius
Transmitter Size 3 ¼” x 2 ¾” x ¾”
Weight 3.2 oz
Calibration
• +/- 1.2% Temperature Error
• Error sources– Thermocouple voltage to
temperature conversion chip has a +/- 3 degree C error
– Program rounds off decimals and converts to degrees F
– Thermal Differences between the thermocouple to circuit connection and conversion Chip
% Error for Range of Temperatures
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 500 1000 1500 2000
Temperature (F)
% E
rro
r
Testing• X-Jet at NASA Ames
– Testing for transmission out of x-jet chamber
– Antenna testing – Distance tests– Precision and Accuracy tests
Results• Clear
transmissions out of test environment
• Temperature data matched rough analytical analysis
• Repeatable Data • Small PCB
antenna worked just as well as larger antenna
Conclusions
• Zigbee RF technology demonstrates a solution to wiring problems
• Integrated sleep mode design would allow for 8 years of operation off of 2 AA batteries
• Initial prototype weighs 0.2 lb reducing sensor system weight by 50%
• Miniaturization and further development is recommended
• Next step will be to implement sensors on a probe flight such as the RISE program balloon