Transcript Flight Readiness Review

Air Electrical Conductivity (ACES 23)
Katherine Blackburn and Joseph Tran
SCIENCE REPORT
OVERVIEW
Time constant and electrical conductivity
 Gerdien condenser
 Results
 Problems
 Future plans
 Possible improvements

2
TIME CONSTANT AND CONDUCTIVITY
Electrical conductivity α (1/tau)
 The total number of positive and negative ions
 Different from thundercloud conductivity

Figure 1
Figure 2
3
EFFECTS OF HUMIDITY
Figure 3
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THE GERDIEN CONDENSER
A cylindrical capacitor that allows ions in
atmosphere to bounce off inner electrode
 Voltage effectively “decays”
 A time constant is used to correlate the decay
to the total conductivity

5
RESULTS
Humidity vs. Time (From Team Philsohook)
100
Relative Humidity (%RH)
90
80
70
60
50
40
30
20
10
0
0
20
40
60
80
Time (min)
100
120
140
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RESULTS
Calculated using initial slope
Time Constant (seconds)
350
300
250
200
150
100
50
0
9000
11000
13000
15000
17000
Altitude (feet)
19000
21000
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SERVICE PROBLEMS
Humidity
 No proper temperature or pressure test to
confirm
 Lack of thermal insulation for circuitry

8
IMMEDIATE FUTURE PLANS
Perform proper pressure and temperature tests
 Test and confirm effects of water vapor on
condensers
 Calibrate sensor
 Rebuild circuitry to confirm functionality

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POSSIBLE IMPROVEMENTS
A cover or door to open after cloud cover
 Rethink nozzle caps, increase velocity
 Use of desiccants
 Heated condensers or heating elements to
reduce condensation

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CONCLUSION
Proof of principal
 Data shows general increase, though not
desirable
 Humidity is a huge factor and should be tested
more
 More improvements can now be implemented
after testing

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SPECIAL THANKS
CSBF
LaACES Staff
Dr. Browne
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REFERENCES
1.Bering, E.A., Few, A.A., & Benbrook, J.R. (1998). The Global electric circuit. Journal of Physics Today, 51(10), 24-30. Aplin, K.L.
(2000). Instrumentation for atmospheric ion measurements. University of Reading Department of Meteorology, 1-274.
2.Aplin, K.L. (2000). Instrumentation for atmospheric ion measurements. University of Reading Department of Meteorology, 1-274.
3.Scott, J.P., & Evans, W.H. (1969). The Electrical conductivity of clouds. Journal of Pure and Applied Geophysics, 75(1), Retrieved
from http://www.springerlink.com/content/x804k7123mqhn3r5/ doi: 219-232
4.Nagara, K., Prasad, B.S.N., Srinivas, N., & Madhava, M.S. (2006). Electrical conductivity near the earth's surface: ion-aerosol
model. Journal of Atmospheric and Solar-Terrestrial Physics, 68(7), Retrieved from http://www.sciencedirect.com/science/ article/
B6VHB-4JDMR5M-1/2/607a27d56c6adbf8ce265ea1ad0d8e0a
5.Ragini, N., Shashikumar, T.S., Chandrashekara, M.S., Sannappa, J., & Paramesh, L. (2008). Temporal and vertical variations of
atmospheric electrical conductivity related to radon and its progeny concentrations at Mysore. Indian Journal of Radio & Space
Physics, 37, 264-271.
6.Aplin, K.L. (2000). Instrumentation for atmospheric ion measurements. University of Reading Department of Meteorology, 1-274.
7.Harrison, R.G, & Bennett, A.J. (2006). Cosmic ray and air conductivity profiles retrieved from early twentieth century balloon
soundings of the lower troposphere. Journal of Atmospheric and Solar-Terrestrial Physics, 69, 515-527.
8.Nicholl, K.A., & Harrison, R.G. (2008). A Double Gerdien instrument for simultaneous bipolar air conductivity measurements on
balloon platforms. Journal of Review of Scientific Instruments, 79,
9.Aplin, K.L., & Harrison, R.G. (2000). A Computer-controlled Gerdien atmospheric ion counter. Journal of Review of Scientific
Instruments, 71(8),
10.Balsey, B. (2009). Aerosol size distribution. Retrieved from http://cires.colorado.edu/science/groups/balsley/research/aerosoldistn.html
11.Gregory, K. (2008). The Saturated greenhouse effect. The Friends of Science Society, Retrieved from
http://www.friendsofscience.org/assets/documents/The_Saturated_Greenhouse_Effect.htm
12.Pierrehumbert, R.T., Brogniez, H., & Roca, R. (2007). Relative humidity of the atmosphere. Caltech, 143-185.
13.Nederhoff, E. (1997). Humidity: rh and other humidity measures. Commercial Grower, 40. 14.Zuev, V.V., Zuev, V.E., Makushkin,
Y.S., Marichev, V.N., & Mitsel, A.A. (1983). Laser sounding of atmospheric humidity: experiment. Journal of Applied Optics, 22(23),
3742-3746.
15.McCabe, Warren, Smith, Julian, & Harriott, Peter. (1993). Unit operations of chemical engineering. McGraw-Hill College.
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Appendix
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COMPLETE REQUIREMENTS (1/2)

Scientific knowledge

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
Gerdien’s original paper shall be revisited to verify existing
science background
Scientific databases for similar experiments including a Gerdien
condensers shall be found to strengthen scientific knowledge
Errors in theory and/or operation
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Errors realized through reevaluation of scientific knowledge shall
be identified
Identify issues in mechanical/physical design
Identify issues in electrical design
Identify issues in software processes and design
Identify issues in sensor design and manufacture
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COMPLETE REQUIREMENTS (2/2)

Design
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Flaws regarding physical design shall be addressed and recalculated with more ideal
dimensions
Design shall be able to measure currents of fA
Design shall be able to measure conductivity of fS/m
Design shall be able to measure ions of mobility of 10-4 m2/VS
Leakage currents from the device in the range of femto-Amperes or greater shall be
minimized
Ground Based Test
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Tests shall be completed to ensure proper operation at ground level
Different types and lengths of wire shall be tested for impact in consistency and range in
values
Several optimized designs of the sensor shall be implemented and tested for consistency
in behavior and accuracy in measurement
Testing shall be commenced for varying temperatures, pressures, and ion concentrations
Consistent and reproducible voltage decays shall be observed at all modes of testing.
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COMPLETE OBJECTIVES
Gather information on past conductivity
experiments for scientific knowledge before testing
 Identify errors in theory and/or operation that
caused the previous design to fail
 Complete a design of a ground-based conductivity
sensor to measure atmospheric conductivity in the
range of femto-Siemens per meter (fS/m)
 Build and calibrate a working, ground-based
conductivity sensor that produces consistent and
reproducible data

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PREVIOUS PAYLOAD
Problems with design
 Dual condenser close together during flight
with no shielding
 Adhesive to outer condenser may have caused
error
 Machine built ABS plastic caps introduced a
low resistance leakage path
 Sensitive air-wired components were placed
through the foam which caused interference
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PREVIOUS PAYLOAD
Figure 3
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CURRENT PAYLOAD
Improvements
 Single condenser to measure positive conductivity
 Teflon caps used because of high resistance
 An outer condenser cage was built to act as shield
 15 V applied to outer electrode to reduce chance
of arching
 Manhattan style board was used for the Gerdien
circuit to minimize coupling between components
and therefore introduce less noise.
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CURRENT PAYLOAD
Figure 4
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SYSTEM DIAGRAM
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POWER BUDGET
Component
Current
required
Time
mAh
required
BalloonSat
80 mA
4 hr
320 mAh
Gerdien interface
22 mA
4 hr
88 mAh
Totals
102 mA
4 hr
408 mAh
Component
Current
required
Time
fAh
required
10 fA
4 hr
40 fAh
10 fA
4 hr
40 fAh
Gerdien outer
electrode
Totals
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WEIGHT BUDGET
Components
Weight
Payload structure
BalloonSat circuit board
3V batteries (10)
1.5V batteries (6)
Sensor Circuit
Sensor setup with case, caps and
condensers
Total Weight
82.0 g (measured)
61.5 g (measured)
29.0 g (measured)
116.0 g (measured)
43.0 g (measured)
317.2 g (measured)
648.7 g
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CONTROL ELECTRONICS
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FLIGHT SOFTWARE
Flight Software
 Initialize variables, declare pins
 Write begin time
 Collect data for 1 sample every second for 30 seconds
 Discharge for 5 seconds
 Apply voltage on condenser, allow to decay
 Repeat until no more memory
 Write end time
Post Flight
 Read data in order it was written
 End
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DATA OBTAINED AT STP (1/4)
Analog Voltage Decay
0.25
Analog voltage
0.2
0.15
0.1
0.05
0
0
200
400
600
800(s)
Time
1000
1200
1400
1600
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DATA OBTAINED AT STP (2/4)
Time Constants
2500
Time Constant
2000
1500
1000
500
0
0
500
1000
1500
2000
2500
3000
Seconds (Linear)
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DATA OBTAINED AT STP (3/4)
Analog Voltage Decay
1
0.9
0.8
Analog voltage
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
1000
2000
3000
4000
5000
Time (s)
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DATA OBTAINED AT STP (4/4)
Time Constants
2500
Time Constant
2000
1500
1000
500
0
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
Seconds (Linear)
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EQUATIONS
Equation 1 - Gerdien capacitor current given V (outer
voltage- inner voltage), L (length), σ (conductivity), b
(inner radius), and a (outer radius)
Equation 4– Capacitor current vs. combined Gerdien
and measurement capacitance and change in outerinner cylinder voltage
Equation 2 - Critical mobility - the minimum ion
mobility (drift velocity/electric field) that will be
captured by the Gerdien capacitor given µ (wind
speed)
Equation 5– Conductivity
𝜎± =
𝑑𝑉𝑐±
𝜀𝑜
𝑉𝑜± −𝑉𝑐± 𝑑𝑡
Equation 6 – Conductivity (derived)
Equation 3– Conductivity vs. exponential fit time
constant
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SAMPLE CALCULATION
1. The voltage on the inner electrode was measured to be -0.37 V initially.
2. This yields a bias voltage, Vb=Vo1-Vc1=-29.63V where Vo1=-30V (the voltage of the
outer electrode) and Vc1=-.37 (the voltage of the inner electrode).
3. A linear fit was applied to a graph of the 11 voltages measured and graphed in
Figure 1 (an initial voltage and 10 measurements as voltage decays). The linear fit
yielded Vc=-8.0818x+70.127.
4. The derivative of this was taken to find dVc/dt=-8.0818 V/s.
5. A derivation of several equations in the technical background yields
𝜎± =
𝑑𝑉𝑐±
𝜀𝑜
𝑉𝑜± −𝑉𝑐± 𝑑𝑡
where σ± is the positive or negative conductivity, ɛo=8.85x10-12 Fm-1, Vo±-Vc± is the
bias voltage of the positive or negative electrode and dVc±/dt is the derivative of the
linear fit of the voltage decay on the inner electrode (9).
6. Using the equation in (5), 𝝈 = 𝟐. 𝟒𝟏𝟒 𝒇𝑭/𝒎𝒔
± measured is 2.414 fS/m.
7. Thus the negative conductivity
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CALIBRATION PROCESS
Gerdien Condenser
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Build Gerdien circuit
Obtain Geiger counter
Obtain fan
Select site at which to test
Read Geiger counter reading and Gerdien circuit output voltage with fan on
condenser
Move to another location and repeat at least 5 times (stay on the same site)
Calculate conductivity based on output voltage from Gerdien circuit
Calculate number of ions based on conductivity calculated
Plot number of ions versus the square root of Geiger counts as in Figure 13
Use linear fit line to obtain an equation relating number of ions to Geiger counts
Modify equation to relate conductivity to Geiger counts
Select another appropriate site and take several more readings
Compare to calculated conductivity from equation obtained in 11
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