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Air Electrical Conductivity (ACES 23) Katherine Blackburn and Joseph Tran. Science report. Time constant and electrical conductivity Gerdien condenser Results Problems Future plans Possible improvements. Overview. Electrical conductivity α (1/ tau) - PowerPoint PPT PresentationTRANSCRIPT
SCIENCE REPORTAir Electrical Conductivity (ACES 23)Katherine Blackburn and Joseph Tran
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
3Figure 1 Figure 2
EFFECTS OF HUMIDITY
4Figure 3
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
6
0 20 40 60 80 100 120 1400
20
40
60
80
100
Humidity vs. Time (From Team Philsohook)
Time (min)
Rela
tive
Hum
idity
(%RH
)
RESULTS
7
9000 11000 13000 15000 17000 19000 210000
50100150200250300350
Calculated using initial slope
Altitude (feet)
Tim
e Co
nsta
nt (
seco
nds)
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
9
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
10
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
11
SPECIAL THANKS
CSBFLaACES StaffDr. Browne
12
REFERENCES1.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/aerosol-distn.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
14
COMPLETE REQUIREMENTS (1/2) Scientific knowledge
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 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
15
COMPLETE REQUIREMENTS (2/2) Design
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
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.16
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
17
PREVIOUS PAYLOADProblems 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
18
PREVIOUS PAYLOAD
19Figure 3
CURRENT PAYLOADImprovements 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.
20
CURRENT PAYLOAD
21
Figure 4
SYSTEM DIAGRAM
22
POWER BUDGET
23
Component Current required
Time
mAh required
BalloonSat 80 mA 4 hr 320 mAhGerdien interface 22 mA 4 hr 88 mAh
Totals 102 mA 4 hr 408 mAhComponent Current
requiredTime
fAh required
Gerdien outer electrode 10 fA 4 hr 40 fAh
Totals 10 fA 4 hr 40 fAh
WEIGHT BUDGET
24
Components Weight
Payload structure 82.0 g (measured)
BalloonSat circuit board 61.5 g (measured)
3V batteries (10) 29.0 g (measured)
1.5V batteries (6) 116.0 g (measured)
Sensor Circuit 43.0 g (measured)
Sensor setup with case, caps and condensers
317.2 g (measured)
Total Weight 648.7 g
CONTROL ELECTRONICS
25
FLIGHT SOFTWAREFlight 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
26
DATA OBTAINED AT STP (1/4)
270 200 400 600 800 1000 1200 1400 16000
0.05
0.1
0.15
0.2
0.25
Analog Voltage Decay
Time (s)
Anal
og v
olta
ge
DATA OBTAINED AT STP (2/4)
28
0 500 1000 1500 2000 2500 30000
500
1000
1500
2000
2500Time Constants
Seconds (Linear)
Tim
e Co
nsta
nt
DATA OBTAINED AT STP (3/4)
29
0 1000 2000 3000 4000 500000.10.20.30.40.50.60.70.80.9
1
Analog Voltage Decay
Time (s)
Anal
og v
olta
ge
DATA OBTAINED AT STP (4/4)
30
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 100000
500
1000
1500
2000
2500
Time Constants
Seconds (Linear)
Tim
e Co
nsta
nt
EQUATIONS
31
Equation 4– Capacitor current vs. combined Gerdien and measurement capacitance and change in outer-inner cylinder voltage
Equation 5– Conductivity
Equation 6 – Conductivity (derived)
Equation 1 - Gerdien capacitor current given V (outer voltage- inner voltage), L (length), σ (conductivity), b (inner radius), and a (outer radius)
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 3– Conductivity vs. exponential fit time constant
Equation 4– Capacitor current vs. combined Gerdien and measurement capacitance and change in outer-inner cylinder voltage
Equation 5– Conductivity
Equation 6 – Conductivity (derived)
SAMPLE CALCULATION
32
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
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),
7. Thus the negative conductivity measured is 2.414 fS/m.
CALIBRATION PROCESSGerdien Condenser 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
33