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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

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

RESULTS

0 20 40 60 80 100 120 1400

100

Humidity vs. Time (From Team Philsohook)

Time (min)

Rela

tive

Hum

idity

(%RH

)

RESULTS

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

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

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

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

SPECIAL THANKS

CSBFLaACES StaffDr. Browne

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.

Appendix

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

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

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

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.

CURRENT PAYLOAD

Figure 4

SYSTEM DIAGRAM

POWER BUDGET

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

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

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

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

DATA OBTAINED AT STP (2/4)

0 500 1000 1500 2000 2500 30000

500

1000

1500

2000

2500Time Constants

Seconds (Linear)

Tim

e Co

nsta

DATA OBTAINED AT STP (3/4)

0 1000 2000 3000 4000 500000.10.20.30.40.50.60.70.80.9

Analog Voltage Decay

Time (s)

Anal

og v

olta

DATA OBTAINED AT STP (4/4)

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 100000

500

1000

1500

2000

2500

Time Constants

Seconds (Linear)

Tim

e Co

nsta

EQUATIONS

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

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

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