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Science report

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)

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Science report

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  1. Air Electrical Conductivity (ACES 23) Katherine Blackburn and Joseph Tran Science report

  2. Time constant and electrical conductivity Gerdien condenser Results Problems Future plans Possible improvements Overview

  3. Electrical conductivity α (1/tau) The total number of positive and negative ions Different from thundercloud conductivity Time constant and conductivity Figure 1 Figure 2

  4. Effects of humidity Figure 3

  5. 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 The gerdien condenser

  6. Results

  7. Results

  8. Humidity No proper temperature or pressure test to confirm Lack of thermal insulation for circuitry Service problems

  9. Perform proper pressure and temperature tests Test and confirm effects of water vapor on condensers Calibrate sensor Rebuild circuitry to confirm functionality Immediate Future plans

  10. 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 Possible Improvements

  11. 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 conclusion

  12. CSBF LaACES Staff Dr. Browne Special Thanks

  13. 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/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. References

  14. Appendix

  15. 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 (1/2)

  16. 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. Complete Requirements (2/2)

  17. 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 Complete objectives

  18. 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 Previous Payload

  19. Previous Payload Figure 3

  20. 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. Current Payload

  21. Current Payload Figure 4

  22. System diagram

  23. Power budget

  24. Weight Budget

  25. Control electronics

  26. 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 Flight software

  27. Data obtained at stp (1/4)

  28. Data obtained at stp (2/4)

  29. Data obtained at stp (3/4)

  30. Data obtained at stp (4/4)

  31. equations 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) Equation 4– Capacitor current vs. combined Gerdien and measurement capacitance and change in outer-inner cylinder voltage Equation 5– Conductivity Equation 6 – Conductivity (derived)

  32. 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.

  33. Gerdien 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 Calibration process

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