Flight Readiness Review

Science reportAir Electrical Conductivity (ACES 23)Katherine Blackburn and Joseph TranOverviewTime constant and electrical conductivityGerdien condenserResultsProblems Future plansPossible improvements

22Time constant and conductivityElectrical conductivity (1/tau)The total number of positive and negative ionsDifferent from thundercloud conductivity3

Figure 1

Figure 2Effects of humidity4

Figure 3The gerdien condenserA cylindrical capacitor that allows ions in atmosphere to bounce off inner electrodeVoltage effectively decays A time constant is used to correlate the decay to the total conductivity5Results6Results7Service problemsHumidityNo proper temperature or pressure test to confirmLack of thermal insulation for circuitry

8Immediate Future plansPerform proper pressure and temperature testsTest and confirm effects of water vapor on condensersCalibrate sensorRebuild circuitry to confirm functionality

9Possible ImprovementsA cover or door to open after cloud coverRethink nozzle caps, increase velocityUse of desiccantsHeated condensers or heating elements to reduce condensation

10conclusionProof of principalData shows general increase, though not desirableHumidity is a huge factor and should be tested moreMore improvements can now be implemented after testing

11Special ThanksCSBFLaACES StaffDr. Browne

12References1.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.

13Appendix14Complete Requirements (1/2)Scientific knowledgeGerdiens original paper shall be revisited to verify existing science backgroundScientific databases for similar experiments including a Gerdien condensers shall be found to strengthen scientific knowledgeErrors in theory and/or operationErrors realized through reevaluation of scientific knowledge shall be identifiedIdentify issues in mechanical/physical designIdentify issues in electrical designIdentify issues in software processes and designIdentify issues in sensor design and manufacture15Complete Requirements (2/2)Design Flaws regarding physical design shall be addressed and recalculated with more ideal dimensionsDesign shall be able to measure currents of fADesign shall be able to measure conductivity of fS/mDesign shall be able to measure ions of mobility of 10-4 m2/VSLeakage currents from the device in the range of femto-Amperes or greater shall be minimizedGround Based TestTests shall be completed to ensure proper operation at ground levelDifferent types and lengths of wire shall be tested for impact in consistency and range in valuesSeveral optimized designs of the sensor shall be implemented and tested for consistency in behavior and accuracy in measurementTesting shall be commenced for varying temperatures, pressures, and ion concentrationsConsistent and reproducible voltage decays shall be observed at all modes of testing.16Complete objectivesGather information on past conductivity experiments for scientific knowledge before testingIdentify errors in theory and/or operation that caused the previous design to failComplete 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 data17Previous PayloadProblems with designDual condenser close together during flight with no shieldingAdhesive to outer condenser may have caused errorMachine built ABS plastic caps introduced a low resistance leakage pathSensitive air-wired components were placed through the foam which caused interference18Previous Payload19

Figure 3Current PayloadImprovementsSingle condenser to measure positive conductivityTeflon caps used because of high resistanceAn outer condenser cage was built to act as shield15 V applied to outer electrode to reduce chance of archingManhattan style board was used for the Gerdien circuit to minimize coupling between components and therefore introduce less noise.20Current Payload21

Figure 4System diagram22

Power budget23ComponentCurrent requiredTimemAh requiredBalloonSat80 mA4 hr320 mAhGerdien interface22 mA4 hr88 mAhTotals102 mA4 hr408 mAhComponentCurrent requiredTimefAh requiredGerdien outer electrode10 fA4 hr40 fAhTotals10 fA4 hr40 fAhWeight Budget24ComponentsWeightPayload structure82.0 g (measured)BalloonSat circuit board61.5 g (measured)3V batteries (10)29.0 g (measured)1.5V batteries (6)116.0 g (measured)Sensor Circuit43.0 g (measured)Sensor setup with case, caps and condensers317.2 g (measured)Total Weight 648.7 gControl electronics25

Flight softwareFlight SoftwareInitialize variables, declare pinsWrite begin timeCollect data for 1 sample every second for 30 secondsDischarge for 5 secondsApply voltage on condenser, allow to decayRepeat until no more memoryWrite end time

Post FlightRead data in order it was writtenEnd26Data obtained at stp (1/4)27Data obtained at stp (2/4)28Data obtained at stp (3/4)29Data obtained at stp (4/4)30equations31Equation 1 - Gerdien capacitor current given V (outer voltage- inner voltage), L (length), (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 (wind speed)

Equation 3 Conductivity vs. exponential fit time constant

Sample calculation32Calibration processGerdien CondenserBuild Gerdien circuitObtain Geiger counterObtain fanSelect site at which to testRead Geiger counter reading and Gerdien circuit output voltage with fan on condenserMove to another location and repeat at least 5 times (stay on the same site)Calculate conductivity based on output voltage from Gerdien circuitCalculate number of ions based on conductivity calculatedPlot number of ions versus the square root of Geiger counts as in Figure 13Use linear fit line to obtain an equation relating number of ions to Geiger countsModify equation to relate conductivity to Geiger countsSelect another appropriate site and take several more readingsCompare to calculated conductivity from equation obtained in 1133