calibration of fdr sensor for irrigation automation
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DESCRIPTIONCalibration of FDR sensor for irrigation automation Mohamed Fahmy Hussein Cairo University The theoretical basis of FDR sensors is often obscure for many scientists and field users. The present work introduces the concept and gives a first local calibration of two affordable VH400 Frequency Domain Reflectometry (FDR) sensors (running at 80 MG Hz) from Vegetronics, Utah, USA, enhanced by local electronic components. The two calibrations were carried out in August 2013 (35°C) and January 2014 (15°C) at Cairo University, Egypt. The full scale relationships of moisture content to mV and soil dielectric, among others, were all non-linear. However, for the narrower scale useful for soil moisture contents, from wilting point to saturation, were acceptably linear. The observed strong linearity in this narrower range makes the sensor practical for irrigation automated control. A famous power dielectric mixing-formula was used to estimate soil dielectric from three components mixing (minerals, water and air). Temperature decrease significantly increased soil dielectric values of the used sand sediments of the Nile bank that were adjusted to given moisture contents. Temperature dependence urges that the calibration process must be run at least four times per year for each soil material. Irrigation automation is particularly needed in for the partial fulfillment of irrigation control in order to tackle Egypt's augmenting water scarcity problems.
2. 3. 4. Two concepts for the use of the Dielectric Constant: and R Time Domain Reflectometry and Frequency Domain Reflectometry ( ) 5. ( ) Concept: Monitoring Soil Moisture to Improve Irrigation Decisions : ---> Dielectric constant measuring sensor probe - based on FDR Sensor for Moisture Detection 6. 45 DC Latching Relay Board Sensor for Detection Relay for Voltage Comparison and Data Transmission Valve or Monitor 7. 4 4 ( ) Dielectric Constant Analog FDR Sensor ---> Volt Output 5-24 100050( )220 470 () () or 10 100 () () 38001200 8. ( ) 9. Reflectometry is a noninvasive technique that allows the analysis of properties of a medium. This technique is based on the reflection of waves at the interface of interest. Waves propagates into a medium (according to the laws of propagation into the medium studied) and when it encounters a discontinuity (impedance break), part of its energy is reflected back to injection point. The analysis of the reflected signal can infer information about the system or the medium under consideration. ( ) 10. ( ) Soil works as part of the electric oscillators capacitor. The soil mixture will show high values for the dielectric constant when moisture content increases (higher dielectric constant in case of higher moisture content and vice versa) 11. LC & RLC ---> ( ) ( ) Oscillation of magnetic energy (in the inductor) and electric energy (in the capacitor) 12. LC ( )( ) Oscillation of the magnetic energy (in inductor) and the electric energy (in capacitor) ( ) ( ) 13. http://en.wikipedia.org/wiki/Capacitive_sensing 14. : () ( .) . . Inductor ELI 15. ( .) 16. ( ) takes place when XL = XC XC f XL f LC http://www.walter-fendt.de/ph14e/osccirc.htm 17. X When = X = , = , and = ( ) 18. 1 2 ------ 19. -- 1 2 20. ( ) 1 2 ( ) 21. 2 ( ) = . and the Sweeping Concept ( ) () () ( ) . 1 2 () 22. () ( ) ( .) ( ) ( ) . ( .) ( ) kappa is polarizability eis dielectric permittivity kappa is infinity for metals kappa is 80 for water, 1 for air 23. ( ) () . . ( ). ( ) https://www.youtube.com/watch?v=e0n6xLdwaT0 () 24. kappa is polarizability 25. https://www.youtube.com/watch?v=rkntp3_cZl4 kappa is polarizability 26. J. Agr. Sci. Tech. (2010) Vol. 12: 339-346 Estimation of Leaf Moisture Content by Measuring the Capacitance A. Afzal1, S. F. Mousavi2*, and M. Khademi2 1 Department of Agricultural Machinery, College of Agriculture, Isfahan University of Technology, Isfahan 84156-83111, Islamic Republic of Iran. 2 Department of Water Engineering, College of Agriculture, Isfahan University of Technology, P. O. Box: 84156-83111, Isfahan, Islamic Republic of Iran. * Corresponding author; e-mail: [email protected] It is expected that when the sensor is made up of 1 plate (not 2 plates that sandwich the dielectric as usual), the capacitance will stay the same (since removal corresponds to theoretically changing A in the nominator and d in the denominator by same factor). 27. Removing second plate means the increase of A & d by the same factor and the same results are obtained when using 2 plates sensor or 1 plate sensor 28. 1 mV = -2.1417*10^3*qv 2 + 3.7157*10^3*mV + 1421.0174 mV = -2.0923*10^3*qv 2 + 4.1320*10^3*mV + 961.2952 29. 2 30. 3 qv = 2.0236*10^-7*mV2 - 3.3777*10^-4*mV + 0.1753 qv = 3.3188*10^-7*mV2 - 8.3151*10^-4*mV + 0.5086 31. 4 Saturation Wilting Point 32. 5 Saturation Wilting Point 33. 6 Saturation Wilting Point displacement to adjust for temperature 34. 7 Saturation Wilting Point composed with temperature-modified data 35. ( ) 8 36. ( ) and a site emphasizing on calibration for each soil type apart and referring to matric potential rather than moisture content http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-73862002000300012 9 a paper mentioned initial work on 0.50 for the exponent in the dielectric mixing-model https://www.researchgate.net/profile/Brian_Borchers/publications?page=2&sorting=newest Power-law dielectric mixing-formula 37. 9 References http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=1288372& url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.js p%3Farnumber%3D1288372 http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=4072240& url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F36%2F40 72232%2F04072240.pdf%3Farnumber%3D4072240 The most important reference is the following http://www.piers.org/piersonline/pdf/Vol4No1Page31to35.pdf 38. 10 39. 11 40. 12 41. 13 42. 14 43. 15 44. 16 displaced to adjust temperature 45. 17 composed with temperature-modified data 46. 18 47. 19 48. 20 49. That is what we are! Really? That is what we are! Really? Have fun with oscillation! Have fun with oscillation! http://en.wikipedia.org/wiki/Body_capacitance