Calibration 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.
10. Two concepts for the use of the
Dielectric Constant:
and R
Time Domain Reflectometry
and
Frequency Domain Reflectometry
ننير دلارة الكهرىب احلقل سليطت عند(بياركه متذبذبة)مكوانهتا ئياتزج عىل تقطابالاس يمت بةرتال عىل
املاءهل اذلى بةرتابل الوحيد املكون هوتقطاىبسا كهرىب عزل اثبتتفعرماملكوانت من بغريه نةرابملقا
13. بةومنا لوحة4مسىف5ملليـ قمي لعرض وشاشة رى وصامم يةرببطا اجملس لتوصيل مسﭭلتوـ
DC Latching Relay Board
Sensor for Detection
Relay for Voltage
Comparison and
Data Transmission
Valve
or Monitor
18. 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.
ننير دلارة الكهرىب احلقل سليطت عند(بياركه متذبذبة)مكوانهتا ئياتزج عىل تقطابالاس يمت بةرتال عىل
املاءهل اذلى بةرتابل الوحيد املكون هوتقطاىبسا كهرىب عزل اثبتتفعرماملكوانت من بغريه نةرابملقا
19.
20. ننير دلارة الكهرىب احلقل سليطت عند(بياركه متذبذبة)مكوانهتا ئياتزج عىل تقطابالاس يمت بةرتال عىل
Soil works as part of the electric oscillator’s 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)
املاءهل اذلى بةرتابل الوحيد املكون هوتقطاىبسا كهرىب عزل اثبتتفعرماملكوانت من بغريه نةرابملقا
21.
22. LC & RLC ننير دارة
الساعة عقارب عكس بتيار ُشحني املكثف مينيلا عىل--->ال عقارب مع يصبحف الاجتاه ينعكس يسارلا عىلساعة
يةربطا من مترمس بتيار تغذيهتا انبدأ ناو حىت التذبذب دارة ىف مرتدد تيار نشأي(ذا ادلارة ىف الرتدد نلىت)
التذبذب ىف ننيرال دارة تبدأ مترمس وأ مرتدد تيار وفصل توصيل عند(اذل املرتدد الكهرىب حقلها نشأياىت)
Oscillation of magnetic energy (in the inductor) and electric energy (in the capacitor)
23. LC نوع من ننير دارة
بني الطاقة تبادل ارربتك ننيرال دارة ىف الرتدد نشأيمكثف(بيةركه طاقة به)وملف(يةيسطمغنا طاقة به)اررمتساب
Oscillation of the magnetic energy (in inductor) and the electric energy (in capacitor)
هبا نشأي ننيرال دارة(الطاقة بتبادل)متذبذب مضاد كهرىب حقل(يةربطا من مترمس بتيار تغذيهتا متت ناو حىت)
45. 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: mousavi@cc.iut.ac.ir
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).
46. 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
58. يبيةرتق خطية خلط معادةل
العزل لثابتتقطاىبالاس
(دياكجون من)
… 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