Characterization of Low-Cost Capacitive Soil Moisture Sensors for IoT Networks
<p>Soil-phase relationships.</p> "> Figure 2
<p>Dielectric mechanisms contributing to dielectric behavior at the microscopic level. Molecular relaxation (dipolar rotational, atomic vibrational and electronic energy states) have been highlighted. With respect to a similar picture in [<a href="#B36-sensors-20-03585" class="html-bibr">36</a>], different branches of <math display="inline"><semantics> <mrow> <msubsup> <mi>ε</mi> <mi>r</mi> <mo>″</mo> </msubsup> </mrow> </semantics></math> are drawn, corresponding to different values of soil electrical conductivity <math display="inline"><semantics> <mrow> <msub> <mi>σ</mi> <mrow> <mi>d</mi> <mi>c</mi> </mrow> </msub> </mrow> </semantics></math>. Electromagnetic wave ranges have also been emphasized.</p> "> Figure 3
<p>A “capacitive” soil moisture sensor. The grazing light image shows the coplanar concentric capacitor of the sensor.</p> "> Figure 4
<p>Schematic of the capacitive sensors. Resistance values are directly taken from component labels. Capacitance values have been measured with an impedentiometer at 50 kHz after removal from a particular sample and are affected by ordinary manufacturing errors.</p> "> Figure 5
<p>(<b>a</b>) Older and (<b>b</b>) recent soil moisture sensor v.1.2. The thin metal path to grounded capacitor plate is clearly visible only in (<b>b</b>).</p> "> Figure 6
<p>(<b>a</b>) TL555I output waveform. The peak voltage exceeds the 3.3 V supply voltage of the TL555I. (<b>b</b>) Double exponential waveform on the anode of the diode of <a href="#sensors-20-03585-f004" class="html-fig">Figure 4</a> measured with a 10 MΩ, 14–18 pF probe connected to the node when the sensor is suspended in air.</p> "> Figure 7
<p>(<b>a</b>) Output voltage and (<b>b</b>) duty cycle as a function of frequency.</p> "> Figure 8
<p>Difference between output voltage in air and in distilled water as a function of duty cycle at 1.5 MHz for a modified sensor driven by laboratory instrumentation.</p> "> Figure 9
<p>The graduated cylinder: (<b>a</b>) no compaction; (<b>b</b>) maximum compaction, soil volume is 620 mL; (<b>c</b>) soil volume is 680 mL with two sensors driven into.</p> "> Figure 10
<p>Sensor output voltage as a function of soil volume at constant gravimetric water content (GWC) of 7.5%.</p> "> Figure 11
<p>Sensor output voltage as a function of GWC at constant soil volume.</p> ">
Abstract
:1. Introduction
2. Soil Water Content Measurements
3. Capacitive Moisture Sensor
4. Experimental Characterization with Silica Sandy Soil
4.1. Sensor Calibration with Constant GWC
4.2. Sensor Calibration at Constant Soil Volume
5. Discussion
6. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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id. | f (MHz) | Duty Cycle |
---|---|---|
S2 | 1.53 | 35.6% |
S10 | 1.51 | 35% |
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Placidi, P.; Gasperini, L.; Grassi, A.; Cecconi, M.; Scorzoni, A. Characterization of Low-Cost Capacitive Soil Moisture Sensors for IoT Networks. Sensors 2020, 20, 3585. https://doi.org/10.3390/s20123585
Placidi P, Gasperini L, Grassi A, Cecconi M, Scorzoni A. Characterization of Low-Cost Capacitive Soil Moisture Sensors for IoT Networks. Sensors. 2020; 20(12):3585. https://doi.org/10.3390/s20123585
Chicago/Turabian StylePlacidi, Pisana, Laura Gasperini, Alessandro Grassi, Manuela Cecconi, and Andrea Scorzoni. 2020. "Characterization of Low-Cost Capacitive Soil Moisture Sensors for IoT Networks" Sensors 20, no. 12: 3585. https://doi.org/10.3390/s20123585