Characterization of capacitive sensors for measurements of the moisture in irrigated soils

Abstract

The irrigation is a technique developed to supply the hydric needs of the plants. The use of the water should be optimized so that the culture just has enough for its growth, avoiding waste. The objective of this work was to characterize the behavior of capacitive sensors of humidity to monitor the moisture in the soils. In first instance, it was appraised sensors with dielectric built of synthetic pomes stone (Rd = 0,4 and Rd = 0,8) and of soil samples (Rd = 0,8 and Rd = 1,0), being the Rd parameter a geometric factor that relates the distance between the capacitor plates with radius of the plates. For the calibration, the sensors were installed in PVC recipient of cylindrical shape, filled with soil. The set (sensor and soil) was humidified by capillary effect and submitted by a natural drying very slowly. The parameter readings were taken daily, which allowed obtain the curves relating the humidity percentage, expressed in terms of dry weight, with the output voltage fort the sensor. The experiments were performed in sand soil and in dark red latossolo. The obtained results allowed to infer that the behavior of the sensor has a specific feature for each type of soil, being, therefore, necessary to develop a own calibration curve for the sensor, when used in soil with specific characteristic

Avaliação de sensor capacitivo para o monitoramento do teor de água do solo

“…Foram confeccionados na forma retangular, em placas de circuito impresso (fibra de vidro, com uma fina camada de cobre em um dos lados), com espessura, largura e tamanho aproximados de 0,002 m, 0,03 m e 0,15 m, respectivamente. As placas são posicionadas paralelamente, definindo os eletrodos do capacitor, separadas em 0,005 m e cobertas por verniz que, segundo RENDE & BIAGE (2002), serve tanto para evitar oxidação das placas de cobre, devido o contato com o solo, como para eliminar o efeito da condutância elétrica da carga por meio do dielétrico. A área da placa que constitui o campo elétrico é de 0,002548 m².…”

Polytetrafluoroethylene Films in Rigid Polyurethane Foams’ Dielectric Permittivity Measurements with a One-Side Access Capacitive Sensor

“…Different solutions for protection of capacitive sensor’s electrodes exist in experimental investigation of other dielectric materials. In [ 6 ] the copper plates of the electrodes are covered with a protecting varnish to avoid the oxidation from contact with the test object (The soil) and to eliminate effect of electric load conduction through the dielectric. A protective layer is often placed over the electrodes in a capacitance sensor to prevent the direct contact to the test object [ 7 ].…”

In-Situ Estimation of Soil Water Retention Curve in Silt Loam and Loamy Sand Soils at Different Soil Depths

“…Some examples of inexpensive sensors used to measure soil water content and potential are capacitance-based sensors, resistivity-based granular matrix sensors, and tensiometers [ 5 , 29 , 30 , 31 , 32 ]. These sensors have been used in a variety of soil applications such as capturing soil water trends, estimating hydraulic properties in different soil textures, and sensor characterization in irrigated soil [ 5 , 33 , 34 ].…”