title: A Novel Low-Cost Instrumentation System for Measuring the Water Content and Apparent Electrical Conductivity of Soils.
abstract: The scarcity of drinking water affects various regions of the planet. Although climate change is responsible for the water availability, humanity plays an important role in preserving this precious natural resource. In case of negligence, the likely trend is to increase the demand and the depletion of water resources due to the increasing world population. This paper addresses the development, design and construction of a low cost system for measuring soil volumetric water content (θ), electrical conductivity (σ) and temperature (T), in order to optimize the use of water, energy and fertilizer in food production. Different from the existing measurement instruments commonly deployed in these applications, the proposed system uses an auto-balancing bridge circuit as measurement method. The proposed models to estimate θ and σ and correct them in function of T are compared to the ones reported in literature. The final prototype corresponds to a simple circuit connected to a pair of electrode probes, and presents high accuracy, high signal to noise ratio, fast response, and immunity to stray capacitance. The instrument calibration is based on salt solutions with known dielectric constant and electrical conductivity as reference. Experiments measuring clay and sandy soils demonstrate the satisfactory performance of the instrument.
authors.affiliation: Department of Control and Automation Engineering and Fundamental Techniques, School of Mines, Federal University of Ouro Preto (UFOP)-campus Morro do Cruzeiro, sn, 35400-000 Ouro Preto, MG, Brazil. alankardek2@gmail.com.
authors.forename: Alan Kardek
authors.initials: AK
authors.lastname: Rêgo Segundo
authors.affiliation: Department of Agricultural Engineering, Federal University of Viçosa (UFV)-Avenida P.H. Rolfs, sn, 36570-900 Viçosa, MG, Brazil. j.helvecio.martins@gmail.com.
authors.forename: José Helvecio
authors.initials: JH
authors.lastname: Martins
authors.affiliation: Department of Control and Automation Engineering and Fundamental Techniques, School of Mines, Federal University of Ouro Preto (UFOP)-campus Morro do Cruzeiro, sn, 35400-000 Ouro Preto, MG, Brazil. pmemop@gmail.com.
authors.forename: Paulo Marcos de Barros
authors.initials: PM
authors.lastname: Monteiro
authors.affiliation: Department of Agricultural Engineering, Federal University of Viçosa (UFV)-Avenida P.H. Rolfs, sn, 36570-900 Viçosa, MG, Brazil. rubens@ufv.br.
authors.forename: Rubens Alves
authors.initials: RA
authors.lastname: de Oliveira
authors.affiliation: Vale Institute of Technology (ITV)-Avenida Juscelino Kubitschek, 31, Bauxita, 35400-000 Ouro Preto, MG, Brazil. gustavo.medeiros.freitas@itv.org.
authors.forename: Gustavo Medeiros
authors.initials: GM
authors.lastname: Freitas
keywords: dielectric constant; electrical conductivity; embedded system; microcontroller; self-balancing bridge