An Intelligent and Customized Electrical Conductivity Sensor to Evaluate the Response Time of a Direct Injection System Heitor V. Mercaldi *§ , Caio H. Fujiwara *§ , Elmer A. G. Pe˜ naloza *§ , Vilma A. Oliveira § and Paulo E. Cruvinel * * Embrapa Instrumentac ¸˜ ao Rua XV de Novembro 1452, S˜ ao Carlos, SP, Brazil § Universidade de S˜ ao Paulo Av. Trabalhador S˜ aocarlense 400, S˜ ao Carlos, SP, Brazil Email: heitor@usp.br, caio.fujiwara@usp.br, egamboa@usp.br, vilma@sc.usp.br, paulo.cruvinel@embrapa.br Abstract—In pesticide application based on direct injection sys- tems, the sprayer response time plays an important role for the spraying quality, mainly when operating in real time. The response time is defined as the time elapsed from the time of injection until the concentration of the mixture (water mixed with herbicide) reaches 95% of its regime value in the spray nozzles. Therefore, in the response time the transport delay and the rise time for achieving the desired concentration are considered. This paper describes an intelligent sensor mounted near the spray nozzles to measure the concentration response time in a herbicide direct injection system, which uses a highly stable sinusoidal excitation signal. The sensor calibration was performed with NaCl solutions at concentrations similar to those found in actual application conditions. Using an integrated system based on the Arduino platform, an algorithm was developed to relate the measurements to the response time. The integrated system comprises the sensor with its own sensing hardware, A/D converter, processing and storage capabilities, software drivers, self-assessment algorithms and communication protocols. The im- mediate application of the integrated system is in the monitoring of the response time of a precision pesticide application. The results point to the next generation of smart devices that have embedded intelligence to support decision making in precision agriculture. Keywords–direct injection; response time; electrical conductiv- ity; intelligent sensors I. I NTRODUCTION Brazil has experienced in the last two decades a significant increase in the use of pesticides for agricultural production. Despite the significant growth of the area cultivated with trans- genic seeds, a technology that promises to reduce chemical use in agricultural production, sales of these products increased by over 72% between 2006 and 2012 and is still rising up according to data from the Brazilian National Union of the Industry of Agricultural Defense Products [1], association which represents the pesticide manufacturers in the country. In the same period, the area planted with grains, fiber, coffee and sugar cane grew by less than 19%, from 68.8 million to 81.7 million hectares, according to the Brazilian National Company for Supply [2]. This means that the average consumption of pesticides, which was just over 7 kilograms per hectare in 2005, rose to 10.1 kilograms in 2011, an increase of 43.2%. Although this amount indicates more protection for products and higher incomes, the uniform rate of application leads to soil and water contamination. A key approach to reduce environmental pollution is to use variable-rate appli- cation. An approach to develop variable-rate sprayer technologies is to install automation and control procedures on conventional sprayers. In this direction the direct injection type of sprayer systems have been used along with electronic controllers. In order to adjust the sprayer operation, reference for variables such as working pressures, traveling speeds, and spraying concentration change rates can be selected to achieve the quality for spraying drop distribution. The agricultural machinery and technologies available to- day enable variable-rate chemical application based on pre- scription maps or sensors [3]. Variable-rate application can be performed by varying the concentration of the chemical on- the-go using a direct injection system [4]. The direct injection system is an electronically controlled system in which the chemical is injected into the carrier stream. The direct injection system has separated chemical and carrier reservoirs and the chemical can be injected into the carrier stream in different positions. In the literature, reports of systems to inject concentrated pesticides into diluent stream began to appear in the 70th decade [5]. In [6], Vidrine and collaborators tested the fea- sibility of injecting concentrated pesticides. In [7], Reichard and Ladd developed a field sprayer which included injection of pesticides at specific rates accounting for variations in travel speed. In [8], Chi and collaborators developed a flow rate control system which allowed the measurements of concen- trated pesticides. In [9], Ghate and Perry developed a field sprayer based on the use of a compressed air to inject chemical into the carrier stream. In [10], Miller and Smith reported on development of a direct nozzle injection system. In general, during the spraying process errors can be observed. Research works on the evaluation of the application rate errors has been shown that errors are not only due to the deviations from the target flow rates but also due to interaction between the dynamics of the systems and sprayer response time. By now, is quite well known that the direct injection system sprayer response time depends on the sprayer dynamics and on the transport delay [11]. The transport delay is due to the flow rate and distance of the nozzle from the injection point. The farther the nozzle is from the injection point larger the mix uniformity and lower the cost but higher the transport delay of the sprayer. Several studies have appeared regarding to the performance of the direct injection sprayers and reducing their response time [12]–[20]. Therefore, the conventional implements can be reorganized to operate into variable-rate ones using control 19 Copyright (c) IARIA, 2015. ISBN: 978-1-61208-426-8 SENSORDEVICES 2015 : The Sixth International Conference on Sensor Device Technologies and Applications