An interference-tolerant nitrate smart sensor for Wireless Sensor Network applications

摘要

As a major contaminant in ground water, nitrate determination is a common practice in environmental analysis, especially the continuous and simultaneous monitoring of its concentration at many different points. For this task, sensor networks are a promising tool, although they require the use of sensors with special features, such as those of Ion Selective Electrodes (ISEs). Unfortunately, their measurements are - to a greater or lesser extent - affected by the presence of other coexisting (interfering) ions. A new methodology is then proposed in this work to deal with major interferences (chloride and bicarbonate in the case of nitrate determination), in such a way that the results obtained in the measurements of the content of NO_3~- with a nitrate selective electrode can be considered as virtually error-free from these interferences. For this purpose, a new sensor node has been developed; it consists of three ISEs (NO_3~-, Cl~-, and HCO_3~-) coupled to a low-consumption, low-cost microcontroller (a small chip containing all the computer components), which receives and processes all signals coming from the electrodes. This information is suitably treated, as described in detail in this paper, to provide an accurate estimation of the true value of NO_3~- concentration. The application of this methodology results in an interference-tolerant nitrate smart sensor capable of being employed within a Wireless Sensor Network in the continuous monitoring of nitrate concentration in aquifers and rivers.