The management of water and ion concentration in nutrient solution is crucial in precision agriculture. Poor management may leads to the increasing of energy consumption and cost as well as low efficiency. The measurement of ion concentration in nutrient solution is prerequisite for optimal control and management of nutrient solution. Real-time detection of NO₃^-, as an important component of nitrogenous fertilizer, is always a big problem over the world. The ion selective electrode is a new branch which appeared in the analytical chemistry field in 1970's. It is a kind of electrochemistry sensor, containing sensitive membrane, internal conductor system and electrode cavity. With its sensitive membrane, the concentration of the ions measured is converted into electrical signal directly and selectively. Because of its special advantage, it offers a promising and practical means for online measurement of ion concentration in nutrient solution and will get more extensive application in precision agriculture. However, during actual measurement, the accuracy is seriously interfered by surrounding temperature. Traditional solution is setting a temperature parameter manually, which leads to the tedious operational procedure and low measurement accuracy, which restricts the wide utilization of ion selective electrode. Moreover, the ion concentration detection systems on present markets are generally large, high cost and hard to carry.

Due to the above problems, this research based on ion selective electrode uses SPCE061A MCU as control core to measure NO₃^- ion concentration in nutrient solution. The measuring methods of NO₃^- ion concentration is discussed in this paper. DS18B20 module is applied to measure temperature of the nutrient solution for auto temperature compensation whose mathematical model is established through theoretical research and determination experiment of ion selective electrode’s input and output features. After all the researches above, this online measurement equipment is designed to measure the solution’s temperature and momentary NO₃^- ion concentration value. The ion selective electrode and the temperature measurement module collect data and send them to SPCE061A MCU. NO₃^- ion concentration is calculated and shown on the LCD screen. This equipment achieves the goal of real-time, automation, intelligence and miniaturization. Contrast tests are conducted before and after auto temperature compensation. The final test experiment shows this equipment can detect NO₃^- ion concentration more accurately which obviously reduces the interference of solution’s temperature. The maximum standard error and relative error of this equipment is 0.022mol/L and 10% respectively, which will have a well prospect in precision agriculture.