AN ISFET-BASED NUTRIENT SENSOR FOR ROCKWOOL CULTURE

Abstract

An application of ISFETs (ion-sensitive field-effect transistors) to nutrient solution control systems in rockwool culture has been investigated. Measuring the ion concentration of a solution in rockwool is difficult and has not been carried out in practice. The authors anticipated that an ISFET, with its advantages of small size and low output resistance, could be used to measure the ion concentration of such a solution in rockwool. In this study, the authors examined the basic characteristics of ISFET-based nutrient sensor probes in rockwool. The characteristics examined were as follows: 1) Sensitivity characteristics for certain ion concentration changes (over a 10−4-10−1M NO3− range). 2) Reproducibility of the output when they were inserted into rockwool repeatedly. 3) Output dependence on the rockwool water content (over a 2080% range). 4) Output dependence on the distance between the ISFET and a reference electrode (over a 10-80 cm range). 5) Long-term stability of the sensitivity and output baseline in rockwool (over 2 weeks). These experiments have shown that the sensors have sufficient stability for use in this kind of measurement. The authors have found that ISFETs are able to measure the ion concentrations for a nutrient solution in rockwool culture.