Impedimetric Sensor System for Edible Oil Quality Assessment

The repeated usage of frying oil is hazardous due to the degradation caused by chemical reactions, which happen while heating. The total polar compounds and the free fatty acids are the main two chemical parameters affected by frying. These parameters increase significantly with the use of oil for frying. For this purpose, sensor systems for oil quality assessment are necessary. In fact, changes of the composition due to frying leads to variation of its dielectric parameters. The main challenge thereby is that the impedance changes are very small. In this context, this work proposes a sensor system with high accuracy able to detect the small changes that occur in the resistance and capacitance under influence of stray capacitances. Theoretical and simulation studies are carried out for different capacitive sensors as well as measurement procedures of its complex impedance. The sensor should provide a high sensitivity to relative permittivity and the electrical conductivity. Interdigital electrodes sensor with a suitable design fulfils all these requirements. We propose, a measurement circuit based on a combination of the method of capacitance to voltage conversion and the phase shift measurement method. By combining both methods together it is possible to measure accurately the complex impedance of edible oil. Experimental results show that measurement system is capable to detect small changes of dielectric parameters, which are correlated to the chemical parameters.