APPLICATION OF REGRESSION ANALYSIS DURING THE ASSESSMENT PROCESS OF FACTOR IMPACT ON THE SENSITIVITY OF THE CAPACITIVE HUMIDITY SENSOR

Abstract

In order to optimize the parameters of creating a moisture-sensitive layer of the capacitive humidity sensor, a multifactorial experiment plan was used in combination with regression analysis of the factor influence. Capacitive humidity sensors are made on a sitall substrate with size 0.7×0.9 mm, on the surface of which is applied a copper film, which forms the plates of the capacitive elements in the form of a meander with the appropriate geometry 7.85·10-2×150·10-6×1.2·10-6 m. Hygroscopic salt is a moisture-sensitive film that serves as a dielectric. Solutions of hygroscopic salt NaCl with concentrations 0.89 mol/l and 5.33 mol/l were used to create a moisture-sensitive film, which were applied to the surface of capacitive humidity sensors by spraying at a distance of 40–50 cm with thicknesses of 5.0 μm and 10.0 μm. Statistical processing of the results of the factor experiment by the Cochran test proved that the factor experiment is reproducible. Using the planning matrix of the full-factor experiment, a regression equation has been developed and on the basis of which it has been found that the concentration of salt solution used to create a moisture-sensitive layer significantly affects the sensitivity of the capacitive humidity sensor. According to Student criteria it has been established that all the coefficients of the regression equation are significant. Sensitivity has been chosen as criteria for parameters optimization of creation a moisture-sensitive layer of such a capacitive humidity sensor. The final regression equation on the scale of real factors makes it possible to optimize the parameters of creation a moisture-sensitive layer of the capacitive humidity sensor with the maximum values of the response function – “sensitivity”. It has been found that the highest sensitivity of 36.32 pF/% is provided by the following optimal parameters of the process of creating a moisture-sensitive layer: the concentration of salt solution, which serves as an adsorbent material, namely hygroscopic salt NaCl – 5.33 mol/l and thickness of moisture-sensitive layer 10.0 μm.