Fig. 7. Measured relation between permittivity of the dioxane–water mixture outside the access tube and normalized sensor reading N. The light gray data are the laboratory measurements; the data represented by the black circles are corrected for the calculated effect N() of the fluorinated ethylene-propylene (FEP) coating. The solid lines are the approximations using Eq. [29] and is the standard deviation between N_i^k measured with the sensors k = 1 to 4.