The relative permittivity is a parameter that indicates the relative charge storage capability of dielectrics compared with free space Moisture measurement technique is based upon the relatively high dielectric permittivity (commonly called DIELECTRIC CONSTANT) of water (80-30) in comparison to the dielectric properties of the polymers (2-5) and also includes the measurement ofdiamagnetic properties of water. The variation of water content within the product, would result in alarge variation in the combined dielectric constant which would then be measured by monitoring the changes in the dielectric signal. Additionally at
particular excitation frequency, measurement is effected by two dielectric absorption peaks for free and bound water molecules when introducing a controlled field. The material being read by the sensor is represented by a MIX of permittivities, mainly from 3 different variables : AIR, WATER and MATERIAL.
Total Capacitance C = Csensor+ ԐAir+ Ԑwater+ Ԑproduct
Each element contributes to the variation of total capacitance of the sensor. Knowing each single contribution of the total dielectric constant allow BRYSCAN sensors to measure the quantity of water.
The patented moisture sensor developed by PROKON mainly comprises two components: the fullydifferential sensing capacitor and the high-precision high-resolution readout electronics.
The fully-differential sensing capacitor detects the changes of moisture based on the edge/fringe effect as shown in Figure 1.
The precision and accuracy of the sensor depends onseveral parameters such as STATIC DISTURBANCE SOURCES (parallelism, Flatness of the electrode etc) and dynamic disturbances SOURCES (Temperature
variations, air humidity variations etc.). All these disturbances are compensated through construction design, components and algorithms in the Software