Why are the capacitance measurements and pixel values converted to normalised values?
For most practical ECT sensors, there is not a simple linear relationship between the capacitances measured between the electrodes and the permittivity of the material inside the sensor. The relatively large number of different measurements required and the fact that the relationship between capacitance and permittivity may be different for each of these measurements, creates potential calibration and operating problems for ECT systems. The method which is commonly used to overcome these problems is to restrict the use of ECT to the case where the sensor contains mixtures of two materials of differing permittivities and to operate the ECT system between the range of permittivities of these two materials. This is done by calibrating the sensor before any measurements are commenced and involves first filling the sensor with the lower permittivity material and measuring all of the inter-electrode capacitances and then repeating this operation with the higher permittivity material. All sub
