Model Based Compensation of Thermal Drifts for Multi Electrode Capacitive Sensing

Capacitive sensing has become a favourable measurement technology for industrial applications. A main advantage of capacitive sensors is the contactless working principle, which enables capacitive sensors for the application in industrial processes with harsh environmental conditions. Multi electrode capacitive sensing is used to obtain information about objects in a region of interest. This requires dedicated model based signal processing techniques and accurate physical models of the measurement process. Industrial processes often entail high temperatures, which leads to thermal drifts of the material values and to thermal expansions within the sensor front end. In order to draw reliable conclusions about the quantities of interest, these effects have to be taken into account. In this paper we present a model based temperature compensation approach for capacitive multi electrode structures, which considers temperature related permittivity changes as well as structural displacements due to thermal expansions to reduce the impact of thermal drifts. The proposed approach is validated on the example of an electrical capacitance tomography sensor.