A measurement algorithm for capacitive speed encoder with a modified front-end topology

This paper presents an angular speed measurement algorithm for capacitive multiple plate angular encoders with disturbed rotational symmetry. The described sensor is aimed for automotive applications and therefore has to fulfill specific requirements. An important point is fast replacement in the vehicle. It is realized with a new asymmetric sensing plate configuration resulting in increased measurement error due to the disturbed symmetry. This paper presents a simple model for the influence of the new, sensing plate configuration on the capacitance between the fixed plates. A measurement algorithm based on a segment capacitance model for the asymmetric plate configuration is proposed. The main advantage of this algorithm is the suppression of steep slopes in the sensor angular measurement error and thus, the reduction of the relative angular speed error.