Contactless high frequency inductive position sensor with DSP read out electronics utilizing band-pass sampling

Abstract

This paper presents a precise, reliable, low cost and contactless inductive absolute position measurement system for rough industrial environments. It offers a high inherent resolution (0.04 % of antenna length), and measures absolute position over a relative wide measurement range. The main property for this kind of sensor is its good immunity to external noise and target misalignment off the measurement axis. The measurement range and the precision are extended by adding additional and finer pitched receive coils. This sensor works on similar principles as resolvers but consists of a rectangular antenna PCB, a small moveable passive LC resonant circuit and a signal processing unit. Furthermore, the used read out electronics utilizes under-sampling to demodulate the sensor output signals and the corresponding position is estimated from a lookup table (LUT) implemented on a digital signal processor (DSP) to avoid singularities in the inverse tangent and cotangent calculation. Moreover, the mechanical transducer arrangement, the signal condition electronics design and measurement results of the transmitter to receiver signal coupling and relative position error will be presented.