Measurement and separation of forces and lift-offs employing an inductance-to-digital converters (LDC)-based orthogonal LC resonance sensor

Abstract

Inductor-capacitor (LC) resonance sensors based on the sensing materials’ electromagnetic properties have potential to replace strain gauges for wheel-rail contact force measurement. However, as traditional eddy current testing acts, the lift-off effects also affect the results of the LC resonance sensing which can cause the misinterpretation between forces or lift-offs. This paper proposed an LDC-based orthogonal LC resonance sensor, combined with an 8-node quadratic interpolation method to achieve the measurement and accurate separation of forces and lift-offs. The four characteristic parameters of the orthogonal LC resonance sensor, Rp1, Frequency1, Rp2, Frequency2, were measured at different applied forces and lift-offs. A new combination pattern referred to the Rp2-Rp1, frequency2-frequency1 plane was proposed, which contained force and lift-off information in both vertical and transverse directions. Through the 8-node isoparametric coordinate transformation, the applied force and lift-off were separated respectively, with the maximum relative error of 22.61% for forces and 1.66% for lift-offs. Results indicated that the proposed method is effective and can be used to measure force/stress under varying lift-offs.