Linearity Range Enhancement of LVDT Position Sensors Using Optimized Coils

This paper presents enhancing the linearity range of linear variable differential (displacement) transformer (LVDT) sensors by optimizing the excitation and pickup coils. The paper aims to increase the linearity without complicating the sensor structure and measurement systems. The linearity range is essential for the efficient operation of LVDT position sensors. Conventional LVDT position sensors usually have one excitation coil and two differentially connected pickup coils for the stationary part. They have one armature with a ferromagnetic core for the moving part. The axial length of the excitation coil and the number of turns in the pickup coils are optimized for the linearity range enhancement. The two-dimensional (2D) axisymmetric finite element method (FEM) is used for analysis and optimization. The optimizations are performed based on a Ferrite core armature with a cylindrical structure and a fixed axial length and radius. A constraint of a maximum total axial length of the coils is also applied for the design optimization. The experiments are conducted to validate the LVDT’s pickup coils optimization to enhance the linearity range using measurement results. The measured nonlinearity error of 1% is achieved using optimized coils for the LVDT position sensors. The maximum repeatability error is below 0.2% for a prototyped position sensor.