Simple Technique for Linear-Range Extension of Linear Variable Differential Transformer

A technique for extending the linear range of a linear variable differential transformer (LVDT) is introduced in this paper. The linear operating range of a commercial LVDT is narrow compared to the full stroke range due to its nonlinear transfer characteristic. The narrow linear range of the commercial LVDT can be extended to maximum stroke range using the proposed technique based on LVDT inverse transfer characteristic. The circuit building block provided the third-order inverse transfer characteristic of the LVDT is established using analog multipliers and operational amplifiers (opamps). The proposed technique requires only commercially available devices, which is attractive in terms of a simple configuration and low cost. Performances of the proposed technique are discussed in detail and confirmed by simulation and experimental results using the commercial LVDT. As a result, the linear range of the LVDT used in this paper can be extended from ±2mm to ±15mm with the maximum absolute error of about 10.23μm or the full-scale error of about 0.068%. It is shown that the linear range of LVDT can be extended greater than seven times.