An Enhanced LVDT Digitizer With Extended Range

This paper aims to develop and optimize digitizing circuits for Linear Variable Differential Transformers (LVDTs) with an extended operational span. Initially, the paper presents a digitizing scheme for four-wire connected LVDTs. The proposed scheme utilizes a sawtooth current exciter and an improved dual-slope-based circuit, providing a direct digital estimate of the sensed position. Further, a simplified digitizer for five-wire LVDTs is introduced. The parameters of the digitizers are optimized using an evolutionary algorithm to achieve a linear and accurate indication of position over a wide span. A thorough evaluation of the proposed scheme is carried out using both simulation and hardware-based tests. Test results show that the developed circuit hardware, when used with a commercial LVDT, renders a non-linearity of less than 0.18% over an 80 mm span. This corresponds to a 16-fold improvement in linearity and about a two-fold enhancement in the effective displacement span, compared to the inherent characteristics of the LVDT.