Linear Variable Differential Transformer Signal Conditioning Circuit Based on Phase-Locked Loop

Abstract

The purpose of this paper is to propose a novel technique for extracting the position signal from an inductive displacement transducer named a linear variable differential transformer (LVDT).In general, the movement of the LVDT core causes its primary inductance change in linear form.The primary winding of the LVDT is used as a time-dependent element for the triangular and square wave generator, which can be called self-oscillation, to generate frequency.The advantage of the proposed technique is that it can measure the displacement using the LVDT without an external oscillator.The change in primary inductance causes the frequency deviation generated by the oscillator.The deviated frequency is captured and converted into a voltage signal using the principle of the phase-locked loop.All the components used in this study are commercially available.The merits of this proposed technique are simple configuration, small size, and low cost.Moreover, the operating range of the LVDT can be extended without the limitation of the nonlinear transfer characteristic.The performance of the proposed technique is discussed in detail and confirmed by experimental implementation.Experimental results show that the maximum error from the proposed technique is about 0.42% and the operating range of the LVDT can be extended to more than 200%.It can be seen that the proposed technique is suitable for embedded measurement in small or micro robots.