Improved Digitizing Scheme for LVDT: Design and Evaluation

This letter proposes an improved digitizing interface for linear variable differential transformer (LVDT). The scheme excites the primary of LVDT using a sawtooth waveform, and intelligently processes the resulting secondary outputs using a simplified dual-slope-based circuit architecture. The proposed interface inherits all the merits of underlying digitizing topology and provides a direct-digital estimate of position. The interface uses a low-complexity circuit, devoid of matched reference voltages and high-quality resistors and several other special circuit blocks, and thereby eliminates the demerits of the similar digitizers in prior-art. The proposed digitizer also has low dependance on many circuits and sensor nonideal parameters. This letter describes the design and analysis of this digitizing scheme, followed by its thorough performance investigation using simulation and hardware-based tests. Test results evidence that the developed scheme, coupled with a commercial LVDT, can provide accurate digital estimate of the shaft position. The nonlinearity error, observed during experimentation, is less than 0.5% over a span of 24 mm.