Oscillator based readout Circuit for lvdt

Abstract

The present work focuses on designing an oscillator-based-readout circuit for LVDT. LVDT readout schemes for both the commercially available ICs and state of the art LVDT signal conditioners are presented. The two well-established methods of LVDT readouts, namely the (i) ratio-based method and (ii) synchronous demodulation-based method has been extensively studied and the design of an architecturally simple and cost-effective readout circuit has been taken up as an investigation problem. Thus, the proposed read-out electronics treats the sensor s secondary inductance as an unknown reactance, thereby incorporating an active oscillator circuit as a resonator to derive the position information. This method avoids the excitation of the primary coil using low-distortion sine wave oscillators and the associated phase compensation circuitry as used in traditional signal conditioning circuits. A discrete component-based readout prototype has been developed with a Colpitts oscillator circuitry and an FPGA-based frequency counter. The demonstration and verification of the prototype developed have been carried out. The performance metrics of the proposed readout circuit such as the resolution, linearity, and cross-sensitivity have been studied and analyzed from the obtained measurement results. It is shown that for the discrete component-based read-out procedure, the resolution is in the range of 8-16 bits with update rates per channel ranging from nearly 10 Hz to 8 kHz, and depending on the procedure used, a worst-case fullscale non-linearity error of +/- 0.14% is feasible. newline