A Simple and Efficient Oscillator Based Read-out Scheme for LVDT

A novel read-out circuitry for Linear Variable Differential Transformers (LVDT) is presented in this paper. The proposed method avoids the use of low distortion sine wave oscillators for primary excitation and the associated phase compensation circuitry. The read-out circuit uses the secondary coil of an LVDT as part of a Colpitts oscillator along with a frequency counter to derive the position information. The proposed method also utilizes ratiometric computation for better linearity. Results of the measurements carried out for the proposed oscillator based read-out circuit are comparable to those obtained from commercially available LVDT signal conditioners. The measurements provide an accuracy of 12 bits over a 26 mm range with an update rate in excess of 4 kS/s, and a linearity error of +/- 0.17% of the Full Scale (FS).