Potentiometric type displacement sensors offer a simple, low-cost solution to measure linear or angular displacement. However, the sliding of the wiper on the sensing element causes wear and tear, thereby limiting the operational life of these sensors. This problem can be altogether eliminated if we make the wiper float over the sensing element without making physical contact with it. When the wiper floats on the resistive element, a coupling capacitance gets formed between the wiper and the resistive element. The value of the coupling capacitance thus formed will vary with: (i) displacement, (ii) presence of impurities, and (iii) vibration. Therefore, a signal conditioning circuit is required to extract the displacement information, independent of the coupling capacitance.

Two different signal conditioning circuits suitable for a resistive potentiometric type displacement sensor with a floating slide are presented in this thesis. The first circuit provides an analog output that is directly proportional to the displacement of the wiper. The second circuit is based on the successive approximation principle of analog to digital conversion. It provides a digital output that is proportional to displacement. At equilibrium, the proposed circuits ensure that the current through and the voltage across the coupling capacitor is zero, thus, removing its effect on the output. Further, whenever the displacement changes, the first circuit adjusts itself to the corresponding output voltage value. A simplified version of this circuit was also developed. However, this circuit is prone to the presence of parasitic capacitances.



Next, a signal conditioning circuit for a non-contact inductive voltage divider type displacement sensor is presented. This circuit is also based on the successive approximation principle, and it gives a digital output that is proportional to displacement. In all the three circuits, the outputs are independent of the value of the coupling capacitance. The results obtained from simulation and experimental studies establish the efficacy of the proffered schemes. The output was found to be linear with worst-case nonlinearity of 0.85 %, 0.8 %, and 0.9 % observed for the first, second, and the third circuit, respectively.