Telemetric Technique for Passive Resistive Sensors Based on Impedance Real Part Measurement at Fixed Frequency

This paper proposes a measurement technique for telemetric systems working with passive resistive sensors from the kilohm order. It permits calculating sensor output through analytical formulas, from system parameters and the real part of system impedance measured at readout inductor's terminals. Impedance measurement is performed always at a fixed frequency, when inductors are at a fixed relative position. Formulas were derived through specific analyses, starting from a circuit model of the system. The technique was validated by finding the output of discrete commercial resistors attached to an inductor. A difference lower than 0.98% was obtained between resistors' values calculated through the proposed technique, and their values measured by means of an impedance analyzer. Finally, we applied the technique to a real application, i.e., temperature monitoring in an enclosed environment. We used a telemetric configuration with a Pt1000 sensor to monitor the temperature inside an oven wirelessly. The results pointed out that the technique permitted to estimate the temperature with an average difference of 2.2 degrees C with respect to a reference. Then, uncertainty on calculated temperature was equal to +/- 1.2 degrees C. In general, work analyses highlight that measuring impedance real part may be preferred than measuring its phase angle. These achievements show the feasibility of estimating the output of a resistive sensor through the proposed technique.