A low-cost circuit for high-value resistive sensors varying over a wide range

In this paper, a low-cost interface for high-value resistive sensors ranging from k Omega to G Omega is presented. The proposed circuit acts as a 'resistance-to-period converter' and overcomes limits of previously developed solutions due to sensor parasitic capacitance. Particularly, this circuit estimates sensor resistance over six orders of magnitude without changing any scaling factor and is able to quantify sensor parasitic capacitance, in the order of pF. Estimation errors, due to real electronic components, are taken into account. Experimental results, obtained by the realized prototype, show a good resolution and repeatability, always better than 0.05%. Thermal effects have been considered and experimentally evaluated from theta = 10 degrees C to theta = 60 degrees C.