Accurate Interface Schemes for Resistance Thermometers With Lead Resistance Compensation

Simple low-cost interfacing circuits for resistance thermometers are proposed in this article. The proposed circuits are designed to provide many salient features, including simplicity of architecture, lead-wire compensation, constant-current excitation, and requirement of minimal number of analog-to-digital converters (ADCs) for digitization. The first of the proposed circuits uses a twin-Op-amp signal conditioner for three-wire sensor. This circuit is then modified to act as an efficient front-end for four-wire resistance thermometer, and thus negate the effect of lead-wire mismatches. The performance of the proposed circuits is extensively verified using experimental studies. Results show that the nonlinearity and relative error of the developed circuits is less than 0.05% and 0.32%, respectively, when tested with Pt1000 sensor. Finally, a comparison study is performed to show the superiority of the proposed techniques.