An Efficient Digital Readout for Four-Lead Resistance Thermometers

Four-lead resistance temperature detectors (RTDs) are often used to achieve accurate measurements in many industrial installations. This letter proposes a triple-slope-based digitizing circuit for four-lead RTDs. The proposed circuit not only provides the meritorious features of its analog counterpart but also renders a direct-digital output characteristic. It also ensures constant-current excitation, and the digitized output is independent of lead-wire resistances and their mismatches. This letter clearly conveys the working mechanism, as well as the performance verification of the proposed circuit using various studies. Results show that the maximum nonlinearity and relative error do not exceed 0.25% and 0.5%, respectively, for the temperature range from −50 °C to 260 °C. Furthermore, the immunity of the circuit toward the noise is also good, and its signal-to-noise ratio is around 46 dB. Later, the actual experimentation is also carried out using a commercial RTD-Pt100 sensor. Results show the suitability of the developed interface for conditioning four-lead linked sensors.