Compact and accurate digital thermometer based on Anderson’s loop and Pt-100 sensor

A simple and practical digital thermometer with an accuracy better than 0.1°C over a near-room-temperature (from −10°C to 50°C) measurement range has been developed. The instrument is compact and battery operated and provides for both digital and analog outputs. A four-lead platinum thermal sensor, driven by a constant current loop, allows for accurate temperature readings with high immunity to the contact resistances and to their variations. A low-noise electronics allows for temperature measurements with a 1 mK resolution. By experimentally characterizing the non-linearity of the adopted Pt-100 sensor, a suitable readout correction table has been calculated in order to compensate for the sensor non-linear behavior. This compensating procedure allows for a wider (from −50°C to +200°C) and higher accuracy (0.05°C) measurement range. The ultimate accuracy was essentially limited by the accuracy of the temperature standard used for calibration.