Compact and accurate digital thermometer based on an Anderson's loop and a Pt-100 sensor

A simple and practical digital thermometer with an accuracy better than 0.1 degrees C over a near-room-temperature (from -10 degrees C to 50 degrees 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-linearity. This compensating procedure allows for a wider (from -50 degrees C to +200 degrees C) and higher accuracy (similar to 0.05 degrees C) measurement range. The accuracy, up to now, is essentially limited by the accuracy of the temperature standard used for calibration.