Sound-card-based Johnson noise thermometer

This article presents a Johnson noise thermometer with a signal acquisition system based on a sound card. The thermometer uses a simple analogue circuit to measure the Johnson noise on a resistor. No external hardware or power supply is necessary, except for a reference multimeter. Data processing is performed in real time on a personal computer using LabView software. The results show that the developed thermometer has an expanded uncertainty (k = 2) of 0.8 ℃ over a temperature range from − 196 ℃ to 300 ℃, with a measurement time of 5 min.