This article presents improvements to the practical acoustic thermometer of the Czech Metrology Institute that enable measurements with argon gas. Through a careful comparison with standard platinum resistance thermometers, the device shows its potential as a reference instrument for the calibration of industrial thermometers with traceability to the thermodynamic temperature scale. The extended temperature range, now from −80 to 80 °C, is characterized by the measurement uncertainty of well below 0.15 °C. Challenges arise above 100 °C, where the microphone approaches its maximum permissible temperature, which leads to discrepancies in the time of flight (τ) measurement results. The lower temperature limit is constrained by temperature-controlled enclosures, suggesting possible redesigns for future improvements. Modifications to the waveguide cover could enable isothermal measurements at higher pressures, which would allow calculation of the speed of sound (u₀). In addition, the upper temperature limit could be extended by lengthening the waveguide or installing a special high-temperature microphone. These results underline the versatility of PAT and provide insights for further improving its effectiveness over a wider temperature range.

International Congress of Metrology