Progress report on the single transducer ultrasonic thermometer using electrostatic actuator.

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.