Acoustic thermometry is capable of phenomenal accuracy, but is a difficult technique to apply in many practical situations. Here, we describe a modification of the technique, which permits robust temperature measurements to be made, potentially with millikelvin resolution, over a temperature range extending from cryogenic temperatures to over 1000 °C. The technique uses measurements of the time of flight of acoustic pulses in tubes, usually filled with an inert gas such as argon. The tubes—typically made of stainless steel with an outer diameter of 6mm—act as acoustic waveguides and can be several meters long and bent into complex shapes. The time of flight is determined by the average temperature along the entire length of the tube. Local temperature information can be inferred in several ways. Typically a second shorter tube is used and the difference in time of flight reflects the temperature in the region at the end of the first tube. If the measurement length is sufficiently long—typically 1m of tube—then a measurement resolution of less than 1mK is achievable. The technique is well suited to measurements in harsh environments in which conventional sensors degrade. Results from early tests are shown, which highlight the strengths and weaknesses of the technique.
