Report from inter-laboratory comparison of air thermometer calibration procedures. EURAMET project 1459

1 Objective The main objective of this comparison is to identify unwanted influences on air temperature measurements, and to provide a basis for recommendations to laboratories that offer air temperature calibrations, or in some way use air temperature measurements as important auxiliary information during other calibrations. It is well known that a host of issues affect the heat transfer between a thermometer and air, such as wind speed, sensor irradiation, air pressure and humidity. A previous EURAMET comparison, P1061, concluded that radiation shielding might alleviate errors due to purely radiative heat loads, but exacerbate errors related to conductive and convective heat transfer (1). However, recent work by de Podesta et al (2) suggests a more insidious connection between the heat transfer properties at the sensor interface, by pointing to an interplay between sensor dimension, wind speed and irradiation. Controlled experiments showed that the magnitude of the discrepancy between thermometer reading and actual air temperature can be of concern even in highly controlled laboratories. This comparison aims to gain further insight into the ways air temperature measurements can be affected by collecting measurements from a number of laboratories employing different techniques to assess air temperature. The data will be used to compute the degree of equivalence (DoE) for the participants using a consensus based reference value, but also to analyse reasons for disparities between laboratories. In addition to the common set of reported results which all participants will be required to supply, some participants will conduct additional measurements that will be taken into account in the analysis. While the primary aim of the ILC is to conduct research it is still vital that participants do not share results during the measurements. Once all the data have been collected the pilots and the coordinator will analyse the data and prepare a report, and from that point the data will be open to all participants.