Long-Term Stability and Calibration of the Reference Thermometer ASL F200: 20 Years of Calibration History – 2025 Update

The aim of this technical report is to provide detailed information about the long-term stability of the thermometer ASL F200 (WIKA Instruments Limited) that is used as temperature reference to calibrate other temperature sensors in the Laboratory of Building Energy and Indoor Environment at Aalborg University – Department of the Built Environment. This ASL F200 thermometer is regularly sent for recalibration at the “Temperature Laboratory” of the Danish Technological Institute, which is a National Reference Laboratory.
In this report, the stability of the thermometer is assessed as the difference in the temperature reading of the instrument at a specific temperature over time. The latter is calculated as the yearly deviation (or stability) in between consecutive recalibrations, which is equivalent to the difference in the calibration correction term in between two consecutive recalibrations divided by the elapsed time in between these two consecutive recalibrations.
The long-term stability of the ASL F200 thermometer is only assessed here for the first channel “Chan 1” of the instrument.
All calculations of this technical report are based on calibrations reports from the National Reference Laboratory of the Danish Technological Institute. The main results of those calibration reports can be found in the Appendix at the end of this document.