An investigation into a calibration scheme for a light pipe based temperature probe

We propose a scheme to ensure traceable calibrations of light pipe based temperature probes. We investigate experimentally and theoretically the properties of a device consisting of a sapphire tube with a tungsten filament at the bottom, filled with an inert gas and sealed to avoid contamination of the filament. The device is used as a contact probe, where the temperature is deduced based on detection and quantification of the Planckian radiation from the filament. The Sakuma–Hattori equation is used to approximate the Planck radiation as a function of temperature, and its parameters are fitted using a small number of calibration points. The impact of a small, temperature dependent emissivity on both the calibration and the interpolation errors is explored, and we find that a dual-band detection scheme is required to reduce the sensitivity to variation in the use conditions.