Climatic Chamber for Temperatures up to $180\,^{\circ }\mathrm{C}$ and Pressures up to 0.5 MPa

Abstract

A new relative-humidity setup was developed for calibrating sensors in the temperature range from $-40\,^{\circ }\mathrm{C}$ up to $180\,^{\circ }\mathrm{C}$ and at pressures down to 700 hPa and up to 0.5 MPa. The setup is based on the chamber-in-chamber model: a small additional chamber is positioned inside a climatic chamber. While the climatic chamber is used to generate the air temperature, a pre-conditioned gas from outside the climatic chamber delivers the required humidity in the new pressure chamber. Validation of the setup at atmospheric pressure showed relative-humidity uncertainties of 0.2 %rh at 5 %rh over the whole temperature range and 0.4 %rh at 95 %rh for temperatures above $0\,^{\circ }\mathrm{C}$. Below $0\,^{\circ }\mathrm{C}$, the maximum uncertainty increases to 0.9 %rh due to the influence of the temperature homogeneity. The temperature uncertainty of the new setup is between $0.10\,^{\circ }\mathrm{C}$ and $0.21\,^{\circ }\mathrm{C}$. Five commercially available relative-humidity sensors, of different type and manufacturer and all suitable for high temperatures, were calibrated in the new setup. The measurements showed deviations outside the stated specifications of the manufacturer and the need of traceable calibration facilities.