Study on the Infrared Lens-Free Irradiation Thermometer Based on InGaAs Detector at NIM

Abstract

A lens-free irradiation thermometer (LF-IRRT) designed for laboratory applications, with $1.55\,\upmu \hbox {m}$ center wavelength based on the InGaAs detector, and a temperature range from $300\,^{\circ }\hbox {C}$ to $1000\,^{\circ }\hbox {C}$, has been developed at NIM of China. The thermometer has no imaging optics for collecting the radiation, for which a major benefit is improved stability compared to other radiation thermometers. This paper introduces the measurement principle, the structure of the LF-IRRT, the multiple-point calibration method, and the stability and expanded uncertainty of the thermometer. The stability of the LF-IRRT is better than $0.070\,^{\circ }\hbox {C}$ at temperatures from $300\,^{\circ }\hbox {C}$ to $1000\,^{\circ }\hbox {C}$ over a period of 1 month. The expanded uncertainty is less than $0.20\,^{\circ }\hbox {C}$ for temperatures between $300\,^{\circ }\hbox {C}$ and $1000\,^{\circ }\hbox {C}$. The size-of-source effect of the LF-IRRT is 0.6 % from the source diameter range from 10 mm to 65 mm.