Realization of NIS Primary Standard Radiation Thermometer

Abstract

One of the principal responsibilities of the National Institute for Standards (NIS), is the establishment, maintenance and development of the national temperature standards and using them for calibration purposes of thermometers used in research, industry, agriculture and health. In order to meet these responsibilities at high temperature range above the freezing point of silver (961.78°C), it was necessary to have a primary standard radiation thermometer for realizing the International Temperature Scale 1990 (ITS-90) above the freezing point ofsilver.

A single • wavelength thermometer was designed and constructed for the purpose of realizing the International Temperature Scale 1990 (ITS-90), above the freezing point of silver.

The thennometer works at a fixed distance of 400 mm from the objective lens which has a focal length of 150 mm (f=150mm). An image of the target is focused by the objective onto a drilled mirror with an aperture of 1 mm diameter. The light passed by the aperture is conveyed by a condenser lens through an interference filter with a nominal center band at 900 nm and a half height bandwidth of 10 nm and then reaches a silicon photodiode detector. The silicon photodiode is a Hamamatsu model S2386-44k that has an active area of3.6x3.6 mm2 .