Research article

Characterizing a linear pyrometer at the National Metrology Institute of South Africa

National Metrology Institute of South Africa (NMISA), Private Bag X34, Lynnwood Ridge, Pretoria 0040, South Africa

^* Corresponding author: eejigu@nmisa.org

Received: 14 September 2022
Accepted: 8 March 2023

Abstract

A linear pyrometer is used to realize the International Temperature Scale of 1990 (ITS-90) for temperature ranges above 961.78 °C in most National Metrology Institute (NMI) radiation thermometry labs. The different components of the linear pyrometer system working together to measure temperature may exhibit some errors which should be accounted for. The errors can be characterized by several equipment parameters that should be measured before the radiation thermometer is used to realize ITS-90 temperatures. Relative spectral responsivity (s), size of source effect (SSE), gain ratio (GR), non-linearity (NL), distance effect (DE), temperature coefficient and zero drift are all major equipment parameters that characterize the efficiency of a linear pyrometer in realizing ITS-90. In this work, an attempt was made to describe and demonstrate these major parameters by using actual measured characterization results of a linear pyrometer. Uncertainty contributions from some of the parameters considered in scale realizations was also demonstrated using the measurement results.