For the measurements of radiance temperatures in the range from 150 ?C to 1000 ?C, low uncertainties in the temperature measurements can be achieved by using near-infrared InGaAs radiation thermometers. We describe the design and construction of the NIST near-infrared radiation thermometer (NIRT) which is optimized for low size-of-source effect and noise-equivalent temperatures. The NIRT utilizes a 50 mm diameter achromatic objective lens with low scatter that images a 4.5 mm diameter spot at a distance of 50 cm away from the objective in an on-axis design. A Lyot stop is implemented in the design with the aperture stop placed after the field stop resulting in a collection f/12. A 3 mm diameter InGaAs detector is cooled to 85 ?C using a 4-stage thermoelectric cooler to obtain high-shunt resistance for linear, low-noise operation at high transimpedance amplifier gains. For thermal and structural stability, the optical components are placed on four, 15 mm diameter graphite-epoxy rods making the optical throughput stable. Optical ray tracing with a commercial program was used to determine the Strehl ratio and other imaging parameters. We discuss a possible approach for a detector-based temperature scale in this range which could result in 10 mK (k = 2) thermodynamic temperature uncertainties at the In-point.
Citation: International Journal of Thermophysics
Pub Type: Journals
ITS-90, near-infrared radiation thermometer, noise-equivalent temperature difference, radiance temperature, size-of-source effect