Chapter 4 Radiation Thermometer Designs

Abstract

Publisher Summary The chapter discusses the instrument design and characterization of spot-radiation thermometers, capable of transferring temperature scales with the lowest uncertainties. Radiation thermometers can be calibrated using the International Temperature Scale of 1990 (ITS-90) or using absolute radiometry for thermodynamic temperature determinations, although the latter is still rare. The chapter discusses radiation thermometers that operate in the visible to the near-infrared wavelength regions. The choice of the detector, optimization of the detector for stability and linearity, and characterization of radiation thermometers for size-of-source effect (SSE) are discussed. The primary consideration in the design of a radiation thermometer is the desired range of operational temperatures. The chapter presents a figure that shows the Planck radiances for blackbodies ranging in temperatures from the freezing point of indium, or 430 K, to 3,000 K. Radiation thermometers typically has either a reflective optic or a refractive lens to collect the radiation and to define the angular field of view (AOV) and the target size. Photodiodes are photovoltaic detectors that usually have advantageous electronic and radiometric characteristics. The chapter also presents the simplest version of a widely used photocurrent meter. Radiation thermometers that operate in the visible or the near-infrared wavelength region are typically constructed using spectral filters to restrict the incident radiation on the diode to a selected wavelength region. The spectral filters can be constructed using interference layers deposited on glass substrates or using broadband absorbing glasses. The chapter also discusses radiation thermometry below the silver point, calibration of radiation thermometers using ITS-90, thermodynamic temperature measurements using radiometric techniques, and so on.