Howard W. Yoon

Calibrated Thermal Microscopy of the Tool–Chip Interface in Machining

This paper presents the results of calibrated, microscopic measurement of the temperature fields at the tool–chip interface during the steady‐state, orthogonal machining of AISI 1045 steel. The measurement system consists of an infrared imaging microscope with a 0.5 mm square target area, and a spatial resolution of less than 5 µm. The system is based on an InSb 128 × 128 focal plane array with an all‐reflective microscope objective. The microscope is calibrated using a standard blackbody source from NIST. The emissivity of the machined material is determined from the infrared reflectivity measurements. Thermal images of steady state machining are measured on a diamond‐turning class lathe for a range of machining parameters. The measurements are analyzed by two methods: 1) energy flux calculations made directly from the thermal images using a control–volume approach; and 2) a simplified finite‐difference simulation. The standard uncertainty of the temperature measurements is ± 52°C at 800°C.

Realization of the National Institute of Standards and Technology Detector-Based Spectral Irradiance Scale

A detector-based spectral irradiance scale has been realized at the National Institute of Standards and Technology (NIST). Unlike the previous NIST spectral irradiance scales, the new scale is generated with filter radiometers calibrated for absolute spectral power responsivity traceable to the NIST high-accuracy cryogenic radiometer instead of with the gold freezing-point blackbody. The calibrated filter radiometers are then used to establish the radiance temperature of a high-temperature blackbody (HTBB) operating near 3,000 K The spectral irradiance of the HTBB is then determined with knowledge of the geometric factors and is used to assign the spectral irradiances of a group of 1,000-W free-electron laser lamps. The detector-based spectral irradiance scale results in the reduction of the uncertainties from the previous source-based spectral irradiance scale by at least a factor of 2 in the ultraviolet and visible wavelength regions. The new detector-based spectral irradiance scale also leads to a reduction in the uncertainties in the shortwave infrared wavelength region by at least a factor of 2-10, depending on the wavelength. Following the establishment of the spectral irradiance scale in the early 1960s, the detector-based spectral irradiance scale represents a fundamental change in the way that the NIST spectral irradiance scale is realized.

Methods to reduce the size-of-source effect in radiometers

In radiometry, photometry and radiation thermometry, accurate measurements of the radiance, luminance or the radiance temperatures of sources requires a knowledge of the contribution from the surroundings to the measured signal from the target area. The dependence of the radiometer or the radiation thermometer on the area surrounding the target area is described as the size-of-source effect (SSE), and minimizing the radiometers sensitivity to SSE is critical in the lowest-uncertainty optical measurements. We describe the dominant effects that influence the SSE, and show that the SSE can be reduced to <5 ? 10?5 as measured using a 50?mm diameter radiance source with a 2?mm diameter, central obscuration. The SSE is found to be dependent on the internal scatter and the optical design of the radiometer. For testing the contributions to SSE, a radiometer is constructed with a 50.8?mm diameter lens in f/12 geometry with a 1?mm diameter target size. If the internal radiometer scatter is reduced, then the SSE is found to be primarily dependent on the scatter from the objective lens such as surface finish, internal lens scatter and the particulate contamination of the lens. Various combinations of objective lenses are measured for SSE, and the relative merits of increasing optical performance at the expense of additional optical elements are also discussed.

Linearity of InGaAs photodiodes

In radiometry or pyrometry, radiometers are often used to assign the spectral radiance or radiance temperatures of sources using ratios of signals which can differ by several decades. For performing ratios between such sources with low uncertainties, the linearity of the detectors used in the transfer radiometers needs to be characterized. The linearity of InGaAs photodiodes has been studied using the flux-addition method using a broadband infrared source with a visible-blocking filter. Using this technique, 18 InGaAs photodiodes from four different vendors were studied without spectral filtering in a broad wavelength region from 900 nm to 1700 nm with the diodes underfilled by the incident flux. The linearity of InGaAs photodiodes was determined within the range of photocurrents from 10−8 A to 10−4 A. All the InGaAs photodiodes demonstrated linearity from 10−7 A to 10−4 A within the expanded uncertainties of 0.08% (k = 2). The uncertainty in the linearity measurement below 10−8 A is increased due to the increased noise in the photocurrent arising from the feedback resistance of the transimpedance amplifier being greater than the shunt resistance of the photodiode.

The kelvin redefinition and its mise en pratique

In 2018, it is expected that there will be a major revision of the International System of Units (SI) which will result in all of the seven base units being defined by fixing the values of certain atomic or fundamental constants. As part of this revision, the kelvin, unit of thermodynamic temperature, will be redefined by assigning a value to the Boltzmann constant k. This explicit-constant definition will define the kelvin in terms of the SI derived unit of energy, the joule. It is sufficiently wide to encompass any form of thermometry. The planned redefinition has motivated the creation of an extended mise en pratique (‘practical realization’) of the definition of the kelvin (MeP-K), which describes how the new definition can be put into practice. The MeP-K incorporates both of the defined International Temperature Scales (ITS-90 and PLTS-2000) in current use and approved primary-thermometry methods for determining thermodynamic temperature values. The MeP-K is a guide that provides or makes reference to the information needed to perform measurements of temperature in accord with the SI at the highest level. In this article, the background and the content of the extended second version of the MeP-K are presented.

Thermodynamic-temperature determinations of the Ag and Au freezing temperatures using a detector-based radiation thermometer

The development of a radiation thermometer calibrated for spectral radiance responsivity using cryogenic, electrical-substitution radiometry to determine the thermodynamic temperatures of the Ag- and Au-freezing temperatures is described. The absolute spectral radiance responsivity of the radiation thermometer is measured in the NIST Spectral Irradiance and Radiance Responsivity Calibrations using Uniform Sources (SIRCUS) facility with a total uncertainty of 0.15% (k=2) and is traceable to the electrical watt, and thus the thermodynamic temperature of any blackbody can be determined by using Planck radiation law and the measured optical power. The thermodynamic temperatures of the Ag- and Au-freezing temperatures are determined to be 1234.956 K (+/-0.110 K) (k=2) and 1337.344 K(+/-0.129 K) (k=2) differing from the International Temperature Scale of 1990 (ITS-90) assignments by 26 mK and 14 mK, respectively, within the stated uncertainties. The temperatures were systematically corrected for the size- of-source effect, the nonlinearity of the preamplifier and the emissivity of the blackbody. The ultimate goal of these thermodynamic temperature measurements is to disseminate temperature scales with lower uncertainties than those of the ITS-90. These results indicate that direct disseminations of thermodynamic temperature scales are possible.

The realization of the NIST detector-based spectral irradiance scale

The realization of a detector-based spectral irradiance scale at the National Institute of Standards and Technology is described. The new scale is established using filter radiometers calibrated for absolute spectral power responsivity traceable to the NIST High-Accuracy Cryogenic Radiometer unlike the previous NIST spectral irradiance scales based upon the gold freezing-point blackbody. The radiance temperatures of a high-temperature blackbody (HTBB) operating near 3000 K are found using calibrated filter radiometers. The spectral irradiances of a group of 1000 W FEL lamps are assigned using the spectral irradiance of the HTBB determined using the knowledge of the geometric factors and the detector-based radiance temperatures. The detector-based spectral irradiance scale leads to a reduction in the uncertainties from the previous, source-based, spectral irradiance scales by at least a factor of two in the ultraviolet and visible wavelength regions, and also leads to a reduction in the uncertainties in the short-wave infrared wavelength region by at least a factor of two to ten, depending on the wavelength. Following the establishment of the spectral irradiance scale in the early 1960s, the detector-based spectral irradiance scale represents a fundamental change in the way that the NIST spectral irradiance scale is realized, and beginning in the calendar year 2001, all spectral irradiance sources are issued using the detector-based scale.

Spectral Radiance Comparisons of Two Blackbodies with Temperatures Determined Using Absolute Detectors and ITS‐90 Techniques

For calibrations of spectral irradiance standards, a high‐temperature blackbody (HTBB) is used as a source of spectral radiance or irradiance as derived from Planck’s radiance law. The temperature of such a blackbody can be determined using radiance ratios to the gold freezing‐temperature blackbody based on the technique described in the International Temperature Scale of 1990 (ITS‐90), or by using a primary thermometer, which is an absolute detector referenced to a cryogenic radiometer. One of the primary motivations of using the detector‐based method is that the uncertainties in the temperature determination of a HTBB can be lower than those assigned using ITS‐90. Previous comparisons of temperatures measured using the two techniques have been at a few, selected wavelengths due to the limited measurement wavelengths of the comparison pyrometer. In this study, the spectral radiances of a HTBB from 250 nm to 2400 nm are assigned using a spectroradiometer from the known spectral radiances of a variable‐tem...

Radiometric measurement comparisons using transfer radiometers in support of the calibration of NASA's Earth Observing System (EOS) sensors

EOS satellite instruments operating in the visible through the shortwave infrared wavelength regions (from 0.4 micrometer to 2.5 micrometer) are calibrated prior to flight for radiance response using integrating spheres at a number of instrument builder facilities. The traceability of the radiance produced by these spheres with respect to international standards is the responsibility of the instrument builder, and different calibration techniques are employed by those builders. The National Aeronautics and Space Administrations (NASAs) Earth Observing System (EOS) Project Science Office, realizing the importance of preflight calibration and cross-calibration, has sponsored a number of radiometric measurement comparisons, the main purpose of which is to validate the radiometric scale assigned to the integrating spheres by the instrument builders. This paper describes the radiometric measurement comparisons, the use of stable transfer radiometers to perform the measurements, and the measurement approaches and protocols used to validate integrating sphere radiances. Stable transfer radiometers from the National Institute of Standards and Technology, the University of Arizona Optical Sciences Center Remote Sensing Group, NASAs Goddard Space Flight Center, and the National Research Laboratory of Metrology in Japan, have participated in these comparisons. The approaches used in the comparisons include the measurement of multiple integrating sphere lamp levels, repeat measurements of select lamp levels, the use of the stable radiometers as external sphere monitors, and the rapid reporting of measurement results. Results from several comparisons are presented. The absolute radiometric calibration standard uncertainties required by the EOS satellite instruments are typically in the plus or minus 3% to plus or minus 5% range. Preliminary results reported during eleven radiometric measurement comparisons held between February 1995 and May 1998 have shown the radiance of integrating spheres agreed to within plus or minus 2.5% from the average at blue wavelengths and to within plus or minus 1.7% from the average at red and near infrared wavelengths. This level of agreement lends confidence in the use of the transfer radiometers in validating the radiance scales assigned by EOS instrument calibration facilities to their integrating sphere sources.

Versatile light-emitting-diode-based spectral response measurement system for photovoltaic device characterization.

An absolute differential spectral response measurement system for solar cells is presented. The system couples an array of light emitting diodes with an optical waveguide to provide large area illumination. Two unique yet complementary measurement methods were developed and tested with the same measurement apparatus. Good agreement was observed between the two methods based on testing of a variety of solar cells. The first method is a lock-in technique that can be performed over a broad pulse frequency range. The second method is based on synchronous multifrequency optical excitation and electrical detection. An innovative scheme for providing light bias during each measurement method is discussed.