Gregory F. Strouse

Ultra-sensitive chip-based photonic temperature sensor using ring resonator structures

Resistance thermometry provides a time-tested method for taking temperature measurements. However, fundamental limits to resistance-based approaches has produced considerable interest in developing photonic temperature sensors to leverage advances in frequency metrology and to achieve greater mechanical and environmental stability. Here we show that silicon-based optical ring resonator devices can resolve temperature differences of 1 mK using the traditional wavelength scanning methodology. An even lower noise floor of 80 μK for measuring temperature difference is achieved in the side-of-fringe, constant power mode measurement.

Final Report on CCT-K7: Key comparison of water triple point cells

The triple point of water serves to define the kelvin, the unit of thermodynamic temperature, in the International System of Units (SI). Furthermore, it is the most important fixed point of the International Temperature Scale of 1990 (ITS-90). Any uncertainty in the realization of the triple point of water contributes directly to the measurement uncertainty over the wide temperature range from 13.8033 K to 1234.93 K. The Consultative Committee for Thermometry (CCT) decided at its 21st meeting in 2001 to carry out a comparison of water triple point cells and charged the BIPM with its organization. Water triple point cells from 20 national metrology institutes were carried to the BIPM and were compared with highest accuracy with two reference cells. The small day-to-day changes of the reference cells were determined by a least-squares technique. Prior to the measurements at the BIPM, the transfer cells were compared with the corresponding national references and therefore also allow comparison of the national references of the water triple point. This report presents the results of this comparison and gives detailed information about the measurements made at the BIPM and in the participating laboratories. It was found that the transfer cells show a standard deviation of 50 ?K; the difference between the extremes is 160 ?K. The same spread is observed between the national references. The most important result of this work is that a correlation between the isotopic composition of the cell water and the triple point temperature was observed. To reduce the spread between different realizations, it is therefore proposed that the definition of the kelvin should refer to water of a specified isotopic composition. The CCT recommended to the International Committee of Weights and Measures (CIPM) to clarify the definition of the kelvin in the SI brochure by explicitly referring to water with the isotopic composition of Vienna Standard Mean Ocean Water (VSMOW). The CIPM accepted this recommendation and the next edition of the SI brochure will include this specification. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Observations on sub-range inconsistency in the SPRT interpolations of ITS-90

The properties of the sub-range inconsistency (SRI or Type-I non-uniqueness) of the standard platinum resistance thermometer (SPRT) sub-ranges of the International Temperature Scale of 1990 (ITS-90) are investigated. Mathematically, SRI has the form of an interpolation error with zeros at each of the fixed points shared by the two interpolating equations, and a magnitude dependent on the differences in the ratios (Wr − 1)/(W − 1) for each of the fixed points, where W is the resistance ratio R(T)/R(0.01 °C) and Wr is the reference resistance ratio defined by ITS-90. The calibration results for a set of 60 SPRTs were analysed to determine the SRI for the water–zinc and water–aluminium sub-ranges. The maximum SRI occurs near 93.15 °C, and has an average value of 0.12 mK and a standard deviation of 0.48 mK. The reciprocal of the ratio (Wr − 1)/(W − 1), which is proportional to the sensitivity of the SPRT, was found to be 1.0 ± 0.0004 for all 60 SPRTs, and was within 0.00005 for all fixed points for any one SPRT. This suggests that a single constraint on the value of the ratio might be a more useful and discerning SPRT-quality constraint than the current three ITS-90 constraints.

Performance of a dual Fabry–Perot cavity refractometer

We have built and characterized a refractometer that utilizes two Fabry-Perot cavities formed on a dimensionally stable spacer. In the typical mode of operation, one cavity is held at vacuum, and the other cavity is filled with nitrogen gas. The differential change in length between the cavities is measured as the difference in frequency between two helium-neon lasers, one locked to the resonance of each cavity. This differential change in optical length is a measure of the gas refractivity. Using the known values for the molar refractivity and virial coefficients of nitrogen, and accounting for cavity length distortions, the device can be used as a high-resolution, multi-decade pressure sensor. We define a reference value for nitrogen refractivity as n-1=(26485.28±0.3)×10(-8) at p=100.0000  kPa, T=302.9190  K, and λ(vac)=632.9908  nm. We compare pressure determinations via the refractometer and the reference value to a mercury manometer.

Progress in Primary Acoustic Thermometry at NIST: 273 K to 505 K

The NIST Acoustic Thermometer determines the thermodynamic temperature by measuring the speed of sound of argon in a spherical cavity. We obtained the thermodynamic temperature of three fixed points on the International Temperature Scale of 1990: the melting point of gallium [T(Ga) = 302.9146 K] and the freezing points of indium [T(In) = 429.7485 K] and tin [T(Sn) = 505.078 K]. The deviations of thermodynamic temperature from the ITS‐90 defined temperatures are T − T90 = (4.7 ± 0.6) mK at T(Ga) , T − T90 = (8.8 ± 1.5) mK at T(In) , and T − T90 = (10.7 ± 3.0) mK at T(Sn) , where the uncertainties are for a coverage factor of k = 1. Our results at T(In) and T(Sn) reduce the uncertainty of T − T90 by a factor of two in this range. Both T − T90 at T(Ga) and the measured thermal expansion of the resonator between the triple point of water and T(Ga) are in excellent agreement with the 1992 determination at NIST. The dominant uncertainties in the present data come from frequency‐dependent and time‐dependent cros...

Effects of different methods of preparation of ice mantles of triple point of water cells on the temporal behaviour of the triple-point temperatures

We report results of an investigation of the temporal variation of the temperature of triple point of water (TPW) cells, in which the ice mantles were prepared by four different techniques using: (i) solid CO2, (ii) an immersion cooler, (iii) liquid-nitrogen-cooled rods, and (iv) liquid nitrogen (LN), first passing cold nitrogen vapours and then LN directly into the wells of the cells. The temperature of the TPW cell water was either approximately 274 K or 295 K when the freezing of the ice mantle was started. No visible cracks formed during the preparation of any of the mantles using the crushed solid-CO2 or the immersion cooler method, but all of the ice mantles cracked when prepared using the LN-cooled-rod and LN techniques. The cracked mantles, however, soon healed. Initially, the temperatures of the mantles prepared by the four methods varied, but after about three or four days they agreed to within 0,1 mK; after one week they agreed to within 0,03 mK, except for mantles prepared by the LN technique, for which nine days were once required for one of the mantles; after eleven days, the results were practically the same. It appears that the temperature variations observed during the first few days following the preparation of mantles could be caused by a combination of (i) temperature decrease due to introduction of strains in the ice and to formation of fine ice crystals during the preparation of the mantle and (ii) temperature increase due to the relief of strains and the gradual conversion of fine ice crystals to larger ice crystals. Mantles that underwent severe cracking thereby released most of the energy associated with the large strains introduced during preparation of the mantle.

Techniques for Primary Acoustic Thermometry to 800 K

The NIST Primary Acoustic Thermometer will measure the difference between the International Temperature Scale of 1990 and the Kelvin Thermodynamic Scale throughout the range 273 K to 800 K with uncertainties of only a few millikelvins. The acoustic thermometer determines the frequencies of the acoustic resonances of pure argon gas contained within a spherical cavity with uncertainties approaching one part in 106. To achieve this small uncertainty at these elevated temperatures we developed new acoustic transducers and new techniques for the maintenance of gas purity and for temperature control. The new electro‐acoustic transducers are based on the capacitance between a flexible silicon wafer and a rigid backing plate. Without the damping usually provided by polymers, mechanical vibrations caused unstable, spurious acoustic signals. We describe our techniques for suppression of these vibrations. Our acoustic thermometer allows the argon to be continuously flushed through the resonator, thereby preventing t...

Performance Assessment of Resistance Ratio Bridges used for the Calibration of SPRTs

Automatic balancing dc and ac resistance ratio bridges are the primary measurement devices used by National Measurement Institutes for the calibration of standard platinum resistance thermometers (SPRTs) on the International Temperature Scale of 1990 (ITS‐90). Performance assessment of these resistance ratio bridges is critical to the determination of both the uncertainties of the measurements and for identifying if a resistance bridge is exhibiting non‐compliant behavior. NIST and NRC investigated the performance of 18 resistance ratio bridges consisting of 14 ASL F18s, 2 ASL F900s, and 2 MI 6010Bs. The assessment techniques included the use of an AEONZ resistance bridge calibrator, an ASL ratio test unit, and complements checks. Additionally, the possible effects from using different ac frequencies were investigated. This paper presents the methods of assessment employed, indicates the performance results obtained for the 18 resistance ratio bridges, describes the determination of measurement uncertaint...

Fiber Bragg Gratings Embedded in 3D-Printed Scaffolds

Abstract: In recent years there has been considerable interest in utilizing embedded fiber optic based sensors for fabricating smart materials. One of the primary motivations is to provide real-time information on the structural integrity of the material so as to enable proactive actions that prevent catastrophic failure. In this preliminary study we have examined the impact of embedding on the temperature-dependent response of fiber Bragg gratings (FBG). Our results indicate that scaffold strain has a significant impact on the embedded sensors temperature response. Thus, the use of embedded sensors will require the development of in corpus techniques that can calibrate sensors while they are embedded.

Effects of Heavy Hydrogen and Oxygen on the Triple‐Point Temperature of Water

The temperature of the triple point of water is dependent on the isotopic composition of the water. The depletion of heavy isotopes arising from the use of fresh water rather than seawater, and from distillation and degassing of the water during manufacture of the cells, leads to cells realizing temperatures up to 80 μK lower than the definition. Five cells of varying isotopic composition were compared to evaluate the practicality of applying corrections for isotopic composition. It was found that the correction constants for deuterium and 18O measured previously by Kiyosawa were consistent with the measurements of the cells. Both of the correction constants are larger than predicted by interpolation between the triple‐point temperatures of the pure isotopomers. Application of the corrections for isotopic composition eliminates a significant bias in the triple‐point temperature and reduces the uncertainty in the triple‐point temperature due to isotopic composition from ±40 μK to better than ±3 μK.