Jun Tamba

Deep Ocean Temperature Measurement with an Uncertainty of 0.7 mK

AbstractThe uncertainty of deep ocean temperature (~1°C) measurement was evaluated. The time drifts of six deep ocean standards thermometers were examined based on laboratory calibrations as performed by the manufacturer in triple point of water (TPW) cells and gallium-melting-point (GaMP) cells. The time drifts ranged from −0.11 to 0.14 mK yr−1. Three of the six thermometers were evaluated at the National Metrology Institute of Japan in five TPW cells and a GaMP cell, and the temperature readings agreed with the realized temperature of the national standard cells of Japan within ±0.14 and ±0.41 mK for TPW and GaMP, respectively. The pressure sensitivities of the deep ocean standards thermometers were estimated by comparison with conductivity–temperature–depth (CTD) thermometers in the deep ocean, and no notable difference was detected. Pressure sensitivities of the two CTD thermometers were examined by laboratory tests, and the results suggest that the deep ocean standards thermometers have no pressure s...

Effects of Heat Treatment on the Inhomogeneity of the Pt/Pd Thermocouple at the Cu Freezing Point

The drift in emf of Pt/Pd thermocouples during successive calibrations at the Cu freezing point was measured. Twelve thermocouples were constructed using wires from a single lot, and a different heat treatment was performed on each thermocouple before the calibration. The purity of the Pt and Pd wires used were 99.999 % and 99.99+ %, respectively. The magnitude of the drift and the inhomogeneity of the thermocouples depended on the heat treatment. The heat treatment at 850 °C or 1030 °C for 100 h resulted in the minimum drift and inhomogeneity.

Johnson Noise Thermometry Based on Integrated Quantum Voltage Noise Source

We performed Johnson noise thermometry (JNT) using an integrated quantum voltage noise source (IQVNS) that generates pseudorandom noise with an RMS value determined by the product of the flux quantum, the clock frequency of IQVNS, fclk, and a calculable coefficient. The working principle is different from the conventional QVNS. The waveform of the IQVNS was analyzed thoroughly, and the source checked to see that it worked properly as intended, particularly in regard to its applicability as a reference for JNT measurements. The thermal noise power of a resistor at the triple point of water was measured with the IQVNS to derive a value of the Boltzmann constant.

Effect of temperature distribution on EMF of thermocouples

A furnace was constructed to investigate the effect of temperature distribution on the EMF change caused by the inhomogeneity in each individual thermocouple. The EMF change of the inhomogeneous Pt/Pd thermocouple was observed by scanning the thermocouple in the temperature gradient region.

Study on the realization of indium point

Indium-point cells were fabricated in NMIJ/AIST using high grade indium samples purchased from some different metal sources. The quality of the indium-point cells were evaluated by conducting temperature measurements during the solid-liquid equilibrium condition, under which the indium fixed-point is defined. Comparisons of fixed-point temperature realized within the cells including the conventional and the newly developed ones were also conducted. The results of these comparisons, termed as direct cell comparisons, as well as the above mentioned temperature measurements under the solid-liquid equilibrium were used to evaluate the effect of impurities to the realization of the indium point. The present paper outlined the cell fabrication, the temperature measurements and the evaluation of impurity effect to the indium point realization.

Pressure‐Controlled Water Heat Pipe for Investigation of the Non‐Uniqueness of the ITS‐90 in the Range from 65 °C to 157 °C

A comparison measurement system based on a pressure‐controlled water heat pipe was developed to investigate the non‐uniqueness of the International Temperature Scale of 1990 (ITS‐90) in the range from 65 °C to 157 °C. Its characteristics, such as the temperature stability and temperature uniformity, were measured, and the uncertainty of each source was estimated. The uncertainty of comparison measurements is only due to the temperature stability, which is within 0.034 mK. Preliminary measurements of the non‐uniqueness were performed using six standard platinum resistance thermometers of the same model. The non‐uniqueness plots show agreement within a maximum width of 0.08 mK, and they are within the uncertainty of the measurements of 0.05 mK (k=2). These results indicate that the developed system can adequately detect the non‐uniqueness of the ITS‐90 in the water heat‐pipe range.

Development of thermodynamic temperature measurement technique based on quantum standards at NMIJ/AIST

We have started development of a thermodynamic temperature measurement system based on Johnson-Nyquist equation. In this measurement power spectrum density of a resistor is measured using electrical quantum standards as references. This thermometer will play an important role in determination of the Boltzmann constant, comparison between thermodynamic temperature and definitions in International Temperature Scale of 1990, and measurement of arbitrary temperature in a wide temperature range.

Study on the realization of tin point

Tin-point cells were fabricated using high grade tin samples purchased from some different metal sources. Temperature measurements during the solid-liquid equilibrium condition, under which the tin point is defined, were conducted for evaluating the quality of the cells. Different methods for the realization of tin point were compared by means of the fabricated cells. Comparisons of tin-point temperatures realized using the conventional and the newly developed cells were also conducted. On the other hand, chemical assay provided by the tin sample manufacturer was used to estimate the tin point departure from that ideally defined by the International Temperature Scale of 1990 (ITS-90). The tin point departure, the cell comparison results and the analysis of the temperature measurements during the solid-liquid phase change were discussed for estimating the uncertainty of tin-point realization due to impurity existence. The present paper outlines the apparatus which includes the tin cell and the furnace, the temperature measurements and the evaluation of impurity effect to the tin point realization.

Anomalous behavior of a tin point cell

At NMIJ, AIST, ensembles of fixed point cells are maintained for each defining fixed point to underpin the confidence for the maintenance of the national standards for thermometry. As a routine work, fixed point cells for the same temperature are realized simultaneously and the temperature differences between them are measured when the liquid fraction (1/F) is between 1 and 2. An anomalous temperature difference of approximately 0.2 mK was observed for one tin point cell. In this paper, we report the details of this anomalous temperature difference, and also the analysis to elucidate its cause. We assume that such anomalous behavior probably occurred due to condensation of impurities by employing a specific realization method repeatedly. Also we present that the anomalous behavior appears to be resolved by adopting another realization method during the experiments conducted under the present work.

Development and evaluation of the tin point in the ITS-90

The freezing point of tin, one of the temperature fixed-points defined in the ITS-90, is newly developed and evaluated. The temperature stability of the furnace is within /spl plusmn/1.5 mK for 24 hours and temperature distribution is within 2 mK over 20 cm. To realize a stable plateau after a large amount of supercooling, the air blow cooling method is introduced instead of the conventional method. The temperature during the plateaus decreases only 0.3 mK for 8 hours and a good repeatability within /spl plusmn/0.026 mK is obtained in ten measurements.