International Practical Temperature Scale Of 1968 Research Articles

On the conversion of thermodynamic properties to the basis of the International Temperature Scale of 1990

The basis and application of the Douglas equations for the adjustment and calculation of differences in thermodynamic properties due to a change in the temperature scale are reviewed. When higher-order terms in the general Douglas equations are discarded, the simplified Douglas equations are obtained. These simplified equations together with the recently revised set of differences between values of temperatures on the International Temperature Scale of 1990 (ITS-90) and the corresponding values on the International Practical Temperature Scale of 1968 (IPTS-68) for 903.765 K<T90<1337.33 K have been used to calculate approximate differences in thermodynamic properties for synthetic sapphire (α-A/2O3). Tables of differences (T90–T68)/K and the derivatives d(T90–T68)/dTare given as a function ofT68/K.

The Platinum Resistance Thermometer Range of the International Temperature Scale of 1990

Within the International Temperature Scale of 1990 (ITS-90) the platinum resistance thermometer (PRT) is used to realize the scale from approximately 13,8 K to 1 235 K. Such a temperature range is wider than the corresponding range in the International Practical Temperature Scale of 1968 (IPTS-68) because the PRT is used up to the freezing point of silver (1 234,93 K). In this way, the ITS-90 can be realized with much more precision than the IPTS-68, particularly between 901 K and 1 235 K where the standard Pt-10% Rh vs Pt thermocouple was previously used.This paper describes some important steps in the construction of the PRT reference function and the criteria for the selection of the PRT interpolating equations of the ITS-90. In contrast to previous international scales, the PRT range of the ITS-90 is based on two reference functions, one from 13,8 K to 273,16 K and the other from 273,15 K to 1 234,93 K. The two reference functions were obtained from two real PRTs.A set of interpolating equations is used to account for the differences of other real PRTs from those on which the reference functions are based. They provide flexibility of calibration and high precision as expressed, for instance, by non-uniqueness and sub-range inconsistency not exceeding 0,5 mK over the range from 13,8 K to 693 K. Such good properties are the consequence of the choice of suitable forms for the interpolating equations and of fine adjustments in the values assigned to some defining fixed points.

The international temperature scale of 1990 (ITS-90)

On 1st January 1990 the International Temperature Scale of 1990 (ITS-90) will come into force. This brief article describes the new scale and gives the differences between temperatures measured on ITS-90 and those measured on the current international scale, the International Practical Temperature Scale of 1968 (IPTS-68).

Spectroradiometric Determination of the Freezing Temperature of Gold.

A direct spectroradiometric determination of the temperature of freezing gold was performed by measuring the spectral radiances of a gold blackbody relative to those of a laser-irradiated integrating sphere which was calibrated with absolute silicon detectors and an electrically calibrated radiometer. The measurements were performed at three laser wavelengths near 600 nm, and the temperature of the blackbody was calculated by substituting the measured spectral radiances into Planck’s radiation formula. The result obtained, TAu=(1337.33± 0.34) K, is 0.25 K below the gold-point assignment in the International Practical Temperature Scale of 1968 (IPTS-68) and has been adopted in September 1990 as the new gold-point value in the International Temperature Scale of 1990 (ITS-90). The effect of this change in the gold-point assignment on pyrometric, radiometric, and photometric measurement services provided by the National Institute of Standards and Technology is assessed.

Differences between Thermodynamic Temperature and t (IPTS-68) in the Range 230°C to 660°C

Determination of the differences between the Kelvin Thermodynamic Temperature Scale (KTTS) and the International Practical Temperature Scale of 1968 (IPTS-68) in the range from 230°C to 660°C has been accomplished by gas thermometry. The estimated random uncertainty of the results ranges from ±0.005°C to ±0.008°C; the major uncertainties appear to lie in the determination of the volume of the gas bulb and the determination of its IPTS-68 temperature. The present results differ noticeably from earlier gas-thermometric determinations in the range of temperature overlap. The value found for the thermodynamic temperature of the freezing point of Al is (660.342 ± 0.015)°C.

A microcomputer-based instrument for applications in platinum resistance thermometry

Platinum resistance thermometers are widely used in temperature measurements not only for calibration purposes but also in industrial applications. A new automatic instrument is described which can determine the actual value of the resistance of a platinum resistance thermometer in less than 0.52 s with a resolution of 8 PPM. The self-heating index can also be determined and the instrument is able to multiplex up to eight different platinum resistances. The temperature is calculated by using the interpolation formulae defined by the International Practical Temperature Scale of 1968 (IPTS-68).

The succinonitrile triple-point standard: a fixed point to improve the accuracy of temperature measurements in the clinical laboratory.

In an investigation of the melting and freezing behavior of succinonitrile, the triple-point temperature was determined to be 58.0805 degrees C, with an estimated uncertainty of +/- 0.0015 degrees C relative to the International Practical Temperature Scale of 1968 (IPTS-68). The triple-point temperature of this material is evaluated as a temperature-fixed point, and some clinical laboratory applications of this fixed point are proposed. In conjunction with the gallium and ice points, the availability of succinonitrile permits thermistor thermometers to be calibrated accurately and easily on the IPTS-68.

Development at the Institut National de Métrologie of sealed cells as IPTS fixed points

Several years ago, the Institut National de Métrologie (INM) began using sealed cells to determine the triple points, melting or freezing points of the International Practical Temperature Scale of 1968 (IPTS-68). Details have appeared in Bonnier and Malassis (1975), Bonnier and Hermier (1978 and 1980). The aim of this paper is to review the different INM cells and the method of using them. Reasons are given why some substances can be studied easily with a permanent flux of heat and why others can be studied only with a calorimetric method. The results will lead to an explanation of the differences between the designs of the cells. It should be recorded that part of the work described was performed at the National Institute of Metrology of Peking, China, by Messrs Ling Shin King and Wou Bi Jin.

A digitally linearized thermistor thermometer referenced to IPTS-68.

We describe a digitally linearized thermistor thermometer that is accurate to +/- 0.01 degrees C from 0 to 60 degrees C at a wattage of 50 microW and a sampling time of 1 s. It is traceable to the International Practical Temperature Scale of 1968 (IPTS-68). Analog and digital outputs are provided, the latter as ASCII RS-232C. The thermistor is a 10-cm long immersible probe, 1.5 mm in diameter. Only 0.5 cm of the probe need be immersed, with proper heat sinking of at least 1 cm of the remaining 9.5 cm, for accurate readings. Error from self-heating of the thermistor is less than 5X 10(-3) degrees C at all power settings from 50 to 1 microW.

Thermometric Fixed Points of Hydrogen

The vapour pressure versus temperature relationship for equilibrium H2 was obtained between its normal boiling and melting points. It was found that impurities other than Ne have no effect on the vapour pressure behaviour, presumably because the non-volatile impurities freeze out onto the cold walls of the apparatus and the only volatile impurity, He, appears to be insoluable in H2 and thus can easily be removed by pumping. The effect of catalysis on the rate of ortho-paraconversion was extensively investigated. It was found that the catalyst should be in contact with most of the sample at low temperatures, if stirring is not possible, in order that conversion takes place rapidly. Catalyst in contact with part of the condensed sample only does not work efficiently, probably because of the slow rate of ortho-para interdiffusion. The triple point pressures were found to be 52.763 mmHg (7034.5 N/m2) and 54.082 mmHg (7210.3 N/m2) for equilibrium and normal H2 respectively. The temperatures of the normal boiling and triple points of normal H2 were found to be 117 mK and 148 mK higher respectively than those of equilibrium H2.Boiling points (at 76 and 25 cmHg vapour pressures) and the triple point of equilibrium hydrogen are all defining fixed points on the International Practical Temperature Scale of 1968 (IPTS-68). This paper describes some experiments performed at the National Research Council of Canada aimed at realizing these thermometric fixed points. In addition vapour pressure versus temperature behaviour for liquid H2 samples of differing purities was also investigated.

The International Practical Temperature Scale of 1968 in the Region 90.188 K to 903.89 K as Maintained at the National Bureau of Standards.

The reproducibility of the International Practical Temperature Scale of 1968 (IPTS-68) in the region 90.188 K to 903.89 K as maintained at the National Bureau of Standards is discussed. The realizations of the triple point of water, the freezing points of zinc and tin, and the boiling point of oxygen are described. The average of the standard deviations of the resistance measurements at the triple point of water of 213 platinum resistance thermometers received for calibration over a two-year period corresponds to ±0.15 mK. The standard deviations of the resistance ratio R(T)/R(0°C) obtained with check thermometers employed for monitoring the zinc, tin, and oxygen point measurements correspond to ±0.28 mK, ±0.30 mK, and ±0.16 mK, respectively; the results of repeated calibrations with five thermometers show comparable reproducibility at the tin and oxygen points but the reproducibility is worse by a factor of two at the zinc point. When suitably packed for protection from possible mechanical shock platinum resistance thermometers can be shipped by common carrier and retain their calibrations.

Thermodynamic temperature and IPTS-68

Thermodynamic temperature and IPTS-68

A Magnetic Temperature Scale from 1 to 83 K

The low frequency (30 Hz) paramagnetic susceptibilities of powdered samples of gadolinium sulphate octahydrate and manganous ammonium sulphate hexahydrate have been measured from 1 to 83 K in order to test the thermodynamic consistency of the International Practical Temperature Scale of 1968 (IPTS-68). The data can be characterized by a physically based expression with essentially two constants as opposed to the twenty-one terms of the IPTS-68 Reference Function for the range 13.81 K to 273.15 K. Variations in the IPTS-68 of up to ± 3 mK about the smooth magnetic scale are found and the 20.28 K (e-H2 b.p.) fixed point is shown to be inconsistent with the other fixed points by about +3 mK. The data also provide a means of thermodynamically extrapolating the IPTS-68 to lower temperatures where comparisons are made with other recent data. The reproducibility of the data is ± 0.5 mK below 50 K and ± 1 mK up to 83 K, while the total estimated measurement uncertainties are from one to three times greater.

高温度目盛設定のための金点黒体

This blackbody at the gold point was newly designed and constructed to establish the temperature scale above the gold point (1064.43°) by the definition of the International Practical Temperature Scale of 1968 (IPTS-68).The blackbody is composed of a graphite crucible and a furnace. The graphite crucible contained a 0.9kg gold ingot with purity of 0.99999 in which opens a reentrant graphite cavity forming a blackbody. The effective emissivity of the cavity was evaluated to be 0.99998. The furnace can maintain the temperature of the crucible at 1064.5° with a power supply as low as about 800W by the aid of the radiation shield. The temperature along the furnace axis is maintained within 0.1K by two control blocks.At the blackbody of the gold point, the slope of the straight lines on the observed freezing plateau and the dispersion of the replication gave estimations that the desired blackbody radiation was correctly realized within the precision of the multiplicative comparator of the spectral radiance which was used to compare the spectral radiance of the blackbody with that of a tungsten strip lamp.Thus the accuracy of the blackbody at the gold point (ΔLλ[T68(Au)]/Lλ[T68(Au)]) is expected to be better than 0.0001.

The International Practical Temperature Scale of 1968 Amended Edition of 1975

The scale presented in this document was proposed by theInternational Committee of Weights and Measures in 1974and adopted by the 15th General Conference of Weightsand Measures in 1975. It constitutes only an amendmentof the International Practical Temperature Scale of 1968(IPTS-68), not a replacement. Any measured temperature,T68, remains unchanged by this amendment of theIPTS-68.

The International Practical Temperature Scale of 1968 in the Region 13.81 K to 90.188 K as Maintained at the National Bureau of Standards.

The reproducibility of the International Practical Temperature Scale of 1968 (IPTS-68) in the region of 13.81 K to 90.188 K using standard platinum resistance thermometers is discussed. The effect of errors above 0 °C on the calibration between 13 and 90 K is analyzed. Calibrations resulting from least squares and "fixed point" treatment of the data are compared. The results show that in general the NBS-IPTS-68 temperature scale maintained at the National Bureau of Standards (NBS) by reference standard platinum resistance thermometers is transferred to thermometers calibrated at the NBS within a few tenths of a mK between about 20 and 90.188 K and within about ±1 mK between 13.81 and 20 K. Agreements within a few mK are shown between the observed values of temperatures, employing platinum resistance thermometers calibrated in terms of the NBS-IPTS-68 scale, and the values of temperatures of the fixed points in the region 13.81 to 90.188 K given in the text of the IPTS-68.

Platinum Metal Thermocouples

As a result of a remarkable piece of international collaboration between three national standards laboratories and seven United States and United Kingdom manufacturers, new reference tables have now been completed for platinum : 10 per cent rhodium-platinum and platinum: 13 per cent rhodium-platinum thermocouples. These new tables take into account the changes in the temperature scale resulting from the introduction of the International Practical Temperature Scale of 1968 (IPTS-68) and also provide reference tables which will be common to both U.S. and U.K. manufacturers and users of thermocouples.

Computation Aids for the International Practical Temperature Scale of 1968 in the Range of 13.81 to 273.15 K

A method is presented to use more conveniently the International Practical Temperature Scale of 1968 (IPTS-68) interpolating equations in the temperature range of 13.81 to 273.15 K (−259.34 to 0°C). Equations for each of the four temperature segments allow calculation of temperature from the measured thermometer resistance and calculation of resistance ratio and resistance at each temperature.

International Practical Temperature Scale of 1968

The new International Practical Temperature Scale of 1968 (IPTS-68) was approved by the Comite International des Poids et Mesures in 1968 and put into force by the National Physical Laboratory on January 1 this year. This revision of the IPTS-48 achieves the two objectives of making it agree with thermodynamic temperature values and of extending its range down to 13.81 K.

The International Practical Temperature Scale of 1968

The Comité International des Poids et Mesures (CIPM) atits meeting in October 1968 agreed to adopt the InternationalPractical Temperature Scale of 1968 (IPTS-68) in accordancewith the decision of the 13e Conférence Générale des Poidset Mesures, Resolution 8, of October 1967. This resolution gavethe CIPM permission to introduce a new Scale to replace theexisting IPTS-48 as soon as the Comité Consultatif de Thermométrie (CCT) made its recommendations.There were two important reasons for revising the IPTS-48.The first of these was the need to extend the Scale to lowertemperatures to achieve a unification of the existing nationalscales in the region 10 K–90 K. Secondly the Scale had notbeen revised significantly over the range from −183 °C to1063 °C since its inception in 1927, and modern gas thermometer measurements showed that the Scale gave values considerably different from thermodynamic temperatures.The CCT agreed on the basic data and methods of interpolation for a new definition of the IPTS at its 8th meetingheld in Washington and Ottawa in September 1967. Provisionwas made to extend the Scale down to 13.81 K, the triple pointof equilibrium hydrogen, and for the use of the best knownvalues of thermodynamic temperatures. The value of c2 usedin the Planck equation was also revised as a result of a betterknowledge of the values of fundamental physical constants.The CCT appointed a small sub-committee to prepare a textof the definition of the IPTS-68 in accordance with its recommendations, with instructions to resolve some points of detail.The final draft of the English text, which is reproduced below,received the approval of all members of the CCT before it wassubmitted to the CIPM. The official text of the IPTS-68 isthe French text which was prepared by the Bureau International des Poids et Mesures from the English text, and ispublished as an annexe to Comptes rendus des séances de laTreizième Conférence Générale des Poids et Mesures.