Determination of the non-uniqueness of the international temperature scale of 1990. (News Briefs).In the range --259 [degrees]C to 962 [degrees]C, temperatures on the International Temperature Scale of 1990 (ITS-90) are defined at a set of natural fixed-points that have assigned temperature values. Between these fixed points, standard platinum resistance thermometers resistance thermometer n. A device measuring temperature by the change of the electrical resistance of a metal wire. (SPRTs) are used as interpolating devices with a prescribed interpolation interpolation In mathematics, estimation of a value between two known data points. A simple example is calculating the mean (see mean, median, and mode) of two population counts made 10 years apart to estimate the population in the fifth year. formula. At any temperature between the fixed-point values, the temperature indicated by an SPRT SPRT Support SPRT SupportSoft, Inc (stock symbol) SPRT Sequential Probability Ratio Test SPRT Standard Platinum Resistance Thermometer SPRT Simple Packet Relay Transport SPRT Standard Quality Platinum Resistance Temperature Detector may depend on the physical or chemical characteristics of that particular SPRT. This irreproducibility of temperature values is one type of so-called non-uniqueness of the ITS-90 and is an inherent limitation of the ITS-90. Although non-uniqueness has been quantified at lower temperatures, measurements at temperatures above 660 [degrees]C demand exceptional skill at achieving thermal equilibrium thermal equilibrium The condition under which two substances in physical contact with each other exchange no heat energy. Two substances in thermal equilibrium are said to be at the same temperature. See also thermodynamics. Noun 1. between multiple thermometers, performing accurate resistance measurements, and preventing chemical contamination See: contamination. of the thermometers over periods of many months. A recent paper by t wo NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. scientists culminates a multiyear effort on making these technically difficult measurements and is a major contribution to the metrology of the ITS-90. These results were presented at the TEMPMEKO 2001 conference in Berlin and will be published in the conference proceedings. The NIST measurements in this range have uncertainties an order of magnitude A change in quantity or volume as measured by the decimal point. For example, from tens to hundreds is one order of magnitude. Tens to thousands is two orders of magnitude; tens to millions is three orders of magnitude, etc. smaller than all other published measurements, and set a conservative upper bound on the non-uniqueness of approximately 0.003 [degrees]C in the temperature range 660 [degrees]C to 962 [degrees]C. This bound is sufficiently low to demonstrate that the non-uniqueness of the ITS-90 in this temperature range may be neglected for all present industrial temperature measurements. The reduction of uncertainty of the NIST dissemination of temperature scales enables secondary calibration laboratories and laboratories in the aerospace and electrical generation industries to perform traceable temperature measurements more readily at a given level of user uncertainty. CONTACT: Greg Strouse, (301) 975-4803; gregory. strouse @rnst.gov. |
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