Calibration and Accuracy of Secondary Standard PRT's to the ITS-90

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Calibration and Accuracy of Secondary Standard PRT's to the ITS-90 (460.2 KB)

The Standard Platinum Resistance Thermometer (SPRT) portion of the ITS-90 was formulated for specific, very high quality PRT's. The accuracy of fit to the ITS-90 of these thermometers is well documented. In many cases, however, "secondary" grade thermometers are used when less accuracy can be accepted. The accuracy of fit to the ITS-90 that can be achieved with these thermometers is much less clear. Additionally, these thermometers are generally calibrated in comparison baths at temperatures which are likely to differ by some amount from the actual ITS-90 fixed points. This project was undertaken to study the behavior of these thermometers over the temperature range of 77.65 K to 693.15 K (-195.5 °C to 420 °C). It is composed of calibration as outlined in the ITS-90 with subsequent comparison calibration to SPRT's. Thermometers from several leading manufacturers are included. The data will be fitted to the mathematical formulae as specified in the ITS-90 and several alternative equations.