The Development of a High-Temperature PRT Calibration
The Development of a High-Temperature PRT Calibration
Michael Coleman, Fluke Corporation
Industry trends are leading toward the need for improved accuracy in field calibration applications. The dry-block calibrator is the most common type of heat source used in field temperature calibrations but can be difficult to correctly address in a comprehensive uncertainty analysis. Significant sources of error or uncertainty are often overlooked or underestimated.

It is proposed that through the use of modern best practices in temperature metrology, the sources of error can be properly accounted for and managed to result in calibration uncertainties from 20 to 50 mK (milliKelvins) over the range -40 to 660°C in a dry-block based PRT (Platinum Resistance Thermometer) calibration system. This will be demonstrated through the presentation of a system recently designed for a commercial secondary-level calibration laboratory. Included in the paper are a comprehensive uncertainty analysis as well as the problems, solutions, and results encountered during the design of the process.

The intent of this paper is to help calibration professionals in industry recognize and properly deal with sources of uncertainty related to dry-block type calibrators in temperature calibration processes. With modern best practices in temperature metrology it is possible to achieve reliable high-accuracy temperature calibrations, even in the field.