The Immersion Characteristics of Industrial PRTs
Immersion effects are one of the most significant sources of error in the use of industrial platinum resistance thermometers (IPRTs). This article combines the development of a mathematical model of immersion error and experimental measurements of the immersion characteristics of a range of IPRTs immersed in different fluids at different temperatures. The mathematical model relates the relative temperature error in the thermometer indication to two exponential terms, with one of the 1/e decay lengths three times the other. The experimental results show that both of the exponential terms are important for shallow immersion, but one is sufficient for long immersion. The decay length for the thermometers depends on the diameter of the probe and on the thermal environment into which it is immersed. For the thermometers evaluated here in mineral oil, silicon oil, and molten salt, the 1/e decay length is about three to four times the diameter of the thermometers. A simple rule of thumb for ensuring adequate immersion in calibration baths is developed.
KeywordsImmersion Platinum resistance thermometer Temperature
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- 1.Kerlin T.W., Shepard R.L.: Industrial Temperature Measurement. ISA, Research Triangle Park (1982)Google Scholar
- 2.J.W. Nicholas, D.R. White, Traceable Temperatures. DSIR Bulletin, vol. 234 (DSIR, Wellington, 1982)Google Scholar
- 3.R.P. Benedict, J.W. Murdock, ASME Trans., J. Eng. Power 235 (1963)Google Scholar
- 4.Kutz M.: Temperature Control. Wiley, New York (1968)Google Scholar
- 5.Incropera F.P., DeWitt D.P.: Fundamentals of Heat and Mass Transfer, 4th edn. Wiley, New York (1996)Google Scholar
- 6.McGee T.D.: Principles and Methods of Temperature Measurement. Wiley, New York (1998)Google Scholar