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Calibration of industrial platinum resistance thermometers

Objective



Industrial platinum resistance thermometers (IPRT's) can be used to accurately measure temperature if they are carefully selected and individually calibrated. The individual calibration of a thermometer involves the fitting of an interpolation curve to a limited number of calibration points so as to be able to describe accurately the variation in the electrical resistance of the thermometer as a function of temperature.

In order to establish a suitable calibration procedure, this project selected two groups of six IPRT's. The IPRT's in one group were calibrated in the temperature range 0 C to 630 C and those in the other group were calibrated in the temperature range 0 C to 850 C.

RESULTS

A number of platinum resistance thermometers were obtained from seven European suppliers. They were first tested for stability and a number of them failed. It was possible however to select six thermometers for each temeprature range that were sufficiently stable. Excessive instability and hysteresis were found with the calibrations above 630 C which also affected the accuracy of the calibrations at lower temperatures. In the temperature range 0 C to 630 C a quadratic curve was shown to be an adequate means to interpolate between the calibration points. Using a fourth order interpolation procedure with the most stable thermometers, it was possible to measure temperature to within +/- 50 mK in the temperature range 0 C to 630 C. As an extension to the exercise, six of the thermometers are currently being calibrated in the temperature range -200 C to 0 C.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Istituto di Metrologia G. Colonnetti

Participants (2)

Institut National de Metrologie
France
National Physical Laboratory (NPL)
United Kingdom
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Queen's Road
TW11 0LW Teddington