Recent Advances in Resistance Thermometry Readouts

Recent innovations and technological advances have significantly enhanced the performance and utility of digital resistance thermometry readouts. The readout is an important component of a temperature calibration system, especially when used with a standard platinum resistance thermometer, since the readout contributes to the accuracy, reliability, and efficiency of the system. Accurate digital readouts offering convenient features in a cost-effective solution have been available for many years, particularly since the introduction of the Hart Scientific “SuperThermometer.” Building on prior work, Fluke-Hart Scientific has continued to improve the technology. This paper discusses some of the recent developments incorporated into a new instrument, which include much improved precision and accuracy; automatic self-calibration of ratio; more stable built-in reference resistors; accurate, traceable sensing current; automatic zeropower resistance and temperature measurements; additional input terminals for thermometers and resistors; and other enhanced features. Results of tests to evaluate the performance of the new readout are presented. The uncertainty evaluation reported in this paper indicates that expanded uncertainties as low as 0.000026 °C at 0.01 °C (a key temperature of the International Temperature Scale of 1990) are achieved. The demonstrated improvements in the resistance thermometry readout are expected to expand capability and increase efficiency in calibration laboratories of all levels.