Electronic recorder with range and precision adequate for the platinum resistance thermometer

THE platinum resistance thermometer is the interpolating device for the 1948 International Temperature Scale from ¿182.97 degrees centigrade to +630.5 degrees centigrade.1¿3 When properly made the reproducibility of its resistance justifies its calibration and use for measurements to 0.01 degrees centigrade or 1/80,000th of its temperature range.3 Mueller attacked this difficult resistance-measurement problem with a hand-operated decade bridge.4 Stull attacked the problem with a mechanically balanced recorder using a slide-wire plus decades5 and explained the value of the recorder, one example being the determination of chemical purity by freezing point measurement.6 While Stull was building his recorder the author and his associates were also building a recorder, using one of the several methods of electronic balancing which had then been developed.7, 8 Based on the experience with these two types of recorders there was developed a third type with improved precision, the experimental form of which is the subject of this paper. The commercial form may differ in details from the experimental form described here.