Recorder for platinum resistance thermometer

THE PLATINUM resistance thermometer is the accepted interpolating device for the 1948 International Temperature Scale from −182.97 degrees centigrade to +630.5 degrees centigrade. When properly made, the reproducibility of its resistance justifies its calibration and use for measurements to 0.01 degree centigrade, or 1/80,000th of its temperature range. E. F. Mueller attacked this difficult resistance measurement problem with a hand-operated multiple-decade bridge.¹ D. R. Stull attacked the problem with a mechanically balanced recorder using a slide-wire plus decades,² and used the recorder for the determination of chemical purity by freezing point measurement. While Stull was building his recorder, the author and his associates also were building a recorder (using one of the several methods of electronic balancing which had then been developed). 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 article.