Performance assessment of resistance bridges and multimeters used at CMS

Automatic balancing ac resistance bridges, ASL F18 and F700, and HP 3458A millimetres are the measurement instruments used by Center for Measurement Standards (CMS) for the calibration of standard platinum resistance thermometers (SPRTs), industrial platinum resistance thermometers (IPRTs), and liquid-in-glass thermometers (LIG) respectively. The inherent non-linearity of these measurement instruments could be a significant source of uncertainty and the absolute accuracy is especially critical to the primary instrument. A resistance bridge calibrator RBC 100, manufactured by 2K electronics, is a resistor network for the purpose of assessing their linearity and absolute accuracies of the foregoing thermometry bridges and meters. Each thirty-five normal measurements gives the linearity with 4.781 x 10-8, 4.982 x 10-7, and 6.371 x 10-5 Ω for F18, F700, and HP 3458A, however this deteriorates to 2.661 x 10-7 and 3.227 x 10-6 for two bridges while considering both normal and complementary data. Additionally, the possible contributions from the F18 bridge to the uncertainty of SPRT measurement at ITS-90 fixed points were investigated also