Secondary Conductivity Standards Stability

Calibration values of secondary conductivity standards obtained on a periodic basis, both for the Boeing Company and for commercial customers, have shown various drift patterns. Presently, a 100-kHz bridge used with an H-P 9825 computer compares unknown secondary standards against carefully built, National Bureau of Standards (NBS) traceable, primary bars in an oil-bath environment. Factors affecting the stability of secondary standard values of conductivity include primary conductivity bar value changes, uneven surface wear, environmental contamination, lift-off due to the presence of foreign material on the surface, and aging of the metal crystalline structure. Some secondary standards, which were large physically, exhibited significant conductivity changes across their surface due to the nonhomogeneity of the metal.