Accurate determination of the balance point of a current comparator bridge for resistance standards measurements

In many cases of balancing a comparator-type bridge, the presence of noise on the galvanometer output obscures precision determination of the resistance ratio which makes it difficult to achieve a balance point to better than 0.1 ppm. The signal-to-noise ratio also deteriorates when increasing the nominal resistance ratio from 1 to 10, The noise causing these effects arises from low-frequency drifts below 1 Hz and the presence of interference. The drift arises probably from unstable thermal emf's derived from the Peltier effect [1].