Automatic Record of Small Amount of Electrical Resistance Change of Metals

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Abstract
An apparatus has been designed and made up for detecting small electrical resistance changes and recording them automatically. It is free from the thermoelectromotive force because of the use of the low frequency alternative current. This apparatus is used for measuring the changes of the electrical resistance caused by quenching and subsequently annealing metal wires. The error of the indication of the recorder is ±0.5 per cent of the full span of the recorder. As for the slow changes of the resistance of the specimen, the resistance change is detectable to 1.7×10-4 per cent of the specimen resistance used in this experiment. This corresponds to 5×10-12 ohm-cm in resistivity. As for the rapid changes of the resistance of the specimen which are caused during a few seconds, the resistance change is detectable to 2.5×10-3 per cent of the specimen resistance. This corresponds to 7.5×10-11 ohm-cm in resistivity.

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