The Measurement of Load Coefficients of dc Resistance Standards Using ac Loading Currents

A new method of measuring the load coefficients of precision direct current standard resistors is described which has many advantages over the presently used direct current methods. Alternating current is used to provide almost all of the load required in the resistor under test while a small direct current is used in the measurement of direct current resistance changes. Problems of measuring circuit design are discussed relating to the simultaneous presence of alternating and direct currents and because of the alternating loading current supply circuit connected to the standard resistor under test. Possible sources of measurement error are considered and comparative curves of resistance change as a function of temperature and load are presented for several direct current resistance standards of differing resistance value and construction.