A resistor for the measurement of large direct currents

摘要

Serious uncertainties in the effective value of low resistances for the measurement of large currents may be caused by variations of current distribution at their terminals, due to the use of many conductors in parallel which are necessary for large currents or to variations in surface contact or pressure of clamping bolts. Temperature-rise is also an important cause of variation. The application of principles for the reduction of these errors has been the basis of the design of a resistor of 20 microhms, which has been found satisfactory as a reference standard for the measurement of currents up to 25000 amperes.