Characterization of loading effects in precision 1 Ω resistors

Precision standard resistors manufactured within the last two decades using improved construction techniques and materials, such as the resistance alloy Evanohm, have been shown to have excellent environmental characteristics. Power dissipation (or loading) effects in several types of resistors have been examined including specifically those made of Manganin and Evanohm, and with the resistor element both sealed within a double wall container, or unsealed. Our recent tests on these resistors demonstrate that conditions of power dissipation within the resistors and the duty cycle of the power applied to the resistor have significant effect on the uncertainty of the measurement.