Abstract
The design and performance of a pair of highly isolated ramping and reversing direct-current sources for use with a cryogenic current comparator resistance bridge and dc superconducting quantum interference device (SQUID) detector are described. The current sources are floating and isolated from one another, and are internally programmed to reverse the output current while maintaining the SQUID feedback control system in lock. The sources are designed to have low zero offset in order to limit the change of the current ratio in the reversal sequence. Sources have been constructed with full-scale current ranges from 0.65 to 100 mA and have been used in the comparisons of precision standard resistors at the 0.01 ppm level.
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