An alternating-current Kelvin bridge has been developed at NRL which meets the requirements of the thermoelectric measure¬ments program, namely, to measure resistance values in the milliohm range or less which wi11 be free of error due to a Seebeck voltage resulting from Peltier heating. The capabilities of the instrument are: a range of resistance from 10-6 ohm to 1 ohm, an overall error no greater than 0.25%, and a reproducibility better than 99.9%. The instrument employs a measuring current frequency of 40 cps (which effectively eliminates Peltier heating) and incor¬porates variable and plug-in resistors to compensate for contact and lead resistance. Standard high-quality components were selected for use in the bridge, which was carefully constructed to have electrical symmetry and a minimum of inductance and dis¬tributed capacitance.
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