Automated High-Ohmic Resistance Bridge With Voltage and Current Null Detection

A high-ohmic bridge for automated resistance measurements in the range between 1 MΩ and up to and above 100 TΩ is described. Whereas similar setups reported so far use only current null detection, the present system developed at VSL can use either voltage or current null detection. We compare the two null detection methods and find no significant difference between the methods over the resistance range between 10 MΩ and 100 GΩ. Voltage null detection is more accurate for resistance values below 10 GΩ at 10 V measurement voltage, whereas for resistance measurements above 100 GΩ current null detection should be used. Careful automation and refinement of the measurement procedure lead to excellent results and uncertainties. For example, the measurement of the 1:100 ratio of the series and parallel connection of a 10 × 100 MΩ Hamon device agrees within (0.5 ± 0.4)μΩ/Ω with the nominal Hamon ratio. The total measurement uncertainty at 1 GΩ equals 1.7 μΩ/Ω (k = 1), which has been confirmed in a recent international comparison.