Round-robin test of SIP laboratory measurements using electrical test networks

SUMMARY This study presents the results of an interlaboratory test designed to evaluate the accuracy of spectral induced polarization (SIP) measurements using controlled electrical test networks. The study, conducted in Germany since 2006, involved 12 research institutes, six different impedance measurement devices and four types of electrical test networks specifically designed to evaluate phase shift errors in SIP measurements. The test networks, with impedances ranging from 100 to 150 kΩ, represent high-impedance samples with different phase characteristics, and pose the measurement challenges typical of such samples, including high contact impedances and parasitic capacitances. Four key findings emerged from the study: (1) Impedance measurements across all devices showed deviations within 1 per cent over a wide frequency range (0.001–1000 Hz); (2) phase errors remained below 1 mrad up to 100 Hz for most devices, but increased at higher frequencies due to parasitic capacitances and electromagnetic coupling effects; (3) lab-specific instruments have lower phase errors than field instruments when used in a laboratory environment, primarily due to the effects of long cables and too low input impedances of the field instruments; and (4) short cables and driven shielding technology effectively minimized parasitic capacitance and improved measurement accuracy. The study highlights the usefulness of test networks in assessing the accuracy of SIP measurements and raises awareness of the various factors influencing the quality of SIP data.