Improved calibration technique for two-probe setup to enhance its in-circuit impedance measurement accuracy

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The in-circuit impedance is a key parameter to evaluate the health and operation of many electrical systems. The two-probe setup (TPS) based on the inductive coupling approach is preferred for in-circuit impedance measurement because it does not require physical electrical contact with the energized system under test. However, the existing calibration technique for the TPS degrades its measurement accuracy at relatively high test frequencies. To enhance the measurement accuracy of the TPS, this paper proposes an improved calibration technique. It considers the frequency-dependent effects of the selected calibration components so that the TPS can maintain good measurement accuracy even at relatively high test frequencies. Using an actual TPS as a test case, experimental results show that the TPS based on the proposed calibration technique maintains good measurement accuracy up to 10 MHz, whereas the same TPS based on the existing calibration technique exhibits significant measurement errors when approaching 10 MHz.