<p>The
online impedance serves as one of the most crucial specification to evaluate
the health status and efficiency of an electrical device or system. The
inductive coupling technique is a preferred approach to measure the online
impedance due to the ease of implementation of the circuit which has zero
physical contact to the live electrical system. The existing inductive coupling
method deployed to measure the online impedance of an electrical device under
test (DUT) adopts two probes in total: an injecting inductive probe (IIP) and a
receiving inductive probe (RIP). An open/short/load (OSL) calibration procedure
is implemented to eradicate the ramifications of the probe-to-probe coupling, however,
based on the assumption that the calibration criterions (shorted, open and 50Ω)
are approximated to their theoretical values in a specified frequency range.
Hence, any measurement with frequency outside the specified range (i.e. larger
than 1 MHz) will not be accurate due to the frequency-dependent residual
inductances and capacitances of the calibration model. To overcome the
aforesaid limitation, this paper introduces an improved calibration procedure
which is applicable for a wider frequency range which takes the frequency-dependent
characteristics into consideration. With the two-probe measurement setup
(TPMS), the adopted improved calibration procedure is introduced to eradicate
the ramifications of the probe-to-probe
coupling with the intention to refine the accuracy of the extracted online impedance.<a></a></p><p></p>
Time-Variant In-Circuit Impedance Monitoring Based on the Inductive Coupling Method
