Study on the Parameters Affecting the Impedance Extraction Accuracy by Inductive Coupling Method

The method of extracting in-circuit impedance using inductive coupling technique is a useful and non- destructive procedure for condition monitoring of electric systems due to its non-intrusiveness and easy-to-use features. The method requires a signal to be injected into the system to derive the online impedance of the system. However, each electrical system has specific characteristics in terms of its impedance magnitude and using the same injecting signal to quantity differing impedance values may lead to measurement inaccuracies. Moreover, the placement of the injective and receiving devices may have some impact on the measurement accuracy due to coupling effects. This paper analyses how different injecting signal levels and the proximity between the injecting and receiving device can affect the impedance measurement accuracy. Experiments were conducted using circuits of different impedances and varying the injecting signal levels as well as by varying the positioning of the injecting and receiving devices to understand how the measured values can be affected. Results show that higher circuit impedances require appropriate injecting signal levels to ensure an acceptable measurement accuracy while the placement of the injecting and receiving device should be wide enough to ignore the coupling effects at higher levels of loop impedance.