Using confidence factor to improve reliability of wide frequency range impedance measurement. Application to H.F. transformer characterization

Impedance analyzers are efficient in acquiring wide range impedance measurements in a wide frequency range. However, when measuring low impedances, short circuits used for compensation process can´t be considered as ideal and analogue problem appears for open circuit compensation. Fortunately, because impedance matrix of a two-port passive circuit is symmetrical, characterizing this circuit by four independent impedance measurements introduces redundancy. That property supplies a useful consistency test we call “confidence factor”. Looking at this factor, several causes of measurement inaccuracy can be detected. Alternatively, extra equation supplied by redundancy can also be used to add one unknown impedance to the three computed. This way, impact of the impedance of a real imperfect short-circuit can be removed. In this paper, we first present the interest of the confidence factor and then we show how to lower errors related to imperfect short-circuit. Finally, we show how to use these advances to better characterize HF power transformers and to measure weak wiring inductances.