IMPEDANCE_METER

Published:2009/7/11 4:19:00 Author:May | From:SeekIC

External AF voltage is applied to unknown impedance through input transformer T1 and calibrated variable resistor R1. Voltage drops across impedance and R1 are checked separately with electronic voltmeter while R1 is varied. When drops are equal, unknown impedance is equal to setting of R1, read directly from its calibrated dial. Voltmeter uses FET followed by two-diode rectifier X1-X2 and microammeter M1. With S2 in position A, volt-meter reads drop across R1 ; in position B, volt-meter reads drop across unknown impedance.Adjust R5 so meter deflection is near full scale to increase comparison accuracy. Common test frequencies used are 400, 500, and 1000 Hz.-R. P. Turner, FET Circuits, Howard W. Sams, Indianapolis, IN, 1977, 2nd Ed., p 143-144.



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