GB1003066A - Impedance meter - Google Patents

Abstract

1,003,066. Impedance testing. HEWLETTPACKARD CO. Jan 7, 1963 [Jan. 30,1962], No. 750/63. Heading G1U. An impedance measuring device (Fig. 1) comprises a probe unit wherein A.C. from wide range tunable oscillator 15 is applied over coaxial line 17 to terminal 11 and load 12, the current traversing the single turn primary of a current transformer 19 whose output over coaxial line 25 is amplified at 27, rectified, and compared at 31 with the output of reference source 29; the error signal controlling the output of oscillator 15 for constant current in the load, the voltage across which is coupled over coaxial line 35 and amplifier 37 to meter 39 calibrated to read impedance values; the gains of 27 and 37 being adjustable in ganged steps for several ranges of variation. Admittance is measured by transposing the outputs of 27 and 37 so that the current in the load is held constant while the voltage is a measure of admittance. In the probe unit (Fig. 2) the conductor 11 intersects as primary the toroidally wound current transformer secondary 23 and the impedance test voltage is obtained from a connection 41 to the conductor. The primary may include plural turns or may be shielded through the transformer core to its junction with the test impedance; an aperture being left for connection 41. In a modification (Fig. 3 not shown) a further single turn winding is added to the current transformer and closed through a variable capacitor drawing a current such as to balance out in its effect on the core flux the current in conductor 21 due to its distributed capacitance.