GB982837A - Method and apparatus for measuring small reactance or impedance - Google Patents

Abstract

982,837. Measuring impedance. KABUSHIKI KAISHA TSUGAMI SEISAKUJO. Feb.16, 1961 [Feb. 25, 1960; May 13, 1960; May 16, 1960; Oct. 12, 1960], No. 5792/61. Heading G1U. An apparatus for measuring small values of impedance or reactance comprises a high frequency power source OSC, a first resonant circuit L1C1 coupled to the source, a second resonant circuit L2C2 coupled to the first resonant circuit, a detecting arrangement (including microammeter G) coupled to one of the circuits and an arrangement for coupling a small impedance or reactance (e.g. #CX) to one of the resonant circuits, the coupling between the first and second circuits being given by the following relationship where Q 2 = #C 2 R 2 ,# being the angular frequency of the source, C2 the value of the capacitor of the second circuit, R 2 the value of the equivalent parallel circuit representing the total loss of the second circuit, Z 0 the value of capacitor or mutual inductance of elements coupling the circuits and Z 2 the value of capacitor or inductor of the second circuit. To set up the circuits with this coupling a switch S1 in parallel with the second circuit is utilized. With this switch closed the capacitor C1 is adjusted to give a maximum in the detector circuit, and then with it open capacitor C2 is adjusted to give a maximum in the detector circuit. This ensures that variations in physical conditions or operating frequency do not disturb the working point of the circuit. With the detector circuit shown, and with identical components in the first and second resonant circuits, when small capacitance #CX to be measured is connected across the second resonant circuit, the detector output indicates this value. A similar arrangement but using two sets of cascaded resonant circuits with two detector windings coupled in opposition to a transformer is also described (Fig. 3 not shown). The circuits may be adapted for measuring resistive loss. After the initial stages of decoupling the second resonant circuit and tuning C1 for maximum in the detector circuit and then coupling the second circuit and tuning C2 for minimum in the detector circuit, the reactance in the second circuit is detuned by an amount #C given by #.#C.R 2 = 1. Thereafter C1 is again adjusted to give a maximum in the detector circuit. Under those conditions if an impedance is connected to the second resonant circuit the change in the detector output will indicate the resistive component or loss of that impedance (Figs. 6, 8, 10, not shown).