GB581246A - Improvements in or relating to the measurement of electric impedances - Google Patents

Abstract

581,246. Impedance and power factor measurements. SHERIDAN, V. A. June 7, 1944, No. 10914. [Class 37] The impedance of an element is measured by associating a known variable impedance therewith to form. a tunable circuit, supplying the circuit successively with voltage at two predetermined frequencies, adjusting the variable impedance to effect resonance at each frequency and computing the impedance from the two frequencies and the difference between the two values of the variable impedance. A coil 10, the impedance of which is to be measured, is connected in parallel with a variable condenser 110 and supplied from an oscillator 1 the frequency of which may be adjusted to two predetermined frequencies by switching condensers 4, 5 alternatively into the tank circuit 2. The condenser 110 is adjusted to effect resonance at each frequency as indicated by a maximum reading on the valve-voltmeter 18. The inductance of coil 10 is then computed from a formula given in the Specification. For direct reading, ganged switches 61, 62, are provided so that a further condenser 111 is switched into circuit in parallel with condenser 110 at the same time as condenser 5 is switched into circuit in the oscillator. Thus, if condenser 110 is adjusted for resonance at the frequency corresponding to the open position of switch 62, the condenser 111 only need be adjusted to effect resonance at the other frequency and may be calibrated to read inductance values direct. The power factor of the coil may be determined in known manner from the-voltmeter 18 reading at resonance. The condensers 4, 5 may be finely adjusted by using a known .inductance in place of coil 10. Capacitance may be measured by using a known variable inductance in parallel therewith in place of elements 110, 111. A plurality of preset oscillator frequencies may be employed to vary the range of measurement.