GB562145A - Apparatus for measuring electric inductance and capacitance values - Google Patents

Abstract

562,145. Inductance and capacitance measurements. STREETE, R. H., and 'WHITTICASE, W. Dec. 15, 1942, No. 17841. [Class 37] Apparatus for testing inductance or capacitance values comprises means for supplying a constant high frequency potential to an oscillatory circuit which includes the inductance or capacity to be tested and a cathode-ray indicator for indicating when the circuit is in resonance with the supply. A crystal-controlled oscillator comprising a valve 14 and quartz crystal 15 is connected by a choke capacityresistance coupling 15a, 16, 17, 18 to an amplifier valve 19 which is biassed so that with no grid excitation the anode current is zero. The output of the amplifier is fed to a tuned circuit comprising two variable condensers 21 and the standard coil or the test coil 22. A resistance 23 may be included to damp the oscillation and make the tuning of the circuit less sharp. A double diode triode 24 has the diode anodes connected together and the diode portion connected across the tuned circuit in series with a condenser 32. This condenser is shunted by a potentiometer 33, the D.C. potential across which is applied to the grid of the triode section of the valve 24, which is operated as a D.C. amplifier. The amplified voltage appearing across the cathode resistances 34, 35 is passed to a " magic eye 25. With a standard inductance 22 in the tuned circuit the variable condensers 21 are adjusted until resonance is indicated on the indicator 25 and the coils to be tested are successively plugged into the tuned circuit in place of the standard inductance, resonance being obtained if the inductance of each coil is within the permissible range. A measure of deviation from the standard may be obtained by adjusting one of the variable condensers until resonance is again obtained. The condenser may be provided with a scale calibrated in inductance values. The capacitance of a condenser may be determined by connecting it in shunt with a coil of known inductance. The apparatus may be mounted in a metal case provided with carrying handles and with cup-like contacts mounted on spring conducting arms to facilitate insertion and removal of the coils.