GB602960A - Improvements in or relating to apparatus for the measurement of electrical reactance - Google Patents

Abstract

602,960. Inductance and capacitance measurements ; determining physical qualities and dimensions of materials. WAYMOUTH GAUGES & INSTRUMENTS, Ltd., and WAYMOUTH, H. Nov. 13, 1945, No. 30339. [Class 37] [Also in Group XXXVIII] Apparatus for reactance measurement of the form comprising an oscillator/filter circuit whose output varied by the unknown reactance is applied through an, amplifying valve to actuate an indicator which acts to restore a predetermined frequency relationship between the oscillator and filter either by adjusting the oscillation frequency or the cut-off point of the filter as described, e.g. in Specification 513,754, is modified by the insertion of a rectifier between the filter and the amplifying valve. In a preferred application as a fuel level indicator for aircraft, the capacity variation of a petrol tank condenser 11, 12 with liquid volume changes the frequency of a Hartley oscillator 20 below the cut-off of an associated low-pass filter 21. The latter therefore passes an oscillator current which is applied to a rectifier circuit 22 wherein a metal oxide rectifier 51. or diode, Fig. 4 (not shown), operates to apply a unidirectional potential to the control grid 58 of a tetrode 59. The ensuing anode current actuates a spring-controlled moving coil instrument, Fig. 3 (not shown), the coil of which in its rotation moves a core within an inductance 29 included in the oscillator 20 to restore the cutoff frequency relationship between the filter 21 and the oscillator 20. A. stable deflection is therefore obtained in the instrument 65 which is a measure of the capacitance 11, 12. The instrument 65 may be calibrated, e.g. in gallons, or the indicating means may comprise a remotely-situated milliammetor 16 in series with instrument 65.