GB558036A - Improvements relating to the operation of electronic vacuum tubes or valves - Google Patents

Abstract

558,036. Frequency and reactance measurements. SARGROVE, J. A. March 28, 1942, No. 4136. [Class 37] [Also in Group XL] Variation in the frequency of oscillations, or in capacity or inductive reactance, are detected by a multi-grid tube having at least two control grids on opposite sides of an accelerating grid. Oscillations of an amplitude sufficient to cut off the anode current during part of the cycle, are applied to the outer control grid and cause a diversion of electrons to the inner control grid, which thus assumes an oscillatory voltage dependent in phase on the nature of the reactance in the inner control grid circuit. The anode current, being dependent on the phase difference of the voltages on the two control grids, thus affords an indication of deviations in the input frequency, or of changes in reactance in the inner control grid circuit. The Specification explains that owing to the transit time to the outer control grid being comparable with the half period of the oscillations, some electrons are returned through the accelerating grid with sufficient velocity to reach the inner control grid. As shown, a triode-hexode valve is used, the triode section being arranged to generate oscillations in a tuned circuit t1 which are applied to the outer control grid of the hexode section. The inner grid is connected to a tuned circuit v, u, the accelerator grids are positively biased through a resistance l, and the anode circuit includes an output load or instrument o and a loco-pass filter j. Changes in frequency of the circuit t1 or of the circuit u, v cause corresponding variation in the anode direct current. A pentode valve may be employed, and piezo-electric crystals may be associated with an oscillation generator connected to the outer grid and with a tuned circuit connected to the inner grid, and the frequency of either crystal may be varied by applying D.C. voltage thereto, Fig. 7 (not shown). The effect of changes in the supply voltage may be balanced out by duplicating the valve circuits and applying the signal input to one only, the output instrument being of a differential type. When two triode-hexode valves are used, one of them may be of the kind having the triode grid connected to the outer control grid of the hexode, and the other of the kind in which connection is made to the inner hexode grid. Radiant energy may be detected by connecting a photocell to the circuit u, v in such manner that its activity varies the phase relationship in that circuit. Specification 487,913, [Group XL], is referred to.