GB708161A - Improvements in and relating to inductor-controlled electrical circuits including electron discharge devices - Google Patents

Abstract

708,161. Dynamometers. BRITISH THOMSON-HOUSTON CO., Ltd. May 9, 1952 [May 9, 1951], No. 11792/52. Class 106 (2). [Also in Groups XXXV, XXXVI, XXXVIII and XL(c)] The amplitude of oscillations produced by a Colpitts oscillator is varied by inserting a variable inductor in the cathode lead and is used to measure strain, force or acceleration. As shown in Fig. 1, the inductor 5 is connected between the cathode and the junction of the grid-cathode condenser 6 and the anode-cathode condenser 8. The inductor 5 may be in parallel with a condenser 13, and the inductor variations are such that the tuning of the circuit 5, 13 varies within limits at one side of the oscillation frequency, Fig. 2 (not shown).. The varying impedance of the circuit 5, 13 varies the negative feedback, and so controls the oscillation amplitude. Bias for the grid is provided by a condenser 9 and resistor 10, and anode current is supplied from a source 12 through a choke 11. The oscillatory output is fed to a grid leak detector 22, and a load 26 is inserted in the anode lead. In a modified circuit, Fig. 3 (not shown), a series condenser replaces the shunt condenser 13, and the inductor 5 is varied within limits close to but above the resonance value. The oscillatory output is rectified by rectifiers connected in the grid circuit of the output valve 22. In Fig. 7 the inductor comprises a coil 64 on a U-shaped ferrite core 65, the reluctance of the magnetic circuit being varied by adjusting the air gap between the core 65 and a movable armature 66. This type of variable inductor may be used as a strain gauge. Fig. 8 shows an application to the measurement of the force 83 applied to a weak spring 82 supporting an armature 81. As the gap between the armature and the U-shaped core 80 of the inductor is diminished, the negative feed-back of the valve oscillator 67 is increased, and the oscillation amplitude reduced. The oscillations are rectified by the rectifiers 91, 92 and charge the condenser 90 negatively. A reduction of oscillation amplitude therefore drives the grid of the valve 86 in the positive direction causing an increased anode current through the indicator 97 and the electromagnet 94. The magnet 94 opposes and balances the applied force 83, the magnitude of which is shown on the indicator. If the force 83 is that of gravity acting on an object, the indicator shows the weight of the object. If the system is mounted on a moving body, the force 83 may be that due to acceleration of the body.