Patent GB-673945-A (GB)
Title: Improvements in or relating to circuits for automatic frequency-control
IPC: H03J7/16
Filed: 1948-12-10
Abstract: 673,945. Non-contact-making relays. PHILIPS ELECTRICAL, Ltd. Dec. 10, 1948 [Dec. 13, 1947; May 22, 1948; July 6, 1948], Nos. 31995/48, 31996/48 and 31997/48. Class 40 (iv). [Also in Groups XXXV, XXXVI and XL (c)] The movable element of a variable reactance comprises a piston or other member mounted in a liquid-filled tube and driven magnetically by a control current, the fixed parts of the reactance being structurally integral with the tube. The reactance may be used for tuning adjustment in an automatic frequency control system, particularly for correcting the oscillator supplying the carrier in a single side-band radio receiver. As shown in Fig. 1, fixed condenser plates 24, 25 are fixed on the outer side of a tube 19 of glass or other dielectric material filled with liquid. A hollow cylindrical piston 20 slides within the tube and constitutes a movable condenser plate, being driven by a coil 17 or 18 influencing a softiron or magnetized plug 22. The piston and plug may have the same gravity as the displaced liquid, and may be balanced by adjustable nuts and screws 23 at the end faces. As the piston moves towards or away from the narrow outer plate 24, the capacity between the plates 24, 25 rises or falls. A variable inductance may be obtained by substituting a coil for the fixed capacity plates, and arranging that the moving piston influences the reluctance of the magnetic circuit of the coil. In Fig. 2, which shows the parts separated from each other, the driving-coils 31, 32 are centrally placed around a liquid-filled glass tube 30 which carries fixed condenser plates 38, 39. The movable plate within the tube comprises an S-shaped member 27 pivoted on a vertical shaft mounted between fixed upper and lower plates 37, 29 connected by uprights 35, 36. The member 27 is of soft iron and as it turns on its shaft varies the capacity between the electrode plates 38, 39. The member 27 is driven by the magnetic field set up between pole-pieces 33, 34 which are circumferentially displaced by 90 degrees. The uprights 35, 36 limit the motion, and their width affects the damping. If a coil replaces the plates 38, 39, rotation of the soft-iron member 27 varies the coil inductance. In Fig. 3, the liquid-filled cylindrical casing 60 has a constricted central portion in which the driving-coils 64, 65 are mounted to co-operate with a soft-iron core 68 attached to the metal piston 67. Between the piston and the adjacent part of the casing 60 is fixed a glass tube 66 open at both ends and carrying metal sleeves 72, 75 whose capacity to the casing varies as the piston moves. Variation in the capacity of the sleeve 75 to the earthed casing as the piston moves is indicated by a meter 78. This capacity, represented at 76, forms one arm of a resistance-capacity bridge which is supplied with A.C. from the source 52 through a transformer 77 having its secondary coil connected across one diagonal. The other diagonal feeds a central-zero meter 78 to which a quadrature voltage is also supplied through a phaseshifting network 79.