Patent GB-821614-A (GB)
Title: Improvements in and relating to quotient-forming instruments chiefly for the execution of measures and synchro-system transmission of indications or measures at a distance
IPC: G08C19/38
Filed: 1955-09-27
Abstract: 821,614. Electric correspondence control systems. HELD, S. S. Sept. 27, 1955 [Sept. 27, 1954], No. 27460/55. Class 40 (1). [Also in Groups XXXV and XXXVI] An instrument for determining the relationship between the magnitudes of two (or more) currents comprises two (or more) parallel, rectangular-shaped, flat, stator windings associated with a ferromagnetic core, and a magnetic rotor freely mounted on a shaft perpendicular to the stator windings, carrying a pointer which indicates the direction of the resultant magnetic field, and therefore the ratio of the energizing currents. The instrument may be used as a ratiometer, and as the transmitter and/or receiver of a synchro system. Construction.-In a first embodiment (Figs. 1, 2) two perpendicular coils 9, 10 are wound on a flat, non-magnetic plate 1, having a central hole in which is located a soft iron disc 2. A centrally-mounted spindle 7 carries a diametrically-magnetized disc 6 and a pointer 12. Eddy current damping is provided by a further disc (not shown) of conducting material, or by using a conducting plate 1. In modifications: (1) the disc 6 is duplicated, the second disc being symmetrically located on the other side of the plate and windings; (2) the coils 9, 10 are wound on separate plates 1, the disc 6 being located centrally between the coils; (3) the coils 9, 10 may be other than perpendicular, e.g. at 45 or 60 degrees to each other, with or without additional windings. In a second embodiment (Figs. 8, 9) the cental hole in the plate 1 carries a magnetic ring core 14 and a coil 15, separated by an insulating ring 16, the central spindle 19 passing through a gap in the centre of coil 15, and carrying the pointer 12 and one, or as shown, two half-plates 17, 18 one on either side of the coils 9, 10, 15. The optimum shape of each half-plate 17, 18 is stated to be that shown. In modifications: (1) the coil 15 is wound on a separate iron core; (2) the coil 15 is located round the outside of the plate 1 (Fig. 10), the flux passing through a yoke 20, the centre portion 7 of the spindle 19 being made of non- magnetic material; (3) the coil 15 is duplicated and mounted centrally one on either side of plate 1, with the coils 15 wound in the same direction and the half-plates 17, 18 diametrically opposite each other, or with coils 15 wound in opposite directions and the half-plates 17, 18 located over each other; (4) the coils 9, 10 are wound on separate plates 1, 1<SP>1</SP> (Fig. 14) with coil 15 and the half-plates 17, 18 located centrally between them. An external soft iron cylindrical shield 27 may be added. Ratiometer (Fig. 16).-Two voltages V 1 , V 2  are cyclically fed to the crossed coils 9, 10 of the ratiometer, the switching being effected at supply frequency by pairs of opposed rectifiers 28-31 across the centre-tapped secondary windings of mains transformers at the transmitter and receiver. D.C. synchro system.-A three-coil instrument is used as the receiver of a synchro system, connected to a ring potentiometer 34 (Fig. 17) with three equispaced tappings. The rotor of the receiver indicates the angular position of the slider 36 of the potentiometer. In a modification (Fig. 18) the ring potentiometer 34 has four equispaced taps and two perpendicular sliders 36<SP>1</SP>, 36<SP>11</SP>, whereby only two perpendicular coils 9, 10 are needed in the receiver. The potentiometer 34 may alternatively be a linear potentiometer, when the receiver rotor indicates the linear displacement of the slider (5). Tachometer.-The receiver rotor of Figs. 17, 18 is associated with a spring-loaded eddy current disc whose angular displacement therefore indicates the speed of rotation of the ring potentiometer shaft. The sliders 36 may be associated with fixed tappings on the ring potentiometer and not the potentiometer wire itself. A.C. synchro system.-As shown (Fig. 21) an instrument of the type shown in Figs. 8, 9, but with the half-plates 17, 18 located over each other, is used as the transmitter of a synchro system, winding 15 being energized with A.C., and utilizing a three-coil stator assembly 9, 10, 13. The receiver R<SP>1</SP> is of the type shown in Figs. 1, 2 but with three coils which are connected to the corresponding transmitting coils through rectifiers 28<SP>11</SP>, 29<SP>11</SP>, 30<SP>11</SP>. In a modification four windings are used at the transmitter and receiver. In another form of A.C. synchro (Fig. 23) the transmitter T and receiver R are both of the type shown in Figs. 1, 2, but with three coils 9, 10, 13 connected in series across an A.C. supply.