Patent GB-616978-A (GB)
Abstract: 616,978. Electric indicating systems. SIGMA INSTRUMENT CO., Ltd., and BOOSEY, F. R. Jan. 10, 1946, Nos. 951 and 952. [Class 40 (i)] [Also in Group XXXVI] In a measuring apparatus, the differential variation of two A.C. energized impedances is reflected in the difference between the D.C. outputs of two rectifier bridges, series connected with the impedances, which is indicated by a galvanometer in magnitude and sense. As shown, an object to be gauged is inserted between gauging anvils 1, 2, the latter being carried by the supporting bar 3, mounted on the lath springs 4, 5. Fixed U-shaped magnet cores 7, 8 co-operate respectively with cores 9, 10 carried by element 11 pivoted at the intersection of the cruciform lath springs 14. Arms 19, 20 fixed to supporting bars 11, 3 respectively, are urged into engagement by the spring 21, and a movement of anvil 2 causes a rotation of the support 11 against the restoring action of springs 4, 5, 14 to reduce one of the gaps and increase the other between the cores 7, 9 and 8, 10. Coils 15, 16 are series connected with one terminal of the secondary, 45 of a transformer, the primary 56 of which is supplied from A.C. source 55. The remaining terminal of secondary 45 and the lead 48 of coil 15 are connected to the opposite terminals of a rectifier bridge comprising rectifiers 30, 31, 32, 33. Similarly the series connected coils 17, 18 are connected in series with the A.C. supply from the winding 50 to the rectifier bridge comprising rectifiers 34, 35, 36, 37 and both bridges are connected in assisting relationship so as to cause a D.C. circulating current in leads 42, 44 and potentiometer 43. The galvanometer G, described in Specification 601,540, [Group XXXVI], comprises a deflection coil 57, rotatable between the pole pieces 58, but subject to the torque of the control coil 61, mounted below, and rotatable between pole pieces 62, designed to give the required form of scale 60. Control coil 61 is supplied with constant excitation from the supply 55 through the rectifier bridge comprising rectifiers 67, 68, 69, 70, either directly from the supply as shown, or from a secondary winding supplied from primary 56. Coil 57 is energized from the connection 44 and the tapping point 77 of potentiometer 43, which is adjusted to effect zero current flow through the coil when no gauging is taking place, i.e. when anvil 2 is not displaced. When anvil 2 is moved by the insertion of a specimen between anvils 1, 2, the gap between cores 7, 9 is reduced and the impedance of coils 15, 16 is raised while similarly, the impedance of coils 17, 18 is lowered. Hence, the D.C. voltages developed between points 38, 39 and 40, 41 are lowered and raised, respectively, to produce an out-ofbalance voltage between the slider 77 and connection 44 which is accompanied by a flow of current through coil 57 and a deflection of needle 59 which indicates the magnitude of the movement of anvil 2. Compensation for source voltage changes is automatic owing to the naturally neutralising effect produced in coils 57, 61. Frequency changes at the source are compensated by the condenser 74 the reactance of which alters correctively, with frequency, to correct for changes in the inductive reactance of coils 15, 16 and 17, 18. In a modification (not shown) the movable core support is mounted on points held in engagement by springs.