Patent GB-754130-A (GB)
Title: Improvements in or relating to arrangement for converting a mechanical torque to a d-c current
Inventor: GILBERT ROSWELL WARD
IPC: G06G7/16
Filed: 1954-01-19
Abstract: 754,130. Electric indicating systems. WESTON ELECTRICAL INSTRUMENT CORPORATION. Jan. 19, 1954, No. 1604/54. Class40(1) [Also in Group XXXVI] A torque, produced, e.g. by a Bourdon tube, a bimetallic temperature sensitive element or an electrodynamometer is measured by balancing it against the torque produced by the D.C. flowing in the moving coil of an induction galvanometer. A.C. energization of the galvanometer magneticcircuit induces in the moving coil a signal voltage of magnitude and phase sense corresponding to the deflection of the coil from a neutral position, this signal being rectified to produce the D.C. which is a measure of the torque. As shown, Fig. 1, for measuring the product of two variables, currents A, B, proportional to these variables, are fed to the respective coils 10, 11 of an electrodynamometer, the spindle 12 of which also carries the coil 15 of an induction type galvanometer, e.g. as disclosed in Specification 604,312 [Group XL(c). The coil 15 moves in the air gap of a permanent magnet 16 on which an alternating field is superposed by a coil 19 fed from the output of an oscillating amplifier 23, whereby there is induced in the coil 15 an e.m.f. of magnitude and phase sense corresponding to the magnitude and sense of the derivation of the spindle 12 from a zero position, i.e. to the magnitude and sense of the torque, exerted by the dynamometer. The A.C. output of the coil 15 is amplified and fed to the amplifier-oscillator 23 to shift its frequency correspondingly. This frequency shift is converted in a discriminator 24 to a corresponding unidirectional current which is fed back to the coil 15 in a sense to bring it back towards its zero position. A portion of the D.C. discriminator output is amplified at 25, and fed through a differentiating network back to the coil 15 to damp out oscillations thereof. Construction. The galvanometer magnet 16, Figs. 1, 2, 3, has its pole pieces 17 slotted to take resin-bonded powdered iron inserts 17<SP>1</SP> to accommodate the A.C. field at the air gap. The coil 15 has a two-piece soft iron core 18 supported on a non-magnetic bar 20, each piece having a similar powdered iron insert 21. The A.C. energization is effected by coils 30, 31 mounted on an insulating tube 32 supported by brass brackets 33, 34 bolted to the pole pieces 17 and to the core 18. The coils carry powdered iron cores 38 adjustable axially by screws 37 so that the coils may be tuned to the mean oscillator frequency. The deflection of the spindle 12 from its zero position is limited by stops Fig. 5 (not shown) to a very small value, so that the fixed dynamometer coils 10 may be made substantially flat. The dynamometer follows normal construction. Its movable coil 11 is mounted perpendicularly to the galvanometer coil 15 and the whole instrument is magnetically shielded Fig. 5 (not shown). Detailed circuitry, Fig. 4. The A.C. energizing coil 19 of the galvanometer is fed from the oscillator 42-43 in series with the primary of the input transformer 46 to the discriminator 49, and is tuned to the mean oscillator frequency by capacitor 44. The A.C. output of the coil 15 is fed over a tuned transformer 45 and a preamplifier 42<SP>1</SP> to the grid of tube 42 whereby the oscillator is frequency modulated in accordance with the magnitude and sense of the output signal. The frequency shift is converted in the discriminator 49 to a unidirectional voltage across the load resistors R, this voltage feeding back a proportional D.C. to the galvanometer coil 15 through a meter 60 (which indicates the torque or product A.B.) and a series resistor 52. The voltage drop across the resistor 52 is amplified in the triode 50 and through a capacitor 53 injects a first derivative component into the D.C. feedback circuit to effect damping of the galvanometer. A further network 54-56 compensates for plate supply ripple and transients. Modifications. Root-mean-square measurements of current, potential, power, and reactive power may be effected by the system in which zero suppression may be used. The meter 60 may be replaced by a D.C. potentiometer operating, e.g. a recorder. The system may be used in automatic A.C. regulating systems, and current balance telemetering of A.C. quantities. Specifications 669,715 [Group XXXV] and 749,251 [Group XL(c)] also are referred to.