Patent GB-610051-A (GB)
Title: Improvements in or relating to electrical measuring or controlling apparatus
IPC: G01R13/00
Filed: 1945-10-10
Abstract: 610,051. Electric follow-up systems. SANGAMO WESTON, Ltd., and SHARP, F. A. Oct. 10, 1945, No. 26519. [Class 40 (i)] An arrangement by which a relay, recording instrument, &c. may be controlled by a weak current comprises a coil movable in the field of a permanent magnet on which is superposed an alternating component so that an alternative current is induced in the coil according to its angular position. A further alternating current is combined with that induced in the coil so that the two currents oppose when the coil is on one side of the zero couplingposition and assist when the coil is on the opposite side. Fig. 1 shows an arrangement by which a master galvanometer 10 controls a recording instrument 24. A moving coil 12 moves in the interpolar gap of a permanent magnet 11 and carries a pointer 14 moving over a scale 15. Shunting the interpolar gap is a laminated electromagnet 16, having a winding 17 energized by A.C. from an oscillator 18 so that air alternating flux is superposed upon the permanent magnet flux. A secondary winding 19 is connected in series with the coil 12 and with a photo-electric cell 13 and the primary winding of an input transformer 20 to an amplifier 21. The amplifier output is supplied through a transformer 22 to a rectifier 23, the D.C. output of which operates the moving coil recording instrument 24. The voltage induced in the winding 19 is arranged to be equal to that induced in the moving coil 12 when this is in either extreme position, the relative phasing of these voltages being such that they are in opposition when the coil is between the mid- or zero-coupling position and the left-hand extreme position 0, so that the resultant combined output of the coils 12, 19 varies between zero and double the voltage induced in the coil 12. Scale distortion due to non-linear rectifier characteristic &c. may be compensated for by using high amplification and inserting a series resistance 25 between the amplifier output and the input to the rectifier bridge 23 and by employing suitably shaped pole-pieces in the master device 10 or alternatively by positioning the pointer stops and adjusting the free zero position of the master device so as to include only the centre portion of the operative range. Zero suppression of the controlled instrument 24 may be effected by supplying an adjustable D.C. voltage in series therewith from a potentiometer 28, Fig. 2, across a D.C. source 27. As shown in Fig. 3, the A.C. output from the moving coil 12 and the further A.C. component may be kept separate and applied to the amplifier 21 by separate transformers 29, 30 with their secondary windings in series. The amplitude of the further A.C. from the oscillation source 18 may be adjusted by means of a potentiometer 32. The periodically varying magnetic field of the device 10 is provided by a winding 17a mounted directly on the magnet 11, which may be a permanent magnet or of laminated soft iron. Fig. 4 shows an alternative arrangement for direct summation of the alternating voltages. The oscillator 18 supplies the winding 17a on the magnet 10 so that current is induced in the moving coil 12, which may be controlled by a photo-cell 13. The circuit of the moving coil 12 includes a load resistance 40 and byepassing condenser 26. The output of the oscillator 18 is also applied through a potentiometer 32 to one input terminal of a cathode follower or other highimpedance follower stage 31, the other terminal of which is connected to one end of the load resistance 40 so that the input to the stage 31 is the sum of the A.C. voltage tapped-off from the potentiometer 32 and the A.C. voltage developed across the load resistance 40 derived from the source 18 by induction in the coil 12. The follower stage 31 feeds the amplifier 21. The output transformer 22 may have a number of secondary windings for operating separate controlled instruments. In a modification, Fig. 6, an integrating meter 33 has its potential coils 34 fed from the oscillator 18 and its current coils 35 fed from the amplifier 21 through a step-down transformer 36. A.C. or D.C. microampere hours, lumen hours, &c. may thus be recorded. Fig. 7 shows an arrangement for recording the product of two variable factors, each of which controls a separate master device 10 connected to the oscillator 18. The outputs of the master devices 10 are supplied through amplifiers 21 to the windings 37, 38 of an integrating meter 39 or a meter of the dynamometer type. Specification 604,312, [Group XXXIX], is referred to.