Patent GB-677272-A (GB)
Title: Improvements relating to electronic repeater systems
IPC: G01R17/08
Filed: 1949-11-16
Abstract: 677,272. Electric control systems. EVERSHED & VIGNOLES, Ltd., and HAYDEN, G. T. Nov. 16, 1950. [Nov. 16, 1949] No. 29361/49. Class 40 (i). [Also in Group XL (b)] Relates to repeater systems of the type disclosed in Specification 589,423 for producing a D.C. current proportional to an applied torque in which the applied torque is autornatically balanced by an opposing torque produced by an electro-mechanical device actuated by the average output current of an electronic valve whose grid voltage is controlled in dependence on any torque unbalance, the said current also passing through a remote receiver indicating the magnitude of the applied torque. Since the valve current is unidirectional, such a system is incapable of indicating torque reversals and this is achieved according to the present invention by superimposing on the torque balancing current an opposing D.C. current so that the resultant current changes sign when the sense of the applied torque changes ; the applied torque may be that produced by a centre-zero wattmeter. As shown the tongue 3 of a torque-balancing polarised relay 2 is fixed radially to the spindle 1 of the wattmeter and the relay winding 4 is connected in series with a remote indicator 5 and resistor 18 in the cathode circuit of valve 8 which is energized from a full-wave rectifier 9, the relay contacts 22, 23 being maintained respectively at voltages positive and negative relative to the cathode 7 of valve 8 and the relay tongue being connected via resistance 21 to the grid of valve 8 which is also connected to the negative terminal 29 of rectifier 9 via resistance 16 and storage condenser 17. Winding 4 and indicator 5 are also connected in series with resistance 19 and fullwave rectifier 14 between the anode and cathode of valve 13 so that the currents from valves 8 and 13 are in opposition in devices 4 and 5, the circuit constants being such that for zero torque the two opposing currents balance out but when torque is applied the relay tongue 3 floats against contact 22 or 23 depending on the sense of the torque thereby maintaining the average value of the current from valve 8 greater or less than the current from valve 13. The voltage across resistance 18 is applied as a bias to valve 13 so that the opposing current from valve 13 is automatically reduced as the current of valve 8 is increased ; resistances 18 and 19 provide negative feedback for valves 8 and 13 respectively. Alternatively, the torque-balancing device may comprise an electro-magnetic moving coil instrument with the coil mounted on spindle 1 as described in Specification 589,423. In a modification, Fig. 2 (not shown), the relay contacts are replaced by two photoelectric cells forming two arms of a D.C. energized bridge, the junction of the cells being connected to the grid of valve 8, and the relay tongue carries a slotted arcuate shutter interposed between a lamp and the cells so that the relative illumination of the cells and hence the magnitude and sense of the resultant unbalance voltage applied to the grid of valve 8 depends upon the magnitude and sense of the torque.