722,359. Automatic speed-control systems. AKTIEBOLAGET SVENSKA METALLVERKEN. June 27, 1952 [June 29, 1951], No. 16233/52. Class 38 (4). [Also in Group XXXVIII] In apparatus for controlling the relative speeds of operation of sections of a continuousprocess manufacturing plant having a driving motor operating each section, a plurality of cascaded tachometer circuits, one for each section, each comprising a tachometer generator driven from the corresponding driving motor and a resistance combination connected in series with each generator, the input and output terminals of each tachometer circuit being constituted by electrical connections to each circuit of the corresponding resistance combination and being respectively connected to the output terminals of the preceding and the input terminals of the succeeding section by two conductors, one of which has inserted therein the sensitive circuit element of the speed regulator of the corresponding motor so that the speed thereof is increased or decreased when the voltage across the sensitive element departs from zero in one sense or the other to restore such voltage to zero; one input terminal at least of each tachometer circuit is constituted by a movable tap on one of the resistances of the resistance combination, and one of the output terminals of the same circuit is constituted by a fixed or adjustable tap on the same resistance such that the tachometer circuit input voltage is adjustable by varying the input tap of the circuit to a valve which may alternatively be higher or lower than the output voltage of the same circuit. Fig. 2 shows a tachometer circuit for controlling the relative speeds of operation of a continuous manu. facturing process involving four sections driven by motors (not shown) which are correspondingly coupled to drive four tachometer generators 10, 20, 30, 40 connected in series with corresponding equal resistance chains each comprising respectively a fixed load resistance 12, 22, 32 or 42, a potentiometer 15, 25, 35 or 45 having a sliding contact and a centre tap, and a variable preset resistance 13, 23; 33 or 43. The junction of the tachometer 10 and resistance 12 is connected to the slider of potentiometer 14 through a reference voltage source LG and the sensitive element 11 of the control system of the motor associated with tachometer 10, and to the junction of resistance 22 and tachometer 20 through the sensitive control element 21 of the motor associated with that tachometer, while the centre tap of potentiometer 15 is connected to the slider of potentiometer 25. Similarly tachometer 20 is connected to tachometer 30 through the sensitive control element 31 of the motor driving that tachometer which in turn is connected to tachometer 40 through the sensitive control element 41 of the motor driving it, and the centre tap of potentiometer 25 is connected to the slider of potentiometer 35 whose centre tap is in turn connected to the slider of potentiometer 45, and so on for successive sections of the plant. The motor driving the first plant section is controlled to run at a speed such that the portion of the voltage of tachometer 10 tapped off at the slider of potentiometer 15 balances the reference voltage source LG so that zero current flows in element 11 and any deviation from this motor speed causes a current to flow in the element to operate the motor control and restore the desired speed. Similarly the motor driving the second section is controlled to run at a speed such that the slider voltage of potentiometer 25 balances the centretap voltage of potentiometer 15, the motor driving the third section is controlled so that the slider voltage of potentiometer 35 balances the centre-tap voltage of potentiometer 25, and the fourth section motor is controlled so that the slider voltage of potentiometer 45 balances the centre-tap voltage of potenitometer 35. When the potentiometer sliders are positioned on their respective centre taps, the motors run at the same speed and the tachometer output voltages are equal, while adjustment of a potentiometer slider away from its centre point increases or decreases the controlled speeds of all the subsequent motors, which, however, run at identical speeds inter se. The apparatus is applicable to speed control of sectionally operating paper making, wire drawing and rope-making machines. In a modification, Fig. 3 (not shown), the speed-control potentiometers and preset resistances for each section may be duplicated and correspondingly disposed at each end of the appropriate load resistance, the input connections from the preceding section being applied to the sliders of the two speed-control resistances whose centre taps are connected to the succeeding section, while the appropriate tachometer is connected across the ends of the two preset resistances. Two separate speed-control resistances are thus available and may be disposed at different parts of the plant. In a further modification, Fig. 4 (not shown), the speed-control potentiometer of each tachometer section may be replaced by a chain of 4 variable resistors, to the centre point of which chain the input voltage is applied while the output is derived from the centre tap of a fixed resistance in parallel with the chain, whose outer and inner pairs of resistances are respectively ganged for reciprocal variation and are adjustable from two different points of the plant.