Patent GB-747555-A (GB)
Title: Remote positioning system
IPC: G05D3/14
Filed: 1952-12-05
Abstract: 747,555. Electric control systems. BRISTOL CO. Dec. 5, 1952, No. 30997/52 Class 40(1) In a control system of the self-balancing A.C. bridge type, arrangements are made whereby abnormal unbalance potentials due for example to a fault do not exercise control on the balancing motor. This may be done by causing the flow of grid current due to the abnormal potentials to paralyse the amplifier controlling the motor (Fig. 1) or by providing a voltage sensitive shunt to the amplifier input circuit (Figs. 3, 4 (not shown) and 5 (not shown)). The invention is described in connection with a control system for the motor in which the sensitiveness of the control amplifier is modified during the operation of the device to eliminate hunting (a) by causing the grid current to bias the amplifier towards cut off and (b) by causing the motor when running to operate a relay either to connect up a negative feed back circuit (Fig. 1) or to apply a gainreducing bias (Figs. 3 and 9). The effect of these provisions is that the motor is energized in a series of pulses which become less frequent as balance is approached. If the motor stops short of the balance position it is re-started but does not get up enough speed to overshoot. Normal operation: Unbalance voltages from the bridge formed by the elements 21, 22, 40, 41, 43, 44 (Fig. 1) are amplified in valves 74, 69 the output from which is, rectified by an electro-mechanical interrupter 34 and in accordance with its phasesense operates a polarized relay 28 in one direction or the other to connect up the appropriate field winding of a reversible motor 25 which drives the controlled object 57 and the slider. 22 of the control bridge. At the same time, relay 87, which 'is in parallel with the motor armature, completes a negative feed-back circuit, Fig. 1, or a back-biasing circuit, Fig. 3, for the amplifier. In both arrangements a charge is built up on a capacitor 89 by the flow of grid current and in due course the signal, weakened by the approach to correspondence between transmitter and receiver and by the circuit connected up by 87 is insufficient to overcome the voltage on 89 and the motor is disconnected. The resulting relapse of 87 increases the effective signal however and the motor is connected up again but the operation of 87 again reduces the effective signal. If the motor stops short of the balance point this operation is repeated but the circuit elements are chosen with a view to attaining balance with a minimum of steps. In a modified arrangement, Fig. 9, the relay 87 is omitted and the polarized relay, by connecting capacitor 163 to ground via resistor 162, increases the negative charge in 89. Abnormal operation: The values of resistors 40, 41, 43, 44 are such that the normal range of signal voltages is small compared with the voltage applied to the amplifier in the case of a fault. The effect of the latter, in the arrangement of Fig. 1, is to produce a paralysing bias on the first amplifier valve 74.from capacitor 79, which is charged by grid current before an effective output can be produced. In an alternative arrangement, Fig. 3 the input circuit of the amplifier is shunted by a capacitor 107 in series with a rectifier 106 which normally is biased to be effectively non-conducting owing to its connection to potential divider 110, 111. Excessive unbalance voltages however, rectified at 108 oppose this bias and render the rectifier conducting and the input is effectively short-circuited. This circuit may be modified by connecting the low-potential end of resistor 88 to the grid of 74 instead of to ground so that the shunting action is supplemented by a back biasing action on the second amplifier valve, (Fig. 4, not shown). In another arrangement (Fig. 5, not shown) the initial bias of the rectifier 106 is derived from a connection to resistor 113. Detail modifications: (a) A two-pole rectifier as described in Specifications 703,772 and 703,773 [both in Group XXXV] can be used instead of rectifier 33 with a single-wound polarized relay (Fig. 6, not shown). (b) A phase sensitive A.C. relay is used instead of a polarized relay excited via a rectifier (Fig. 7, not shown). (c) A fluid operated motor is used instead of an electric motor (Fig. 8, not shown). (d) A single valve amplifier is used (Fig. 10, not shown).