GB579118A - Improvements in or relating to remote control arrangements - Google Patents

Abstract

579.118. Electric signalling and control systems. STANDARD TELEPHONES & CABLES, Ltd., and SCULLY, C. T. Sept. 30, 1941, No. 12662. [Class 40 (i)] Signalling and control is effected by transmitting pulses of constant amplitude with subtantially linear trailing and leading edges, the duration of the pulses being varied in accordance with a controlling variable, e.g., the position of a meter. The pulses are transmitted directly or by carrier trains, and at the receiver are shaped by amplification and removal of the tips and roots, the mean D.C. value obtained from them being indicated or used to control a motor for effecting a desired operation. The transmitter, Fig. 6, comprises a valve having constant A.C. input from source f and variably biassed by potentiometer R2 controlled by the instrument or variable by the reading the value of which it is desired to transmit. The valve therefore passes the positive peaks of the A.C. voltage, as shown in Fig. 3, the amplitudes being dependent on the value of the variable. The resultant impulses are amplified and limited in amplitude by valve V2 to provide the wave form shown in Fig. 4 which is used to modulate a transmitting oscillator V3, the depth of modulation being determined by potentiometer R11. In a modification, Fig. 7 (not shown) the amplitude of A.C. voltage from a constant source is determined by a variable condenser controlled in accordance with the instrument reading or value of the variable. One form of receiving arrangement is shown in Fig. 10, in which the output of the high frequency receiver is applied to the cascade amplifier shown. The second and third valves are respectively, positively and negatively, biassed to saturation and cut-off to remove the distorted upper and lower portions of the wave form and retain the central undistorted portions. A voltmeter connected across XZ or a galvanometer G provides a reading of the average intensity. In a modification shown in Figs. 11, 12 utilizing a servomotor at the receiver for driving a load in accordance with the transmitted variable, the apparatus 10-14, Fig. 11, comprises the transmitter previously described, and 16, 17 comprise the high-frequency receiver and limiting amplifier. The load 18 is moved by motor 19 and a device 23 positioned in accordance therewith is used to control an A.C. source 21 applied to impulse generating and limiting stages 22, 24 as at the transmitter. The source 21 may be a saw-tooth oscillator synchronised by the received pulses at 17. The outputs from 17 and 24 which represent respectively the controlling variable and the position of the load 18 are used to control differential relay arrangements 25, 20 which control the motor. The differential relay, Fig. 12 comprise valves V12, V13 receiving respectively the outputs of 24, 17 and having anode resistances R33, R34 coupled by condenser C16 having a suitable time constant. The two positions and centre zero relay W operate contact X or Y depending on the relative values of the outputs to control the motor 19.