Patent GB-571687-A (GB)
Title: Improvements in or relating to electrical indication at a distance
IPC: G08C19/16
Filed: 1941-03-11
Abstract: 571,687. Electric selective signalling systems. STANDARD TELEPHONES & CABLES, Ltd., HARTLEY, G. C., McWHIRTER, E. M. S., and HANDLEY, J. March 11, 1941, No. 3300. [Class 40 (i)] [Also in Group XXIV] A magnitude is transmitted in the form of a series of signal elements of one of two possible conditions, each element being a digit of a number representing the magnitude in the binary scale (digits 0-1). The invention is applicable to the transmission of bearings as determined by direction-finders. A simplified transmitter for providing indications of multiples of 45 degrees and using 3 binary digits is shown in Fig. 1. The switch S, Fig. 1, is set manually or by a direction-finder, each position representing a 3-digit binary fraction the digits of which (1 or 0) are determined by multipled connections between the three banks and relays NP, PP. The first digit (wiper a) depends on whether the angle is within 0-180 degrees or 180-360 degrees, the second (wiper b) on which quadrant within the 180 degrees and the third (wiper c) on which sector of 45 degrees. Transmission is effected by distributer D which operates NP or PP as the case may be to send over line L a positive or negative impulse for each digit separated by open-line intervals. The digits are received by a back-stroke switch D1, Fig. 2, and storage relays A ... D (D being an unused extra relay) controlled by oppositely polarized relays P, N. When the sluggish relay CA relapses on termination of the transmission CC, which has been holding the storage relays, falls back to home the switch, the holding circuit being maintained by a back contact of CA. The binary number is translated into an angular position by a no-normal switch s1, Fig. 3, driven by a motor under the control of a main clutch relay CD. The bank contacts are multipled correspondingly to those of the transmitting switch but the connections are taken over contacts of the storage relays A-C to reverse drive clutch relays BD, FD so that the switch is set to a definite position after a series of back-and-fro movements. A common switch may be used for transmitting and receiving. To obtain greater accuracy, switches with a large number of positions are necessary, for example, 4096 positions are required for an accuracy approximately within 5 minutes. To obtain this accuracy, two 64-position switches s1, s2, Fig. 4, may be used and switch s2 is driven through a 64 to 1 reduction gear. As one step of s2 corresponds to a complete traverse of s1, the position of s2 for some positions of s1 may not be precise. To obviate this, s2 has two sets of wipers engaging the same banks and angularly displaced corresponding to half the distance between the centres of successive contacts. One pair is shown at A, B, Fig. 5, one being made effective for positions 1-32 of s1 and the other for positions 32-64 under the control of relay CO, B being effective over the earlier part of the movement and A (behind B) being effective over the latter part. The bank of s1 which controls CO is diagrammatically shown as extending over a complete revolution of a single-ended wiper. The complete arrangement for driving the switches s1, s2 is shown in Fig. 7. Shaft DS driven by gearing 13 by motor M drives two reversing gears B, B 1 which respectively drive a pinion D geared to the shaft IS1 of the left-hand sun-wheel of differential gear F and a pinion CG on the differential cage. The right-hand sun-wheel drives shaft IS2 which is geared to drive switch s2, shaft IS1 being geared to drive switch s1 (not shown). The switches are controlled by a circuit, such as Fig. 2, with 12 storage relays and two circuits, such as Fig. 3, controlled respectively by the first and second groups of 6 storage relays and controlling the pairs of clutch magnets of the reversing gears B, B1. Each reversing gear is arranged as shown in Fig. 9 and comprises a plate CP freely mounted on the driving shaft DS and carrying a pair of gears B, C, of which B is constantly in mesh with the driving pinion A and B or C in mesh with driven pinion D depending on the angular position-of plate CP which is controlled by the clutch magnets BD, FD and is normally biassed to the central free position. The shaft of the switch s2 is set under the control of its own banks marked by the digits representing the six higher powers of the radix and in addition, through the differential and other gearing arranged to provide a 64 : 1 reduction, a fine setting corresponding to the setting of switch s1 under the control of the markings by the digits representing the six lower powers of the radix. In the arrangement described, one revolution of pinion D drives s1 one step and a revolution of pinion CG drives s2 two steps due to the action of the differential, but this dissimilarity could be obviated by altering the gear ratio for the drive to s2. In order that the pinions should proceed to full step positions in spite of inaccuracy in timing of the operation of the clutch magnets, the pinions carry heart-shaped cams HF, HC, the latter having two depressions 180 degrees apart, engaged by jockey rollers SR1, SR2 carried by spring-pressed levers 14, 15. The levers 14, 15 may also control offnormal contacts such as ons, Fig. 3, for maintaining the circuits of the clutch magnets until the full step position is approached. The mechanism shown in Fig. 7 may be used as the switch s, Fig. 1, for transmitting, the switches s1, s2 being set manually, or automatically by controlling the clutches from the directionfinder with the help of coarse and fine adjustment relays.