Patent GB-698335-A (GB)
Title: Improvements in or relating to electrical remote signalling systems
IPC: H02J13/00
Filed: 1950-07-24
Abstract: 698,335. Electric selective signalling systems. ERICSSON TELEPHONES, Ltd., and STEVENS, J. R. H. July 23, 1951 [July 24, 1950], No. 18382/50. Class 40 (i). In a system in which apparatus at a controlled station is selected from a controlling station by means of code signals over a transmission line and on which checking signals are sent in the reverse direction, the signals in both directions are determined by the electrical condition of contacts wiped by switches connected directly to the trarismission line. In the system shown, a manually operated switch SS, Fig. 2, is used to select any one of the 25 lamps LP, Fig, 4. A coding switch MA, Fig. 1, then hunts for the position marked by SS and a combined sequence and sending switch SA runs through a cycle in which the number of the selected lamp is transmitted as a 5-digit binary number in accordance with the position of MA. The system is such that after each digit transmitted, an acknowledging signal is received from the controlled station and after the whole number has been transmitted, the number received is sent back to the controlling station and checked against the position of switch MA. The cycle must be completed before the selected lamp is lit and the cycle cannot be completed (a) if no signal is received in response to a signal transmitted or (b) if the binary number registered at the controlled station differs from that registered at the sending station. The binary number is decoded at the controlled station by a switch MB, Fig. 3, which remains inert if the signal in any position represents zero, moves 16 steps if the digit of highest denomination (sent first) is 1, 8 steps if the next is 1 and so on, moving one step if the digit of lowest denomination (sent last) is 1. Setting coding switch. When switch SS is moved to a new position, K falls back and, provided that switch SA is in its normal position 1, energizes PA which is followed by DA and by driving magnet SADM. The latter releases PA whereupon DA and the magnet are released and the switch SA moves to position 2. In this operation MA hunts for the position marked by SS under control of K. On the operation of the latter, PA, which has been short-circuited, operates via bank SAe and DA is re-energized and co-operates as before with PA and SADM to drive the switch SA to position 3 in which battery is connected across the transmission line in the normal direction, i.e., with the + pole to the A wire to give a starting signal and switch SA moves automatically to position 4 to terminate the signal. In the odd positions of SA, from which the switch is always stepped automatically, DA is short-circuited until the operation of PA to delay the automatic step. Transmitting code signal and receiving acknowledging signals. In response to the starting signal, relay YB at the controlled station, which is polarized by rectifier MR4, energizes PB which locks and is followed by DB and when YB falls at the end of the starting signal, driving magnet SBDM is energized, PB and DB fall and the switch SB moves to position 2 in which normal battery is connected across the line to operate YA (polarized by MR2) at the sending end and PB, DB co-operate to step the switch to position 3 after a brief delay due to the fact that DB is short circuited in the first five even positions of SB. The operation of YA energizes or does not energize relay RA according to the position of coding switch MA. In every case, however, PA is operated and interacts with DA to drive the switch SA to position 5 on which it connects normal or reverse battery across the line, according as RA is or is not energized, to produce the first digit signal. As indicated above, the switch then moves automatically to position 6. Every signal impulse causes the switch SB to step on and connect normal battery across the line, and this energizes YA to energize RA if necessary, according to the position of MA, and to step SA out of its even positions and so actuate the transmission of the next digit signal. The last impulse is sent from position 13 and the switch moves to position 14. Decoding received signal. If XB, polarized by MR3, is energized by the first digit signal (representing the digit of highest denomination in the binary number), SB being in position 3, the decoding switch MB makes 16 automatic steps under control of bank MBa. If YB is operated the switch remains inert but the operation of YB is necessary to initiate the transmission of the acknowledging signal. Similarly in positions 5, 7, 9, and 11 the switch makes 8, 4, 2 and 1 steps, if XB is energized by the respective digit signal, under control of banks MBc ... MBf. Repeating back number received. After the reception of the final digit, switch SB moves automatically to position 13 (two steps). During this movement RB is or is not energized according to the position of MB to determine the direction in which battery is connected across the line in position 13. The switch then moves automatically to position 14 after a brief delay to await the acknowledging signal from the control station. The latter receives the first checking digit with SA in position 14. XA (polarized by MR1) or YA responds, and provided that the signal is correct, as determined by wiper MAa, drives SA to position 15 in which an acknowledging signal is sent and from which SA is driven automatically after a short delay, to await the next checking digit. The final acknowledging signal is sent in position 23,of SA and received in position 22 of SB. The latter then goes automatically to position 25 in which it sends a terminating signal and then to position 1 in which the selected lamp is lit. The terminating signal causes SA to leave position 24 and proceed automatically to its normal position 1. If at any stage the operation is faulty, the cycle cannot be completed and the selected lamp is not lit.