Patent GB-581021-A (GB)
Title: Improvements relating to electric signalling systems
IPC: H04M19/02
Filed: 1944-04-15
Abstract: 581,021. Automatic exchange systems. SIEMENS BROS & CO., Ltd., and HENSLER, B. A. April 15, 1944, No. 6986. [Class 40 (iv)] [Also in Group XXXVIII] In a system for high speed transmission of digits such as telephone numbers a code is used comprising a sequence of elements obtained from a choice of three signalling conditions. The individual signalling conditions might be x a given frequency, y another frequency and z a combination of the two frequencies ; or x a direct current in one wire, y a direct current in another wire and z either direct current in both wires or direct current in a third wire. Methods are described for transmitting such codes from a keyboard and receiving and registering them on a 4-relay register. In the code used, when the z element occurs in a sequence it is always the first element of the sequence. In the key-sender, Fig. 1, the individual frequency sources, commoned at C, are connected to XW, YW and the combination of the frequencies to ZW, and are transmitted to the signalling wire SW by high speed relays XY, XA, XB, YA and YB. The first element of the sequence is produced by operating either XY, XA or YA, through a direct circuit, e.g. key 3 for XA. The second element is obtained by operating either XA, YA or XB through their respective retard coils RA, RB, RC. The third elements are retarded with respect to the second elements by operating YA, XB or YB through retard coils RB, RC, RD and contacts of the relay operated immediately previously. Thus if key 9 had been operated the relay sequence would be YA, XB, YB thus transmitting the code y, x, y. In the register, Fig. 6, the respective incoming tones operate high speed relays XY in the receiver SR. Operation of X or Y removes the short circuit from relay S which operates to prepare locking circuits for the high speed relays A ... D through relay DS which, when operated, operates HA which prepares a circuit for relay GA. Relay A registers receipt of x frequency, relay B that of y frequency and relay D receipt of x and y frequencies together. If y frequency follows an x frequency relay C operates over a2 and relay A whose coils are wound differentially releases during the change over of c2. Rectifier MRA short circuits relay B to prevent it operating should Y still be operated when A falls back. Thus the number 9 whose code is y, x, y would operate relays B and C of the register. On the termination of the first sequence, absence of tone causes S to be short circuited and so to release, the respective hold circuits for relay A ... D now being maintained through storage relays CA ... CD via contacts of GA and looking contact L. The storage relays lock over their own contacts and disconnect DS. Release of DS removes the short circuit from GA which operates in series with HA, to extend the locking circuits of relays A ... D to a succeeding set of storage relays via contacts of GB. GA also transfers the control by ds1 to relays GB, HB whose functions are similar to those of GA, HA. Further storage sets are connected up similarly. When the stored information is no longer required locking contact L is released to restore the register to normal. The register given in Fig. 7 (not shown) stores the incoming digits direct on the storage relays without the use of intermediate relays such as A ... D, Fig. 6. Two and three-wire intermediate D.C. circuits, Figs. 2 and 3 (not shown), can be used to apply the code to signalling wires remote from the keyboard. 2-Wire or 3-wire D.C. signalling, Figs. 5 and 4 respectively (not shown), can also be used throughout.