Patent GB-665129-A (GB)
Title: Improvements in or relating to telecommunication systems
IPC: H04Q3/00
Filed: 1949-02-03
Abstract: 665,129. Automatic exchange systems. MERCER, R. Feb. 1, 1950 [Feb. 3, 1949]. No. 3040/49. Class 40 (iv). In an automatic telephone or like system, in setting up a connection an element of a relay, cross-bar, or like switching device is selectively' operated by means of cyclically-operated switching device such as a set of motor-driven cams or a set of relays closing contacts cyclically. In the embodiments described the switching devices in the talking circuit are groups of relays but cross-bar switches or similar assemblies of electronic valves or discharge tubes may be employed. A set of cams extends battery over individual leads to one side of each of the relays of a switching stage at instants in a cycle peculiar to each relay. The cams simultaneously extend ground to a set of individual leads and the reception of a digit causes the earth lead corresponding to that digital value to be connected to an operating lead extending to the other side of all the switching relays of the stage in multiple. Thus, at the instant in the cycle corresponding to the digit received, the relevant relay receives battery and earth simultaneously and is operated. System without switching relays, Figs. 1, 2. In this system a relay of a first group is selected by an impulse in the first half of a cycle, and a relay of a second group selected by the first group relay is selected by an impulse in the second half of a cycle while the control of busy signalling and ringing is effected by successive impulses at the end of a cycle. Throughout the description a digit is represented by 1, 2, or A (A being the maximum value of a digit) and only the circuits for these three values are shown. The control circuit comprises contacts C1, C2, CA and CA+1, CA+2, CA+A, operated by the registers (not shown) in response to dialled digits. An impulse generator consisting of a cyclically-operated multiposition switch (cams I to 2A+2), connects earth and battery respectively to the leads IE to 2A + 2E, and 1B to 2A + 2B at corresponding instants in a cycle. The rectangle SD represents switching devices by which connection is established between the control circuit CC and a selected battery feeding set BFS which is in turn connected over speaking leads LE, LB, hold lead HE, and operating lead OL to successive selecting devices represented by relays 1, 2, A for the first digit and relays A1, A2, AA for the second digit. It is assumed that contacts CA and CA+A and hold contact HC are closed, and that leads HE, OL are extended via SD to BFS and to relays 1, 2, A. At instant A in the cycle relay A comes up over CA in series with digit control relay DCR and both relays lock to HE. At instant A+A relay AA comes up over CA+A in series with 2DCR provided line AA is idle. Called line busy. In this case one of the other relays having access to AA is already operated and at instant A+A earth will be extended from A+AE over common lead CLAA to the side of resistance RA+A remote from battery and AA being short-circuited remains down. At the next instant 2A+1 busy relay BR comes up, locks to HE, and connects up busy tone. The caller then hangs up and releases HC to initiate release. Called line idle. Relay AA operates, locks to HE, and brings up COAA which connects the leads LE, LB to line AA. Relay 2DCR which comes up with AA disconnects BR and at instant 2A+2 switching relay SR operates and connects up ringing current via ring- trip relay RTR. On the reply of the wanted party RTR locks up and extends the called line to battery feed relay BFR. After the operation of SR the calling line is connected to a battery feeding set on the left of the condensers shown (Fig. 1) to energize a battery feeding relay and connect up an alternative hold earth at HEC. Contact HC is opened together with another contact (not shown) and SD disconnects OL, HE from BFS. Relays RTR, SR, A, AA, and COAA are therefore held and 2DCR and DCR relapse so that the equipment to the left of SD can be used for another call. Release. When the calling party hangs up contact HEC is opened and initiates release. System with switching relays, Figs. 3, 4. The provision of an auxiliary relay for each switching stage which disconnects the operating lead from the relays of the stage as soon as one relay thereof has been operated allows the same control impulses (1 to A) to be used for each digit. Relays 1DCR, 2DCR, 3DCR, and 4DCR are the digit control relays and contacts 1DC1-A, 2DC1-A, 3DC1-A, and 4DC1-A, the control circuit contacts corresponding to the four digits. Of the selecting relays 1DS, 1D1, 1D2, 1DA represent the set allocated to the first digit; 2DS, 2D1, 2D2, 2DA, the set allocated to the second digit where the first digit is A; 3DS, 3D1, 3D2, 3DA the set for the third digit where the first two digits are A, 1; and 4DS, 4D1, 4D2, 4DA the set for the fourth digit where the first three digits are A, 1, 2. To set up a call to line A12A contacts 1DCA, 2DC1, 3DC2, and 4DCA are operated. At instant A in the cycle earth over contact 1DCA is extended over back contacts of the DCR relays to lead OL and thence via the left-hand winding of 1DS to the right-hand ends of relays 1D1, 1D2, 1DA. The last named relay which has battery connected via AB to its other end at this instant pulls up in series with 1DCR and 1DS and all three lock up. Relay 1DA extends the leads LE, LB, HE and OL to the second set of relays and the auxiliary relay 1DS disconnects OL from the first set. At instant 1 in the next cycle 2DCR, 2DS, and 2D1 operate in like manner over contact 2DC1; and at instant 2 3DCR, 3DS and 3D2 come up over 3DC2; 4DS operating over HE immediately after switching through has taken place. At instant A in the same cycle 4DCR and 4DA operate if the line A12A is idle and COA12A pulls up to lead HE to connect LE, LB to the called line. At instant A+2 SR pulls up over lead OL1 and locks to earth at HEC (closed by the battery feeding relay of the calling line) or if HEC is not yet closed, at HC (HC releases after HEC has operated). SD is held operated under control of HC by means not shown. From this stage operation is similar to that of the first system. Called line busy. If A12A is busy then at instant A earth is placed on the side of resistance RA remote from the battery connection via front 4DS and common lead CLA to which AE is connected by means (not shown) which may be a relay similar to 4DA giving access to A12A or the cut-off relay COA12A. Relay 4DA remains down and at instant A+2 FR pulls up so that at instant A+1 in the next cycle BR follows and reverts busy tone in the usual way. The calling party hangs up and the equipment is released.