Patent GB-626065-A (GB)
Title: Improvements relating to electric selecting systems
IPC: H04Q3/42
Filed: 1946-07-31
Abstract: 626,065. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., and CHRISTIAN, D. A. July 31, 1946, No. 22760. [Class 40 (iv)] In a system of the revertive control type, pilot contacts passed over by the selector are counted off by a counting device and the testing circuit for the outlets is only connected up when the setting of the counting device agrees with that of the register. The invention is described with reference to a system using 200-outlet switches, double hunting being used in the group selectors and the final selector giving access to two hundreds groups, the particular hundreds group to be selected being determined by the route of access over which the switch is seized. A feed bridge circuit is associated with the first group selector and has access to a common control circuit. In the group selectors the pilot contacts are in the first arcs and precede each group of outlets. In the final selectors, separate arcs T, U are provided for the tens and units pilot contacts, the former being at the first position of each decade. Setting of group selectors. Impulse and release relays A, B operate in the bridge circuit and connect up GN in the first group selector. The common control circuit is taken into use over switch H and dial tone is transmitted.. Relay N operates followed by R in the control circuit, and the dialled digits, repeated by relay A, are received alternately on digit switches DA, DB to allow of an extended hunting time for the selectors as described in Specification 623,184, CA, CB being dialling relays and SA, SB change-over relays associated with the respective switches. Relays C, L in the bridge circuit are operated during each digit. LL operates when the switch moves off-normal and connects up SA. On release of dialling relay CA, R releases operating CB and energizing the power magnet of the group selector over wire l. As the switch passes the pilot contacts positive pulses are sent back alternately from arcs P1, P2, over the + and - wires to energize GCA, GCB which operate the relay counting chain CI... CXI. When the setting of the chain corresponds with that of DA test circuits are made for relays TA, TB over the + and - wires to the wipers P1, P2. When a free outlet (or pair of outlets) is found, TA or TB (or both) operate to stop the selector and R, TTA or TTB follow to apply either a weak or strong positive potential to the p-wire to operate the appropriate one of the switching relays GS, GZ, the latter being marginal. The operated switching relay locks to the subsequent earth on the p-wire. If both TA and TB operate, TTB does not operate, being disconnected at tal. Relay R releases SA, which restores the counting chain, and remains operated until CB releases at the end of the next digit, whereupon it releases operating SB in place of SA and the next selector is started to search in a similar manner for an outlet in a group corresponding to the setting of DB. Setting of final selector. Relay FN operates on seizure and depending on the route of access S operates or not to control wiper switching. Outlets to a final selector are characterized by a high resistance earth which operates K (but not I) in the control circuit to bring up KA which disconnects GCA, GCB and connects FCA and FCB to the - wire. The tens and units pilot contacts in the banks T, U are connected alternately to earth and -50V potential over resistances. Relays FCA, FCB which are connected to a point of potential - 25V operate alternately to count the pilot contacts passed by the wiper T on the chain CI ... CXI, and when that number agrees with the registered tens digit, TA operates to - ve battery on the +wire, followed by R and TTA, the latter applying +ve battery to the p-wire to operate FR in the final selector. When R again releases after the reception of the units digit the final selector is restarted and the counting chain registers the number of pilot contacts passed by the wiper U. If the required outlet is free, TA, R and TTA operate and stop the switch. Relay K re-operates with R after each selection and brings up first KB and then KC which connects earth through a resistance to energize ringing relay F (but not J) which releases the common control circuit. When the called subscriber answers, ring trip relay TR operates followed by feed relay Y and during the subsequent release of L a booster metering pulse is applied to the p-wire. Busy conditions. If all outlets of a group (or the particular outlet in the final selector) are (or is) busy the selector continues until the counting chain saturates, when CXI operates BT which transmits busy tone. Outgoing junctions. These are characterized in the L arcs of the selector by direct earth which on seizure operates I in the control circuit to bring up both F and J in the bridge circuit. The former releases the control circuit and the latter brings up the ring-trip relay TR and also substitutes the polarized back bridge relay D for the feed relay Y. The remaining digits are transmitted over the junction by contact a2, contact c2 providing an impedancefree impulsing loop. When the called subscriber replies battery reversal over the junction operates D to effect metering as above. PBX hunting. The resistances connected to the pilot contacts of all the lines except the last are reduced so that marginal relay PX operates in series with FCA or FCB and owing to the reversals of current as the selector passes over successive outlets, PX releases intermittently to step the digit switch in synchronism with the selector to maintain the test circuit. If all outlets of the group are busy PX fails to operate on the last outlet and busy tone is reverted in the manner described above. The selector may be arranged to move slowly over decades containing PBX groups to enable the digit switch to keep pace with it. Specification 623,177 is referred to in the Provisional Specification.