Patent GB-325280-A (GB)
Title: Improvements in or relating to toll switching trunk circuits for telephone exchange systems
IPC: H04M3/523
Filed: 1928-11-16
Abstract: 325,280. Standard Telephones & Cables, Ltd., (Roome, F. A.). Nov. 16, 1928. Automatic and semi-automatic exchange systems. - A toll operator's position equipped with a number of connecting circuits for making connection between incoming and outgoing lines is also provided with one or more circuits similar to the connecting circuits and over which a connection may be prepared when all the connecting circuits are busy, the connection being subsequently transferred to an idle connecting circuit. In the arrangements described, the connecting circuits are individual to incoming toll lines at an operator's position and each circuit comprises a switch which hunts for an idle outgoing junction in the desired direction which the operator marks by means of keys or bv a marking switch set by impulses. First arrangement, Fig. 1. To set up a connection over an idle connecting circuit TST, the operator throws key JHK which connects the circuit to the incoming toll line TL and energizes relay Jhr to prepare the starting circuit for the hunting switch TF, which is provided with a terminal bank d for transfer purposes to be described later, and with a bank e in which each group of terminals corresponding to junctions in any particular direction is strapped together. The a, b, c terminals are multipled throughout the switches at a group of operator's positions but the d and e terminals are multipled over switches at a particular position. Operation of one of the direction keys DK1, DK2 completes the circuit of the power magnet PTF and connects the test relay Ptr to a particular group of e terminals. When an idle junction is found, battery over relay Tar is connected over terminals c, e to relay Ptr which opens the driving circuit and substitutes ground from DK over relay Shr for ground over its high resistance winding. Relays Shr, Cgr, Clr pull up in turn. Relay Clr locks up, disconnects the c and e wipers, connects Slr to the c wiper, and switches through. On seeing lamp SL alight, the operator restores the direction key DK, and the relays Ptr, Shr and Cgr, common to the group of hunting switches including the group PF in the preparatory circuit, fall back. If all the connecting circuits TST are busy, the operator throws PHK and the switch PF of the preparatory circuit PC selects an idle junction in exactly the same manner as TF, the circuits of the two switches being identical except for the connections between the d and e wipers. When a trunk circuit becomes free, the operator throws key JHK but presses a transfer key TK instead of a direction key. Relay Tpr connects marking potential to the d wiper of PF and starts TF, and relay Dbr disconnects the normal test wiper c of TF, the current of test relay Ptr being completed over the d and e wipers of both PF and TF. When the marked junction has been found. Glr switches through as before and the operator restores keys PHK and TK, to complete a homing circuit for PPF and release the common relays Ptr, Shr, Cgr. The connecting circuit is restored to normal when the operator releases key JHK. Signalling arrangements; busy marking an outof use junction. Relay Tar, operating when an idle junction is seized, connects battery over Tbr to the third wire of the outgoing junction circuit, so that Tbr may be controlled by the circuit at the distant exchange. When operated, Tbr throws both windings of Tar into the circuit of Slr which thereupon falls back and extinguishes. SL. A free junction which is out of use is arranged to connect battery to the third wire to operate Tbr which busies the junction by connecting both windings of Tar, in series, to the test terminal. Second arrangement, Fig. 2. To set up a connection over the 'connecting circuit TST, the operator throws the junction, listening, and dialling keys JHK, JLK, DK. Relay Shr operates over JHK, and impulse relav Isr of marking switch S pulls up over the dial springs and energizes Rrr. The first impulse operates Zcr, Zer, the impulses being repeated by Zer to magnet SM, Zcr, Rrr remaining energized during the train. Zer closes an additional circuit for itself over the interrupter springs T to ensure a full impulse. In the case of a single digit (1 to 9), Zcr falls back at the end of the train and Psr energizes over wiper B, but if there are two digits, first digit 0, Psr does not pull up and lamp WDL warns the operator that a second digit is to follow; Psr energizes at the end of the second digit and starts the finder TF. Provision may be made for more than two digits. Test relay Ptr is connected over the marking wiper C to the e terminals of the desired group of junctions and when an idle one is found, Ptr, Shr, Clr, Clir pull up in turn. The subsequent operation is the same as in the first arrangement except that the switch-through is performed by a separate relay Clir which also disconnects the impulse relay Tsr. Relay Rrr falls back and completes the homing circuit of marker S. If all the connecting circuits are idle, the connection may be prepared over the circuit PC in exactly the same manner, the transfer of the connection to an idle circuit TST being effected by throwing keys TK, JHK as described in the first arrangement.