Patent GB-157817-A (GB)
Abstract: 157,817. Relay Automatic Telephone Co., Ltc., (Assignees of Betulander, G. A.). Dec. 31, 1919, [Convention date]. Automatic and semi-automatic exchange systems.-In a system having mixed automatic and semi-automatic service, the same trunks of the first selective stage are common to both classes of subscribe, and are provided with means for connecting themselves temporarily to an impulse receiver, if the call is from a full-automatic subscriber, or to an operator's position if the call is from a semi-automatic subscriber. The invention is descrbed in its application to a system in which select on is effected entirely by means of relays. Each group of calling lines is divided into sub-groups such as L1 - - L4 (other subgroups being represented by the sub-group relays GR2, GR3) and a calling line is connected to an idle trunk such as FL1, selected by a common searcher S1, by the conjoint action of a relay such as M1, R3 individual to the calling line and a relay such as A1, R, individual to the trunk, these relays co-operating mechanically so that only those contacts K3G1 of the relay A1R1 are closed which correspond to the relay M1R3. By similar means, but under control of a different type of searcher S2, the trunk is connected over RL1, RL2 &c. to an idle impulse receiver, or over SL1, SL2 &c. to an idle operator's circuit, such as EP1. Specification 141,007 is referred to. Semi-automatic call. Connection to idle trunk under control of searcher S1. The line relay LR3 of a calling semi-automatic line L3 energizes the corresponding relay M1R3, which locks itself up in series with the sub-group relay GR1 and a relay IR. The relay GR1 connects the test wires of the trunks FL1 - - FL3 to the test relays PR1 - - PR3 of the searcher, so that the test relays of idle trunks are energized in series with the corresponding trunk relays A1R1 &c. The test relay of the first idle trunk (say FL1) opens the circuits of the succeeding test relays and closes a locking-circuit for the relay A1R1. The line L3 is now connected to the trunk FL1 over the contacts K3G1, and line relays AMR1, AMR2, Fig. 3, are energized. Relay AWR2 energizes relay CR1, which closes a 'circuit through the upper winding of relay A1R1 and the cut-off relay UR3, which de-energizes relays LR3, M1R3 so as to release the searcher S1. Connection of trunk to idle operator's circuit under control of searcher S2. The relay CR1 closes a circuit through relay M2R1, individual to the trunk FL1, in series with relay HR2, which energizes the searcher starting-relay SR and the first of the relays RR1 - - KR5. The relay KR1 energizes the next relay KR2 (which locks itself over the back contacts of the succeeding relays) and connects a relay P1R to the test wire P1L1 of the trunk SL1 to the operator's circuit EP1. If this circuit is idle the relay P1R receives current over a resistance R2, open-circuits relay KR2, and closes a circuit over a front contact of relay KR1 to energize relay A2R1, which co-operates with relay M2R1 to close the contacts K1G11, connecting the trunk FL, to the circuit EP1. If on the other hand this circuit is busy, the relay P1R is not energized, the relay KR1 is de-energized by relay KR2, and the trunk SL2 to the next operator's circuit is tested over the wire P1L2. The relay KR2 being now energized and KR, de-energized, a circuit is closed to energize KR3, which unlocks KR2. Successive relays are energized in the same way, each relay energizing the next and unlocking the preceding relay, until an idle circuit is found. If all the circuits are busy, the energization of the relay KR5 again energizes relay ER1, and the searcher re-commences its cycle and continues testing until a circuit becomes idle. Assuming that the first operator's circuit EP, is idle, the relay A2R1 is energized as described above, locks itself under control of relay CR1, releases the searcher by opening the circuit of relay HR2, and energizes a call relay BR to light a lamp ARL. Extension of call by operator. The operator. having enquired the wanted number and recorded it on a key-set KS, presses a starting-key SK, which energizes relays T1R. ER,. the former relay locking itself in series with relay DR2, which starts the transmission of impulses over the wires a<1>, b<1>. The relay ER1 energizes relay DR, in series with relay VR1, which looks itself and connects the trunk FL, to a common selector GV, which receives the first set of impulses and controls relays such as A3R1 to extend the call in the wanted direction. While the selector GV is engaged, a re@ay HR3 disconnects relays VR2, VR3 &c. to prevent interference by other calls. When a connecting-relay such as A3R1 is energized, it disconnects relay VR1 so as to release the selector GV. When the wanted connection has been completed, a relay ER2 at the operator's position. de-energizes relays DR2, T1R, ER1. When the relay ER1 was energized it also energized selflocking relays HR1, O1R2, which transferred the locking-circuit of relay A2R1 to the control of relay ER1, so that relay A2R1 is now also de-energized and disconnects the trunk FL1 from the operator's circuit EP1. Automatic call. The operations by which an automatic line, such as L4, is connected to a trunk such as FL1, and by which this trunk is connected over a circuit such as RL1 to an impulse receiver, differ from those already described only in the following respects. A relay OR1 in the searcher S, is energized in series with relay M1R4 of the line L4 and energizes relay O1R2 in the trunk FL1, which transfers the starting-circuit of the searcher S2 from relay HR2 to relay OR3, which energizes HR2 in series with relay OR4, whict transfers the test circuits of the searcher from back-contact lines P1L1, P1L2 &c. to front-contact lines P2L3, P2L4 &c., so that the searcher hunts for an idle circuit RL1, RL2 &c. leading to an impulse receiver instead of for an idle operator's circuit SL1, SL2 &c. Preferential treatment of automatic calls. This is secured by the arrangements described in the previous paragraph, for if simultaneous calls arrive from automatic and semi-automatic lines, the immediate energization of the relay OR4 ensures that the searcher S2 will search for an impulse receiver in preference to searching for an operator's circuit. Preventing false connections (such as of a semiautomatic line to an impulse receiver) in case of simultaneous calls. This is effected bv connecting resistances R3R4 &c. 'between the relays M2R1, M2R2 &c., so that not more than one trunk FL1, FL2 &c. can be in a connectible condition at the same moment. These resistances are normally short-circuited by back-contacts of the corresponding relays but if the relay M2R1 for example is energized it cuts the resistance R3 into the circuit of the succeeding relays and prevents any of then from being simultaneously energized.