Patent GB-275709-A (GB)
Title: Improvements in or relating to relay interrupters for automatic telephone plants
IPC: H04M19/02
Filed: 1926-05-07
Abstract: 275,709. Marks, E. C. R., (Lorenz Akt. Ges., C.). May 7, 1926. Automatic exchange systems.- Stepping impulses for the call finders and for restoring the connectors, tone currents for the busy and dialling signals, and alternating current for ringing, are generated by a single pair of relays RII, RIII which are started up when necessary by a relav E. The invention is described with reference to a small system in which calls are established by means of call finders and single motion connectors. Call-finder. When a call is made, the contact X energizes the relay C in the allotted link circuit. Relay E pulls up in a circuit c3, i1, DMAS, and starts the interrupters which at r III 2 periodically short-circuit the relay E allowing the magnet DMAS of the back stroke drive call-finder AS to pull up. The finder is stopped on the calling line by the line relay J which pulls up over its winding I and the test wiper and cuts relay V into the stepping circuit. Relay V locks up, cuts off relay C and energizes relay U over U1, 4, DMLW. Relay J now holds up over its line windings and a third winding III receives impulses from the interrupter unit to give the dialling signal, relav E being held over JIII. u2, DMLW. Connector. Relay J repeats the impulses dialled to magnet DMLW by short circuiting at i2 the high resistance winding 1 of relay U. When the wiper 4 moves off normal, a resistance is cut into the impulsing circuit large enough to prevent relay U from holding over this winding but during the impulsing, the winding II receives impulses over DMAS, i1, u4. At the end of the digit however relay U falls back completing the test circuit 3, P, u5, i2, p4, v5. Busy signal. If the wanted party is busy relay P is unable to pull up and a tone signal is sent bach as in the use of dialling tone except that the resistance z is cut out. Ringing current. On the energization of test relay P the sluggish relay RI is energized in series with relay E (II) and energizes the driving magnet DMRW of a switch RW. Magnet DMRW short circuits relay RI and the switch advances automatically and somewhat sluggishly because of the short-circuit on relay RI. The driving circuit between silent positions includes wiper 1 and strapped terminals such as 14, 15 to make it independent of the circuit u4, p3, v4. The relays RII, RIII continue to vibrate and at rIII1 generate alternating current while wiper 2 is on terminals such as 14, 15. The current passes to line via relay C(II) and relay (II) and is audible to the calling party. When the called party answers, relay C pulls up only its armature c2I allowing relay U to pull up in a circuit u4, UII. V, DMAS, completing the connection and cutting off relay C and the ringing equipment. Restoration of selectors. When both subscribers hang up, the relay J short circuits relay V which after an interval releases relays U, P. Relay E then pulls up over E (I), p5, in series with magnet DMLW and the interrupters RII, RIII intermittently short-circuit relay E causing the switch to step on to normal,