GB252452A - Improvements in automatic or semi-automatic telephone systems - Google Patents

Abstract

252,452. Western Electric Co., Ltd., (Deakin, G.). Feb. 26, 1925. Party-line systems.-Ring-back apparatus for use in revertive party-line calls in an automatic exchange system is set in operation by an auxiliary calling device at the calling substation. The invention is described as applied to a register-controllersystem of the well-known revertive impulse type. The ring-back equipment Rv is located in the leads entering the registering apparatus Rg, a controlling differential relay DR being inserted in the dialling circuit in series with the stepping relay SSR of the registering apparatus. A subscriber A on the party-line desiring to call another subscriber B on the same party-line, removes his receiver and is extended in known manner over a line finder and register selecting sequence switch Re to an idle register-controller Rg. The differential relay DR energized over the calling loop in series with the stepping relay SSR does not respond : dialling tone is applied to the calling line in known manner. The calling party now depresses the revertive call key RK breaking the loop circuit and grounding the b wire, therby unbalancing the relay DR which responds. Three interrupters which rotate once every 4 seconds are provided in the ringing equipment: the contact segments on these interrupters are of such size and are so positioned that the following circuit conditions are fulfilled. At the commencement of a cycle of rotation, the interrupter 1 momentarily grounds its wire thereby energizing a ringing relay RR over the attracted armature of relay DR. Relay RR locks up over interrupter 2 until just before the interrupter 1 again closes, and applies alternating current to the a and b wires to ring the bells at both stations A, B, whereupon the calling party releases the key RK. Relays DR, SSR are held over their lefthand windings and the interrupter 3, which remains closed until just before the interrupter 2 opens. As the end of the cycle approaches, the interrupter 3 opens first and de-energizes relays DR, SSR causing the release of the register controller. A moment later, after the register controller has restored, the interrupter 2 opens and unlocks relay RR, which disconnects the ringing current. The release of the register-controller causes the cord circuit sequence switch to move to its talking position in known manner. If the called party does not answer during the first ringing period the calling party hangs up and repeats the operation.