Patent GB-190904594-A (GB)
Title: Improvements in Telephone Exchanges.
IPC: H04M15/10
Filed: 1909-02-24
Granted: 1909-07-22
Abstract: 4594. Siemens Bros. &. Co., [Siemens & Halske Akt.-Ges.]. Feb. 24. Metering systems. - In telephone exchange systems, service registers provided with a holding- on circuit are restored to their inoperative condition by short-circuiting or bridging the holding- on circuit instead of by breaking this circuit. This arrangement permits the use of a single lead only between the meter and the third spring on the enquiry jack. Fig. 1 is a simplified diagram of an arrangement in which the meter magnet a is shortcircuited when the enquiry plug is withdrawn from the jack K. The depression of the metering-key T completes the circuit of the battery B through a resistance W, a jack-spring c, and a magnet a, which completes a holding-on circuit through its armature g, a resistance W<1> and the battery B. When the enquiry plug is withdrawn, the magnet a is shunted by the low resistance W<2>. The operator maintains the key T depressed until the armature g is attracted; which is shown by the lighting- up of the indicating-lamp CL due to current passing over the resistance W<1> and the armature g. It will be seen that only a single lead is necessary between the meter Z and the jack-spring c, whereas if the meter magnet were de-energized by breaking the holding-on circuit, two leads for each meter would be required. In a modified arrangement, the magnet a is shortcircuited by a contact which is closed when the connecting-plug is restored to its position of rest. In the further modification, shown in Fig. 3, the depression of the metering-key T completes the circuit of the meter magnet a through the lead i, relay R and battery B. The high resistance of the magnet u prevents the energizing of the relay R, so that the indicating-lamp CL remains alight until the magnet a attracts its armature and completes the holding-on circuit through the resistance W<1>, when the current through the relay R is increased and the lamp CL consequently extinguished. The short-circuiting of the magnet a is effected by a connexion n, which is earthed over the unattracted armatures of the relays TR, X, which remain energized until the connecting-plug is withdrawn and the calling subscriber hangs up his receiver. The armature of the relay TR can be earthed directly as at n', in which case the contact on the relay X is dispensed with, and the short-circuiting of the magnet a is controlled by the position of the connecting-plug only. In the modification shown in Fig. 4, the meter cannot be operated until ringing current has been sent to the called line. The magnet a is short-circuited by the connexion n, and this shunt is not removed on the insertion of the connecting-plug, since the relay TR is short-circuited by the lead o, which includes a contact under the control of a relay RR in the ringing-circuit. When the ringing-key RS is depressed, the relay RR is energized, and opens the shunt round the relay TR, which at once attracts its armatures, opening the contact p so that the short-circuit is not re-established when the relay RR is de-energized. The metering-circuit can then be completed as before by depressing the key T, and the magnet a is short-circuited by the connexion o when the relay TR is de-energized on withdrawing the connecting-plug.