Patent GB-190906878-A (GB)
Title: Improvements in Telephone Installations.
IPC: H04M15/28
Filed: 1909-03-22
Granted: 1909-07-08
Abstract: 6878. Siemens Bros. & Co., [Siemens & Halske Akt.-Ges.]. March 22. Semi-automatic exchange systems; metering systems. -Relates to metering arrangements for telephone systems in which sub-stations on branch lines are connected to common exchange leads by means of automatic switching-mechanism. The meters are located at the automatic branch station, and are controlled jointly by a calling subscriber and the exchange operator. When a subscriber is called by the exchange, the ringing-currant causes a cut-off relay to cut out the meter of the called subscriber. The invention is described as applied to a system in which the exchange operator selects the required sub.stations by using currents of different frequencies which energize a selective harmonic relay. The Figure shows two sub-stations A', A<2> connected to the automatic branch station, which comprises a call relay ra, a cut-off relay rb, a meter relay ZR, and a meter Z' for each sub-station, together with relays Ra, ZAR, common to all the subscribers The contacts of the selective harmonic relay RS referred to above are connected to the cut-off relays rb of the various subscribers. When the subscriber A' removes his receiver, current passes from the battery B through the winding 32 of the call-relay AR, line a, choking coil Dr<1>, contacts 5, 11, sub-station A', call-relay ra, contacts 16, 10, choking-coil Dr<2>, line b, and winding 31 to earth. The relay ra attracts its armatures, thereby establishing a fresh circuit from the line a, through the common cut off relay Ra, contact 12, sub-station A', and contact 15 to lead b. The excitation of the relay Ra opens the contact 20 and prevents any other branch subscriber from calling the exchange. When the answering-plug AS is inserted, the meter relay ZR is energized by current from battery B passing through the choking-coil Dr<3>, line b, choking-coil Dr<2>, contact 23, relay ZR, and contact 14 to ground. The contact 17 completes a locking- circuit to ground, and the contact 18 prepares the circuit of the meter Z', which is actuated when the operator, having established the required connexion, depresses the key ZT, thereby connecting the same pole of the battery B to both line-wires in parallel. This results in the de-energizing of the relay ra, one armature of which completes at the contact 13 the circuit of the meter Z', which passes from earth, over contacts 13, 18, meter Z', lead 2, line b, plug-contact 27, and key ZT, to the earthed battery B. The actuation of the meter completes at 19 the circuit of the relay ZAR, which thereupon opens the contact 23 in the circuit of all the meter relays ZR and completes a holding-on circuit at 22, thereby preventing the possibility of a second actuation of the meter. The exchange operator selects one of the branch sub-stations by sending current of the required frequency through the selective harmonic relay RS, this relay being normally connected across the exchange leads in parallel with the bells of all the subscribers. If it is desired to select the sub-station A<1>, the armature i<1> of the relay RS is attracted and earths the cut-off relay rb over the line b, so that the sub-station A<1> is connected to the line-wires a, b over contacts 11, 5<1>, and 16, 10<1>. The excitation of the relay Ra prevents any other branch station from calling the exchange. The actuation of a called subscriber's meter is prevented by the breaking of contact 35 by the relay rb. A separate meter may be provided at the exchange to register the total number of calls received over the line from all the sub-stations, thus serving as a check on the separate meters.