Patent GB-221619-A (GB)
Abstract: 221,619. Coventry Automatic Telephones, Ltd., (Arter, R. C.). July 30, 1923. Automatic exchange systems; metering.-The operation of a calling subscriber's meter is made dependent upon the response of the called party and takes place after the release of one or more of the connecting switches. The restoration of the first group selector is in turn made dependent upon the operation of the meter, failure of this selector to release being notified to an attendant by the illumination of a warning lamp. The invention is described as applied to a system in which connections are established over individual line switches of the no-normal kind, and Strowger type first and second group selectors and final connectors which perform their rotary stepping movement before their vertical movement. Statistical meters are provided for recording the number and time of calls attempted when all the trunks to a wanted group are busy. Release occurs when the calling party replaces his receiver, means being provided for lighting an attendant's warning lamp if the called subscriber hangs up and the calling party does not. Three methods of carrying out the invention are described. First method, line switch, Fig. 1. When the calling party A removes his receiver, the response of the line relay 1 closes the usual series circuit for the switching relay 3 and the stepping magnet 5. The line switch wipers 6 are now rotated until a trunk to an idle first group selector is engaged, upon which the switching relay 3 extends the calling line and disconnects the line relay 1. First selector, Fig. 1. Two line relays 13, 14 energize in series over the calling loop, the eircuit including the right-hand winding of a metering relay 7. The relay 14 places holding ground on the line switch test wiper, and closes a circuit for the left-hand winding of the metering relay 7 in such a direction that the two windings of this relay oppose one another and the relay remains inert. The relay 13 energizes a slow-release relay 9, and a circuit is closed for another slow-release relav 10, which connects dialling tone to the calling line. The relay 9 also energizes a relay 11 which connects further ground to the line switch test wiper. The calling party now dials the first digit of the wanted number, causing interruptions in the circuit of the line relays 13, 14. At each relapse of the relay 14 a circuit is closed for the rotary magnet 15, which steps the wipers 18 round to the desired vertical row of bank contacts. On the cessation of this impulse series, the slow-release relay 10 (which during the impulses is held over the contacts of the rotary magnet 15) relapses and closes a circuit for a relay 8, which energizes the vertical magnet 16 over its right-hand armature. At the first vertical step the circuit of the relay 8 is opened at the off-normal contacts 20, but as long as the bottom test wiper of the selector engages grounded contacts, the relay 8 remains held, and the vertical stepping movement continues until an idle second group selector is seized and the relay 8 relapses. The vertical magnet 16 is then de-energized and a circuit closed for the switching relay 12. Statistical metering and busy release. If all the trunks in the wanted group are engaged, the wipers 18 are raised to an eleventh terminal set. A relay 29 which is energized over the right-hand armatures of the relays 8, 9, closes a circuit for a statistical meter 28, and busy tone is transmitted to the calling party over the lead 27. The relay 13 is held over the upper selector wiper and an impedance coil 30 until the calling subscriber hangs up, when the relays 13, 9, 11 and 12 deenergize, and a circuit is closed for the release magnet 17. A graphic recording meter may be provided for obtaining a time record of overloads. This comprises a uniformly-advancing drum marked by a pen actuated by a magnet in which the current is proportional to the number of conductors 52, Fig. 6, carrying current in a cable. The conductors 52 are earthed at the first selectors over leads similar to those over which the relays 29, Fig. 1, are energized, and may be connected up over switches 53 to record the overloads on any particular group of second selectors. Second selector. This is operated by the second digit, in the same manner as the first selector, to select a trunk 123 - - 125, Fig. 3, leading'to an idle connector. Connector, Fig. 3. When the calling line is extended to the connector, the line relays 213, 214 are energized, the former energizing a relay 234 and the latter closing the circuit of a slow-release relay 232, which causes in turn the response of slow-release relays 233, 239. The third digit is now dialled, the relapses of the line relay 214 closing the circuit of the rotary magnet 215. At the first step a switching relay 237 is energized, and on the cessation of the impulses, the relay 233, which is held during the rotary movement over contacts of the magnet 215, relapses and energizes a change-over relay 231. The de-energizations of the relay 214 when the final digit is sent, energize the vertical magnet 216, which raises the wipers to the wanted line. On the cessation of these impulses, the relay 233 falls away and causes the de-energization of relays 231, 239. Ground potential is now applied to the test conductor 225, and the called line cut-off relay 2b energized, the switching relay 3b and the line switch stepping magnet remaining inert on account of their relatively low resistance. Busy test. If the wanted line is engaged and the test conductor 225 grounded, upon the relapse of relay 233 and before the relapse of relay 231, a circuit is completed for a test relay 230, which applies busy tone to the calling line and energizes a relay 239 to disconnect the ringing current. Ringing and preparation of metering. If the wanted line is idle, interrupted ringing current from the source 241 is applied to the called line over contacts of the relays 239, 237, ringing potential also being transmitted to the calling line over the left armatures of relays 239, 238 and the right armature of relay 234. The interrupter 240 alternately applies ringing current and uni-directional current to the called line through the right-hand winding of a marginal cut-off relay 238, which responds and locks up over its left-hand winding when the resistance of the called loop is reduced by the removal of the receiver. The relav 238 cuts off ringing current and de-energizes the relay 237, thereby completing a circuit over the called loop for feed relays 235, 236. The relay 235 closes a circuit for a relay 212, which extends the calling line, and reverses the current over the calling loop and through the right-hand winding of the metering relay 7, Fig. 1, which short-circuits its right-hand winding and prepares the circuit of the meter 4. Release and metering. This occurs when the calling party hangs up. Relapse of the line relays 213, 214 is followed by the de-energization of relays 232, 234, 238, and by the. energization of relay 237, which completes a circuit for the release magnet 217. Release of the connector removes guarding potential from the test wire 125, and the second selector is then restored. The consequent removal of earth from the test conductor 25, Fig. 1, causes the relapse of relay 11, which de-energizes the relav 12. A series circuit is now completed for the release magnet 17 of the first selector and the left-hand winding of the meter magnet 4, but the high resistance of this winding prevents the response of the release magnet 17. The meter magnet 4, however, pulls up and records the call, at the same time shunting its high resistance winding by a low resistance right-hand winding and causing the response of the release magnet 17. If the called party hangs up first, the relapse of the relay 235 closes a circuit for an alarm lamp 244, which is disconnected at the middle armature of the relay 238 when the calling party hangs up. Should the calling party omit to replace his receiver and prevent release of the connection, the lamp 244 remains lighted. Second method. In this modification the metering relay 7 is connected in the grounded side of the first selector trunk instead of the battery side, in order that a fault or ground on the subscriber's line will not cause operation of the metering relay. Third method, Fig. 5. In this modification a single-coil metering relav 50 is used, the energizing circuit of which is independent of the calling loop. During the operation of the connector both ends of the winding of this relay are connected to the same potential, but when the called party answers, the potential at the right-hand end is reversed and the relay responds, locks up, and disconnects itself and the relay 13 from the upper trunk. The call is metered at release as in the first method, the circuit of the relay 50 being broken at springs (not shown) of the release magnet 17, when release takes place. The first selector release magnets 17 are connected to battery through a pilot relay 48 controlling an alarm lamp 49, which remains lighted if the circuit through the release magnet 17 is completed but the selector fails to release. This supervisory arrangesment may also be provided in the systems describing the first and second methods. Specification 3497/12 is referred to.