Patent GB-697342-A (GB)
Title: Improvements in or relating to telephone systems
Inventor: PEARCE OWEN AVIS
IPC: H04M17/02
Filed: 1950-12-16
Abstract: 697,342. Exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. Dec. 12, 1951 [Dec. 16, 1950], No. 30729/50. Class 40 (iv). In a multi-exchange system in which at least one of the exchanges is provided with a plurality of operators' positions to enable calls chargeable on a duration-and-distance basis to be set up from prepayment coin-box substations, the collection of the charge for any period of the call may be supervised by an operator at any position. The drawings show apparatus at a group centre exchange comprising a coin-box discriminating group selector, Figs. 2 and 3, a coin-box relay set CBRS, Figs. 4 and 5, and an operator's position IP, Fig. 5. Call from local regular (non-coin-box) subscriber. The group selector operates as described in Specification 588,790. Relays A, B, C are energized on receipt of a call over path AP, and relay A repeats dialling impulses to vertical magnet VM. The operation of offnormal contacts N1-3 brings up relays HA, HB so that relay C is shunted and released at the end of the impulse train. Rotary magnet RM then drives the switch over the selected level, relays HA, HB testing over wipers P2, P1 respectively for an idle outlet, indicated by absence of earth. If this is found by P1 or by both P1 and P2, relays HB, HA release, reoperating relay C which brings up relay HA again to switch through the calling line over wipers - 1, + 1. Relays A, B are released, and the seized equipment returns earth over wiper P1 to hold HA. If P2 alone finds an idle outlet, HA releases, re-energizing C to extend the calling line over wipers - 2, + 2. Backward holding earth on wiper P2 now holds HB energized. Local call from coin-box substation. Relays A, B, C operate as before. If the calling substation is on the group centre exchange, battery is applied by the line-finder to lead 14, energizing relay CB. In the case of a caller at a satellite exchange, a differential relay DF is briefly energized by earth applied to the centre of the calling loop and brings up relay CB. In either case CB holds and prepares markings on a vertical bank AB of the selector. The outlets on level " 0," which extend to the zone centre exchange, are barred to directly dialling coin-box subscribers, and other barred levels are strapped from vertical bank AB to a lead 18. Accessible (local) levels are strapped to a lead 17, and if one of these is dialled the selector operates as described above. If the caller dials a barred level, relay BA is energized over the vertical wiper and disconnects rotary magnet RM. The release of relay C at the end of the impulse train applies busy tone from lead 11. Coin-box call chargeable on a duration-anddistance basis, set up with the aid of an operator. Relays A, B, C, CB operate as above. To reach an operator, the caller dials the digits " 00 ". The first digit raises the wipers to level " 0 " whereupon relays OL, BA are energized so that the relapse of relay C at the end of the impulse train completes a circuit for rotary magnet RM including release alarm earth lead 12. The switch releases rectangularly, and at the home position relay DA operates to bar all levels except " 0 " by connecting leads 17 and 18 together. Relays OL, BA release and C is re-energized. The second digit dialled again raises the wipers to level " 0," and relay ST is energized, relay C falling back as usual. Relay ST places battery potential on lead PF extending to a coin-box relay set CBRS, Figs. 4 and 5, and also applies earth to a lead 15 connected in common to a group of such relay sets. In each idle relay set a relay STA operates to start a switch SF hunting for the relevant selector. One of the switches SF encounters on its bank SF3 the battery potential on lead PF, and a relay T in the associated relay set CBRS operates to stop the switch and bring up a relay K. In the selector, relay SW operates to the earth returned over lead PF, splitting the calling line to release relay A, followed in turn by relays B, CB, DA, and ST, only SW remaining energized. The selector wipers go home. In the relay set CBRS, relay K extends the calling line to energize relay L, sends back ringing tone from lead 30, and brings up relay FL which lights a lamp LPC at each of a plurality of operators' positions IP. Relay BB is energized, and T and STA are released. Any one of the operators answers the call by operating her key KS. This completes a talking circuit and energizes relay S which brings up relay SS to disconnect the ringing tone and release relay FL, thereby extinguishing the calling lamps LPC. The calling subscriber informs the operator of the wanted number and the operator supervises the collection of the requisite coins, thereafter actuating a " dial " key (not shown) to operate relay DC which opens the talking circuit and brings up relay DB. This lights a supervisory lamp (not shown) and extends the operator's dialling loop to the "OUT" path of the selector, where relays A, B, C operate. The operator now dials the wanted number. Assuming that the call is to be routed via the zone centre exchange, the first dialled digit is " 0 ". Following the customary release of relay C, the selector hunts over level " 0 " for an idle outlet to a repeater associated with a route to the zone centre. Earth at N1 is extended over switch bank SF6 to operate relay TC in the relay set CBRS. When the selector seizes a repeater, relays C and HA or HB operate and A and B release. Positive battery potential extended from the relay set CBRS over wiper SF7 and selector wiper P1 or P2 indicates to the seized repeater that it is to take into use its associated metering selector and timing apparatus. This battery signal is removed and the dialling loop restored by the relapse of relay TC at the first break period in the second digital impulse train. The second and subsequent digits are repeated to the zone centre and the call is routed in known manner. The second and third, and possibly the fourth, digits actuate the metering selector, which is of the type described in Specification 664,261. On completion of dialling, the operator restores her " dial " key to release relay DC, which switches through. When the called subscriber answers, the reversal of potentials energizes relay D which extinguishes the operator's supervisory lamp. The operator may then clear from the connection by restoring her key KS, releasing relay S. The metering selector sends positive battery pulses back over wipers P1 or P2 and SF7 to relay CC which repeats them to magnet DSM so that uniselector wipers DS1, DS2 are stepped accordingly. A thermal relay TH is energized and, after a delay, brings up relay R, disconnecting itself at the same time. After a further delay TH restores and relay FC is operated to prevent any subsequent pulses from affecting magnet DSM. The total delay in operating FC is arranged to be longer than the time required for the longest train of metering pulses. Collection of fees for subsequent periods of the call. At the end of a prescribed period the timing apparatus at the repeater causes a warning tone to be transmitted and the metering pulses to be sent as before. Relay CC operates and connects flicker earth lead 31 to relay FL which flashes the calling lamps LPC at all the operators' positions IP. Any one of the operators may enter the connection by operating her key KS, bringing up relay S to release relay CC and stop the flashing of the calling lamps. To discover the charge for the second period of the call, the operator presses a " display " key KCD. Relays DR, CD are energized to actuate a charge indicator comprising lamps LPA1-24. The relevant lamp is illuminated, having been selected by wiper DS2 under the control of the metering selector as described above. If the parties wish the call to continue, the operator supervises the collection of the requisite coins and then withdraws from the connection by restoring her key KS, releasing relay S. Further extensions of time may be granted in the same manner. Further facilities controlled by operator's keys. The operator may converse privately with the calling party by operating a key KCT as well as KS. Relays CT, SWA are energized so that the called party is disconnected from the talking circuit but the forward holding loop is maintained. The operator may break down the connection by actuating a key (not shown) to connect earth to lead MT so that relay DB is short-circuited and released, breaking the connection and initiating release of the equipment. Trunk offering may be initiated by the operator's pressing a key KTO.