416,421. Exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, London, EDWARDS, H. J., 5, Summerhill Road, Dartford, Kent, and CHRISTIAN, D. A., Morven, Charlton Road, Charlton, London. March 9, 1933, Nos. 7195 and 34158. [Class 40 (iv).] Relates to systems in which waiting calls at an operator's position are dealt with in an order depending on the order of arrival and comprises a number of arrangements in each of which one of a number of common circuits concerned with influencing or deciding the order in which the calls are to be dealt with is automatically associated with an incoming junction circuit when a call arrives. In one arrangement, the common circuits have a chain-starting circuit and each contains a timing-switch which after different periods of delay causes the calling lamp of the associated junction to be flashed at different frequencies. In another arrangement, the common circuits, known as " mechanical monitors," are allotted in turn by an allotting-switch and one or more priority-control circuits associate themselves with the engaged mechanical monitors in turn in the same order, causing a particular " urgency signal to be displayed in the associated junction circuit. In a third arrangement, the circuits associated with mechanical monitors are automatically connected in turn in the order of arrival to free operator's connecting circuits under the control of a priority-control circuit, the operators concerned being also selected in rotation. In a fourth arrangement, a calling lamp in addition to being flashed in its turn under the control of a priority-control circuit is flashed also when there is congestion in any particular group of incoming junctions. In a fifth arrangement, waiting calls and available operators are " queued up " by " queueing-up " switches in the mechanical monitors and at the operators' positions, the call at the head of one queue being automatically connected to the operator at the head of the other queue and the remaining calls and operators moving up one step in their respective queues. In the second and fourth arrangements, means are provided for dealing with the case in which two operators simultaneously answer the same call. First arrangement, Figs. 1-4. A plurality of time-measuring equipments connected in a chain, Figs. 2-4, one being shown in full in Fig. 3, are associated with a plurality of callanswering circuits such as that shown in Fig. 1. When a call arrives at this circuit, relay LL lights lamp CL and a thermal relay TH is energized so that after a predetermined delay, ground at contact l1 is extended to the common start-wire SW of the time-measuring equipments. Relay ST in the first available circuit in the chain is energized, each relay ST being provided with an opposing winding (ii) connected to ground over resistances YC in all the busy time-measuring equipments, and the arrangement being such that ST will only operate when the number of ground connections to wire SW exceeds the number of connections to winding (ii). Relay S operates connecting up the latch magnet LM of finder switch DMB and when the calling circuit, Fig. 1, is reached, relay T operates and energizes TA(i). Winding (ii) of TA is connected to booster battery and cannot operate to ground at plowing to rectifier R, but when contact ta4 changes over, TA(ii) holds over LL(ii) and this winding which is differential is energized over R, p1, and releases LL. Relays SR, SO and magnet DMA now interact to step a timing switch DMA1-3 and at wiper DMA1 relay P is successively impulsed by interrupters C1-C4 of different speeds to produce corresponding flashing of lamp CL to give an indication of the period of waiting. Statistical meters connected to the bank of wiper DMA3 indicate the number of times particular delays occur. When the call is attended to, relay TA releases and the finder and timing switches return to normal or become associated with another calling circuit. When the end of the bank is reached, relay TT operates in series with relay WS which switches over to a second testing bank DMB2, and when the penultimate contact in this bank is reached TT operates again and the locking circuit of WS is opened at bank DMB3. The thermal relay TH may be omitted, a calling circuit then being connected to a time-measuring equipment immediately a call arrives. Second arrangement, Figs. 6-10. When a call arrives on the two-way telephonetelegraph circuit, Fig. 6, relays L, G, LL, operate, and the start relay S of the allotted mechanical monitor, Fig. 8, is energized. (The calling circuits are divided into two sub-groups each associated with a different set of wipers of the switches SC, different start relays S, SW, being operated over different wipers AS1, AS2, of the allotter.) Relay S operates latch magnet LM of switch CS and when the calling circuit is found, relays T, TG, TA, operate in succession. When a predetermined number of mechanical monitors are in use, a relay GP of a priority control circuit, Fig. 9, is able to operate over a corresponding number of parallel connections such as YA, ta5. The relay GP is associated over a rectifier REA with a resistance YB connected to booster battery and when a number of priority control circuits are employed they may be brought into use at successive stages of congestion by giving the resistances YB different values. Relay GP causes the priority control circuit to associate itself with the first of the calling circuits over switch PCS and when relay M is operated, which occurs when the number of waiting calls exceeds the same or a different predetermined number, relay FL is operated in the calling circuit to flash lamps CL to indicate urgency. When an operator plugs into jack IJ, relays CO, LO, operate, releasing LL, TA, and causing the priority control circuit to advance. In modifications, relay FL may light an extra calling lamp or may effect the first lighting of lamp CL, or the extra lamp may be directly connected to bank CS2 in place of FL. In a further modification, designed to ensure that lamp CL will re-light if two operators answer simultaneously and then immediately clear, the operation of LO is delayed for a short period after the operation of CO by means of a second differential winding under the control of one of two alternately-used thermal relays in the mechanical monitor circuit. Relay FL may be operated over a second winding to flash the calling lamp under these conditions. Third arrangement, Figs. 14-17. When the priority control circuit moves into engagement with a mechanical monitor as in Figs. 6-10, the latch magnet LMC of a hunting switch DS individual to the incoming junction AB is energized to hunt for an idle connecting circuit at the position of the next operator in turn as determined by wiper PCS3. When such a circuit is found relay TT operates over wipers DS3 and DS4 and energizes TB. The junction AB may be selected for outgoing calls by a selector FS. Fourth arrangement, Figs. 18- 24. The prioritycontrol circuit, Figs. 20, 21, operates relay J (i) to connect interrupter IA in the mechanical monitor to relay FL and thereby flash the calling lamp CL. Relay J is also operated over winding (ii) when relay P common to all the junctions of a particular incoming group is energized and this occurs when more than a predetermined number of calls exist in this group owing to the energization of winding (ii) of a differential relay N over resistances YD in parallel. By means of an opposing winding (ii) of relay P this relay can be arranged to release when the number of waiting calls in the group falls to any desired value. Subscribers of a special class may be characterized by a battery connection to the a-wire which operates relay SR to connect up interrupters IB, IC, instead of direct earth and interrupter IA. If two operators plug in simultaneously, relay DC operates over two resistances YE in parallel energizing CD which either flashes position lamps PL by connecting up interrupter IE controlling relay OF or connects up interrupter ID to flash lamps CL at a characteristic frequency. When one operator clears the opposing winding (ii) causes relay DC to release. Fifth arrangement, Figs. 25-30. When a call arrives at an incoming circuit, Fig. 25, it becomes associated with a mechanical monitor as in Figs. 6-10 and relay TA energizes the stepping magnet DMD of a queueing-up switch MQ. If there are no other waiting calls, the switch stops on the contact connected to relay A which lights lamp MQL and the call occupies the head of the queue. The operation of A marks the connection to relay B so that the switch MQ of the next call will stop one position short of the first, and so on. Available operators are similarly formed into a queue by switches PQ at their positions under the control of relays ASP energized by the closure of position keys KA. When there is both a waiting call and an available operator, relay ST energizes operating SS which causes MQ and PQ corresponding to the head of each queue to advance one step. Relays OQ, PS, then operate and latch magnet LMC causes a finder switch OLF at the leading operator's position to hunt for the calling circuit at the head of the queue of waiting calls. When this is reached, relays TP, ATP, operate over wipers OLF3, CS3, MQ2, in series with JA which energizes KK to switch through and release the mechanical monitor. Relay JA also energizes the opposing winding (ii) of SS which releases and cannot again operate until JA releases, this only taking place when switch MQ is restored to normal. The release of SS causes all other queueing-up switches in use to move up one step. In the operator's circuits, relay ATP energizes CT and releases AQT which causes magnet DME to return the queueing-up switch PQ to normal. Lamps PQL indicate the position of the operator in the queue. The first Provisional Specification also describes an arrange