Patent GB-625276-A (GB)
Title: Improvements relating to telephone systems
IPC: H04M3/523
Filed: 1946-08-30
Abstract: 625,276. Telephone exchange systems. SIEMENS BROS. & CO., Ltd., CLARK, R. I. H., and STALLWORTHY, F. A. Aug. 30, 1946, No. 26219. [Class 40 (iv)] In call-distributing arrangements of the kind in which calls are formed into a queue as they arrive and are dealt with in the order of their arrival, the average waiting period of a call in the queue is determined and indicated by arranging that a call-timing circuit is closed for each call entering the queue, and that the changes of voltage across a timing condenser or condensers resulting from such closures during the period in which a predetermined number of calls enter or pass through the queue in succession cause a counting device to be set to a position which represents the average waiting period. Three arrangements are described which operate in different ways. First arrangement, Figs. 1, 2. The group of queue relays comprises as many relays (say twenty) as there are positions in the queue and calls in a group, and by known arrangements (not shown) these relays are operated in turn as calls enter the queue, each relay remaining up for the waiting time of the call with which it is associated. The only contacts of queue relays shown are those of the primary and final relays A and U respectively. Each of the similar call-timing circuits consists of a high resistance, e.g. YA, in series with a make contact of the relevant queue relay, and all these circuits are connected in parallel across the timing condenser QC. The apparatus is brought into use by operation of the start key STK, whereupon relay ST pulls up, closes the heater circuit of the pentode VA and energizes the thermal relays TH and the control relay AM. AM operates at once and closes a circuit for rapidly charging QC so as to bring the control grid of VA to the same potential as its cathode. As soon as the valve warms up the marginal relay AN comes up, opens the charging circuit for QC and disconnects AM, which releases slowly. Provided there are calls in the queue, QC discharges through the closed call-timing circuits until the voltage across it reaches a value such that the potential of the control grid is sufficiently negative with respect to that of the cathode to cause AN to release. Relay AMthereupon re-operates and QC is again charged, AN operates and the cycle is repeated. In this way AM is impulsed at a rate which varies with the number of calls in the queue and the number of operations of AM taking place between successive operations of A is taken as a value of the average waiting period. After TH has energized, relay P comes up momentarily when A next operates and is followed by PG which locks up, closes an energizing circuit for the driving magnet SB of a secondary counting uniselector, and brings up SG. Relay SG releases TH, opens the circuit of SB and holds PG. The uniselector steps and BA comes up over wiper SB5. so that the next operation of AM energizes the driving magnet SA of a primary counting uniselector, and its next release steps this uniselector. Stepping of the primary switch continues under control of AM until such time as the first call of a new group enters the queue or relay F operates. In the former case, which is the more usual, relay A is released when the call which operated it leaves the queue and is again operated when the first call of the new group arrives. On the release of A, PG falls away and when A re-operates, P comes up, re-operates PG and completes a homing circuit for the secondary counting uniselector. As soon as this switch has homed P falls away, followed by BA. Relay AA then operates over wiper SA5 and lights the appropriate one of the display lamps DL to indicate the average waiting period corresponding to the setting of the primary counting uniselector. The secondary counting uniselector is then stepped under control of AM in the same manner as described for the primary switch. If as before, stepping is terminated by the entry of the first call of yet another group into the queue, P again re-operates and the primary switch is homed ; P and AA release and BA re-operates lighting the display lamp appropriate to the setting of the secondary switch. The process is then repeated, with the primary switch being stepped under control of AM. In the case where either of the counting switches is stepped to its last contact position, F comes up over SA3 or SB3 and prevents further stepping. The next operation of A brings up P as usual and the display lamp corresponding to the last contact position of the operated switch is lit. While this lamp is lit FE is operated over SA3 or SB3 and gives an urgency signal to the operators. Provision is also made for operation of FE in positions of the counting switches, other than the last, which indicate high value waiting periods by strapping the later contacts of SA3 and SB3  (other than the last) to front contacts of AA and BA respectively. Second arrangement, Figs. 3, 4. The calltiming circuits which are closed in rotation as calls enter the queue are all similar and have constant current characteristics. A timing condenser is individually associated with each circuit so that the value which the voltage across each condenser reaches is linearly proportional to the corresponding individual waiting period. Ten timing circuits are provided for a queue, the number of calls in a group being twenty. The call timing circuits themselves are not shown and only two of the timing condensers, QA and QK, connected to the corresponding circuits over wires WA and WK respectively, are indicated in the drawings. These condensers are associated with condenserswitching relays AA and KA. Twenty storage condensers (one per call in a group) are provided of which three SQA, SQK and SQU are shown. The arrangements for forming calls into, and releasing them from the queue are not shown, but it is arranged that earth is applied to wire WST each time a call is about to be released and is removed when the release is completed. A detaching control uniselector, of which only wiper RA1 and its bank are shown, is stepped once each time a call is released. Upon the connection of battery to the apparatus, relays PA, PB and PC pull up and the sequence switch C, if not in its normal position, is homed over wiper C1. If the condenserswitching uniselector A is not lined up with the detaching control uniselector, it is stepped until lining up is effected. Each time the detaching switch is stepped, the switch A is stepped to line up with it. The timing uniselector E, which is a high-speed motor-driven switch, is homed, if off-normal, and relay N pulls up in the normal position. Two triodes VA and VB which are provided for the control of high-speed relay TE are connected so that wiper E1 of the timing uniselector controls the cathode bias of VA and the cathode is made more negative as the switch is driven from normal. Normally the anode. current of VB is sufficient to operate TE and a similar highspeed relay T, so that when N comes up a further driving circuit for E is completed. Consequently the anode current of VA continues to increase until a surge through the coupling condenser QZ is produced which is sufficient to cause a momentary cessation of anode current in VB, whereupon T and TE release. The timing switch is thus stopped and the operation of TC connects up low resistance YD to short-circuit the twenty storage condensers, and disconnects PA, PB and PC. When PA, PB and PC have all released, S comes up if, or as soon as, TA and STA are respectively up and back. Normal operation then commences, the next call to be released from the queue being taken as the first of a group. When this release is about to take place, earth over wire WST brings up STA  which energizes the driving magnet of the sequence switch and the condenser switching relay associated with the timing condenser appropriate to the call at the head of the queue. The latter relay disconnects the timing condenser from the call-timing circuit and connects it in parallel with the appropriate storage condenser, e.g. if the condenser switching uniselector is in position 1 AA operates and connects condenser QA in parallel with SQA ; in position 10, KA operates and connects QK with SQK, while in position 20, KA operates and connects QK with SQU. In each case the storage condenser concerned receives a charge proportional to the waiting period for the call about to be released from the queue. When this release occurs, STA falls away, releases the operated condenser-switching relay and de-energizes the magnet of the sequence switch, which switch advances one step. The detaching control uniselector also steps and the condenser-switching uniselector follows. This sequence of operations is repeated for each further call released until the last call of the group has been released and all twenty storage condensers have been charged. The sequence switch is then advanced to position 21 where Z comes up over wiper C2, prevents further operation of the condenser-switching relays and releases N. Relays TE and T thereupon re-operate and TC falls away, re-operating PA, PB and PC, so that the storage relays are all connected in parallel and S releases followed by Z. The sequence switch and the timing uniselector thereupon go home. Relay N then operates, connects the storage condenser to the grid of VA and completes a further driving circuit for the timing uniselector which therefore continues stepping until TE releases. The connections of the bank contacts associated with wiper E1 are arranged so that the position in which the timing uniselector is stopped represents the average waiting period of the group. When TE falls away TC comes up and completes circuits over wipers E2 and E3 to the appropriate " units " and " tens " display lamps to indicate this waiting period. Relay TC also connects resistor YD across the storage condensers to discharge them, and releases PA, PB and P