Patent GB-654848-A (GB)
Title: Improvements relating to telephone systems
IPC: H04M3/523
Filed: 1947-12-19
Abstract: 654,848. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., and HENSLER, B. A. Dec. 19, 1947, No. 33693. [Class 40 (iv)] In a system for setting up trunk and toll calls on an " on demand " basis in which calls set up by operators and failing to find an idle trunk in the wanted group are held by storage equipment particular to that group, the position circuits of operators dealing with certain classes of calls, e.g. incoming long distance trunk calls, are modified to ensure preferential release from the storage equipment of calls pertaining to these classes. The system includes readily interchangeable demand A positions and positions terminating incoming long distance trunks. The positions are provided with cordless connecting circuits and register senders as described in Specifications 654,849 and 654,852 and calls are set up over a first selector and a first trunk group selector which together with its control circuit is more fully described in the latter Specification. The latter selector is provided with storage equipment, and supervisor's equipment for indicating probable delay to operators is also provided. Extension of incoming long distance call by a trunk operator. The operator throws a speaking key to assign a connecting circuit, Fig. 2, and her instrument circuit is connected to the incoming trunk. When she has ascertained the caller's requirements, she depresses a send call key and an idle sender, Fig. 1, connects over a coupling switch SC to the outgoing side of the connecting circuit, and is switched through to the first trunk selector. The supervisory lamp CSL is lit. The operator keys up the digits in the sender, and transmission of the first digit causes a marking to be applied over wire m1 to a group of outlets from the first trunk selector. The latter seizes a 4-wire trunk, Fig. 3, terminating at a trunk group selector W, Fig. 4. When the sender coupled to the connecting circuit, a circuit was completed over earthed connection PP and wiper SC13 for a priority relay PRS. PRS operates and locks to connect battery to the outgoing N - wire over wiper SC8, and relay PR pulls up and connects the incoming s-wire to the outgoing N - wire to transmit a priority signal to the storage equipment should this be necessary. Impulsing relay A in the group selector control circuit, Figs. 5-8, operates over a closed loop in the sender, and relays B, JB, JC follow to disconnect the testing-in circuit, and to light a pilot lamp PL. Relays K, KA couple the control circuit to the selector W. Relay TX operates to earth over the N+ wire from the sender and completes a circuit over wiper TN7 of the digit switch TN for relays LO, C, S. The latter connects low resistance battery to the N+ wire to short-circuit TX and to signal the sender to transmit the next digit. The selector W gives access to both groups and individual lines, and each group is provided with separate storage equipment, the storage contacts being located near the end of the selector bank. In response to one or two digits denoting a group, the switch TN connects marking earth over wiper TNS and a lead m1 to the outlets of the wanted group and the relevant storage contact. Relays S, C release and GS pulls up for the uniselector to hunt. All outlets of wanted group busy. The selector W is stopped on reaching the marked storage contact by the operation of test relay TA to battery connected over shunted relay OF(I), lead SC and wiper W6. Auxiliary relay HC pulls up, and OF operates to open the circuit for a switching relay H. Relay ON(II) pulls up in series with the holding winding II of OF and connects battery over a resistance to the incoming N + wire to release the sender. Relays HA, HB operate and lock, battery is connected over resistance YB and the outgoing N+ wire to the storage equipment, the control circuit is uncoupled from the selector W and interrupted NU tone is sent to the operator over leads INUS, INUSR. The release of A following the opening of the sender loop initiates the return of the control circuit to its normal condition. Storage of trunk call. The storage equipment, Fig. 9, is similar to that described in Specification 454,739. When the last idle outlet of the group is seized, earth is removed from lead gp and relay GP pulls up, followed by relays PS, GQ. A congestion lamp CL is lit at a supervisor's position, Fig. 10, and pulsating earth is connected over lead PE to cause relay R to periodically earth the centre point of the primary winding of a transformer T. Relay X operates and holds, and relay M pulsates in phase with R. When the selector, having failed to find an idle outlet, reaches the storage contact, the connection of the battery over the resistance YB and the N+ wire to the upper side of the primary winding unbalances the latter. The resulting operations are as described in Specification 454,739, lamps L1- L9 being lit at the supervisor's position to indicate the number of calls stored. Release of trunk call from storage. When an outlet becomes free, earth applied over lead gp releases relay GP, and intermittent earth over lead IE and the N - wire flashes the supervisory lamps CSL associated with the stored trunk calls. Relay PR operates to prevent the release of the very sluggish relay PS. When, in response to the flashing of her supervisory lamp CSL, the operator throws the associated speaking key and so closes contact s4, the low resistance winding of relay CS is connected to the s wire and relay RR pulls up to mark a contact in the bank TN6. If or when the control circuit is free, relay TR operates and RS follows to disconnect the testing-in circuit and to light the pilot lamp PL. RS also connects up relay LO which causes the digit switch TN to hunt for the marked contact, and, when successful, relay KA pulls up in series with a test relay P to connect the control circuit to the selector. Relay RT operates to disconnect OF. Relay HA falls back, disconnects the interrupted NU tone and removes the battery connected over the resistance YB from the outgoing N+ wire, thus unbalancing the primary winding of the transformer T and causing the storage equipment to indicate the decreased number of stored calls. Relay RR releases followed by P to remove the short-circuit from relay S(II). The digit switch TN rotates until on reaching the lead m1 connected to the storage contact on which the selector W is resting, test relay TA operates followed by GS. Relays S, RT, TA, TR fall back, and the selector W searches for the idle trunk. Extension of a call by an operator at a demand A position. In this case the connection PP is not made, and thus when a call is extended neither the sender priority relay PRS nor the selector priority relay PR is energized, and the incoming s-wire is connected to the outgoing s-wire instead of to the outgoing N+ wire. When an idle outlet in the wanted group becomes free, the supervisory lamps at demand A positions are flashed only providing that there are no priority calls stored, i.e. providing that relay PR does not operate during the release period of PS, which on release connects interrupted earth to the s-wire. Supervisor's equipment, Fig. 10. This comprises a congestion lamp CL, lit when all the trunks of the group are busy, the calls stored indicator lamps L1 ... L9 and a six-arm, twelve position, switch DM. The supervisor prevents incoming trunk calls direct from distant exchanges having access to the trunk group when congested, by rotating the switch DM to position 1. Lamp BAL lights and a lead BA connected to the appropriate contact in the bank TN8 of the tens digit switch TN is earthed. Thus, when such a call attempts to connect. to the trunk group a circuit is completed over wiper TN8 for ON to connect battery to the incoming s-wire to cause the incoming selector to route the call to a local manual switchboard position. When delay working is in force, the supervisor positions the switch DM to light the delay lamp DL and to complete circuits over wipers DM1 ... DM4 to operate a combination of relays in the sender which connect up different combinations of resistances in the circuit of a delay indicating instrument at the operator's position.