Patent GB-332904-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H04M3/12
Filed: 1929-04-29
Abstract: 332,904. Siemens Bros. & Co., Ltd., Christian, D. A., and Peters, C. L. April 29, 1929. Automatic exchange systems and apparatus.- In an automatic telephone system wherein on the recurrence of permanent loop conditions e.g., when a line assumes a calling condition and no impulses are sent within a prescribed time, common exchange apparatus is released and the faulty line is disabled, the arrangement is such that only those lines more prone to faults are provided with disabling arrangements and discriminating means are, employed whereby as a call finder may be required to effect connection with a line provided with disabling means or with one not so provided, the call finder responds differently in the two cases, viz., in the former case to operate the disabling means and'then release and in the latter case to remain in connection with the calling line. The class of line is intimated to the common exchange apparatus by the provision in the call finder of an additional wiper and bank, the lines which are provided with disabling means being marked in the bank. A convenient form of two-motion switch having an additional wiper and bank is described in Specification 203,759. Alternatively, the necessary intimation of the class of line is given over the starting circuit of the call finder by marginal operation or by the use of an additional wire. As shown, when a subscriber initiates a call, line relay L operates to start an assigner, Fig. 2, which is common to a group of lines and hunts for a free controlling circuit, Fig. 4. The controlling circuit includes a finder switch which hunts for a free connecting circuit, Fig. 3, the call finder CF of which searches for the calling line. Dialled impulses are received by the controlling circuit, and are repeated to the connector switch CS, Fig. 3, which is stepped on to the contacts of the wanted line. The call finder CF is provided with an additional bank and wiper E which effects the discrimination between the lines of ordinary type as shown in Fig. 1, and those, provided with disabling arrangements as shown in Fig. 5. The controlling circuit may form part of a. register controller. The connecting circuits are stripped of common apparatus which is embodied in the controlling circuits. Operation of assigner, Fig. 2, to choose free controlling circuit. When a call is made, line relay L, Fig. 1, is operated over winding 1 to short-circuit, relay AS, Fig. 2. and marks the test wire over the second winding II of the line relay. If the assigner is standing on contacts of a free control circuit, relay T is operated, but if standing on busy contacts, on the release of relay AS, relay G operates the stepping magnet DM and interaction continues to drive the assigner until when wiper 1 engages idle contacts marked over wiper LS3, Fig. 4, relay T operates to open the stepping circuit and mark the wipers 2, 3. Searching for free connecting circuit. Upon the operation of relay T, relay 5 is operated over wiper 3 of the assigner to operate test relay T, Fig. 4, if the finder switch CCA marks idle. If busy, the switch searches for a free outlet under the control of relay GMA and stepping magnet DFA which are brought into use by the relay S. When a free outlet is found, test relay T operates over wiper A3 in series with relay TT, Fig. 3, to prevent further stepping and mark the circuit busy against other finders on the same multiple. Relay T also operates relay CMB and stepping magnet DFB which interact to drive the finder switch CCB until wiper 131 closes a circuit for relay TA over wiper A1. The finder switches CCA, CCB now occupy the same positions and contact with leads in the same connecting circuit. Relay TA connects the impulse relay R to wipers A4, A5 and connects relay PG<1> over wiper B5 to wiper E of the call finder, but this circuit is opened immediately by relay GD which energizes over wiper LS4. Operation of call finder. Relay GD initiates the cyclic alternate operation of relays X, Y the relays delivering impulses to the vertical stepping magnet VM of the call finder OF over the wiper A6 and also to the stepping magnet LS until the wiper LST engages the contact marked by the calling line and relay M is therebv operated. Relay M opens the circuit of the stepping magnets VM, LS, the wipers being brought to rest in the level of the call finder corresponding to the calling line. The circuit of the rotary magnet RM also is closed and the call finder is rotated until when the test wiper C finds battery over the winding II of the line relay L relay TC is operated to (i) prevent further stepping (ii) switch the calling line over the wipers A, B of the call finder and wipers A4, A5 to the impulse relay A, (iii) apply busy marking to the test wiper C which fully energizes line relay L to effect disconnection of the line relay from the line and open the start circuit of the assigner. Dialling tone. The impulse relay A now operates relay V to operate stepping magnet OS of the sequence switch SS which moves one step and energizes relay D. Relay D energizes AS(II) and thereby de-energizes relays T, S. In this position of the sequence switch dialling tone is transmitted from lead DD over wiper A4 and wiper A of the call finder. Operation when subscriber dials impulses. Dialled impulses operate relay A and through the intermediary of relay O, which holds during impulsing sequence switch moves another step and the impulses are repeated at a<1> to the vertical magnet V<1>M of the connector switch over the wiper A6. At the end of the first digit, sequence switch SS moves into its next position and the first impulse of the second digit operates the sequence switch and impulses are repeated to the rotary magnet R<1>M over wiper A7. The sequence switch operates relay G which prepares for a fleeting test of the wanted line over wiper B7. At the end of the digits, switch SS takes another step and the called line is tested over relays PP, P the latter of which marks the test wiper of the connector switch engaged. Ringing called subscriber. Upon release of relay G ringing current is supplied to the called line from lead RG over wipers B3, B4 and relay T2 and a ringing signal is given to the calling line from lead RS over wiper A4. Metering and control circuit release arrangements. When the called subscriber replies relay TR operates relay VA, VY, over wiper B6 to mark the test wipers oi the call finder and connector respectively and thereby hold the line relays operated. Relays VA, VY also switch through the connection between the call finder and the connector and relays AA, YY operate to maintain relays VA, YY energized and operate relay MR which actuates the metering relay SM. Relay MR also releases V which initiates the release of the controlling circuit and causes restoration of switches SS, LE to normal. The switch CC9 also is operated a further step and the controlling circuit is freed for further use. Busy test. If the called subscriber's line is busy, relay P does not operate and consequently relay PA remains de-energized and upon the release of relay G busy signal is transmitted from lead BS over wiper A4. Release. At the end of conversation relays AA, YY release and release relays VA, YY to close the circuits of the release magnets ZM, Z<1>M respectively to restore the switches CF, CS to normal. In the event that the calling subscriber fails to release, relays AA, VA remain energized and an alarm circuit is closed over contacts va5, vy5. The same circuit is closed if the called subscriber fails to release. Forced release and discriminating operation of call finder under calling loop fault conditions. Upon operation of the relay V when the calling line is found, a circuit is closed for setting into motion a switch for the forced release of the apparatus if it. is not released within a prescribed time due to say failure of called subscriber to answer, loop fault, failure to dial &c. Relay V connects relay SA to lead 10 which is periodically earthed and operation of SA, which locks up, prepares relay ZA. After the lapse of a prescribed time earth is applied to lead 11 and if release of the controlling circuit has not been initiated by release of relay V, relay ZA opens the circuit of relay V, and provided the calling line has no disabling means relay VA is operated in the event that the called subscriber has not answered within the prescribed time. Relay VA connects up relay AA and the line remains connected to the call finder and is marked engaged so long as the calling loop is closed. If the seizure of the line circuit is due to a loop fault and no impulses have been received, relay PP remains inoperative and short circuits relay VY and consequently upon operation of relay ZA the alarm circuit is closed over contacts va5, vy5. For a line provided with disabling means, Fig. 5, the call finder is not held under fault conditions but is restored for further use, the faulty line being disconnected from the exchange common apparatus so long as the condition exists. When the calling line is found, the relay PG, Fig. 5, is energized over its winding I. Contacts are provided in the earthed bank of wiper E in positions corresponding to lines provided with relays PG and in consequence when the call finder engages such a line relay PG<1> is energized upon release of relay GD to open the circuit over wiper B6 and prevent energization of relay VA. When relay ZA operates, relay V releases and the release of the controlling circuit follows. The circuit over wiper C of the call finder is opened and relay L de-energizes and relay PG is maintained held to disconnect the line relay L from the line and operate an alarm PL. As relay VA remains de-energized release of the controlling circuit effects restoration of the call finder to normal ready for further use. In a modification the marked contacts in the bank E may correspond to lines not provided with disabling means. Su