Patent GB-141106-A (GB)
Abstract: 141,106. Sterling Telephone & Electric Co., and Davey, W. C. Dec. 31, 1918. Automatic exchange systems.-A subscriber seizes and operates a selector over one line, transfers the operating-circuit from one selecting-device to another over the other line, and rings the called subscriber by putting his lines in contact. The transfer or change-over is controlled by a differential relay, the windings of which are oppositely excited by the initial movement of the selector and are subsequently put out of balance when the impulse-sender returns to its normal position. Connexion of calling-line to idle selector. In the relay switching-arrangement shown in Fig. 1, each subscriber has a line relay L, a group relay G, and switching-relays FI, FII, &c. for each selector trunk except the last. The subscriber's impulse-sender is represented as a Morse key K, of which contact 1 is closed at each impulse and contact 29 at the end of each set of impulses to effect the necessary change-over. When the subscriber operates his impulse-sender without having removed his receiver, his line relay L is energized over the a-line, and if all the selectors are free, closes a circuit through the high and low resistance windings of the group relay G and lead c and relay HI of the first free selector. The relay G disconnects the line relay, locks up over its low-resistance winding and lead c, extends the calling-line over contacts 7, 8 and 9, 10 to the first selector, short-circuits the disconnecting-relay D at contact 55, and at contact 13 connects the a and b multiples so as to mark the line busy. If the selector I is in use, relay G is not energized over the lead c of that selector, since it is shunted by the low-resistance winding of another relay G, but a circuit is closed over relay FI, lead 'd, contact 15 of relay HI of the busy selector I, to earth at contact 16 of relay HII of the free selector II. Relay FI locks up over its lower winding, extends the calling-line over contacts 17, 18 and contacts 9, 10 of relay FII to the second selector, and closes at contact 19 a circuit for relay G, which energizes and functions as before, except that the calling-line is extended to selector II instead of to selector I. Simliarly, if selector II is in use, relay FII energizes and extends the calling-line to selector III. In the modified ar. rangement shown in Fig. 3, no group relay is provided, but relays F<1>I, F<1>II, &c. are provided for each selector trunk. When the calling-subscriber operates his impulse-sender, his line relay L<1> energizes over his a-line and the normal contacts of relays F<1>I, F<1>II, F<1>III, and closes operating-circuits for all these relays. The relays associated with idle selector trunks all energize temporarily, but the relay associated with the first idle selector trunk at once opens the holding- circuits of all the other relays, and also the energizing-circuit of the line relay L<1>. The relays F<1>I &c. also close circuits corresponding to those controlled by the relay G, Fig. 1. In an exchange of fifty subscribers, divided into five groups of ten subscribers, to which five selectors are allotted, five different combinations of the selectors taken three at a time may be assigned to each group of ten subscribers. Operation of selector, Fig. 2. The first closure of the contact 1 of the impulse-sender not only causes the connexion of the calling-line to an idle selector, but also energizes relay A of that selector. Successive impulses are repeated to the vertical magnet V over contacts 24, 23, 22. During the transmission of these impulses over the a-line, the b-line is open at the sub-station, and after the first vertical movement of the wipers, the differential relay B receives current from battery over contact 52 of relay C, contacts 51, 58, right and left windings of relay B, to contact 25 and earth. The relay B is not energized by this current, but when the impulse-sender closes contact 29 at the end of the tens impulses, the bell Z is connected in parallel with the left winding of relay B, the balance of which is upset. Relay B is thus energized and, by opening contact 26, disconnects its left winding, so that its circuit over contacts 30, 31 is dependent on relay A. Since relay B is energized but not relay A, a circuit is closed over contacts 32, 33 for the change-over relay C, which locks up dependent on relay P and substitutes the rotary magnet X for the vertical magnet V. A circuit is also closed to notify the calling-subscriber that the call has so far proceeded satisfactorily, this circuit passing from battery, contact 37 of relay C, vibrator N, contact 39 of relay B, and over the b-line to the subscriber's bell and earth. The subscriber then sends in the units impulses, which are repeated by the relay A to the rotary magnet X. The first operation of relay A opens the circuit of relay B, which de-energizes but is again excited when contact 29 is closed at the end of the impulses to connect up the vibrator N to notify the subscriber that his call is completed. Busy test and busy release, Fig. 2. If the wanted subscriber is the calling-party in an existing connexion, the a and b multiples of his line are connected together by his relay G, Fig. 1, as already described, so that the wiper relays P, Q are at once energized, and relay P energizes a restoring-relay R, which opens contact 6 in the circuit of relays HI, G, Fig. 1, thereby disconnecting the calling-line from the selector, which is restored by the release magnet Y. Similarly, if the wanted subscriber is a called party in an existing connexion, relays P, Q, R energize as just described. If the wanted party is being rung by a third party, the ringing-current on his b-wire will energize relay Q, which excites relay R as before. Thus, if the wanted line is busy, the calling-subscriber's bell does not ring, and all the exchange apparatus is restored without the subscriber having removed his receiver at all. Ringing-current, Fig. 2. If the subscriber's bell rings, he knows that the call is completed and removes his receiver, thereby closing the loop circuit and energizing relays A, B simultaneously, whereby relay R is energized; but this does not release relays HI, G, since the circuit of these relays is now completed over contact 44 of relay A. Relay R then connects the vibrator N over the b-wiper to the called-subscriber is b-wire and his bell. When the called party removes his receiver, relays P, Q are energized over the called line, and relay P opens the holding-circuit of the change-over relay C, which disconnects the vibrator N. Talking circuit. The two lines are connected through the condensers 48, 49, microphone current being supplied through relays A, B and P, Q respectively. The disconnecting-relay D between the a-multiple and the a-line of the called subscriber is energized when a call is received to disconnect the line relay of the called line. Release is effected when either party replaces his receiver. If the calling-party first hangs up, relay A de-energizes and opens the circuit of relays HI, G, Fig. 1. Relay HI energizes the release magnet Y, and relay G disconnects the calling-line from the selector. If the called party first hangs up, relays P, Q de-energize, and relay P at contact 51 short-circuits relay A and effects release as before. Operation of selector, Fig. 4. In the modified system shown in Fig. 4, the relay A, Fig. 2, is replaced by two relays A<1>, U, of which relay U acts as the impulse relay to control the vertical and rotary magnets V, X. In order that relay U may be disconnected during speaking, it is connected to battery over a back contact of relay B': The interrupter N, Fig. 2, is replaced by two interrupters N', N", Fig. 4, of which N' is a high frequency interrupter and is used to indicate the progress of the call, being connected over back contacts of relays A', R' and a front contact of relay B' to the subscriber's b-line, which is earthed at the sub-station through his bell Z' and receiver M' in parallel. Ringing-current, Fig. 4. When the calling- subscriber removes his receiver, the relays A<1>, B<1> are energized simultaneously over the loop, thereby energizing relay R', which connects the lowfrequency interrupter N" over contacts 73, 74, 75 to the wiper and thence to the wanted line. Specifications 141,311 and 141,312 are referred to.