Patent GB-717681-A (GB)
Title: Improvements relating to automatic telephone and like selective systems
Inventor: LONG DOUGLAS PERCY
IPC: H04Q3/00
Filed: 1951-06-01
Abstract: 717,681. Automatic exchange systems. SIEMENS BROS. & CO., Ltd. May 30, 1952 [June 1, 1951], No. 13057/51. Class 40 (4) A selector whose access to one or other of two groups of outlets is controlled by a wiperswitching relay has a control bank, common to the two groups, over which may be reverted A.C. control signals which are different for corresponding outlets in the two groups, the two control signals being transmitted to a bank contact over oppositely poled rectifiers, differentiation between the signals being effected in the control signal receiving circuit by a relay polarized in accordance with the condition of the wiper-switching relay. The invention is described in relation to a partyline system in which the reverted signals control coded ringing. Normal call.-The selector is set and the required outlet is tested to ascertain whether the wanted line is free, busy, or whether the call is revertive as described in Specification 646,519. When the switching relay H operates earth applied to wire BW brings up relays X, FBB and HA in that order. The first applies holding earth to the P-wire over a low resistance of winding of CD. If the call is neither a toll nor a revertive call then CD operates to battery connected to the P-wire by the preceding and succeeding switching relays. CD operates before FBB. Relay CD brings up ringing relay R. Relay FBB inserts the feed-bridge in the + and -wires and relay FBA therein operates to the calling subscriber's loop. Relay R earths the start wire STW -of the ringing-code control circuit, Fig. 4, and prepares a circuit for the application of ringing current to the + wire. The ringing start wire RSW is earthed just prior to each cycle to bring up RS which then locks and connects the code-ringing relay CC to the code control wire CCW. The latter wire is connected via ws contacts and polarizing rectifier to the code control wiper CCC. Five different ringing codes may be used and corresponding signals are applied from the code-ringing circuit, Fig. 4, in pairs to the bank CCC. The coderinging circuit is therefore provided with 25 different terminals each corresponding to a pair of codes, 5 of these terminals 31 ... 35 being shewn. Each code is provided by a circuit; such as that shewn, comprising relays ECE, ECO and OCE, OCO (one pair of which is normally disabled by a plug in jack EDJ or ODJ) which are pulsed according to the desired code (say code number 3), over wire PW3. Thus (assuming ECE and OCE are operative) earth is applied over lead EC to rectifiers F31, F32, F34, F35, in accordance with code 3. Likewise rectifiers S31, S32, S34, S35 have earth applied to them in accordance with codes 1, 2, 4, and 5 respectively. Since the F and S rectifiers are oppositely poled it follows that if, say, lead 31 is connected to a bank terminal CCC either the S31 or the F31 circuit must be blocked according to the. manner of connection of rectifier PRE by the wiper switching relay WS. The unblocked circuit causes half cycles of ringing current from lead RGW, Fig. 3, to operate relay CC in accordance with the appropriate code. Clearly where, as with the terminal 33, the pair consists of identical codes no S and F rectifiers are necessary. Relay CC thus connects ringing current to the + wire in accordance with the desired code. The outlets of the final selectors may be so connected to the line that the substation bells may be connected to different legs of the party line thereby enabling ten subscribers to be connected to one party line. When the called party answers ring-trip F operates over the called party's loop to release CD and R. Release of R causes backbridge relay D to operate, and RS to release. The call then proceeds on a last-party-release basis. Revertive call.-In this instance the preceding selectors are released by the calling subscriber hanging up, before the switching relay H operates and CD cannot operate in series with H alone. Relays HA and FBB come up to earth on BW as before. A revertive call is signalled by momentary battery applied by relay TD (identical with that in Specification 646,519) to wire RCW for a short period after the operation of the switching relay H. Relay HR in the feed-bridge circuit is thereby brought up. Since the caller has cleared FBA does not come up when FBB operates. When HA then operates it energizes CD (ii) and R. Code ringing takes place as previously described with the exception that with HR operated the momentary starting earth on RSW operates RR to put ringing current on the negative wire as a ringing indication to the calling subscriber should his bell and the called party's bell, be connected to different legs of the loop. When the called party answers, ring-trip relay F operates to release R which in falling back releases FBB by short-circuiting it. Continued operation of F is left dependent on the operation of back-bridge relay D. Toll calls.-When the final selector is seized from a toll repeater earth is extended therefrom over the P-wire so that operation of X does not bring up CD. Ringing is effected by unbalancing the incoming line loop to operate TR. Relay BTC follows and locks and brings up CD and the ringing relay R and ringing takes place as described above. A called subscriber who has hung up may be re-rung by again operating TR which besides initiating ringing operations as described above, opens the hold circuit for the ring-trip relay F.