Patent GB-500959-A (GB)
Title: Improvements in or relating to semi-automatic telephone or like exchange systems
IPC: H04M3/60
Filed: 1937-08-17
Abstract: 500,959. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd., HARTLEY, G. C., and SNELL, M. S. Aug. 17, 1937, No. 22588. [Class 40 (iv)] An operator may break down an established connection and set up a fresh one merely by keying up a new number. The invention is described in connection with a P.B.X. in which incoming calls are extended by an operator over a single motion switch JFM set by marking by two digits, the breakdown of a connection being effected by the operation of a retay ST the normal function of which is to start switch JFM after the first digit has been keyed. Instead of keying a number, the operator may have a strip with a key individual to each P.B.X. line for marking the junction switch directly. A P.B.X. party engaged in a main exchange call may be Connected to another P.B.X. party without releasing the junction. Night service facilities forming the subjectmatter of Specification 500,958 are also described. Incoming call over junction at the right of Fig. 2. Relay AC is operated by ringing current and the superposed battery energizes RB which opens the start leads 8LS (see later) of local links. Relays R and BR pull up, the calling lamp LL is flashed over lead FGL which may also operate a buzzer, and the ring- ing and tone equipment is started over lead MSL. The operator throws the junction speak key SK, and CA pulls up followed by S, SD in the position circuit, Fig. 3, other speak keys being disabled by SD. The keys SK may be of double throw type associated with pairs of junctions. Relay CA operates CB and locks up and Z pulls up. The ringing is tripped over the loop circuit leads XVIII, XIX including coil IL, contacts of dial DL and key NSK, the speaking set RT being connected across coil IL over the splitting key SPLK. The wanted number (two digits) is keyed up, the first digit being registered on AX-CX and the operated relay or relays locking up in series with Y which connects up the second register AY-CY. The operated relay or relays of the second register lock up in series with SZ which disconnects the key set and together with ST, operated after registration of the first digit, makes a self-interrupting circuit for JFM, the group and line in bank jfm4 being marked over cross-connecting frame CCF and contacts of the 1st and 2nd registers respectively. When Q pulls up over the group marking lead, JFM stops and O operates and locks to complete the line marking over contacts of AY-CY whereupon Q falls back, JFM restarts and, Q reoperates when the marked line is reached. Relay K pulls up slowly and ST relapses slowly to release the registers and control relays. CL and RR pull up during the release of ST and release R. If the speak key is restored before the release of R, lamp LL is flashed over lead FGL. The wanted line is tested by intermittent potential on load TPL and if it is busy LL is flashed over BFL, but if it is idle H pulls up, lights LL steadily and completes the ringing circuit over F. On reply, F operates, releases RR to prepare the speaking path and falls back, restoration of the speak key releasing S, SD, CA, CB and completing the speaking path. Relay L pulls up over the loop and holds Z, relays H, CL and BR remaining operated. Incorrect keying. First digits 1, 7, 8, 9, 0 are not used and if one of these is keyed, NU pulls up and connects tone to the left-hand winding of coil IL. Transference of connection by re-keying on request of calling party if the called party is busy, does not reply, or an undesired party is called. Assuming the speak key SK still thrown, CA, CB, S, SD, CL and BR are operated in all cases together with one or other or both RR and H. On keying a new number, ST pulls up as before after registration of the first digit and releases RR, H, whereupon a fresh connection is set up in normal manner.  Release. When the P.B.X. party hangs up, L and Z fall back and clearing alternating current is applied from lead CLL over the junction wires in parallel so that when the junction is unbalanced by release at the main exchange as described in Specification 472,993, relay AC pulls up and releases CL which disconnects the clearing signal whereupon AC, BR and H fall back and the circuit is normal. If the main exchange party holds on, AC is not operated, lamp LL lights and the operator makes enquiries. Connection of one P.B.X. party to another during an exchange connection. The P.B.X. party presses a button to ground both legs of his line, operating differential relay D followed by RC which connects up a " call-back " circuit, Fig. 5, and holds in series with MC therein which opens the operating circuit for other RC relays. Relay RC bridges and holds the exchange line and transfers the P.B.X. connection to a spare line circuit SEL, Fig. 5, over differential relay DR which also pulls up. When the sub-set button is released, DR relapses to remove a shunt on DC which pulls up. The spare line circuit seizes a local link circuit which returns ground to operate and hold K and the P.B.X. party sets up the connection over the local link by dialling, the link being arranged to return a fourth wire ground after the second digit to operate SD which locks to the third wire. SDD also operates and locks, relay K being now held by Z over lead XXV. If the P.B.X. party desires to return to the exchange connection he presses his button to re-operate DR whereupon PR pulls up and takes control of RC so that on the relapse of DR followed slowly by PR, relay RC relapses, releases the call-back circuit together with the local connection and re-connects the exchange line. If the P.B.X. party wishes to transfer the call to the other party, he replaces his receiver whereupon L and Z fall back and K in the call-back circuit relapses, the local link being held under the control of the other (called) party. Relay TR thereupon pulls up in parallel with MC and grounds leads XXIII and XXIV to release H and operate F in the exchange connection. TR also connects battery over M and a resistance in parallel to the fourth wire of the local link which over a wiper of the connector marks bank jfm5 of the junction switch which hunts for the new marking until stopped by FT whereupon H pulls up again. Relay M in the call-back circuit operates in series with FT and during the consequent slow release of DC, MM pulls up and grounds the third wire of the local link to release it. Relay RC released by M disconnects the call-back circuit. P.B.X. party to a connection calls operator by pressing his button twice. The first operation of DR brings in the call-back circuit as before and the second operation, since SD is not operated, grounds lead XXVI to operate,R in the exchange line circuit, whereupon the flicker lead FGL is connected to lamp LL and PR operates to release the call-back circuit as previously described. Night service. In one arrangement, an incoming call operates bells or buzzers distributed about the building and any P.B.X. party responds to the call by dialling 8 to a local link whereupon the junction switch sets itself on the responding line and the local link is released. The dotted connections of key NSK are wired up, connections marked X and relays NS, NC, ND, R (left) being dispensed with. A call operates RB, AC, R and BR as before but R and RB fall back since R has no locking circuit, and the buzzers are operated over leads XIII, BVL and the thrown key NSK. When a party replies by taking a local link and dialling 8, a common relay operated over a vertical bank of the final selector grounds a common lead 8LS which is taken over key NSK to the upper left-hand corner of Fig. 1 to operate F in the calling junction circuit, switch JFM thereupon hunts for the calling line of the local link which is marked over the local finder and bank jfm5 by a further relay (individual) operated over the vertical bank of the final selector. JEM is stopped by FT which shunts a high resistance winding to shunt and release the holding relay of the local link. Relay H switches through, LG pulls up over the P.B.X. loop, energizes L by connecting it across the exchange line (incidentally tripping the ringing in this case) whereupon Z pulls up and completes the normal speaking path, LG being released. In an alternative arrangement using only the full line circuits and key NSK thrown to route the call to a night line, an incoming call operates RB, AC, R and BR as before but R locks. Relay NS operates in series with NC and energizes CA whereupon CB, ME, S and SD pull up. Relay Z also operates and ND pulls up. It will be seen that the operation of NS substantially performs the operations of the speak key SK, but ringing has not been tripped. Relay NC holds to the ringing return battery on the + ve wire in the case of an automatic main exchange or alternatively over contact pz in the ringing and tones equipment in the case of a manual main exchange. The contact pz is opened at intervals to prevent permanent lock-up on abandoned calls. Relays AX, AY of the two registers are now arbitrarily set in turn by machine impulses over lead IEL, ST, Y and SZ are operated as in a normal call and switch  JFM is started up but as NC is operated the registers do not perform any marking. function and Q stops the switch over lead V, lead II jumpered to the contact of jfm4 corresponding to the night line. Relays O and K pull up in turn and the registers including ST, release with the exception of SZ which is locked by NC. Remaining operations up to and including response to the reply of the night line party take place as for a normal call, but in addition IA pulls up over leads XV, XVI and the called loop, releases NC followed by ND, SZ and NS and other operated relays including CA and CB whereupon the speaking , path is switched through and main exchange ringing is tripped. Outgoing calls. The operator ascertains which junctions are busy by throwing key JTK whereupon JT lights lamps LL of busy junctions, or