Patent GB-343009-A (GB)
Title: Improvements in or relating to exchange systems for interconnecting telegraph apparatus
IPC: H04L12/04
Filed: 1929-11-06
Abstract: 343,009. Telegraph exchange systems. STANDARD TELEPHONES & CABLES, Ltd., McWHIRTER, E. M. S., and FLINT, J. G., Columbia House, Aldwych, London. Nov. 6, 1929, No. 33855. [Class 40 (iii).] In a manual printing telegraph exchange system, communication between the calling and called s u b - scribers and the operator is carried out solely by printing telegraph apparatus over a complete metallic circuit comprising two wires only connecting each subscriber with the exchange, and the apparatus at the called station is automatically set in operation, to receive a communication, on the completion of a connection thereto. The subscriber's apparatus is controlled by a motor TM, connected through a switch CK to mains P1, P2, and by transmitter contacts TC, a receiving relay PM and a polarized relay PR which operates on a battery reversal. Each subscriber's apparatus is connected by two lines L1, L2 to jacks CJ, AJ at the exchange. Calling operation. The calling subscriber momentarily depresses the key CK, Fig. 1, thus starting the motor TM which closes the contact TMC thus operating the contact TMO which is controlled by the relay PM and energizing also the calling relay CR at the exchange in a circuit from positive pole of battery B, contact of jack CJ, line L1, relay PM, contacts TC, pr1, key RK, contact TMC, line L2, contacts of jack AJ, relay CR, contacts of jack CJ, negative pole of battery B. Relay CR operates, lights calling and pilot lamps CL, PL and rings an alarm bell at the exchange. The operator inserts her plug AP, Fig. 2, into the jack AJ and switches her key CCK to the right thereby spreading the left hand springs of this key. This connects her machine OM in series with the subscriber's apparatus, whereon she can, by typing, ascertain the number of the wanted subscriber. The connection between subscriber and operator is as follows :-positive pole of battery B, contacts of jack CJ line L1, calling subscriber's apparatus, line L2, ring spring of jack AJ, ring of plug AP, contacts of key CCK, operator's machine OM, back contact of relay CSR, contacts of key CCK, tip of plug AP, tip spring of jack AJ, contacts of jack CJ, negative pole of battery B. Local call. If the required subscriber is on the same exchange as the calling subscriber the operator inserts her plug CP into the jack CJ belonging to the called subscriber. This operates the relay CSR through the grounded sleeve of the jack CJ, disconnects the called subscriber's battery B and connects the calling and called subscriber's apparatus in series, from the left hand contacts of the key CCK,through the operated contacts of the relay CSR, the right hand contacts of the key CCK, the tip and ring of the plug CP to the tip and ring springs of the called subscriber's jack CJ. The operator switches the key CCK to the left, thus spreading the right hand springs and reversing the connection to the called subscriber. This operates the called subscriber's polarized relay PR and completes the circuit for the motor TM over the contact pr2. Contact TMC closes and, on restoring the key CCK to normal relay PR restores and relay PM operates and closes the contact TMO for the motor TM. Communication can now take place even in the absence of an operator at the called station. The operator at the exchange can monitor on the circuit by switching the key CCK to the right thus operating the left hand springs and connecting her machine OM in series with that of the two subscribers. When the key CCK is restored a slow release relay SR is included in the circuit and controls the operation of a thermostat relay after transmission is concluded. Clearing operation. The calling subscriber presses the key RK, thereby de-energizing the relay PM, opening the contact TMP and stopping his motor, at the same time relay PM at the called substation de-energizes and the motor TM at that station also ceases to rotate. Relay SR de-energizes and closes the circuit for a thermostat relay THR which operates and lights a supervisory lamp at the exchange. If the called subscriber is on another exchange the operator inserts the plug CP in the jack OJ of a junction circuit, Fig. 3, connecting with the called subscriber's exchange. This circuit includes two polarized transmitting relays A, C each having two windings A1, A2, and C1, C2, one relay being at each end of the junction line JL1, JL2, and two single-winding polarized receiving relays B, D similarly arranged. The relays A, C control the contacts a and c and the relays B, D control contacts b, d. The contacts of the relays are normally biassed magnetically to the spacing position, but contacts a, c of the transmitting relays are normally held to the marking position against this bias, their windings A1, C1 being energized in similar circuits, as in the case of winding A1, from contact b in spacing position, back contact of relay M, back contacts of relay P, upper contact of relay M, resistance, battery, winding A1, contact b. The junction lines JL1, JL2 are therefore normally in series with the windings B, D, A2, C2 over contacts a, c. When the ply CP is inserted in the jack OJ relay M operates through the earthed contact of the jack OJ and switches the battery B through to the winding A1. The operator then switches the key CCK to the left thus reversing the connection to the winding A1 of relay A which operates and connects the windings D, C2 in series with a battery over the operated contact a. Contact d then moves over to marking. Relay F is now energized in series with winding C, and operates its contacts so as to energize a cal'ing relay CR and light a calling lamp at the called exchange. The operator at the called exchange inserts her plug AP into the jack IJ on the right hand side of Fig. 3. Relays Q and N operate to local contacts on the jack IJ and a circuit is prepared for the winding C, through upper operated contact of relay N, upper operated contact of relay Q, battery EB, lower operated contact of relay Q, tip spring of jack IJ, second operator's apparatus, ring spring of jack IJ, contact d (not yet closed) and winding C1. When the operator at the first exchange restores the key CCK to normal, relay A, closes its contact a to its marking contact thus de-energizing the windings D, C1 and moving the contact d over to its spacing contact. Relay N also operates to de-energize relay CR and extinguish the calling lamp. Communication between the operators of the first and second exchanges then takes place and is relayed over the contacts a, d (sending) and c, b (receiving). The calling subscriber, being in series with the first exchange operator's machine can follow the progress of the call. The operator of the second exchange inserts her plug CP in the jack CJ of the required subscriber and calling and communication take place as before except that the signals are relayed to the called subscriber, the battery EB supplying current for his apparatus. Either operator can monitor on the circuit by pressing her key CCK to the right. Release of the connection takes place in the same way as for a local call. If a subscriber desires to be connected to a plurality of subscribers simultaneously, the operator inserts her plug CP in a jack BJ1, the tip and ring spring of which are connected to the winding of a telegraph relay TR. Contacts of this relay are connected in series with a battery to tip and ring springs of a jack BJ2 into which the operator inserts a plug APB which is connected to a number of plugs CP1, CP2 &c. in parallel. These plugs are inserted into the jacks CJ of the wanted subscribers or of their junction circuits and sleeve relays SR1, SR2, &c. operate to complete the connection to the plugs. The key BCK is pressed in order to start the motors of the called subscribers. The sleeves of jacks,contacts of which are connected to signalling batteries, are grounded in order to protect the operator from shock.