Patent GB-463874-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1935-10-07
Abstract: 463,874. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd. Oct. 7, 1935, No. 27662. Convention date, Nov. 7, 1934. [Class 40 (iv)] A two-way junction is normally completely disconnected from the automatic switches in the exchanges and is adapted to be connected to one or other of two branch circuits at each exchange, connection over one branch being effected in response to seizure thereof on outgoing calls, and over the other branch on incoming calls in response to an alternating current signal transmitted over the junction. Alternating current of the same frequency is used for impulsing and signalling, 60# being used in case of normal junctions and 120# over junctions used also for telegraphy, but when repeatered junctions are used, the seizing supervisory and releasing signals comprise 1000 # alternating current modulated at a higher frequency (60#) than the frequency of interruption of the switch setting trains which consist of unmodulated impulses of 1000#. A relay set responding to incoming signals differentiates between modulated 1000# signals, switch setting impulses, and 1000# components occurring in speech. Calls over non-repeatered junctions, 60# signalling, Figs. 2 and 3. On an outgoing call, group selector S3 seizes an outgoing repeater IR3 and on applying ground to the release wire operates relay 213 which removes the shunts on the left hand repeating coils and shortcircuits a resistance 270 in the speaking path. Line and release relays 203, 204 pull up followed by 205 which switches the repeater through and operates 214 on the outgoing side whereby 216 pulls up to transmit over the junction a seizing pulse of 60# current and to operate 217 slowly, the pulse being terminated by the release of 214, 216 by 217 which locks up. On the first impulse of the outgoing digit, line relay 203 operates slow relay 218 which holds during the digit and releases 213 to restore the lefthand repeating coils to their shunted condition with resistances 270, 271 inserted to improve operation of 203 on lines of varying character. Relay 218 also operates 214 to prepare for the transmission of 60# impulses. The impulses are repeated to 219 and thence under control of correcting relays 221 ... 225 to relay 216 which applies to the junction 60# current filtered to remove harmonics by coil 215 and associated condensers. It will be assumed that the normal <6>/10# break and 4 /10# make impulses are to be repeated. Relay 219 operates for <6>/10# and energizes 223 which due to choke 222 and a shorted winding does not pull up until <4>/10# has elapsed. When this occurs 216 applies 60# current to the junction and 221 pulls up after a further <2>/10# to hold 216 and energize 225 which also operates after a delay of <4>/10# so that when 219 and therefore 223 relapse after <6>/10#, 221 and therefore 216 hold until 225 pulls up or the next operation of 219 commences. When this occurs, 221 relapses followed by 225 and the cycle starts again. Relay 216 therefore repeats <6>/10# impulses of 60# over the junction. The Specification discusses the action of the corrector for larger and smaller make-tobreak ratios and for impulse speeds of from 8 to 12 per second. When all the digits have been sent, the repeater is in the condition in which relays 203, 204, 205, 213 and 217 are operated and a backward impulse of 60# is received indicating response of called party. This impulse operates A.C. relay 226 so that answering relay 202 responds in two steps, reverses the connections to 203 for supervision or metering, and transfers its own original operating circuit to 201 which eventually responds to the release signal. Incoming call. When the seizing pulse of 60# comes in over TL2, A.C. relay 226 responds and operates 208 in two steps thereby switching the repeater to the incoming selector S5. Slowoperating relay 207 used for effecting release does not operate in parallel with 208 since the pulse of A.C. is relatively short. Relay 208 grounds the release wire to guard the repeater and operate 213 to condition the repeating coil for speech, and polarized relay 212 (upper) is connected across the speaking wires to operate the line relay at the incoming selector, 212 remaining inert in view of the polarizing lower winding energized by 208. Relay 208 also connects the impulse wire from 226 to impulse repeating relay 219. Slow-releasing relay 220 is now operated by 219 instead of 218 operated thereby in outgoing calls so that the impulses are repeated by the corrector relays to a loop circuit including conductor 273, resistance 271 and upper winding of 212 shunted by the condenser in the left-hand repeating coil. Relay 213 is released during impulsing. When the group and final selectors have been set and the called party responds, the reversal of current at the final selector operates 212 which releases 213 so that 212 is controlled over its lower winding only to prevent interference due to irregular switch-hook operation. Relay 212 operates 214 which energizes 216 to send the answering A.C. pulse terminated by the operation of 217 as described in the preceding paragraph, 217 also operating answering supervisory relay 210 which re-operates the repeating coil conditioning relay 213 and releases 217. Release. Assuming that the called party is first to replace his receiver and that the repeater, Figs. 2 and 3, is the one at the called exchange, the restoration to normal of the direction of current feed back from the final selector releases 212 whereupon 211 pulls up, locks to ground on 275 and extends this ground to operate 214 which causes 216 to apply a pulse of A.C. to the junction, the pulse being terminated as before by 217 which, however, does not lock up since 210 is operated. On operation, 217 also shunts down 210 which releases 211 followed by 214 which opens the operating circuit of 217. Turning now to Figs. 2 and 3 as representing the repeater at the calling exchange, the backward pulse of A.C. operates 226 which energizes 201 in two steps since answering relay 202 is operated. 201 locks up and releases 202 which restores the direction of current feed to the calling party. This is mainly to give a signal in case the call is from an operator. When the calling party restores, line relay 203 relapses and operates 218, 219 whereby 214, 216 are operated to connect A.C. to the junction, this condition being maintained until release relay 204 relapses, whereupon switching relay 205 falls back and releases 218 to bring about the release of 214, 216 to terminate the A.C. pulse which is therefore a prolonged one. This pulse results in prolonged operation of 226 at the called exchange so that impulse repeating relay 219 operates 220, 221, 223 and 225 which energizes slow-operating relay 207. This relay, which was not operated by switchsetting impulses, operates and makes 208 dependent on the ground extended to 207. When the pulse terminates, this ground is removed, whereupon 208 releases quickly, followed by 207 slowly. Relay 208 finally removes ground from the release wire and opens the loop to the selectors in the called exchange. Dealing with abnormal conditions. Release of an incoming repeater is forced if the release signal is not properly transmitted to it or if it has been seized by irregular operation of A.C. impulse relay 226, e.g. by an electrical storm. When 208 pulls up to seize an incoming selector, time pulse lead 276 is connected to relay 209, and if answering relay does not become operated or the connection is not in the meantime released in the case of a busy line, 209 operates in two steps on successive pulses so that 207 is operated by the third pulse and effects release as described in the preceding paragraph. Substantially simultaneous seizure of repeaters at both ends is also dealt with. If the seizing impulses are precisely simultaneous they are without effect since 214 is operated at each end of the junction. If, however, selector seizing relay 208 is operated by an incoming call before the repeater switching relay 205 is operated by line and release relays 203, 204 on an outgoing call, 206 pulls up and sends busy tone to the party making the outgoing call. This party hangs up, thereby releasing 203, 204 and 206 in turn so that during the release period of 206 the release wire 262 is ungrounded to release the switches seized by this party but is subsequently grounded to busy the repeater. If the calling party abandons the call at any time after the seizure of an outgoing repeater, the long release signal is sent out. In a particular case in which abandonment occurs during the transmission of the seizing impulse, this impulse is converted into a long one, since the relapse of line relay 203 operates 218 until 204 and 205 release and 218 disables 217 which regulates the time of the seizing impulse. This prolonged impulse does not seize the incoming repeater since although 208 is operated one step at the commencement of the impulse, 207 pulls up before its termination to disable the full operating circuit of 208. Use of 120# for signalling when the junction is composited for telegraphy also. In this case, the receiving relay 226 is replaced by the set shown connected by dashed lines. The receiving relay proper 228 is tuned by coil 227 and condenser 254, and flutters a neutral armature to operate slow relay 229. Relay 228 may have an adjustable shunt resistance. Voice-frequency signalling on repeatered junctions, Figs. 4 and 5. The signalling equipment comprises detector and amplifying valves 338-336 fed with various operating potentials from a 110 volt supply in known manner, and common transformers 361, 364 for supplying 1000# signalling current and 60# modulating current. The incoming pulse relay 326 is normally operated by plate current of 338 and operates 321, and incoming signal repeating relay 309 is normally operated to hold release-control relay 307 energized. On an outgoing call, line, release