Patent GB-949322-A (GB)
Title: Telephone signalling converter
IPC: H04Q1/446
Filed: 1960-11-28
Abstract: 949,322. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. Nov. 28, 1960 [Dec. 2, 1959], No. 40759/60. Heading H4K. A converter is employed between exchanges of different type in order to convert signals from one exchange into signals suited to the other and vice versa. The signals for which conversion is provided are ringing current and D.C. loop signals from a common battery, manual or dial central exchange, or ring down current from a switch-board or a magnetophone exchange; the conversion being to and from S, U, X, Y and Z tones peculiar to an electronic exchange. Ringdown and common battery signals may be transmitted by carrier over a 4-wire trunk, see Fig. 2c, not shown. As shown in Figs. 3, 4 and 5, the 2-wire line 300 from the common battery or ringdown exchange connects to a 4-wire path 307, 308, to and from the electronic exchange. Face-to-face diodes D1 across line 300 limit voltage on the line to 150 volts peak to peak while Zener diodes ZD1, ZD2 limit the voltage across hybrid windings to 5 volts. Switches 315 to 318 when bridging contacts a, b, as shown, condition the converter to common battery signals on line 300, but when they bridge contacts b, c the converter deals with ring-down signals. Connection from common-battery to electronic exchange.-Having connected with the line 300, as with any other outgoing line, the common battery exchange applies ringing current which is detected in the converter by circuit 320. Detector 320 discriminates between the amplitude of speech and ringing signals and applies a voltage to a signal-end detector 440 for the duration of ringing, detector 440 providing an output at the end of ringing to what is called a 1-2 switch 441. Input to the lower terminal of switch 441 gives output to the lower or normal output terminal unless the upper input is also energized when output is given to the upper or off-normal output terminal. In the present instance, output from 440 is normal to set a toggle circuit 442 output from which, over OR gate 433, triggers a 5-second pulse from a timer 432 to inhibit the ringing current detector 320 so as to prevent further response to ringing current. The output of toggle 442 also sets toggle 422 to energize a relay 311, contacts 310 of which close a loop across line 300 to operate the ring-trip relay at the common battery exchange. In the same circuit a busy lamp 344 lights at an operator's position 316 to indicate that the path is employed. Equipment in the electronic exchange is seized by transmitting S-tone from gate 531 marked over gates 523 and 443 by the output of toggle 442, S-tone being returned with dial tone to signal acceptance of the call at the electronic exchange. This acknowledgement is relayed by a constant output amplifier 511 to an S-tone detector 510 which generates an off-normal output from 1-2 switch 424 so that a 100 milli-second pulse is produced by timer 548 to send UX-tone over gate 533 for this duration. A 200 millisecond pulse is also produced by timer 544 so that 100 milli-seconds after UX-tone has ceased a further burst of UX-tone is sent as signal end detector 546 triggers timer 548 to produce another 100 milli-second pulse. The sending of UX-tone disconnects the S-tone sender by inhibiting gate 443 for as long as timers 544 and 548 are active. In response to UX-tone the electronic exchange disconnects the acknowledgement S-tone and the cessation of output from S-tone detector 510 produces an output from signal-end detector 429 to set toggle 428. With 428 set a line switch control circuit 427 operates relays 412, 450, to connect the send and receive paths 307, 308, dial tone now being heard at the common-battery exchange which can proceed with the call. The output of toggle 428 also resets toggle 442 to prevent sending of further S-tone and also inhibits S-tone receiver 510 to guard against speech intrusion, an additional guard being provided by inhibition of timer 541 and signal end detector 542. Release of converter:-Release can be effected from the electronic exchange which sends YZ tone or can be forced at any time if there is silence from the electronic exchange in excess of 3 minutes. Considering forced release first, once enabled by toggle 422 a busy detector 421 relays speech from amplifier 511 to start and continuously reset a 3-minute timer 420 which, if allowed to time out, produces an output. By this means incoming ringing is disabled by inhibiting detector 320 and by resetting toggle 442 should this have been set. Toggle 442 is reset direct and a 1-second pulse triggered from timer 322 inhibits gate 427 and triggers a 5- second pulse from timer 432 which inhibits the detector 320. A 3-second pulse is also generated by timer 521 which restores toggles 422 and 428, 422 releasing the 3-minute timer 420, extinguishing operator's lamp 344, and releasing relay 311 to open the loop across line 300 and signal release to the central battery exchange. Restoration of toggle 428, unless preceded to the same effect by the inhibition on gate 427, releases the line control circuit 426 and dependant relays 412, 450, to disconnect the send and receive paths to the electronic exchange. A timing circuit 430 is activated for so long as toggle 428 is set and continues to give output 200 milliseconds after the toggle is reset, thereby inhibiting gate 522 so that the sending of disconnect YZ-tone over gate 530 for the duration of the 3-second pulse from 521 is held back until the unbalance of the line arising from disconnection subsides. The electronic exchange releases in response to YZ tone and the converter is idle. If release is initiated by the electronic exchange it is done with YZ tone from the exchange which energizes the Y and Z tone detectors 512, 513, to enable AND gate 431. Output from gate 431 effects release in the same way as described above for forced release except that a 1-second pulse is not required from timer 322 to provide the guarding inhibition on gate 427. Connection from electronic exchange to central battery exchange.-Seizure of the converter is effected with a burst of S-tone from the electronic exchange giving output from S-tone detector 510 which is relayed over the normal (lower terminal) output of 1-2 switch 424 to set toggle 422. Output from 422 energizes relay 311 to loop the line 300, thereby signalling the common battery exchange to prepare for the call. Output from 1-2 switch 424 also triggers a 250 millisecond pulse from timer 541 which connects S-tone by gate 531 at the end of which signal end detector 542 triggers a further 250 millisecond pulse from timer 543 to connect YZ-tone by gate 532. Should the electronic exchange respond to the initial burst of S-tone, the S-tone it transmits itself is terminated and the signal end detector 429 sets toggle 428 to inhibit signal end detector 542 and prevents generation of the burst of YZ- tone. Should the electronic exchange not respond to the S-tone it responds to the following YZ-tone and by disconnecting its own S-tone sets toggle 428. Line control switch 426 is now energized to operate relays 412, 450 to connect the line. Release of the converter is the same as if the call had been set up from the commonbattery exchange as described above. An operator is called into the connection when S- tone is sent to the electronic exchange since the output of timer 541 sets toggle 323 to light a line lamp 345 and sound a buzzer. Toggle 323 may be reset by the operator or during release is reset with toggles 422 and 428. Connection from a ring-down exchange to an electronic exchange.-For such a connection switches 315 to 318 bridge the b and c contacts. Circuit 320 detects a burst of 20-cycle current and causes the converter to seize an inlet to the electronic exchange in the same way as described for a call from a common battery exchange except that no acknowledgement is given to the ring-down exchange. Connection from an electronic to a ring-down exchange.-This proceeds as described above for the case of a call to a common battery exchange, seizure being made with S-tone which is reverted to the electronic exchange by the 250 millisecond pulse from timer 541, this pulse also triggering a 1-second pulse from timer 322 to energize relays 311 and 351. By this means the ring-down exchange is signalled with a pulse of 20 cycle current while the hybrid is disconnected. Release of a ring-down connection.-This is largely the same as for release of a commonbattery connection except that release can be effected by a burst of 20 cycle current from the ring-down exchange detected by circuit 320. At the end of the burst signal-end detector 440 provides input to the 1-2 switch 441, the upper input terminal of which is marked throughout the call from timer 430 which is continuously energized from toggle 428. The upper, offnormal, output of 1-2 switch 441 is therefore active to generate a 3-second pulse from timer 521 causing release of toggles 422 and 428. With 428 reset timer 430 releases after 200 milliseconds to remove the inhibition on gate 522 so that the electronic exchange is released with a burst of YZ-tone. Should the electronic exchange initiate release it sends YZ-tone with the effect described above for a common battery connection, the output of AND gate 431 in this connection operating relays 311 and 351 to send 20 cycles to the ring-down exchange. Supervision.-A fault location arrangement is shown with jacks 350 and 400 but is not described. A manual release circuit is shown from jack 460 but is not described.