567,049. Exchange systems. AUTO. MATIC TELEPHONE & ELECTRIC CO., Ltd., and MURRAY, L. J. July 21, 1943, No. 11836. [Class 40 (iv)] In a system in which the supervisory signals for a number of speech junctions or carrier channels are carried by a common junction or channel in the form of alternating current of a frequency characteristic of the junction or channel, the signals that the called party has replied and that he has cleared are single impulses of predetermined length. The signals for the respective directions are taken by separate junctions or channels. The invention is described with reference to working between manual offices and working between a manual position or a selector at an automatic office and the selectors at another. Manual-manual working. Figs. 2 and 3. When the outgoing operator plugs in, sleeve relay M energizes MM and a timing switch TSO moves by self-interruption to position 6. Off-normal relay CO energizes FLS to operate the lamp of the next idle junction. In positions 1-5, FX is operated and sends a tone signal over the outgoing signal channel O/G. Relay X (not shown) responds at the incoming end and energizes L which locks, energizes N and controls the lighting of the calling lamp. When the incoming operator plugs in, sleeve relay S energizes SS which unlocks L and holds N. When she throws her speak key, the resistance of the sleeve circuit is modified and differential relay DR, which has hitherto been balanced, pulls up and is followed by TS, CL, whereupon timing switch TSI runs round to its middle position, energizing FY in positions 1 to 6 to send back an impulse to the outgoing office Relay Y (not shown) responds to this signal and operates SO to dim the supervisory lamp by altering the resistance of the sleeve circuit. SO also connects battery to the ring wire to repeat the signal over the talking circuit. At the end of the pulse, SR is no longer shortcircuited and operates in the locking circuit of SO. As a result, the next impulse, which is sent when the restoration of the speak key drops DR, TS, CL and sends TSI to its home position, shunts out SO to re-operate the supervisory lamp and causes the relapse of SR. When the called party replies, TS is operated over the speaking circuit and is followed by CL and a pulse is sent as before to re-operate SO, SR and dim the lamp and when he clears, TS, CL fall and the resulting impulse drops SO, SR. When the outgoing operator removes the plug, M, MM fall and the switch TSO runs round to its last terminals. Two impulses are sent over the signalling circuit, the first operating CC at the beginning and CD at the end and the second operating CR which locks. The resulting modification of the sleeve circuit resistance gives a signal to the incoming operator, who removes the plug, releasing S, SS, N, CR. Between the relapse of SS and CR a. signal pulse is sent back to operate SO and cause TSO to step on to normal. CO then falls, releasing SO, SR and the circuit is normal. To flash the distant operator, the outgoing operator presses her ringing key to operate RR. RA pulls up and locks and TSO (in position 6) drives round continuously until the key is released and then stops in position 6. During each rotation, one comparatively long signal pulse (540 milliseconds) is sent out followed by a slightly shorter pause. At the incoming end, CC, CD respond to the first impulse, but CC has time to fall back before the next arrives. Consequently CR is not connected up and CC repeats the impulses to the sleeve circuit. The incoming operator gives a flash signal by throwing her speak key and then intermittently operating her ringing key. TS and CL pull up in response to the speak key operation and TSI runs round half its bank, sending back a signal. Each operation and each release of the ringing key then operates and releases RR to release and re-operate CL and cause another half-rotation of the timing switch and another signal. At the outgoing end, SO, SR respond to the signal as previously described. Manual-automatic working. Figs. 4 and 5. When the operator plugs in, sleeve relay AM energizes AMM which flickers the supervisory lamp, marks the junction busy to selectors and operates ACZ to drive the timing switch ATSO off-normal. The latter then drives automatically to position 3, causing a momentary operation of AFX to signal the distant office While the switch is off-normal, ACO is operated and AFLS allots the next idle junction. At the incoming end, AX energizes AL which locks and, at the end of the pulse, energizes AAR which is followed by ARU. AIL is operated in series with the selector line relay and energizes AN. On the operation of the dialling key, ARR is operated and S followed by AAM, AB, the latter releasing ARR. Subsequently, AAM repeats the dialled impulses as alternating current impulses over the signal circuit. At the incoming end, AX (not shown) repeats the impulses to AAR which passes them on to the selector, the impulse circuit being improved during the digit by AC which releases AIL. AP also is energized and locks up. At the end of the digit, AC falls and AIL pulls up again. On the restoration of the dial key, ALR is operated over the sleeve circuit and locks up, and AAM, AB are released. ALR connects direct earth to the sleeve circuit to light the supervisory lamp steadily. When the called party replies, AIL is released and AI is operated and releases AL. The timing switch ATSI is thus driven off-normal and runs to its middle position, operating AFY to send back a signal in positions 1 to 6. At the outgoing end, AY energizes ACT which removes the ground connection from the sleeve to dim the associated lamp, connects battery to the ring wire to repeat the signal over the talking circuit and shunts AQA which is provided to improve impulse repetition. At the end of the impulse, ACZ is energized in the locking circuit of ACT and arranges for the next impulse, which is sent in response to a clearing signal by the called party which releases AI and reoperates AIL, to cause ACT, ACZ to release. When the operator removes the plug, AM, AMM are released and the timing switch runs round to its penultimate terminals and is then stepped slowly to normal. During this operation, a comparatively long impulse is sent forward. ACR operates and locks and energizes AC and AAR is released. At the end of the impulse, AN falls and releases AC, AP and the latter unlocks ACR. The release signal is also effective after a busy condition has been encountered. Busy flash energizes AIL, AI together and no circuit is made for giving a false answer signal. Automatic-automatic working. When the junction is seized by a selector, AA, AB, ACZ pull up and ATSO moves to position 3 to time the seizing impulse as before. AA repeats the impulses over the signal circuit. The reply signal operates ACT as before, the effect in this case being to reverse the connections of the impulse relay AA. When the called party clears, the reverse operation takes place and when the calling part clears, a long clearing pulse is sent on the relapse of AA, AB.