Patent GB-452038-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1935-02-15
Abstract: 452,038. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, and PEARCE, O. A., 107, Quarry Street, Woolton, both in Liverpool. Feb. 15, 1935, No. 4992. [Class 40 (iv)] In a system in which a sub-office accommodating several subscribers' lines is connected to an exchange by a single two-wire line, the latter terminates at the sub-office in two separate switches which are operative alternatively in the case of incoming and outgoing calls. Two corresponding stepping switches at the exchange send impulses of high voltage to set one or other of the suboffice switches dependent on the polarity of the impulses. Revertive calls are set up by the operation of both switches, feed current being supplied over the exchange line. Specifications 396,738 and 411,443 are referred to. Outgoing call. Normally energized relays A-D are shunted to enable start relay ST at the exchange to pull up, closing a circuit for stepping the switch FR by impulses derived from an interrupter-controlled relay FL, relay PG being provided to prevent clipping of the first impulse. Impulses of high positive voltage are repeated over the lower line wire to relay E in series with a neon tube NT and rectifier MRB to step the switch FS at the sub-office. Relays A-D and ST are released at the first impulse and in due course stop relay SZ energizes over the calling loop and locks in series with line relay L and differential relay DR. Release relay B energizes and starts a finder, and when the line is found K, CT pull up in parallel, extending the calling loop to line relay L and connecting up HR. The first impulse received is repeated by L, and TR, OG operate, the latter completing a direct circuit to the first selector for subsequent impulses. The calling party's meter is actuated over wiper FRI in the usual manner. Upon release the switch FR steps to normal and sends impulses as described above to home the switch FS. Incoming call. The final selector, Figs. 5, 6, may be taken into use by a subscriber over the upper set of incoming wires or by a toll operator over the lower set. In either case, line relay A energizes, followed by B, C and J, while in the latter case relay CN also energizes. Two trains of impulses are effective, dialling relay C being operative during both trains and relay E during the second train. Upon the relapse of C, relay G pulls up and the wanted line is tested during the release period of E. If the line is idle, relay H energizes and disconnects G, while if the line is busy, G remains locked and sends back busy tone. If the selected line leads to a suboffice, relay K, Fig. 3 energizes in series with H, connecting up CT, HR, PR and OG, release relay B being inoperative, and high potential is extended back over wiper P1 to operate GS in series with a rectifier MRA, and this relay opens the ringing circuit and closes a circuit for repeating the final impulse train to the switch AD. Relay PR falls back at the end of the train and connects up H, Fig. 2, which completes a circuit for stepping the switch AD by impulses from relay FL, impulses of high negative voltage being repeated over the lower line wire to relay F in series with the neon tube NT and rectifier MRA to step the switch SS at the sub-office. The subscribers' lines are wired to the switch SS in reverse order, so that it is set on the wanted line when the switch AD arrives home. Stepping then ceases and ringing takes place from the final selector, in which GS falls back slowly after the final impulse train. Upon release, the switch AD moves one step due to an impulse when HR relapses and then steps on to normal again sending impulses as before to home the switch SS. Revertive calls. Upon receiving dialling tone, the calling party presses a button PB to operate differential relay DR which connects up RV, and dials only the last digit of the wanted number, which is repeated by line relay L to set the switch AD. He then hangs up, so that L falls back, releasing the finder and first selector and connecting up relay D which re-operates C, holds B, K and CT and initiates the setting of the switch SS which takes place as described in the preceding paragraph. Relay C relapses when the switch AD arrives home and ringing current is sent to both parties. Relay F pulls up on the reply of the called party and disconnects D, which reconnects the junction to line relay L. Metering does not take place. Upon release the switches FS, SS restore in turn in the manner already described. Toll calls. When the final selector is seized by a toll operator, relay CN removes a shortcircuit about ring-trip relay F so that it energizes immediately on the operation of H and connects up BD which applies toll busy tone to wiper P. The operator initiates ringing at this stage or after dialling a further digit by actuating a key to effect the operation of differential relay DF which releases F by short-circuiting. If however the wanted line is busy, G remains up instead of H, and actuation of the operator's key brings about the operation of F by removal of short-circuit to offer the call. A second key-actuation leads to the operation of BD and H, since G is now back, and results in the release of the existing connection by the application of earth to wiper P through relay T1 if the wanted line is an ordinary one, or of high potential to wiper P1 if the wanted line leads to a suboffice. In the latter case, relay BD, Fig. 3, responds in series with TR and a rectifier MRC and sets up the normal release conditions. The call then proceeds like an ordinary incoming call, except that TR sends back dialling tone and that ringing is controlled by the operator's key. P.B.X. hunting. This is controlled in the final selector over wiper P1, earth on the first line of a group bringing about the operation of relay HS if that line is busy to complete a rotary stepping circuit under the control of G. If all lines of the group are busy, G is held by battery on the last line and sends back busy tone.