Patent GB-834203-A (GB)
Title: Improvements in or relating to connecting means for local enquiry calls in automatictelephone exchanges
IPC: H04Q3/62
Filed: 1957-07-18
Abstract: 834,203. Automatic exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON. July 18, 1957 [July 26, 1956], No. 22804/57. Class 40 (4). At least one subscriber to a PABX has a set of keys to apply tones to the line and after the establishment of a call to a main exchange the subscriber may hold the main exchange line and prepare for the setting up of a local enquiry call by depression of one or more of the tone keys. In the exchange shown in Figs. 1 and 2 subscribers' sets may be of two sorts, one sort setting up calls by means of an ordinary impulse transmitter such as subscriber A2, while the other sort sets up calls by the use of ten damped tones produced by push buttons P0-P9 such as subscriber A1. With the set A1, to prevent interference, it is necessary to isolate the microphone M during the generation and emission of tones. This is achieved by rectifiers E1 and E2 current being supplied to the set during and before the emission of tones over line b, bell B, contact K4, rectifier E2, contact K1 and line a, while after tones have been emitted current of reverse polarity is supplied over line a, contact Kl, rectifier E1, microphone M, and line b. To disconnect a main exchange line in preparation for setting up a local enquiry call subscriber A1 presses button P0, or buttons P0 and P9 simultaneously, to break the loop, while subscriber A2 achieves the same object by dialling 1. To reconnect the main exchange line and release the enquiry path the procedure is repeated. Seizure of register and marker.-A line circuit LR1 or LR2 responds with a group circuit GR to seize an idle register REG over the relay chain RB1 to RBn, it being assumed that RB1 responds. A relay set VR is taken into use to control register connector RV which selects an idle line finder S to connect with the calling line which when found causes S to initiate slow operation of RE3 at the register. If subscriber A1 is calling, RE2 is connected to feed the loop over rectifier E2 but does not operate on account of resistors r1, r3. When RE3 responds RB1 is released to remove r3 and allow RE2 to operate. A1 is then connected to a circuit TM to receive tones and set register RM. If subscriber A2 calls, no resistor r1 is found in the loop so that RE2 responds before RE3 finally operates and consequently operates RE4. A2 is then connected to circuit IM to receive impulses and set register RM. In either case dial tone is returned from RM over RE2 when marker M is seized and in turn seizes a free final selector or an outgoing trunk. Local calls.-The digits for a local call enable RM to operate relay NR1 over connector RV thereby disconnecting the register and reversing battery to the subscriber by transferring feed to relay NR2 which responds and operates NR3 to mark a finder GV which under control of the marker M connects the line to a final selector over line LV. Trunk calls.-The digits for a trunk call enable the register to operate relay NR4 to mark finder GV. Marker M starts GV and tests for the line over a circuit including relay R1 in the outgoing trunk relay set shown in Fig. 2. R1 extends the line to the trunk HL and R3 supplies battery of suitable polarity for further tone signalling from A1. If A1 is in fact calling, marker M over its lead e1 operates relay R15 to unmask resistor R7 in the line. If A2 calls, R15 remains unenergized. Register M retires and in the trunk relay set R3, R4, R11, R10 and R7 respond to the loop; R7 disabling R11 which releases slowly. While R11 releases R5 operates to connect up R6 and R8; R6 initiating the slow release of R5 and R8 connecting resistor r4 into the line with R9. When R5 falls back a loop is connected across the line HL and R9 responds. Dial tone is received from the main exchange which, if A1 is calling, is conditioned to receive tones by the presence of r7 in the loop. If A2 is calling, impulses are repeated by R3 and R4 which releases R6 during each pulse, R5 being operated at the end of each pulse to reoperate R6 which initiates the slow release of R5. In consequence R5 interrupts the main exchange loop for a predetermined interval of time for each pulse. R7 and R8 hold up during each pulse train. When digits have been sent an interruption of the loop or a current reversal is returned from the main exchange to release R9 and R10 which connects up R2 to release R3 and connect the subscriber's line to R4 which reverses the polarity of current on the line so that should A1 be calling microphone M is connected over rectifier E1. Enquiry call.-If during a trunk call subscriber A1 wants to make a local call he depresses button P0 to break the loop at contact k. To prevent breaking the loop when tones are being sent an additional contact q may be connected in parallel with k so that P0 and P9 must be pressed together to break the loop. To gain an enquiry path subscriber A2 breaks his loop by dialling 1. In either event the break impulse releases R4, R2 and R6. during the impulse and causes R3, R4, R5, R6 and R8 to respond at the end of the impulse. Reoperation of R6 releases R5 to release R8. During operation of R8 relays R12 and R13 are energized, R12 not responding due to oppositely connected windings but R13 with only one winding connected responding to disconnect the trunk line HL, connect holding resistor r6, and extend the calling line to line a2, b2, c2, which has access to a register REG. When R8 falls back R12 operates and operation of R9 to the loop provides a holding circuit for R10 which was operated by R13. Since R2 is back R3 supplies the calling line with a polarity suited to the emission of tones by subscriber A1. By causing R5 and R8 to operate at the end of the impulse from a subscriber wanting an enquiry path operation of the circuit is independent of the time subscriber A1 may hold the button P0, or P0 and P9, depressed. To restore the call to the trunk line HL the calling subscriber repeats the procedure of breaking the loop with a single impulse which is repeated as before by R8 to release R13 immediately. R8 responds and releases R12 when R8 falls back. Specifications 790,442 and 834,204 are referred to.