Patent GB-899711-A (GB)
Title: Improvements in or relating to circuit arrangements for ensuring that the two setting steps of final selectors in a telecommunications installation are effected in a desired sequence
IPC: H04Q3/42
Filed: 1959-02-18
Abstract: 899,711. Automatic exchange systems. SIEMENS & HALSKE A.G. Feb. 18, 1959 [March 10, 1958; May 9, 1958], No. 5667/59. Class 40(4). In a system in which a selector is required to be set in accordance with two digits using a common control circuit which may be released between digits, the control circuit on effecting setting to a group of outlets in response to the first digit reverts a signal for storage in a relay set in the switch train, which signal is subsequently used to ensure correct operation of the control circuit for the second digit, i.e. to ensure that an outlet within the already selected group is selected, rather than that a further group of contacts is selected. Layout.-A calling subscriber obtains access to a finder/lst group selector link comprising a battery feed circuit for the calling subscriber and a mechanical impulse recorder and regenerator which operates as described in Specification 899,14Q. The first group selector gives access to a battery feed circuit 3SpUe for the called subscriber which may be connected directly, or via further group selectors to the final selector LW. Registration of the state of connection of the final selector is effected by the operation or non-operation of a relay in the battery feed circuit 3SpUe. Operation of final selector. First embodiment.- Seizure of the control circuit ES is effected by receipt of battery over the a-wire, from the finder/lst group selector link, which battery operates start relay AN. Relays E, V follow the latter starting the final selector hunting switch which is stepped automatically by alternate energization of its field windings NA, NB. When the final selection LW is formed, test relay P operates to stop the switch by connecting its field windings together. The connection of the low resistance windings of P to the a-wire signals the recorder circuit that the tens impulse train may be sent. Relay P operates C and releases AN, E the latter deenergizing the switch windings NA, NB. The tens digit is received as impulses consisting of interruptions of the a-wire circuit. Relay P repeats these interruptions to the A relay which registers the digit on the relay chain RSTW. At the end of the train V releases followed by P and the former completes a circuit over the dwire for relay U in the feed circuit 3SpUe and UA in the control circuit, the operating circuit being completed to earth provided from the recorder circuit over the c-wire. Relay U in the feed circuit locks up independently of the succeeding circuit. Relay UA also locks in a circuit which holds C up and brings up D. The latter complete a circuit for the alternate energization of the field magnets MA, MB of the final selector LW. Marking of the decade contacts thus takes place over contacts of either UA (up), C (up) or UB (back). When the selector reaches the marked tens contact, test relay P operates to stop the switch by connecting its windings together. Relay P releases A which keeps the selector windings connected together, and UA and P then release. Relay P removes low resistance earth from the a-wire as a signal to the recorder that the selector has been set and D reconnects the start circuit. The control circuit is now available for use with another final selector. When the next digit is to be sent from the recorder the control circuit is seized as before and the digit is received on the chain RSTW relay A operating as before. At the end of the train V releases followed by P, but now with U up in the feed circuit 3SpUe, no earth exists on the d-wire and UA in the control circuit cannot operate. Thus, when U releases, C also releases and UB operates. With UA back, C back and UB up the units wires are now marked in the d bank in accordance with the setting of RSTW. Relay UB operates D to start the selector. Test relay P operates when the marked outlet is found and stops the switch. Relay A then releases to bring up busy relay C in the feed circuit 3SpUe over the d-wire. Relay A also releases P, D and UB and the control circuit is then restored to normal. Busy relay CG comes up during the release of UB and connects the incoming c-wire to the outgoing d-wire and includes in its circuit the " pressure magnet " AD which, however, does not operate at this stage. In the feed circuit 3SpUe relay C reverts battery on the a-wire and also operates T, G following to release T again. During the release of T, P tests the called line over the dwire and the c-wiper of the final selector. If the called line is free, P operates, re-energizes T and brings up R. Thermistor HL eventually warms up and lowers its resistance sufficiently to energize the opposing winding (ii) of the relay T which releases together with R. Relay R is now connected to an intermittent energizing source Sch. Relay R controls the application of ringing current RW and ringing tone FZ to the called and calling subscriber's lines. Relay P also short circuits resistance Wi97 in the c-wire circuit to bring up the " pressure magnet " AD in the final selector. This latter presses on the speech wipers a, b of the selector to effect switch-through. Relay T also earths the d-wire and hence the c-wiper of the final selector to busy the called subscriber. When the called subscriber answers, relay A (in 3SpUe) operates to the loop, switches through, and disconnects the circuit for the ringing relay R. Relay A brings up Z which releases U followed by G which reverts battery on the b-wire to the finder/lst group selector link as a called party answer and signal. Release is on a last part basis dependent upon both removal of earth on the c-wire from the finder/lst group selector link and on the release of A by disconnection of the called subscriber's loop. Metering is effected by arrangements in the finder/1st group selector link which pulse the meter consequent upon release of the connection. If the called subscriber is busy, P fails to respond so that busy tone is reverted from source BZ. Operation of final selector. Second embodiment. PBX hunting.-An alternative final selector and control circuit, Fig. 4 (not shown), includes the following features: As soon as the control circuit is seized relay U, Fig. 2, is operated in series with a relay 5U (not shown) in the control circuit. Relay U locks independently of the final selector circuit. Because 5U is operated, the control circuit causes the incoming digit to be registered on a relay chain and the final selector is set to a decade contact in accordance with the marking supplied by the relay chain. The control circuit is then released. When the control circuit is next seized for the units digit setting, relay 5U cannot operate because relay U which has opened its operating circuit. With relay 5U down, the incoming impulses are arranged to be applied alternately to the two field magnets of the line-finder which is thus stepped directly by the units digit. First PBX lines have bank contacts connected into a circuit which is completed at the end of impulsing to bring up a relay which then causes the final selector to hunt in the normal way for a free outlet under the control of a test relay. Last PBX lines are connected into a circuit which causes the test relay to operate in any case and busy testing is then carried out on the last line in the normal way.