Patent GB-389623-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H04Q3/00
Filed: 1932-02-02
Abstract: 389,623. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, and DIXON, R. G., 162, Westmount Road, Eltham Park, both in London. Feb. 2, 1932. No. 3103. [Class 40 (iv).] In a graded service system using finderconnector links the lines are grouped in the finder banks in accordance with the degree of access permitted to them and in the connector banks in accordance with the degree of restriction in access to them and prohibited calls are prevented by means of a circuit involving additional group contacts and wipers on both switches. The invention can be carried out with single-motion switches or with bi-directional switches having an additional bank and wiper of ordinary type but is described with reference to a system using bi-directional switches having vertical wipers for discriminating between permitted and prohibited calls. The arrangement may be used for a system in which the switches are used in common by two groups of subscribers, calls being possible only within the groups. In the system described certain subscribers may break in on certain calls and have conference facilities or alternatively may operate distant apparatus such as door locks. In the link circuit employed, the back-bridge relay co-operates with the dialling relay in changing over the impulse circuit and in making the momentary test circuit. Setting switches. When a subscriber calls, his two-step line relay L pulls up partially (contacts l1, l2) in series with the common starting relay S which energizes RC which energizes CI. If the allotter is on a busy link, the driving magnet DM is energized and interacts with CI until an idle link is found whereupon T connects up the wipers and energizes TA. RC(i) is thus cut off, but the relay is held temporarily by RC(ii) which is energized in series with the finder release magnet ZF. RC on falling releases CI and energizes the vertical magnet VF which thereafter interacts with G until the vertical wiper FA. finds the marked level whereupon G is held temporarily by its winding G(ii) in series with RD which locks up and initiates rotary hunting. When' the line is found HC pulls up, locks, cuts the drive, short-circuits S, and energizes the finder switching relay B. Relay L now operates fully and cuts off its line windings. The relapse of S releases T which is followed by TA, a single impulse being given to the allotter magnet. Relay A in the link pulls up over the loop, holds B, energizes C, sends back dialling tone and subsequently repeats the digits to the magnets VC, RC. The change-over is effected by the back-bridge relay D which is energized by the relapse of C at the end of the first digit. Busy test and completion of permitted connection. At the end of the second digit the relapse of C releases D which falls sluggishly, owing to a short-circuit on its second winding to provide the testing interval. If the line is busy, the test relay H is unable to pull up and, on the relapse of D, energizes TR which locks and sends back busy tone. If the line is idle H pulls up in series with the line and cut-off relay and ringing current goes out over TR(ii) which pulls up when the called party replies and completes the talking circuit. Prohibited call.. At the end of the 1st digit TR is connected to the vertical wiper CB and if this wiper is standing on a level which is prohibited to the particular calling party the circuit of TR is completed over the vertical wiper FB of the finder. TR disconnects the rotary magnet and sends back busy tone. Privileged call ; conferences. On receiving busy tone, a privileged subscriber operates RWK to complete a circuit from b4 to the vertical wiper CA of the connector and, unless the wanted line is immune from breaking-in, H is operated over wire 11 and locks up completing the speaking circuit to the busy line. A number of privileged subscribers may thus get connection to the same line or to a special unwired number for conferences. Immunity from breaking in is given to subscribers on whose level the CA terminal is unwired. Calling parties absent from their telephones. If this facility is desired a fourth bank S is provided on the connector and a special number say 90 is allotted for this purpose. The 90 terminal in the S bank is grounded so that when H operates TR is energized at once and the subscriber influences code calling apparatus by dialling. Distant control facilities. For this purpose the terminals PFT, RWT are connected together and the CA terminals of the levels over which these services are given are connected over 14 to wuiper.S. The O terminals in the S bank are connected to the apparatus concerned. When the appropriate number (XO) is dialled there is a circuit from b4 over PFT, RWT. S for operating the apparatus. Outgoing calls. Each connector may have a separate junction numbered 00.. The 00 terminal in the S bank may be grounded to prevent ringing. Irregular working. If the finder of a seized link fails to release, a thermal relay TH shunts out the starting relay S. Relays T, TA fall back and the allotter resumes its hunting. If B fails to cause full operation of the line relay the allotter is moved on as in a normal call and then continues to hunt since S pulls up again.