Patent GB-614177-A (GB)
Title: Improvements in or relating to electrical signalling systems
IPC: H04M15/08
Filed: 1946-05-25
Abstract: 614,177. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., and BAKER, G. T. May 25, 1946, No. 15906. [Class 40 (iv)] Line identification signals are fed to a set of 10 leads in sequences different for each lead through secondaries of 4 transformers whose primaries are energized in turn by single contact high-speed relays, the leads being strapped to the subscriber's lines in accordance with the identification signals to be transmitted. The subscriber's lines are strapped over non-linear resistances ARB, ARA, to appropriate ones of two sets of 100 conductors such as 24, 35, which transmit the thousands and tens, and hundreds and units digits respectively, each conductor deriving both its digits from the same set of leads-either M/T 1 ... 0 or C/U 1 ... 0 through change-over relays MA, CA, which operate when the thousands and hundreds digits have been sent. In the system described, each digit is represented by a code whose elements consist in the presence or absence in various combinations of 750 c.p.s. pulses in gaps (designated successively WXY and Z) between regularly recurring 600 c.p.s. pulses. Transmission of digits. When the outgoing relay set OGRS is seized A operates, followed by L and H in the distant incoming relay set ICRS, which in turn operates D in OGRS. Relays SI and ZI then operate and lock, followed by the start relay ST in the subscriber's line marking equipment SMLE, which is busied at contact st2. A vibrator VIB is started and its contacts vib3 control relays SA, SB, DA ... DD to operate MW ... MZ in turn. Relays TA and TB operate and release once per two WXYZ cycles causing relays CX ... CZ to replace MX ... MZ in the hundreds and units cycles. Relay MR followed by MA operates at the beginning of the hundreds cycle to change over the strappings on conductors M/T 1 ... 0 and CR and CA operated at the end of the hundreds cycle performs a similar switching on conductors C/U 1 ... 0. When all the digits are transmitted SZR operates, followed by SZ, which releases SA, SB, SI and ST. Relay DR controlled by contacts vib 2 alternately transmits 600 c.p.s. tone to line and connects (e.g. in the case of the thousands or tens digits) 750 c.p.s. tone to one of the transformers TRC ... TRF according to which of relays MW ... MZ is operated. The sending equipment may be used for sending identification signals for more than one line at a time (over other contacts of MA, CA) and in order to avoid back coupling between secondaries of transformers which would cause spurious signals, all transformers not in use have their primaries short-circuited over back contacts of MW ... MZ. Rectifiers ARA, ARB are biassed so as to be non-conducting, except when the line associated with them is busy (i.e. the meter wire is earthed), thereby reducing the power necessary for the 750 c.p.s. source. Receipt of digits. Relay H operates HR which connects up the common distributor relay set DRS. Relay Y of the VF receiver 2VFR responds to 600 c.p.s. pulses and at its first operation connects up guard relays B, BA. Relays WP ... ZP operate on successive releases of Y and WQ .. YQ operate on the respective re-operations of Y to direct pulses, due to the operation of X by 750 c.p.s. current, over appropriate wipers of switch S to the thousands storage relays SW ... SZ. Relay XQ releases WP, WQ ; YQ releases XP, XQ and ZP releases YP, but YQ remains operated until the last pulse of the WXYZ cycle is received whereupon it steps the back-drive switch S so that the next digit is registered on the hundreds storage relays and so on. When all the digits have been received, B releases and during the slow release of BA, H falls to release the distributor relay set DRS. The storage relays may be multipled on the banks of S to avoid unnecessary homing. Alternatively, the digits may be received alternately on two sets of high-speed relays, the information then being transferred to four sets of high-resistance storage relays in the incoming relay set. In large systems the digit transmission may be preceded by exchange identification signals. Specifications 539,823, 589,469 and 603,789 are referred to.