Patent GB-539823-A (GB)
Title: Improvements in electrical signalling systems
IPC: H04M15/08
Filed: 1940-03-23
Abstract: 539,823. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., TAYLOR, R., and BAKER, G. T. March 23, 1940, No. 5349. [Class 40 (iv)] In an arrangement of the kind described in Specification 525,902 in which lines in a calling or other condition are identified at another stage of the connections of which they form part by the application of code markings to the test wires by a rotary switch or its equivalent, the lines are grouped in several different ways according to the identity of the successive digits of their numbers so that the markings in respect of each digit can be applied over a common lead to the appropriate lines, the lines making up any group being isolated from one another except when the group markings are being applied. As shown, the test wires of each 100-line group are connected through a pair of individual static connecting devices (referred to later) such as SCD1, 2 to ten common leads each representing a particular tens digit and to ten common leads each representing a particular units digit. The corresponding common tens leads from the 100-line groups having the same thousands digits are then multipled together, so that for each thousands digit there are ten common leads which correspond to different tens digits and extend to the armatures of a thousands switching relay such as 1MA. These armatures when operated apply markings characteristic of the thousands digit and when back connect over ten common leads to the armatures of the tens marking relays VT-ZT. Similarly the corresponding common units leads from the 100-line groups having the same hundreds digits are multipled to ten common leads extending to the armatures of a hundreds switching relay such as ICA, these armatures when operated applying the hundreds markings and when back connecting to armatures of the units marking relays VU-ZU. Alternating current is used for signalling, and the static connecting devices such as SCD 1, 2 may comprise condensers or multi-electrode neon-tubes. Preferably however they consist of units of non-linear resistance material such as a mixture of silicon carbide with carbon and/or tungsten or molybdenum agglomerated in the form of discs. The common leads to which the discs are connected normally extend to negative battery to improve the isolating effect when the majority of the test wires are grounded. The identifying signals are sent over each connection to an outgoing relay set at the originating exchange, and are in general stored until required, for example, on a mechanical impulse generator, as described in Specification 528,971. As soon as any outgoing relay set is taken into use, start relay STR energizes to ground on common lead ST, and the sending switch MS starts rotating under the control of impulse springs IPB, while synchronizing impulses are sent over lead PU to the relay sets from springs IPA. The signalling code employed is of the five-unit type, each digit being represented by two impulses. The three exchange digits are sent directly over common lead EC by relay ECR which is connected to appropriate contacts 2-16 of MS. It may be sufficient however to send one or possibly two digits to identify the exchange designation. In positions 17-21, markings are applied over leads TH to energize the thousands switching relays 1MA-10MA at the proper times for transmitting the code impulses representative of each thousands digit to the appropriate group of lines, and in positions 22-26 the hundreds switching relays 1CA-10CA are controlled.in a similar manner. In positions 27-36, the tens and units marking relays VT-ZT, VU-ZU are energized in turn to transmit the code impulses for the tens and units digits. Relay SZR now operates and ground is removed from common lead Z to signal the end of the cycle. Impulses springs 1PA, 1PB are disconnected and MS returns to normal, when SZR falls back in readiness for a further cycle when required. For the purpose of re-transmission from the outgoing relay set to the exchange where the recording equipment is located it is preferable to use the 50-cycle mains frequency for 'spacing signals and a combination of this frequency with a 150-cycle frequency for marking signals. The combination may be derived from the 50-cycle source by the use of a non-linear resistance disc NLR1, similar to SCD1, 2, in association with a transformer TRB, the relative strength of the third harmonic, i.e. 150 cycles, being adjustable by means of a variable resistance R1. The pure 50-cycle frequency is supplied over a transformer TRC. The group switching relays may be dispensed with if four static connecting devices per line are employed. Specifications 458,095 and 541,722 are referred to.