Patent GB-652881-A (GB)
Title: Improvements in or relating to circuit arrangements for telephone or like signallingsystems
IPC: H04Q3/00
Filed: 1948-01-16
Abstract: 652,881. Automatic exchange equipment. MERCER, R. Jan. 16, 1948, Nos. 1481 and 25040. [Class 40 (iv)] In an automatic exchange in which the busy or idle condition of each of a group of equipments is determined by testing a lead common to the group, a potential is applied at distinctive instants in a cycle to each of a plurality of leads each individual to one equipment of the group and each equipment when in a particular condition (e.g. busy) connects its associated lead to the common lead. As shown, I1 to I10 are a series of cams mounted on a common shaft which is motor-driven at constant speed, which apply ground to leads L1 to L10 at successive instants in a cycle. Determination of condition of equipments in Group A. Group A comprises 10 equipments, e.g. switches or lines, each including a relay contact, e.g. TCA1, which is closed when the equipment is in a particular condition, e.g. busy. The lead LA common to group A is connected by switch SDA and rectifier URA to the common operate lead of the ten test relays R1 to R10, to which battery over resistance R is also connected by any suitable means (the purpose of relays SR and FR is described below). Assume that equipments 1, 3, 4, 9 and 10 of group A are busy, SDA is at position 4, SDB, SDC and SDD are home, and resistance battery is applied to CL at instant 5 in the cycle, i.e. when 15 closes its contacts. The ground applied to L5 is extended over the righthand winding and back contact of R5 to lead CL and thence to resistance battery. As the only TCA contact set whose moving contact is grounded at this time is TCA5 (connected to L5) and this contact is open, no ground is fed over URA to CL, so that R5 operates and locks up on its left-hand winding and " X " contact. The test relays are two-step relays which when energized over the right-hand winding close their " X " contacts only, but operate fully over the left-hand winding. At instants 6, 7 and 8, R6, R7 and R8 operate in a similar manner, but at instant 9 the ground applied to L9 is extended by TCA9 to LA and thence via URA to CL, thus effectively short-circuiting R9. R10 is similarly prevented from operating. Ignoring for the moment instant S when IS closes its contacts, the next instant in the cycle is instant 1 at which R1 is short-circuited. The cycle continues, R2 operating and R3 and R4 remaining down. At instant 5 no change takes place unless the connecting up of R at instant 5 in the previous cycle was too late to allow R5 to operate, in which case R5 operates. The cycle is thus completed and R2, R5, R6, R7, and R8 are operated corresponding to the idle equipments in group A. Determination of 1st equipment in group A in the particular condition. Assume that the same equipments are busy and that testing starts at instant 5 as above. To initiate the test contacts IC1, IC2 are closed by a key, relay, switch or the like. Battery is thus connected to SR, the other end of whose winding is wired by lead LS to the contacts of IS which are open. No test relay can therefore be operated since until SR pulls up the resistance battery is not connected to CL. At instant S, however, SR pulls up, locks to IC2 and connects up the battery to CL. The next instant 1 results in the short-circuiting of R1, but at instant 2 relay R2 operates and locks in series with FR to ground at IC2. The operation of FR in this circuit disconnects the battery from CL, thus preventing the operation of any other test relays, so that only R2 corresponding to the first idle equipment of group A is operated. If the test is made with a view to taking into use this first idle equipment it is desirable to mark it busy immediately. This is done by the inner right front contacts of R2 which connect L2 to the right-hand side of URA thus simulating the action of the closed TCA contact of a busy equipment. If any one idle equipment is desired to be found, not necessarily the first in numerical order, IC1 and relay SR may be omitted. Battery is then connected to CL as soon as the test commences and is removed by FR when the first test relay operates. Selecting an idle route through a plurality of switching stages. Assume TCA1 to TCA10 to be associated with the selectors of a group, each group corresponding to a different value of the first digit of a called number ; TCB1 to TCB10 with one of a number of groups each corresponding to the same first digit and a different second digit; TCC1 to TCC10 with one of a number of groups each corresponding to the same first digit as TCA1 to TCA10, the same second digit as TCB1 to TCB10 and a different third digit ; and TCD to TCD10 with one of a number of groups each corresponding to the same first digit as TCA1 to TCA10, the same second digit as TCB1 to TCB10, the same third digit as TCC1 to TCC10, and a different fourth digit : and that each switch in group TCA has access to the correspondinglynumbered switch in group TCB and so on. To select an idle route, i.e. an idle switch in each group having the same number, all four groups are tested simultaneously. The test leads LA, LB, LC and LD are connected up by the switches SDA, SDB, SDC and SDD and rectifiers URA, URB, URC, and URD respectively to the common lead CL. To select the first idle route IC1 and IC2 are operated (SR equipped) and effective testing begins at instant 1. If any switch in the first route (i.e. TCA1, TCB1, TCC1 or TCD1) is busy, the ground on L1 is extended to CL to shortcircuit R1. The testing cycle continues until when the first idle route is found absence of ground on CL allows the corresponding test relay to operate, thus bringing up FR to stop the test, and extending the relevant one of leads L1 to L10 to the right-hand side of URA, URB, URC and URD to busy the selected route. To restore the apparatus IC1 and IC2 are opened. The apparatus may equally well select a route, the stages of which comprise some forward-selecting and some backwardselecting switches, e.g. battery feed over selectors C and D to called line, and over finders B and A to calling line.