Patent GB-618815-A (GB)
Title: Improvements relating to telephone and like selective systems
IPC: H04Q3/00
Filed: 1946-11-08
Abstract: 618,815. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., and LONG, D. P. Nov. 8, 1946, No. 33309. Addition to 605,131. [Class 40 (iv)] In a high-speed single-motion selector of the type disclosed in the parent Specification having a plurality of wiper sets, each comprising two line wipers and a test wiper, and a marking wiper common to all the sets, selection is effected in response to either one or two digits. For differentiation between markings by first and second digits, a first digit that is to be followed by a second digit brings about a change of the marking connection to the arc of the marking wiper and prevents movement of the selecting switch until the second digit has been received. As shown, the selector is a motor-driven uniselector with 16 wipers and is similar to that employed in the parent Specification. The marking arc G has contacts 1 and 52 earthed and the intervening 50 contacts connected in four groups to marking circuits. The digit switch has the contact arcs M2, M3 and M4 in the speaking and test wires, the contacts of which are connected in pairs to corresponding wipers of the selector; while its other arcs are used for homing (M1), marking (M5, M6), and overflow metering (M7, M8). In general, marking in respect of first digits is obtained by cross-connections between contacts of the arcs of M5 and G, and in respect of second digits by connections to arc G controlled by relays operated over arc M6. Impulsereceiving relay A, guard relay B and dialling relay C pull up when the junction with which the selector is associated is taken into use, and dialling tone is transmitted to the caller. Impulses received by A are repeated to DM and the digit switch is stepped. At the end of the first impulse train, C falls away, thus disconnecting the delayed-alarm relay lead DA. If the first digit is one denoting a group of outlets to be searched, the selector driving mechanism MU is energized and the selector is driven in search of a free outlet in that group. If the digit is odd, the group of contacts OA in the arc of wiper G is marked by ground over wiper M5 and an odd contact in the associated arc. Search is made in the corresponding group of outlets over the wiper set of the selector connected up by the digit switch, high-speed test relay T pulling up to the first idle outlet encountered. If the digit is even, wiper M5 marks the group EA. However, if the digit is one of a pair of adjacent odd and even digits in response to which search is to be made in both the groups connected up over wiper M4, then both the groups OA and EA will be marked. This is done by cross-connecting the odd valued contact in the arc of M6 to EA, and the even valued contact to OA, thus ensuring the marking of both groups for either digit. In this case, differentiation between the two values is performed at the succeeding stage and is initiated as described below. If the first digit denotes that a second digit is to determine the group to be searched, the corresponding contact in the are of M6 is cross-connected to terminal r or x, to operate R, or R and X respectively. In either case, MU is disconnected and the digit switch homes, whereupon S comes up, releases R, disconnects the. marking leads from M5, and prevents the transmission of dialling tone. If relay R is operated alone, the group of outlets B in the arc of wiper G is marked; whereas if both X and R are operated, X locks up and the group C is marked. The digit switch responds to the second digit and when C falls away, MU is energized and the switch is driven in search of a free outlet in the marked group. The operation of T to an idle outlet cuts the drive to MU, busies the outlet and brings up the holding relay H, which switches through the line wires, and releases A and B. Earth reverted on the test wire from the succeeding circuit brings down T and holds H. At the end of the conversation H is released and the digit switch and selector home. If an outlet is to be selectable by a pair of values of a digit, a discriminating signal is sent forward. If the digit value is odd, then when H comes up the A relay of the succeeding stage operates round the junction loop in series with a discriminating relay, whereas if it is even, the positive junction wire is earthed over wiper MS and the discriminating relay is shunted to prevent its operation. The release of relay A on the operation of H disconnects wiper M6 and prevents earthing of the positive wire by ground over the cross-connections from odd contacts in its arc to group EA. If an outlet group is congested, the selector is stopped on the last contact by battery over resistance YC and busy tone and busy flash are reverted over the junction, the appropriate overflow motor being operated over M7 or M8. Specification 378,585 is referred to.