Patent GB-376265-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1931-03-31
Abstract: 376,265. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, TAYLOR, R., 30, Oulton Road, Wavertree, both in Liverpool, MASON, J. A., 52, Belgrave Street, Liscard, Wallasey, Cheshire, and McCLEW, J. W., 27, Arlescourt Road, West Derby, Liverpool. March 31, 1931, Nos. 9794 and 19482. [Class 40 (iv).] A group of double-wiper two-directional finders is associated with three control circuits dealing normally with calls in levels 1 .. 4, 5 and 6, and 7 .. 10, respectively, but arranged so that in the case of congestion in any of these sub-groups of lines, two or all three of the control circuits may be employed in extending simultaneously calls in the same subgroup. Each control circuit PC1, Fig. 5, has separate switches PDS, ODS, for allotting ordinary and overflow finders, the ordinary finders being associated directly with group selectors over the dotted connections at the frame IDF, Fig. 3, whilst the overflow finders are associated with group selectors over secondary finders SCF and the full-line connections at the frame. For each overflow call, three secondary finders SCF controlled by separate control circuits SC1 are set into operation and their hunting takes place simultaneously with the setting of'the primary finder. During the rotary hunting operation of the primary finder, the selected level is marked busy to other finders. Certain features of the system shown form the subject-matter of a divided Specification 376,697. Normal operation. An ordinary primary finder is preselected by a testing circuit over wiper 1a, relay G operating over its left-hand winding in the case of a busy finder and interacting with magnet PDM. If a call is made in level 1 or 2, by line 10, 11, Fig. 1, say, relay SA operates energizing starting relay ST in the first control circuit PC1. A call in level 3 or 4 operates relay SB which also normally takes into use circuit PC1, but the simultaneous operation of relays SA, SB, takes into use control circuit PC2 also. Similarly, on the simultaneous operation of relays SA. SB, SC, or SC, SD, SE, all three control circuits are taken into use. Relay ST completes a circuit from conductor 14 over both windings of relay LK to wiper 1a and if the preselected finder is in order, relay LK operates over resistance YM common to half the finders. Relay LK short-circuits its left-hand winding but the closure of a locking circuit for this relay is deferred for a short interval to prevent double connections since two such relays cannot remain operated in parallel over their righthand windings only. Relay LK completes a circuit over wiper 8a for the vertical magnet VM in series with relay C which operates relay VR, which in turn operates one of the finder switching relays HB. The operation of the vertical magnet connects battery over wiper 3a to operate relay G which then interacts with the magnet until the calling level is reached when relay VT operates. Relay C releases and relay RS operates completing a circuit over wiper 6a for the other finder switching relay HA which connects up the rotary magnet RM. Rotary stepping now occurs under the control of relay G in a similar manner until the calling line is reached when one of the test relays 1P, 2P, operates, rectifiers RCT3, RCT4, being included in the test leads to prevent operation by booster battery. The operated test relay locks up in series with relay CO which causes the release of one of the switching relays HA, HB, to complete the through connection. During the rotary hunting, the seized level is marked busy over contacts N2, hb2, ha1. Overflow conditions. When all the regular finders are busy, relays RFZ, RFB operate, removing ground from the last contact of wiper 1a so that switch PDS comes to rest in this position and gives access to overflow distributor ODS. (If the overflow finders are connected to the bank of switch PDS, contacts rfb6, rfb7, Fig. 1, remove the normal busying earth from the corresponding terminals and connect up battery over resistance YM or YN.) Relay OFC operates over wiper la connecting up magnet ODM which interacts with relay G to select an idle overflow finder. Relav RFB completes circuits for relays OB, Fig. 3, in each of the start sets SS1 provided that at least one secondary finder served by this set is available. Relay OB energizes relay FB which closes testing circuits over relays GG, DK, in each of the three control circuits such as SC1 served by the start set SS1, relays GG interacting with magnets SEM to preselect finders SCF. Relay G in the primary control circuit PC1 in addition.to testing for the absence of earth on the contact engaged by wiper 1b tests simultaneously over wiper 2b for the absence of earth over conductors 44, 32, indicating that the overflow finder being tested has at least one secondary finder available to it. Rectifiers RCT1, RCT2, in the two testing leads prevent faulty operation of relay LK. When a call is initiated under overflow conditions the operation of relay LK starts the overflow-primaryfinder hunting as before and connects ground over conductor 44 to operate relay DS which energizes relays DK in each control group SCI to complete hunting circuits for each of the three allotted secondary finders SCF. When one of these finds the primary finder, relays FK, SK, SF operate, and when the primary finder has found the calling line it switches through as before. If all secondary finders are busy, relay EB operates to prevent useless hunting of switch ODS. Statistical metering. When all overflow finders are busy, relay OFB, Fig. 5, operates, disconnecting the control circuits PC1, PC2, PC3 and connecting up statistical meters over contacts ofb1, ofb2, ofb3. Faults. If the control circuit PC1 is not freed within a predetermined time, relays TA, TB, operating in succession transfer the start circuit to another control circuit and operate alarms FAL, 39, 40. If the faulty control circuit is associated with a finder, relay TC operates, and the finder is restored to normal and marked busy. Artificial busy conditions. If a group selector associated directly with a primary finder is artificially busied, relay HB operates over vertical wiper VW in its normal position to mark the finder busy. If a group selector associated with a secondary finder is artificially busied, earth on conductor 43 busies the finder to wiper 1c of switch SC1, but resistance YB prevents the short-circuiting of relay OB. Routine testing. A connection across jack springs TRE, Fig. 4, causes the primary finders to hunt in turn to the eleventh terminals in their tenth levels. The first Provisional Specification describes a system with substantially similar circuits but in which for each call two finders each controlled by a separate control circuit are set into operation. Specifications 293,294, [Class 40 (iv), Telephones &c.], and 366,143 are referred to.