Patent GB-260018-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04M3/32
Filed: 1925-06-24
Abstract: 260,018. Standard Telephones & Cables, Ltd. (formerly Western Electric Co., Ltd.), (Polinkowsky, L.). June 24, 1925. Automatic exchange systems. - Inter-office trunks and their incoming selectors are tested from the outgoing office with the aid of a trunk and selector used for extending calls. In the system described there are 10 bays of 11 selectors of the kind described in Specification 184,249. One of these, GS1, has no trunks outgoing from its first terminals which are connected as shown, the a-terminals to a relay Ar, the b-terminals to a relay Btr and the c-terminals to separate relays Str, each of which is associated with a particular bay. In the remaining selectors, the first terminals of a particular level may be devoted exclusively to testing in which case they are connected as indicated in full lines. Alternatively the testing terminals may be normally connected to trunks TRS and only connected to the relays Lr, Lir &c. of the testing arrangement on the energization of relays Stir which correspond to the relays Str of the other arrangement. The test is carried out a bay at a time. The special trunk and those of the bay to be tested are tested with the tip of the plug and if they are idle the relay Br lights lamp CL. They are then disabled by means of the jacks BJ and one of the keys 1 - - 10 corresponding to the bay to be tested is pressed. Setting modified selector. The numerical key energizes relay Lar which connects relays Pr, Prr in series over the a-wire. Relay Pr pulls up sluggishly and energizes relay Nr which locks itself up and disconnects relay Pr. Relay Prr locks itself up in series with relay Plr which connects ground over D, 211, relay 219, 209, relay 208, 207. Relay 210 energizes the sequence switch magnet 204 and relay 202 pulls up in series with the stepping relay Sr which energizes the relay Scri - - Scro corresponding to the depressed key. In position 2 the magnet 217 rotates the trip spindle which sends back impulses from 226 to short circuit the relay Sr. The counting chain is thus built up in known manner and when the relay Tcro is reached, relay Tcr opens the fundamental circuit and the selector hunts in known manner, stops on the first terminals and moves into position 5. The relay Tcro energizes the magnet RM of the test set sequence switch which moves straight on to its home position, the magnet circuit being maintained from 3 to 16 by relay Hr. In position 10, relay Dr unlocks the counting relays, locks itself up and connects relay Pr over the b-wire to relay Btr which short-circuits relay Prr but holds relay Plr. Testing. Key Tsk is pressed to energize relay Qr which locks up and energizes relay Ar at the special selector to connect a special potential to the a-terminals of the bay under test. The plug is then inserted in the first trunk of this bay and relay Tr drives the test-set sequence switch to 3 in Which relay Sr is bridged across the trunk and the line relay 202 of the selector energizes relay 210 to drive, the sequence switch to position 2 in which the trip spindle is driven and sends back impulses to relay 2Sr. In this case the ground for locking the counting relays is obtained from the circuit E, C and the number of steps is determined by the point of connection of the middle right hand contact of relay Lar to the chain. The selector sequence switch moves to the hunting position and the test set sequence switch leaves position 3 on the energization of relays Tcr, Tcro. In 4¢ (of the test set) relay Br pulls up over the b-wire and relay 208 (which does not pull up) in the selector. Br drives the test set sequence switch to position 6 in which the counting relays are unlocked. Meanwhile the selector stops on the first terminals of the test level and its sequence switch moves to 5 in which the loop is extended to the a and b terminals and relay Sr pulls up in series with relays Lr, Ir (which however remain unenergized) and energizes relay Mr to drive the test set sequence, switch out of 6 from which it moves to 9. If the selector is functioning properly, relays Sr, Mr remain energized and the test set sequence switch is moved out of 9 over back contact Bkr. If relay Sr falls back the sequence switch cannot move beyond 9. In position 10, relays Sr, Mr fall back, battery is connected to the k-wire and relay Ir removes the test potential from the c-terminal whereupon relay 210 in the selector falls back and relay 202 pulls up and the sequence switch is moved out of 5. In position 9 of the selector and position 14 of the test set a tone signal over front contacts of Or is connected to the attendant's telephone. Relay Ir holds up in series with relay 235 which short-circuits the highresistance winding of relay 208 allowing relay Sr to pull up over the a and b wires energizing relay Mr to drive the test set sequence switch to position 15. Relay 208 of the selector energizes relay 202 which over 218, 290 energizes relay Lr which releases re1ay Or to cut off the tone signal and also relays Lir, Ir whereupon relays Sr, Mr fall back and relay Bkr drives the sequence switch to position 16 in which a clearing lamp CL is let. The plug is then withdrawn, the selector is thus released and the relapse of relay Tr energizes relay Hr which drives the test set sequence switch home. If the selector fails to function correctly the test set sequence switch will be held before reaching 16. Progress lamps A, B, C are lit in combinations at different stages to indicate the position in which the sequence switch sticks. When another bay is to be tested the bay key is released to release relays Lar, Dr, Nr, and the selector GS1 is released and is then re-set by depressing another key. The Provisional Specification refers also to the use of the test set with incoming selectors giving access to ring-down trunks.