Patent GB-168474-A (GB)
Abstract: 168,474. Relay Automatic Telephone Co., Ltd., (Betulander, G. A., and Palmgren, N. G.). July 2, 1920. Automatic and semi-automatic exchange systems.-A relay searcher, which is temporarily taken into use to mark an idle line preparatory to its seizure, comprises a chain of relays which are energized successively to connect the different lines to a test relay, which is energized when an idle line is reached and holds the chain relays against further operation. The lines may be tested in groups, a number at a time, as many test relays being provided as there are lines in a group. For example, in the arrangement shown in Fig. 2, relays KR1 - - KR5 are energized in cyclical succession to connect the test wires G1 - - G5 of five pairs of lines a pair at a time to test relays PR1, PR2. The operation is started by a relay SR, which closes the circuit 9 of relay KR1, which energizes relay KR2, and relays KR2 - - KR5 become energized in succession, each of them locking itself in a. circuit through back contacts of succeeding relays, unlocking the preceding relay, and preparing a circuit by which the next relay is energized on the relapse of the preceding relay. The circuit prepared in this way by the last relay KR5 energizes the first relay KR1, so that the operation is cyclical. When an idle line is reached, test relay PR1 or PR2 is energized and closes a corresponding marking circuit, shown at the left of the Figure. The energized test relay also cuts out the other test relay and opens contact 10 or 11 to prevent further operatior of the relays KR1 - - KR5, only the last-energized relay of the series remaining locked. In the arrangement shown in Fig. 2, different groups of lines HG1, HG2, HG3 are tested in successive cycles of the chain-relays KR1, KR2, KR3, which, in this modification, are energized at intervals determined by an interrupter RS. The operation is started by energizing relays LR, NR which close a circuit 17 through relays G1R1, G2R1. Relay G1R1 connects the test wires of the group HG1 to the searcher and closes a circuit 19 through a slow-release relay SR and relay KR1. At the next closure of the interrupter RS, relay KR1 energizes relay KR2, and both these relays lock themselves through the interrupter, relay KR2 also locking itself through a back contact of relay KR3 in series with relay SR. At the next opening of the interrupter, relay KR1 is unlocked and prepares a circuit for relay KR3, which is energized at the next closure of the interrupter and locks itself in series with relay SR. At the next opening of the interrupter, relay KR2 is unlocked and prepares a circuit for relay IR, which is energized at the next closure of the interrupter, completing a circuit 26 to lock relays G1R1, G2R1 in series with relay BR, and a circuit 25 for relays G1R2 G2R2, which lock themselves in a circuit through a back contact of relay G2R3. Relay BR unlocks relay KR3, which de-energizes relays IR, BR, and a fresh test cycle begins, the lines HG2 being now connected to the searcher by relay G1R2. At the end of this cycle relays IR. BR are energized again and bring relays G1R3, G2R3 into action, so that in the third cycle lines HG3 are tested. When an idle line is found, test relay PR1 or PR2 is energized and closes a corresponding marking circuit through contacts of one of the relays KR1, KR2, KR3 and one of the relays G3R1, G3R2, G3R3, which are in parallel with relays G1R1, G1R2, G1R3. Numerical relay selectors. Numerically-different groups of lines may be selectively brought under test. For example, if the a wire instead of the b wire of line L is earthed, relay MR is energized instead of relay NR and brings into play relays G1R6, G1R7, G1R8 instead of relays G1R1, G1R2, G1R3, so that lines HG6, HG7, HG8 are tested instead of lines HG1, HG2, HG3.