GB529534A - Improvements relating to telephone systems - Google Patents

Abstract

529,534. Exchange systems. SIEMENS BROS. & CO., Ltd., LONG, D. P., and HUMPHRIES, H. E. June 2,1939, No. 16270. [Class 40 (iv)] The device shown is connected by an access switch (not shown) to busy junctions and tests them for the presence of steady (tone) or interrupted (speech) voice-frequency current and may apply a releasing tone current to a faultily-held junction, When the test is started ST is operated and if the access switch is on an idle line the operation of FT shortly afterwards causes the stepping on of the access switch and the release of ST. When a busy junction is encountered, however, TA comes up and ET completes the circuit of a slow-tooperate relay TB. TA also connects the junction to the input circuit of a valve V<SP>1</SP> the biassing arrangements of which are such that the output is substantially constant for different values of input. The resulting currents are rectified at MR and fed to a D.C. amplifier V2 with a relay S in its plate circuit. The sensitiveness of the arrangement is adjusted in accordance with noise conditions by a biassing and reverse reaction resistance YC associated with V1 and a biassing resistance YB associated with V2. If the junction is silent S remains inert and when TB comes up W is energized and connects a resistance YH to a time-measuring apparatus (not shown) to cause it to measure a period of from one to three minutes. At the end of this period a circuit is made over contacts a, e of the device for AR which locks, lights a lamp and gives an alarm. If the junction is in use S responds intermittently to the speech currents and, after energizing Z or W on the operation of TB, energizes Y or X on changing over and subsequently the other relays of this group whereupon TA is released followed by TB and W ... Z and the access switch moves on. If the junction carries a steady tone, S is energized steadily and Z only is operated. After an interval, which in this case is from 15 to 60 seconds owing to the connection of resistance YK instead of YH to the time-measuring apparatus, a circuit is made for the alarm relay AR which lights a lamp L2. If the key RCK is thrown and the junction is silent relay P is operated over interrupter contacts tp, which close for an instant every six seconds, after the closure of the delay device contacts a, e and locks in series with Q which connects steady tone from RT to the junction and arranges for the temporary operation of R on the next closure of contacts tp to cause the release of P, and the removal of the tone. If the releasing signal is effective TA falls and releases TB. If not the next closure of tp energizes alarm relay AR to give a signal. During testing the balancing circuit of the junction circuit is modified by connection of YE or YF according as the detecting set or the tone source . is connected up. Speciification 462,862 is referred to in the Provisional Specification.