Patent GB-519256-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04M15/08
Filed: 1938-10-10
Abstract: 519,256. Automatic exchange systems. BRASHER, W. K., and MOSS, B. F. Oct. 10, 1938, No. 29271. [Class 40 (iv)] The arrangements described in Specification 479,554 for enabling an operator to check the number of a calling subscriber are applied to the case in which the calling party is at a P.B.X. by causing the final selector of the checking train to step over all the lines in the group by use of a rotary connector or under the control of the operator. A normal trunk offering connector may be caused to hunt over the group if seized for checking. The supersonic oscillator and receiver may be at a trunk exchange and the checking train at a distant automatic exchange. The Provisional Specification describes the use of an indicator at the operator's position stepped in synchronism with the final movement of the checking connector. When the operator receives the call she sets up the calling number on the key-set having control circuits shown in Fig. 3, and plugs into jack 7, whereupon S and SS pull up and connect the supersonic receiver 10 over alternator 14 to oscillator 12. Relay A pulls up if these equipments are functioning correctly, and prevents AA from operating so that IA pulls up and connects flicker lead 15 to lamp FL to inform the operator who throws key 16 at the ,sender. Relays DCT, RR and DT pull up, the last mentioned locking itself and releasing RR and A. When the key-sender was taken into use a relay KR (not shown) was operated so that DKT now energizes and transfers the output leads 22 of the sender from the normal sending leads 20 to the checking path: On termination of impulse transmission, key 16 having been restored and relay KR released DCT, DKT relapse in turn and TCH pulls up and locks in series with lamp BL and relays S and LR, the last-mentioned relay now operating to release DT whereby relay A is re-connected to the supersonic receiver 10. Relay TCH connects the oscillator 12 over leads 23 to the cord-circuit and line over which the call was made, and LR loops the checking path over relays D and I, relay I being operated by the battery feed so that B pulls up and connects receiver 10 to the checking path. Successful check of a regular line or individual line of a P.B.X. group. The supersonic current operates A which releases AA to hold B which maintains the check lamp CL (CR has been operated by TCH). Removal of plug 5 releases the checking train. Unsuccessful check. Relay A does not operate, AA releases B to connect the receiver directly to the oscillator, A pulls up to release AA, and B re-operates, this cycle of operations being repeated to cause flashing of the check lamp. Normally the operator makes a second check and if unsuccessful transfers the call to a supervisor. Group checking. When a P.B.X. number is dialled, the connector returns ground over the P.B.X. arc to the trunk offering distributer used in the checking train which brings about current reversal to operate D. If the line in use checks correctly, check lamp CL will be lit as before, but if not, the operation of DA by D leaves the checking line loop under the control of B and AA so that when these relays interact with A as described above for an unsuccessful check, impulses are sent to the connector to step it over the group. If supersonic tone is found on any line, A is maintained and the successful check is signalled, but if not, the current reversing relay in the distributer releases at the end of the group and D, DA fall back, but relays A, AA, B continue interaction to flash the check lamp. In the case of a large P.B.X. group extending over contacts of two wiper sets, both banks may be tested simultaneously by connecting the pairs of speech wipers over condensers which pass the supersonic frequency but not speech. Check connector busy. The busy flash signal controls I which flashes lamp BL.