Patent GB-387373-A (GB)
Title: Improvements in or relating to semi-automatic telephone systems
IPC: H04M3/60
Filed: 1931-08-04
Abstract: 387,373. Semi - automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. and BAKER, J. H. E., Columbia House, Aldwych, London. Aug. 4, 1931, No. 22058. [Class 40 (iv).] In a semi-automatic system, busy tone and flash are returned to an operator if a tested line is busy and busy flash only if the call has failed due to all outlets being busy. Breaking- in facilities are provided, the clearing of a subscriber after a toll call has been offered being tested over one of the speaking leads. The invention is described as applied to a by-path system in which Fig. 2 shows the operator's outgoing circuit, Fig. 3 the first numerical stage, and Fig. 4 the penultimate path circuit. Setting of selectors. When an operator plugs into the jack, Fig. 2, relays S, SS pull up and the operator's lamp (not shown), connected to the sleeve of the plug, flickers. The operator throws her dial key, RR, DT pull up and A, B, BB, Fig. 3, operate. The first digit is repeated. by A to IR1 and, when IR1 steps off normal, IR2 moves to the contact marked by IR1. M energizes over ir21, ir15 and EH pulls up, followed by P, Q. M releases. IR2 now hunts for a free outlet in the marked group and either P or Q energizes. If P energizes, H pulls up over ir23 and if Q operates, both H and J pull up, relay J changing over to the second set of wipers. Relay H extends the impulsing circuit, over a lead such as BI, to the penultimate by-path circuit and connects V to lead BPT. Relay V operates, from earth returned from the next stage, EH releases and IR1 steps until it reaches the contact marked by IR2, when M re-operates, over ir22, ir16. Succeeding switches are set in known manner and when the final switch has been set, G, Fig. 4, operates and if the line is free is held by earth on lead H. Earth is also connected to BS, Fig. 4, to operate relay H, Fig. 4, which locks in series with Z, Fig. 3. Ringing the wanted subscriber. When the operator finishes dialling she restores her dialling key and marginal relay LR pulls up. DT is released. When the tested line is found to be free IL energizes and S pulls up to give a supervisory signal to the operator. The operator momentarily operates her ring- ing key and RG operates to connect ringing current to energize AC, Fig. 3, which was connected to the lower speaking conductor by Z. Relay AC completes a circuit for RR, which locks up and connects ringing current to the called subscriber. When the subscriber answers, F .energizes and RR releases. Relays D, Figs. 2 and 3, energize and DD pulls up to extinguish the operator's supervisory lamp. Called subscriber busy. If the called subscriber is busy G, Fig. 4, does not remain energized and relay H, Fig. 4, operates to ground on BS. As no ground is sent back along the H lead, J operates and locks in series with Z, Fig. 3. Ground is sent back along the negative lead to operate BY, Fig. 3, and BZ pulls up. With BZ up and RR back, busy tone and flash are returned from BFT to the operator. Offering the call. The operator re-throws her ring key and ringing is sent to the negative line to re-operate relay AC. RR operates and locks, connecting the operator over AFC to the wanted line. Either relay SC or SD will pull up in series with the feed relay on the other call. The operator offers the call and when the subscribers have cleared, the operated SC or SD relay will release. Relays X, XX pulled up when SC or SD operated and these now fall away slowly in turn. With X back BY, BZ will release and the supervisory lamp glows. The operator re-operates her ring key, RG pulls up, and AC, RR re-operate to connect ringing current to call the wanted line. All outlets busy. If IR2 fails to find a free outlet, relays P Q remain de-energized and M operates over the last line of the group. EH remains up and G operates, connecting busy flash only to relay D which repeats the flash to the calling operator. The impulsing circuit is opened by G to prevent further impulses influencing the switches.