Patent GB-405133-A (GB)
Title: Improvements in and relating to the transmission and automatic registration of signals in automatic telephone installations
IPC: H04M1/57
Filed: 1933-03-22
Abstract: 405,133. Automatic exchange systems. ZOLLER, E., and VILLIGER, J., 83, Talstrasse, Zurich, Switzerland. March 22, 1933, No. 8696. Convention date, March 24, 1932. [Class 40 (iv).] In a system provided with facilities for sending telegraphic signals from a calling sub-station to a called sub-station, particularly in the absence of the called party, the signals comprise alternating current impulses produced by connecting up a source of A.C. across the impulse contacts of the normal impulse transmitter. As described, this source is a buzzer which is operated by the exchange battery during the break periods of the impulse transmitter. A thermionic valve oscillator may also be used. At the called sub-station, a step-bystep switch started off by the initial periods of calling current steps automatically through positions in which the signal receiving circuits and recording apparatus are prepared, to a final position in which the circuits are effectively connected to the line. If the called party replies during the initial or preparation periods or if the calling party hangs up his receiver, the teleprinter circuits and apparatus are restored to normal Connection to the wanted substation is set up in known manner and the first period of ringing current operates E, Fig. 4, and F pulls up in parallel and connects up magnet M, Fig. 5, which interacts with stepping relay P to advance a sequence switch m1-m7 one step (m8, m9 are contacts of the magnet M). Stepping relay P is now disconnected and further periods of ringing current operate E and F to step the sequence switch directly to position 5. In position 5, stepping relay P is again connected up and interacts with M to step the sequence switch to position 19. The first closure of contact m8 of the magnet loops the line over G (i) to trip the ringing and G connects up a high resistance series winding(ii). The load imposed by G on the line approximates to that normally imposed by subscriber's instrument. The intermittent short-circuiting of G (ii) during the stepping of the sequence switch from 5-18 informs the calling subscriber that the teleprinter has been connected up. Relay G connects up the driving motor 21 for the tape, prepares the circuit of writing magnet 22 and connects anode, filament and grid potential to the valve 18. The grid potential is such that, in the absence of signals, anode current does not flow. The switch remains for the present in position 19 (the last one) in which the input circuit of valve 18 is completed. The calling party throws switch 15, Fig. 2, to connect buzzer D across the impulse contacts 12 so that he may by dialling send out impulses of alternating current which are repeated by relay H in the anode circuit of valve 18 to writing magnet 22. Release, normal and forced. On release of the connection by the calling party, G, Fig. 4, falls back and P interacts with M to step the sequence switch one step from 19 to 0 whereupon the teleprinter circuits are restored to normal. If the called party removes his receiver during the stepping of the sequence switch or standstill conditions arise, a time switch such as thermal relay K pulls up followed by J, and P, M interact to step the sequence switch to normal.