Patent GB-490325-A (GB)
Title: Improvements in impulse senders of the type used in telephone systems
IPC: H04M1/272
Filed: 1937-06-04
Abstract: 490,325. Automatic exchange systems. GENERAL ELECTRIC CO., Ltd., and CHUBB, A. A. June 4, 1937, No. 15502. [Class 40 (iv)] In a keyboard-sender, each digit is stored by charging or discharging one or more condensers of a group. As described, each group comprises four condensers charged respectively by digits 1 to 4, digit 5 being represented by absence of a charge, and digits 6 to 0 being stored in a similar manner but with a charge on an additional condenser. The digits are distributed by switch D to the condenser groups which are connected in succession to the contacts of sending control switch T by a switch C, the impulse trains being terminated by the operation or release of a relay in the anode circuit of a thermionic valve having its grid connected to the test wiper of the control switch, or directly by a relay. Depression of a key operates G and CN which opens discharging circuits over wipers of D for the first condenser group, one of condensers 11 .. 14 with or without auxiliary condenser 15 being charged over the key. On release of the key G and CN relapse, back-stroke magnet DM operated by G releases to step the switch, and the second group of condensers are discharged. Further digits are stored in similar manner. When switch D steps out of coincidence with switch C, normally operated relay ST falls back and energizes vibrator relay V followed by M which loops the impulse wires. Relay IG pulls up, operates backstroke magnet TM of the control switch and releases relay V the armature of which vibrates at standard rate and impulses M which steps the control switch T and sends impulses over the loop. When T reaches a charged condenser, positive potential connected to the grid of valve P2 causes E to operate whereupon EE pulls up, shunts the impulse contacts of M and releases IG which connects up a further shunt, makes a self-stepping circuit for T, and re-energizes the vibrator relay V. In the meantime, anode relay E has released but EE remains held so that when T runs on to the second group of commoned contacts of bank T1, IG re-operates and releases V which impulses M to step T by timed impulses over this group to provide the inter-digital pause. When T reaches the third commoned group in T1, IG releases to restore the selfstepping circuit of T which returns to normal, re-energize the vibrator relay and release backstroke magnet CM of switch C which connects up the next condenser group. Relay EE also falls back, and the circuits are ready to send the next digit. In the case of digit 5, ground (positive) is directly connected to the 6th contact of T4 since there is no condenser for this digit. In the case of digits 5 ... 0 auxiliary condenser 15 is charged so that E pulls up over the 1st (normal) contact of T4 and operates X which opens the grid circuit of the valve to release E and prevent its re-operation on the first five impulses since X is held for this period over T3. As shown, provision is made for eight storage condenser groups, but if key operation is so rapid that switch D arrives on contacts 8 before C has moved, then at the next key operation, G holds over banks D1, C and holds CN. Cancellation. The cancel key CNK operates CO followed by X which interacts with DM until switch D coincides with C whereupon ST re-operates and stops D. CO also opens the loop and releases IG and V, if energized, so that T goes to normal by self-interruption of TM.