| 摘要 |
549,453. Automatic exchange systems. STANDARD. TELEPHONES & CABLES, Ltd., BRAY, F. H., and BROWN, L. R. May 19, 1941, No. 6417. [Class 40 (iv)] Selecting impulses are transmitted over a junction in direct-current form as described in Specification 486,764 but are received by a pair of hot or cold cathode gas-filled discharge tubes A, B. These tubes normally pass current and so acquire a temperature that is not substantially changed during .signal reception. When the receiver is seized however, ST pulls up removing a shunt from relay HSA in the main gap circuit of A, breaking the main gap circuit of B and reducing the control-gap voltage of both tubes to a value insufficient to start a discharge. The discharge in A persists however, energizing HSA to prepare an alternative main gap circuit for B. ST also completes the impulsing circuit to the terminating apparatus. At the beginning of each signal impulse tube B receives an impulse at its control gap and becomes conducting, and HSB energizes HSC to break the impulsing circuit to the terminating apparatus and interrupts the main gap circuit of A. HSA then falls and releases HSB by opening the main gap circuit of B. The relapse of HSB is delayed by a condenser discharge and HSC is held subsequently over a back contact of HSA. At the end of the signal impulse, however, A receives an impulse at its control gap and HSA pulls up, releasing HSC to terminate the repeated impulse and preparing the circuit of HSB in the main gap circuit B. The control gaps are given a suitable normal bias from potentiometers connected across the main discharge gap of a third tube C. A method is described by the manipulation of the links shown associated with various test jacks for adjusting the bias centrally to the correct value with the aid of tell-tale lamps which indicate when a discharge is passing in the associated tube. |
