Patent GB-583574-A (GB)
Title: Improvements relating to electric selective signalling systems
IPC: H04Q1/18
Filed: 1944-11-03
Abstract: 583,574. Automatic exchange systems. SIEMENS BROS., & CO., Ltd., and CHRISTIAN, D. A. Nov. 3, 1944, No. 21603. [Class 40 (iv)] [Also in Groups XXXVIII and XL] In a multi-potential marking system, a particular line or group is indicated to a switch by two markings over distinct circuits from the register, one marking causing current to flow in a thermionic tube when the switch encounters the desired line or group and any line or group having a higher number and the other causing current flow in a second tube when the desired line or group or any line or group of lower number is encountered. The completion of a test circuit of ordinary kind is made to depend on the simultaneous flow of current in both tubes. The register may be part of a registercontroller for controlling the whole train or may be individual to a switching stage. Group selector, Fig. 2, of latch-magnet type. Line and release relays A, B operate in known manner and the digit is registered on a switch DS, the terminals of which are connected to different negative potentials arranged in ascending order in one bank and in descending order in the other. The terminals engaged by switch wipers d1, d2 are connected to similar sets of positive potentials. On the relapse of dialling relay C, the latch magnet operates and the switch advances. When the positive potential encountered by wipers d1, d2 is equal to or greater than the negative potential selected by the register wipers ds1, ds2, the corresponding tube VA, VB conducts and its anode relay TA, TB is operated. In the case of the selected group, both relays operate and a test circuit over relay T is completed. When an idle line is found, T pulls up and H switches through A, Band T fall and the register goes home. Final or P.B.X. final selector, Fig. 3. Tens and units registers TS, US are set in known manner and each selects a pair of characteristic negative potentials. On the completion of the units digit, the switch is started and when it reaches the wanted line, but in no other position, both tubes concerned with tens marking and both tubes concerned with units marking are conductive simultaneously and all the anode relays TA ... TD are operated. If the line is idle, T pulls up and stops the switch and initiates the usual ringing operation. If the line is busy, the switch proceeds to an extreme position and a busy tone is sent. The outlets of a P.B.X. group all have the same marking. Modified arrangements. Instead of contacts of anode relays, the circuit of the test relay may include the anode/cathode path of a third tube, the grid potential of which depends on the current in a resistance common to the anode circuits in the discriminating tubes, Fig. 4 (not shown). In a similar arrangement, Fig. 5, the tubes are gas filled. The discriminating tubes have inductance-condenser combinations in their anode circuits so that with a suitable grid-potential they generate impulses, these impulses being rectified and applied to two control electrodes of a gas-filled tube VT in series with the test relay. The last-mentioned tube only breaks down when an appropriate potential is applied to both control electrodes. In another arrangement, Fig. 6, using hard tubes, an alternating voltage is applied to the grids and is effective to cause a fluctuation of anode current only when the positive potential applied to the grid circuit by the switch has the matching value or a value in excess of this. Preferably, this matching value is greater than the negative potential, but it may be equal as in the other arrangements. When the desired line. or group is reached, effective fluctuations take place in both anode circuits and the resulting alternating output after rectification by VR produces a sufficient voltage across RE to render tube VT in the test circuit conductive.