Patent GB-567819-A (GB)
Title: Improvements in or relating to electrical timing arrangements
IPC: H04M3/12
Filed: 1943-08-28
Abstract: 567,819. Current-duration meters. AUTOMATIC, TELEPHONE & ELECTRIC CO., Ltd., WRIGHT, D., and ASTON, A. Aug. 28, 1943, No. 14075. [Class 37] In an electrical timing arrangement for timing periods defined by the opening or closing of a circuit, a plurality of gas discharge tubes are arranged to be connected succes sively over the wiper of a switch rotating at constant speed to which stimuli are applied at appropriate instants, whereupon the tube connected at the moment of application of any stimulus strikes and remains conducting, thereby furnishing a persistent visual indication. A mains-driven synchronous motor SM is used as a time base and drives a wiper CW which makes one revolution in 150 milliseconds and wipes over a circle of 150 studs connected. respectively with 150 cold-cathode three-electrode gas discharge tubes such as CCT, for instance of the neon type, also arranged in a circle. An impulse to be tested may take the form of an earth potential of characteristic duration applied to either of two terminals 1, 2, and this energizes the primary winding of a high step-up ratio transformer which may comprise either a retard PR or a relay P. With relay contacts S2 closed, the secondary transformer windings are connected to the wiper CW by means of which they are successively connected for a period. of one millisecond to each of the tubes CCT. Resistances YA, YB, YC, YD are provided for current limiting purposes. Assuming the impulse is applied to the retard PR, i.e. that earth is connected to the terminal 2, a potential of sharp peaked form is induced in the secondary winding causing the tube with which the wiper CW is connecting to break down across the electrodes 10, 11 and maintain the discharge across its main electrodes 12, 11, each tube being operated from a supply of the order of 240 volts. On the termination of the applied current impulse, the collapse of the flux in the retard PR produces a secondary surge voltage which flashes the tube with which the wiper CW is connecting at this time and this also remains ionised. The two tubes give a visual indication by their glow and by turning a rotatable scale so that its zero lines up with the first tube the distance between the tubes may be read on a scale calibrated in milliseconds. To measure the operating lag of a relay, a key is arranged to apply earth to the terminal 2 at the same instant as the energization of the winding of the relay so as to cause a tube to flash. When the relay operates, it applies earth to the terminal 1 and energizes the primary winding of the relay P, causing a surge voltage which flashes a second tube. The spacing between the two flashed tubes measures the operating period of the relay. At the end of the test the H.T. supply to the tubes is momentarily disconnected so as to restore the flashed tubes. The timing of the releasing period of a relay and the breakto-make ratio and speed of impulses may be determined by suitably modified circuits. For varying the range of measurement the wiper CW may be driven fit a lower speed by changespeed gearing.