Patent GB-475903-A (GB)
Title: Recording transients on electric power circuits and the like
IPC: G01R13/32
Filed: 1936-05-29
Abstract: 475,903. Oscillographs. STANDARD TELEPHONES & CABLES, Ltd., and McGILLEWIE, D. I. May 29, 1936, No. 15230. [Class 37] An arrangement for recording transient phenomena consists in connecting the line, transients upon which are to be recorded, through a condenser to the centre electrode of a three electrode spark gap, the outer electrodes of which are maintained at a high positive and negative potential respectively, and in connecting one of the outer electrodes through a small condenser and high resistance to a cathode-ray tube of the hot cathode type, so that a pulse of potential is generated upon the breakdown of the spark gap on the occurrence of a surge which raises the potential of the modulating electrode of the tube and thus causes the formation of a beam of cathode rays in the normally inactive tube. The tube is rendered normally inactive by the application of a negative potential to a modulating electrode 3 and in the arrangement shown in Fig. 1, this potential is obtained from a potentiometer P, tappings on which supply the potentials required for the cathode '2, anodes 4 .. 6, and a pair of deflecting plates 8. The line carrying the transients to be recorded is connected through a condenser to an electrode 9 of a three electrode spark gap, the two outer electrodes 10, 11 being connected to a high potential source as shown. The electrode 10 is connected through a high resistance R1 and condenser C to the modulating electrode 3 of the tube, while both electrodes 10, 11 are connected through resistances R3 to the deflecting plates 8 of the tube, a condenser C3 being arranged in shunt thereto. Resistances R2 and a condenser C2 connected across the two outer spheres of the spark gap maintain the discharge for a sufficient time once started, and upon the occurrence of a transient the voltage of the sphere 10 rises and a positive potential is applied to the electrode 3, which permits the beam to form instantaneously. The condenser C3 commences at the same time to discharge and the decreasing voltage across this condenser applied to the tube plates 8 sweeps the beam across the screen of the tube to form a time-base, the speed of which may be adjusted by varying the condenser C3 and resistances R3. In a modified arrangement, using either a gas-focused tube or the tube shown in Fig. 1, the modulating electrode 3, Fig. 2, which is connected to the potentiometer P as shown, is given a negative potential sufficient to extinguish the beam by connecting it to the anode of a valve V, the grid of which is connected through a high resistance R7 to the cathode and through the condenser C1 and resistance R1 to the positive sphere 11 of the three electrode spark gaps. The time base and other connections are the same as those of Fig. 1. Normally the valve B is conducting and the electrode 3 is at a negative potential, but upon the occurrence of a transient the grid of the valve becomes negative and the anode current falls, with the result that the electrode 3 becomes positive with respect to the cathode 2 of the tube and the beam of cathode rays is obtained. The apparatus may be used for recording surges on power lines or for use in medical work, small voltages being suitably amplified if necessary before being applied to the sphere 9 and the deflecting plates 7.