Patent GB-625916-A (GB)
Title: Improvements in or relating to display arrangements for cathode ray oscillographs
IPC: G01S1/02
Filed: 1946-09-27
Abstract: 625,916. Cathode-ray oscillographs. STANDARD TELEPHONES & CABLES, Ltd., and MOODY, N. F. Sept. 27, 1946, No. 28960. [Class 37] A multiple trace arrangement for a single beam cathode ray oscillograph comprises a plurality of thermionic switching valves, each connected in an anode follower circuit, means for applying a corresponding signal potential to the control grid of each valve, means for connecting the anode circuits of all the valves in common to a deflecting element of the oscillograph, and cyclically operating means for blocking all the valves except one, the arrangement being such that the valves are all unblocked in turn, one at a time. A multiple trace switching circuit is shown for producing two simultaneous traces on the screen of a cathode-ray oscillograph. The circuit comprises two exactly similar halves, corresponding elements being given the same reference numbers distinguished by letters A and B. Each anode follower circuit comprises a valve 1 having its anode connected through a small current limiting resistance 2, a relatively large resistance 3, and a small current limiting resistance 4, to the control grid of the same valve. The junction point of the resistances 2, 3 is connected through a common load resistance 5 to the H.T. positive terminal 6. The junction of the resistances 3, 4 is connected through a high resistance 8 to the movable contact of a potentiometer 9 connected between an earth terminal 7 and the negative terminal 10 of a first negative bias source. A single adjustable resistance 11 common to both valves is connected between the cathodes and earth. A signal potential is applied through a blocking condenser 12 and a small current-limiting resistance 13 to the control grid of an input valve 14 arranged as a cathode follower, the anode of which is connected directly to the terminal 6. The cathode is connected through a low-resistance potentiometer 15 and a high resistance 16 to the negative terminal 17 of a second negative bias source, which may have a higher potential than that of the' first bias source. A high resistance 18 connects the junction of the elements 12, 13 to earth. The junction of the resistances 3, 4 is connected to the movable contact of the potentiometer 15 through a resistance 19. The anode of a diode 20 is connected to this junction, and the cathode is connected to a terminal 21. The resistances 3, 19 are shunted by very small phase correcting condensers 22, 23. The common point of the resistances 2, 3, 5, is connected to the output terminal 6, which is connected to one of the deflecting plates of the oscillograph. The terminals 21 are connected to a generator 31 of two trains of negative rectangular pulses differing in phase by 180 degrees. The duration of these pulses is slightly less than half the repetition period and their amplitude is such that each will cut off the valve 1A or 1B to which it is applied. Thus, traces corresponding to the signal potentials applied through the valves 14A, 14B will be recorded on the oscillograph screen in alternate periods of time. Each of the diodes 20 passes negative potentials to the grid of the corresponding valve 1 but blocks positive potentials, thereby, preventing positive potentials from the generator 31 from affecting either valve when it is unblocked. The switching of the valves 1A, 1B is controlled by the time-base circuit 33 so that one of the valves is unblocked at the end of each forward stroke of the time base, when the cathode beam is normally suppressed. By adjusting the grid bias of the valve 1 by means of the potentiometer 9, the mean anode voltage may be changed so that the zero line of the trace may be shifted up or down on the oscillograph screen. The amplitude of waves recorded on the oscillograph may be measured by measuring the bias voltage tapped off from the potentiometer 9. This may be effected by a voltmeter plugged into a jack 32B by a centre zero voltmeter connected between the terminals 7, 27B.