Patent GB-633081-A (GB)
Title: Improvements in or relating to cathode-ray oscillograph apparatus
IPC: G09G1/16
Filed: 1946-11-12
Abstract: 633,081. Cathode-ray oscillographs. MANS. FORD, H. L., and SCANTLEBURY, S. P. Nov. 12, 1946, No. 33555. [Class 37] Oscillograph apparatus comprises a cathoderay tube and means for deflecting the beam along an axis at a predetermined frequency, means for modulating the intensity of the beam at the same frequency so as to provide a trace during each deflection of the beam, and means for advancing or delaying each modulation by a time which is a predetermined function of the instantaneous value of a variable magnitude. For obtaining the frequency response curve of a tuned circuit, a low-intensity cathode-ray beam is arranged to be deflected along two perpendicular axes O, X ; O, Y, Fig. 1. The frequency of oscillations applied to the timed circuit is cyclically varied so that it gradually increases from a predetermined minimum value to a predetermined maximum value and then falls rapidly to the minimum value the cycle being regularly repeated. The beam is deflected along the axis O, X under the control of the frequency-varying means so that it deflects in the direction O, X in accordance with the instantaneous frequency and then returns rapidly. The beam is also deflected along the axis O, Y at a frequency which is high relatively to that of the deflection cycle along the axis O, X and then rapidly flies back to the axis O, X. During each of these deflections the beam is modulated by a pulse of short duration producing a bright dot at a distance along O, Y representing the amplitude of the output of the tuned circuit at the corresponding frequency. The basic repetition rate of the pulses is equal to the frequency of deflection of the beam along the axis O, Y, but the actual occurrence of each pulse is advanced or delayed to an extent depending on the amplitude at the frequency concerned, producing a bright dot, shown by an open circle, during each deflection along O, Y. The deflections along the axes O, X ; O, Y are arranged to be asynchronous so that there is a continual drift in the direction O, X, producing an apparently continuous curve. The circuit includes a pair of cathode-coupled valves 1, 2, Fig. 2, arranged to operate as a trigger circuit having two states of stable equilibrium and adapted to generate pulses of short duration, e.g. one microsecond, at the input of a shortcircuited delay network 3. The deflections of the beam along the axis O, X are controlled by saw-tooth oscillations which also control the instantaneous frequency of the oscillations applied to the tuned circuit, and signals proportional to the amplitude of the output of the tuned circuit are applied to the control electrode 4 of the valve 1, providing a varying bias as shown by waveform 5. Saw-tooth oscillations 6, of the frequency of deflection along the axis O, Y are applied to the control electrode 7 of the valve 2 and during each sawtooth oscillation the bias on the control electrode 7 rises until the bias on the control electrode 4 is overcome, whereupon the circuit is tripped and a pulse of duration equal to twice the delay of the network 3 is developed in the output circuit of the valve 1, the trigger circuit tripping back during the rapid fall of the saw-tooth voltage. Accordingly the occurrence of each pulse is advanced or delayed by a time proportional to the instantaneous value of the amplitude of the output from the tuned circuit. The saw-tooth oscillations 6 are generated by a circuit comprising valves 9, 10 and a condenser 11, which is charged through a resistor 12 and is connected through a resistor 13 to the control electrode 7. The electrode 7 is connected to the anode of the valve 9, which is normally non-conducting so that as the charge on the condenser 11 increases the positive bias on the control electrode 7 increases. A series of pulses 15 of the frequency of deflection along the axis O, Y are applied to the control electrode 14 of the valve 9, each pulse causing the valve 9 to conduct and discharge the condenser 11. The valve 10 determines the lower limit of discharge of the condenser 11 and is arranged to act as a cathode follower as the lower limit is reached so that the potential of its cathode 16, which is connected to the upper electrode of the condenser 11, cannot fall below the fixed potential of the electrode 17, which may be adjusted by a potentiometer 19. The upper limit of the charge on the condenser 11, i.e. the amplitude of the saw-tooth oscillations 6, is determined by adjustment of the resistance 12. The beam may be additionally modulated so as to produce a plurality of traces each representing a cursor line parallel to the-axis O, X and corresponding to a known value of the output amplitude as shown by full circles in Fig. 1. The deflection along either or both of the axes O, X ; O, Y may be arranged to follow a logarithmic law.