GB663818A - Improvements in oscillograph apparatus - Google Patents

Abstract

663,818. Cathoderay oscillographs. BRITISH THOMSON-HOUSTON' CO., Ltd., WELCH, D. F., and GRIEVE, A. June 3, 1948 [Dec. 18, 1946], No. 37289/46. Class 37. [Also in Group XL (c)] In a time base generator operated by pulses of variable recurrence, a first saw-tooth generator is triggered by the pulses and has its rate of change of voltage varied just to complete a cycle during the recurrence period, a second generator being triggered from the first so that the commencement of the sweep occurs at a selected point in the cycle of the first generator. A negative going triggering pulse applied to the grid of valve V1 causes the flip-flop V1, V2 to reverse its state to generate a negative-going pulse at the anode of valve V2 which cuts off the valve V3 at the suppressor grid. Valves V3, V4 are connected as a Miller integrator and a paraphase valve respectively, the pulse causing the sweep to terminate and the flyback to occur. When the flip-flop restores, valve V3 is rendered conducting to initiate a linear run-down at the anode and a corresponding rise in the anode potential of valve V4, the saw-tooth potentials being fed over switch S11 to the deflection plates of the Cathode-ray tube. During the fly back, the fall in anode potential of valve V4 causes the diode V6 to conduct when its cathode potential falls below that of the negative line. The diode ceases to conduct at a point in the sweep so that valve V5 discharges capacitor 15 over part of the cycle, the capacitor being partly recharged over resistor 19. A steady state is reached so that the potential to which the grid resistor 12 of Miller valve V3 is returned is varied in accordance with the amplitude of the saw-tooth oscillations to maintain them substantially constant. The anode of valve V3 is connected directly to the grid of valve V7 of cathode coupled pair V7, V8 so that when the anode potentials fall during the sweep a positive pulse is generated at the anode of valve V7 which is differentiated over capacitor 23 and resistor 24 and squared in biased valve V9 to produce a negative pulse which is applied to valve V10. Valves V10 and V11 are connected similarly to valves V3, V4, the grid resistor 26 being returned to capacitor 15 to stabilize the saw-tooth amplitude. It is stated that a fast time base results when the negative pulse is applied to valve V10. The feed-back capacitor may be selected by switch S10 to give a desired sweep expansion, the switches S10, S11 being ganged so that the deflection plates are fed from valves V3, V4 or V10, V11. A black-out wave is derived from the sawtooth output over capacitor 31 and resistor 32.