GB713962A - Improvements relating to electric circuit arrangements for controlling sweep voltages - Google Patents

Abstract

713,962. Automatic control systems. METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. Aug. 12, 1952 [Oct. 16, 1951], No. 24120/51 Class 38(4) In order to maintain the datum level of a saw tooth waveform, e.g. for a timebase, at a predetermined potential, the waveform and earth potential are alternately applied for comparatively long periods to a valve which is gated to conduct only during the datum period, i.e. between successive saw tooth sweeps, so as to produce an alternating signal the amplitude of which depends upon the error in the datum level, which signal controls the charge on a condenser controlling the datum level. The output of the waveform generator is connected to the control grid of the gating valve V2 via a cathode follower V1 and a switch S1 which alternately connects the grid of V2 to earth. A synchronizing circuit coupled to the waveform generator acts on the suppressor grid of valve V2 so that it conducts in pulses in the intervals between successive sweeps. Hence its output consists alternatively of sets of pulses having an amplitude proportional to the actual waveform datum level and sets of pulses having an amplitude representing the desired level. The pulses are amplified by valve V3 and applied to detector V4, from the cathode of which are obtained positive going pulses having an amplitude proportional to the difference in amplitude between the two sets of pulses. This signal is applied to the control grid of a gated valve V5 rendered alternately conaucting and non-conducting by bias sources B1, B2 switched by a switch S2 in synchronizm with the switch S1. During the periods that V5 is cut off, a condenser C1 (controlling the datum level) charges through resistors R7, R8. When V5 is rendered conductive, it conducts to an extent dependent upon the amplitude of the signal applied from V4 and discharges condenser C1. The arrangement is such that under normal conditions the discharging of C1 substantially compensates the charging. In a modification, negative going pulses are applied to V5, and S2 is changed over so that C1 is discharged at a constant rate through V5 and is charged at a rate which is controlled by the amplitude of the pulses. In a further modification, Fig. 4 (not shown), the gating valve V2 is automatically biased in accordance with the magnitude of the error signal so as to increase the gain for small errors.