To short-term stress peaks or - pulses responsive means for control - and measurement purposes

摘要

661,890. Peak voltage measuring. PYE, Ltd., and LAX, L. Dec. 15, 1949 [Dec. 17, 1948], No. 32767/48. Class 37. [Also in Group XL (b)] An arrangement for measuring of using, for control purposes, the peak voltage of short duration pulses comprises a D.C. restoring circuit consisting of a rectifier the cathode of which is maintained at a predetermined potential and connected, through a leakage resistor, to the anode, to which the waveform to be D.C. restored is fed through a condenser, and one or more additional rectifiers are provided having their cathodes connected to the cathode of the first rectifier and their anodes interconnected by resistors to the anode of the first rectifier and also connected through condensers to the source of the waveform to be D.C. restored. This arrangement provides a circuit which may be employed for D.C. restoration (or for the measurement of very short voltage peaks by incorporating it in the peak-voltmeter described in Specification 656,002) and which has an initially flat decay curve so that the condition established by a short peak (e.g. a short " black " peak in a television waveform) is maintained during the interval between successive peaks. In the embodiment described with reference to the (Prov.) drawing the wave-form, the peaks of which are to be measured or with reference to which the D.C. level is to be restored, is fed, in the negative sense, from a cathode follower stage VI to a D.C. restoring circuit comprising C1, R4 and the first section of valve V2 with which is associated three further rectifying paths comprising the second section of V2 and the two sections of V3, the cathodes of all of which are connected to the cathode of the first sections of V2 and the anodes of which are interconnected by resistors R1, R2, R3 and connected to the output of V1 via C2, C3, C4. With this arrangement the discharge through the leakage resistor R4 is prolonged, since the discharge of condensers C2, C3, C4 is progressively delayed, so that the potential to which the waveform is restored (i.e. that of the common cathodes which is determined by R5, R6) is maintained for a considerable period (e.g. in the case of a television system for at least one complete frame even though that frame may have only a very small black portion). To prevent spurious operation during television line re-trace periods valves V2, V3 are cut-off by means of negative blanking pulses derived from the screen-grid of V4 to the control grid of which positive blanking pulses from the television transmitter waveform generator are applied. The D.C. restored waveform is then amplified in V5 and fed to the output terminal C via a diode V6, the cathode potential of which is maintained at a value slightly below the black level potential. The potential of the cathode may be varied by varying the bias on the control grid of V7 by means of potentiometer P.