2/27/2024 0 Comments Cathode ray oscillograph![]() These specifications determine the amplitude, duration, and frequency ranges of the signals to be studied. The important specifications of an oscillograph that determine its possible uses are (1) the deflection sensitivity, which is the ratio of the input-signal voltage to the beam deflection that is produced by the voltage and which is measured in volts (V) per cm or V per gradation (2) the passband, which is the frequency range in which the deflection sensitivity drops no more than 3 decibels (dB) from its value at the middle, or reference, frequency (3) the rise time, τ r, during which the transient response of the oscillograph rises from 10 percent to 90 percent of the amplitude value, which is often used instead of the passband the upper-boundary frequency f u of the passband is related to τ r by the equation f u = 0.35/ T R where f u is measured in megahertz (mHz) and τ r in nanoseconds (nsec) (4) the deflection factor, which is the ratio of the time τ r to the amount of beam deflection produced by the time-base voltage during τ r, expressed in sec per cm or sec per gradation and (5) the writing speed, which is the maximum speed at which the beam can move on the screen and still guarantee that a one-time signal will be photographed or-in storage oscillographs-retained. The former only supplies the tube, while the latter supplies the electronic circuit of the other components and sub-units of the apparatus. An oscillograph also includes high-voltage and low-voltage power supplies. In the absence of a delay line, only that part of the signal (represented in Figure 1 by curve B) that appears after time t\ is visible on the tube’s screen. ![]() The delay line compensates for the operating times of the synchronizer and the time base, since these times are slightly shorter than the time delay of the signal. Since the signal under study triggers the time base, and since the synchronizer and time base do not respond instantly but with a delay of fractions of a microsecond, a delay line must be introduced in the vertical-deflection channel in order that the initial part of the signal be observed. The pulse is a square wave with positive polarity and a duration equal to that of the forward sweep of the beam. In order that the electron beam may be visible only while it is sweeping forward, that is, when t 2- t 1 > 0, the time base produces a pulse, E, to brighten the beam that is fed to the tube’s control grid, which acts as a modulator. This is achieved by passing the signal from the vertical amplifier to a synchronizer that forms a trigger pulse, C, for the time base at a selected point in the signal. In order to project on the tube’s screen a stable image of the signal under study, every new sweep must begin at the same phase of the signal. The electron beam is moved horizontally at a constant rate, thus creating the linear time base. The sawtooth voltage is fed to the input of the horizontal-deflection amplifier, which in turn feeds its output voltage, F, to the horizontal-deflection plates of the tube. The beam is moved horizontally by a time-base generator that produces a sawtooth voltage, D, which varies linearly with time. The signal under study, A, is fed to the input amplifier for vertical deflection, which has an adjustable gain and is designed to make the magnitude of the beam deflection correspond to the magnitude of the input signal. Simplified block diagram of a cathode-ray oscillographįigure 1 is a simplified diagram of an oscillograph circuit. In some apparatus, the image of the signal under study is compared with that of a calibrating signal or the balanced method of measurement is used ( see BALANCED METHOD).įigure 1. Thus, the amplitude and temporal characteristics of an entire signal or parts of a signal can be simultaneously measured and observed, as well as the parameters of random signals or signals that appear only once and are not prolonged. From it can be determined the polarity, amplitude, and duration of the signal.Īn oscillograph is frequently calibrated in volts on the vertical scale of the tube’s screen and in seconds on the horizontal scale. An oscillogram usually depicts the shape of an electrical signal with respect to time. The cathode ray produces a graphic image-an oscillogram-on the tube’s screen that can be observed, measured, and photographed. The electrical signals that represent the parameter or function are fed to two mutually perpendicular pairs of deflection plates in a cathode-ray tube. An instrument for observing the relationship between two or more parameters or functions, which can be electrical or convertible into electrical impulses.
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