The standard frequency is the adjusted unit the pattern appears as a circle or an ellipse, indicating that both signals are of the same frequency. CATHODE RAY EXPERIMENT DIAGRAM GENERATORAn accurately calibrated standard variable frequency source is used to supply voltage to the X plates, with the internal sweep generator switched off. Lissajous patterns may be used for accurate measurement of frequency.The signal, whose frequency is to be measured, is applied to the Y plates. when its slope is negative as in the figure(b), the phase angle is either between 90° and 180° or between 180° and 270°.įrequency measurement of cro or cathode ray oscilloscope : If the major axis of the ellipse lies in the first and third quadrants (i.e., its slope is positive) as in the below figure(a) the phase angle is either between 00 to 90° or between 270° to 360°.When the major axis of ellipse lies in second and fourth quadrants i.e. Referring to figure, the sine of the phase angle between the voltages is given by :įor convenience, the gains of the vertical and horizontal amplifiers are adjusted so that the ellipse fits exactly into a square marked by the lines on the graticule. Regardless of the two amplitudes of the applied voltages, the ellipse provides a simple means of measuring phase difference between two voltages. CATHODE RAY EXPERIMENT DIAGRAM SERIES(ii)) It is clear from the below figure, that for equal voltages of same frequency progressive variation of phase voltage causes the pattern to vary from a straight diagonal line to ellipses of different eccentricities and then to a circle, after that through another series of ellipses and finally a diagonal straight line again. If the Y voltage is larger, an ellipse with vertical major axis is formed while if the X plate voltage has a greater magnitude, the major axis of the ellipse lies along the horizontal axis. However, if the two voltages are not equal and/or out of phase an ellipse is formed. (ii) Two sinusoidal waveforms of the same frequency produce a Lissajous pattern, which may be a straight line, a circle or an ellipse depending upon the phase and magnitude of the voltages.Ī circle can be formed only when the magnitude of the two signals are equal and the phase difference between them is either 90° or 270°. On the other hand, a greater horizontal voltage makes the angle less than 45° with the horizontal. An increase in the vertical deflection voltage causes the line to have an angle greater than 45° with the horizontal. The angle formed with the horizontal is 45° when the magnitudes of voltages are equal. (i) A straight line results when the two voltages are equal and are either in phase with each other or 180° out of phase with each other. When two sinusoidal voltages of the same frequency are applied : Grab it now for very less price.Ī number of conclusions can be drawn from the above discussions. This textbook “ Electrical and Electronics Measurements by S. An ellipse is also obtained when unequal voltages of the same frequency are applied to the CRO. When two equal voltages of equal frequency but with a phase shift (I) (not equal to 0° or 90°) are applied to a CRO we obtain an ellipse as shown in the below figure. Thus when two equal voltages of equal frequency but with 90° phase displacement are applied to a CRO, the trace on the screen is a circle. Lissajous pattern with equal frequency voltages and zero phase shift.
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