Phase Measurement
When sinusoidal voltages simultaneously applied to vertical and horizontal plates, the pattern, appearing on the CRT is called as Lissajous pattern in this method the standard known frequency is applied to X-plate or horizontal plate. The resulting pattern appeared on the screen depends on phase relationship between the two frequencies.
Equal voltages of same frequency but of different phase angles- cause the pattern to vary from a straight diagonal line to ellipses of different eccentricities. The sine of the phase angle between the voltages is given by equation,
SinĪ = y1 /y2 = x1/x2
Equal voltages of same frequency but of different phase angles- cause the pattern to vary from a straight diagonal line to ellipses of different eccentricities. The sine of the phase angle between the voltages is given by equation,
SinĪ = y1 /y2 = x1/x2
As shown in figure 6.1 the gains of horizontal or vertical amplifiers are adjusted so that ellipse fits exactly into a square marked by lines on the screen.
Frequency Measurement
Lissajous pattern also helps to measure frequency. The signal whose frequency is to be measured is given I F-plates or vertical plates and the signal whose frequency is given to X-plates or horizontal plates. Now the know frequency or standard frequency is adjusted so Lissajous patterns can be obtained on the screen which depends on the ratio of two frequencies. In the given figure (2), Let, fv - Unknown frequency signal applied to vertical plates. fh - Known frequency signal applied to horizontal plates.
Two lines are drawn, one vertical and one horizontal so that they do not pass through any intersection o Lissajous pattern. Then the number of intersections of the horizontal and vertical lines with the Lissajous patterns and counted separately.
So after finding the tangencies if we know we can easily calculate the unknown frequency applied to vertical plate. All electronic circuits in the oscilloscope like attenuators, time base generators, amplifiers cause some amount of time delay while transmitting signal voltage to deflection plates. We also know that horizontal signal is initiated or triggered by some portion of output signal applied to vertical plates of CRT. So the delay line is used to delay the signal for some time in the vertical section of CRT.
So after finding the tangencies if we know we can easily calculate the unknown frequency applied to vertical plate. All electronic circuits in the oscilloscope like attenuators, time base generators, amplifiers cause some amount of time delay while transmitting signal voltage to deflection plates. We also know that horizontal signal is initiated or triggered by some portion of output signal applied to vertical plates of CRT. So the delay line is used to delay the signal for some time in the vertical section of CRT.
