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Oscilloscope Voltage & Phase Measurement

The document describes how to use an oscilloscope to measure voltage, frequency, period, and phase difference of signals. It provides examples of measuring the peak-peak voltage of waveforms using the volts/div setting. It also describes how to determine frequency from period measurements and how to calculate phase difference by measuring divisions between waves. Lissajous patterns created by applying signals to both oscilloscope axes are discussed for discerning frequency ratios and measuring phase angles between signals of the same frequency.

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707 views8 pages

Oscilloscope Voltage & Phase Measurement

The document describes how to use an oscilloscope to measure voltage, frequency, period, and phase difference of signals. It provides examples of measuring the peak-peak voltage of waveforms using the volts/div setting. It also describes how to determine frequency from period measurements and how to calculate phase difference by measuring divisions between waves. Lissajous patterns created by applying signals to both oscilloscope axes are discussed for discerning frequency ratios and measuring phase angles between signals of the same frequency.

Uploaded by

NEXUS BLADE
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as DOCX, PDF, TXT or read online on Scribd
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Oscilloscope Application

(a) Voltage Measurement

The most direct voltage measurement made with an oscilloscope is the peak-peak value. The
rms value of the voltage can easily be calculated from the peak to peak measurement if desired.
The peak to peak value of voltage is compute as

Vp-p = (vertical p-p division) x volts/div

Example 1

Figure 3: The peak-peak voltage of a waveform is measured by multiplying the


VOLTS/DIV setting by the peak-peak vertical divisions occupied by the waveform. The
time period is determined by multiplying the horizontal divisions for one cycle by the
TIME/DIV setting.

Refer to figure 3, find the peak-peak voltages for each wave.

Wave A : Vp-p =(4.6 divisions) x 100 mV = 460 mV


Wave B : Vp-p = (2 divisions) x 100mV = 200mV

(b) Period and frequency measurement

The time period of a sine wave is determined by measuring the time for one cycle in
horizontal divisions and multiplying by setting of the time/div control

Period, T = (horizontal divisions / cycle) (time / div)


Frequency, f =1/T

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(c) Phase difference measurement

Phase difference, θ = (phase difference in divisions) x (degree/div)

Example 2
The phase difference between two waveforms is measured by the method illustrated in figure 4.

Figure 4

Each wave has a time period of 8 horizontal divisions, and the time between commencements of
each cycle is 1.4 div

one cycle = 8 div = 360o


 1 div= 45o

Thus, the phase different is

θ = (1.4)(45o/div)
= 63o

5
Example 3
Determine the amplitude, frequency and phase difference between two waveform illustrated in
figure 5.

TIME/DIV
TA

VA VB
VOLTS/DIV

TB

Figure 5
Solution
VA peak-peak = (6 vertical div) x (200mV/div) = 1.2 V
TA = (6 horizontal) x (0.1 ms/div) = 0.6 ms
fA = 1/T = 1667 Hz

VB peak-peak = (2.4 vertical div) x (200mV/div) = 480 mV


TB = 0.6 ms
fB = 1667 Hz

one cycle = 6 horizontal div = 360o


 1 div= 60o

Phase difference, θ = 1 div = 60o

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LISSAJOUS PATTERNS
(a) Frequency measurement

If we apply input signal to both horizontal and vertical deflection plates of x-y oscilloscope
and time base generator is disconnected, it forms a vector pattern that allows us to discern the
relationship between the two signals. Such diagram are called Lissajous pattern.

F  number of times tangent t ouch top or bottom


Y
F number of times tangent t ouch other side
x
number of horizontal tangencie s

number of vertical tangencie s
or  number of positive peaks
number of right hand side peaks

where FY = frequency of signal applied to Y-plates (vertical)


FX = frequency of signal applied to X-plates (horizontal)

Horizontal tangencies

tangent

tangent
Vertical
tangent

2:1 3:1 1:3

Figure 6 Lissajou patterns with different frequency ratios

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Figure 8: Lissajou Pattern

(b) Phase Angle computation

Oscilloscope can also be used in the X-Y mode to determine the phase angle between two signals
of the same frequency.

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Figure 7: Lissajous patterns for selected phase angle

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Y1 Y2

X1

X2

Figure 8: Determination of angle of phase shift

The phase angle:

sin   Y1  X 1
Y X
2 2
where:
θ = phase angle in degrees
y1= Y-axis intercept
y2= maximum vertical deflection

Figure 9

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Example 4
If the distance y1 is 1.8 cm and y2 is 2.3 cm, what is the phase angle?

Solution
sin   y 1
y2
 1.8

 2.3
 0.783
  51.5o

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