Laboratory 1 et201

ET201 - Electrical Circuits

LABORATORY 1 AC VOLTAGE MEASUREMENT

1.0) OBJECTIVES:

At the of the lab, students should be able to :

1.1 Identify common oscilloscope controls

1.2 Display AC waveform on an oscilloscope

1.3 Measure the peak-to-peak voltage, the peak voltage, frequency and the periodic time of AC waveform

2.0) EQUIPMENTS:

2.1 Oscilloscope

2.2 Function generator

2.3 Multimeter

3.0) DESCRIPTION AND BACKGROUND

Voltage Measurements

Voltage is the amount of electric potential, expressed in volts, between two points in a circuit. Usually one

of these points is ground (zero volts) but not always. Voltages can also be measured from peak-to-peak from the

maximum point of a signal to its minimum point. You must be careful to specify which voltage you mean.

The oscilloscope is primarily a voltage-measuring device. Once you have measured the voltage, other

quantities are just a calculation away.

Figure 1 shows the voltage of one peak, Vp and the peak-to-peak voltage Vp-p, which is usually twice Vp.

Use the rms (root-mean-square) voltage, Vrms to calculate the power of an AC signal.

Figure 3.1: Voltage Peak and Peak-to-peak Voltage

You take voltage measurements by counting the number of divisions a waveform spans on the oscilloscope's

vertical scale. Adjusting the signal to cover most of the screen vertically, then taking the measurement along the

center vertical graticule line having the smaller divisions makes for the best voltage measurements. The more

screen area you use, the more accurately you can read from the screen.

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Figure 2: Measure Voltage on the Center Vertical Graticule Line

Formula:

Time and Frequency Measurements

You take time measurements using the horizontal scale of the oscilloscope. Time measurements

include measuring the period, pulse width, and timing of pulses. Frequency is the reciprocal of the period,

so once you know the period, the frequency is one divided by the period. Like voltage measurements,

time measurements are more accurate when you adjust the portion of the signal to be measured to cover a

large area of the screen. Taking time measurement along the center horizontal graticule line, having

smaller divisions, makes for the best time measurements. (See Figure 3.)

Figure 3 : Measure Time on the Center Horizontal

Graticule Line

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Formula:

4.0) PROCEDURES :

1. Connect output from function generator to channel 1 oscilloscope as shown in Figure 4.1

Figure 4.1

2. Set the frequency of the function generator to 100 Hz and the voltage V1 to 6V as indicated on the multimeter

3. Set the main time/div setting to 20ms/div and delay time/div setting to 10ms/div. Draw the waveform as seen on

the screen, in Figure 5.1. Measure the peak-to-peak voltage, the peak voltage and the periodic time of

waveform.

4. Change the delay time/div setting to 5ms/div. Draw the waveform in Figure 5.2

5. Then change the main time to 1ms/div. Draw the waveform in Figure 5.3.

6. Measure the peak-to-peak voltage, the peak voltage and the periodic time of waveform for step 4 and 5.

7. Set the delay time/div back to 10ms/div. Increase and decrease the frequency of the applied voltage. Write your

observation.

3

Function Generator

Osciloscope


5.0) RESULTS:

5.1 For step 3

Figure 5.1

Vp-p = _______________________________________________________

Vp = _______________________________________________________

T = _______________________________________________________ (8m)

5.2 For step 4

Figure 5.2

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Vp-p = _______________________________________________________

Vp = _______________________________________________________

T = _______________________________________________________ (8m)

5.3 For step 5

Figure 5.3

Vp-p = _______________________________________________________

Vp = _______________________________________________________

T = _______________________________________________________ (8m)

Observation

.

.

.

.

Lecturer’s name:

Signature : Date:

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QUESTION

1. Calculate the rms voltage, average voltage, peak factor and form factor for each waveform in step 3 and 4

(8m)

2. Determine the average value of a waveform that measured 16Vp

(2m)

3. What is the frequency of a waveform that has a period of 200µs?

(2m)

DISCUSSION

(5m)

CONCLUSIONS:

(2m)

Lecturer’s name :

Signature : Date :

Score :

6


;7

Laboratory 1 et201

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