HET183 Electronics, Telecommunications Systems and
ProjectsTitle: The Cathode Ray Oscilloscope (CRO)Aim: To understand
the way Cathode Ray Oscilloscope (CRO) works and obtain graphical
measurements of the signals.Introduction: The CRO is used to show
and make measurement on the amplitude and frequency of the
electrical signals. The signal can be observed on the screen of the
oscilloscope where the x-y graph of voltage or current on the
y-axis against time on the x-axis. A signal generator can control
the amplitude and frequency of the generated signal to the
CRO.Method:Before the measurements are taken, the probe is
connected to the oscilloscope whereas the ground terminal is
connected to the ground.Equipments: Oscilloscope, signal generator
and probe.Procedure:1. After the oscilloscope is switched on, the
display screen and all the controls such as the vertical deflection
controls and trigger controls are observed and taken note. 2. The
probe is set to x1 and plugged into Channel 1 while the probe tip
and reference is connected to the PROBE COMP terminals. 3. A
functional check is performed before measurements are taken to
ensure CRO is operating correctly.4. The autoset button is pushed
to obtain a waveform with 5V peak to peak at 1kHz.5. The vertical
deflection control is being adjusted to 2 volt/div while its
horizontal deflection control l is adjusted to 100 s/div. 6. The
signal generator is switched on and linked with the tip and
reference of the probe of the oscilloscope. 7. The frequency on the
signal generator is adjusted to 2 KHz and the sine wave is
chosen.8. The output on the signal generator is adjusted so that 5
Vpp is shown on the display screen of the oscilloscope. 9. The
waveform formed on the oscilloscope is observed and recorded. 10.
The vertical position control is adjusted until a new waveform is
formed and recorded.11. Other waves such as square wave and
triangle wave are chosen and the waveforms are recorded. 12. Each
waveforms recorded are measured to determine its amplitude,
frequency and period.13. Next, the vertical deflection control,
horizontal deflection control, amplitude control and frequency
control are adjusted variedly, and the changes for each wave are
recorded respectively. 14. Subsequently, connect another signal to
Channel 2. The display of plus and minus of the two signals are
observed.15. The x-y option is pushed and the observation is
observed. Observations:
Figure 1: Sine wave
Figure 2: Square wave
Figure 3: Triangle wave
Figure 4: Combination between two signals (+)
Figure 5: Combination between two signals (-)Discussion:The
vertical deflection control is used to centre the trace of the
signal on the screen and the frequency of the waveform is varied as
the time-base setting is changed. As shown in figure 1, 2 and 3,
the CRO can show three types of waveforms which are sine wave,
square wave and triangle wave. The x-axis and y-axis of the screen
shows the time and voltage respectively. As the x-axis is adjusted
to100 s/div and y-axis to 2 volts/div, while the signal generator
is adjusted to a frequency of 2kHz, the peak to peak voltage shown
for the three waveforms is around 5V shown on the CRO. The period
can be calculate using the formula, f=1/T, where f is the frequency
of the signal (2kHz) and T is the period. As a result, the period
of the waveforms is about 500 s.When the amplitude control of the
signal generator is changed to higher amplitude, the height of the
waveforms increased and vice versa when changed to lower amplitude.
When the frequency control of the signal generator is adjusted to
higher frequency, the number of complete waveforms increased and
vice versa when adjusted to lower frequency. As the volts/div
control of the CRO is decreased, the data are collected with higher
sensitivity and therefore the result obtained is more accurate. For
example, when the volts/div control is adjusted from 2 volts/div to
1 volts/div, the number of division occupied by the waveforms on
the y-axis will increase by double and the waveforms will increase
in height without changing the actual amplitude. With that, the
data can be calculated with higher accuracy. As the time-base
control of the CRO is increased, more number of complete waveforms
is shown on the screen. For example, when the time-base control
changed from 250 s/div to 500 s/div, the number of complete
waveforms is doubled.When the second signal is connected, there are
two signals formed on the screen and display options such as plus
and minus can be chosen. The results of the combination between the
both signals can be obtained in the middle of the screen as shown
in figure 4 and 5.As for when x-y option is selected, the signal is
plot against another signal. As a result, one loop appeared on the
screen and the shape changed from time to time. It changes from a
straight line to the shape of ellipse and later a circle. The
result is known as the Lissajous figures and the shape will show
the phase differences between the two signals.Conclusion:CRO is a
signal analyzer and the signal formed can be used to determine the
amplitude, frequency and period of a certain signal. Besides that,
the control option on the CRO can be adjusted to form the most
suitable waveforms on the oscilloscope for more accurate
determination. The CRO also have other functions such as the plus
and minus of two signals as well as to discover the phase variance
among several input signals by using the x-y option.Amy Chin Swin
Yee (4302435), Caleb Bong Teck Paw (7440596), Hannah Wong Sze Yee
(7439423)