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)