Download Using a cathode ray oscilloscope (CRO) A CRO is a vital tool in the

P2 4.1a – Student practical sheet
Using a cathode ray oscilloscope (CRO)
A CRO is a vital tool in the measurement of electrical signals. It gives far more information than a
simple voltmeter.
Aim
To learn how to set up and use the controls on a CRO so that it can be used to measure amplitude
and frequency of waveforms.
Equipment
●
power supply with a.c. and d.c. outputs up to 12 volts
●
CRO
●
leads
●
tuning fork
●
microphone
●
squared paper
Safety
●
Be careful of trailing leads from power supplies and CROs if there is not much space to
work in.
What you need to do
1
Your teacher will have given you some instruction on how to use the CRO. Collect the
equipment and make sure the power supply is turned off.
2
Connect the yellow a.c. output terminals on the power supply to the input of the CRO.
3
Turn the voltage to minimum and turn the power supply on.
4
Increase the voltage to about 5 V.
5
Use the timebase control and Y sensitivity to get a trace on the screen.
6
Adjust the timebase so that there is a clear wave visible. Set the timebase to ‘cal’ (calibrated).
7
Use the timebase to measure the time for one complete wave. Record this time, making sure
you check the timebase control position.
8
Set the voltage on the power supply to 2 V. Use the voltage sensitivity control to make the
wave as big as possible while still fitting on the screen. Record the peak voltage of the wave
form. Record both of these voltages in a suitable table.
9
Repeat the measurement for voltages up to 12 V in 2 V steps. You may have to change the
voltage sensitivity control.
10 Make sure that the input selector is set to d.c. and repeat the measurements but use the d.c.
output of the power supply (the red and black terminals).
11 Unplug the power supply from the CRO and switch it off.
12 Connect the microphone to the CRO and check that you get a signal when you click your
fingers near it. You may need to change the Y sensitivity to get a visible signal.
13 Tap the tuning fork and hold it near the microphone.
14 Accurately draw the trace that you get on a piece of squared paper.
15 Repeat the measurement for two other tuning forks.
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P2 4.1a – Student practical sheet
Using the evidence
1
Check that the time you wrote down for the period of the wave from the power supply is 0.02 s
or 20 ms. (1 mark)
2
Check the cathode ray oscilloscope voltage against the power supply voltage for the a.c.
supply and comment on how accurate the power supply voltage scale is. (1 mark)
3
Check the cathode ray oscilloscope voltage against the power supply voltage for the d.c.
supply and comment on how accurate the power supply voltage scale is. (1 mark)
Evaluation
4
Check that you have measured the period and frequency accurately with your teacher.
(2 marks)
Extension
5
Connect the microphone to the CRO and check that you get a signal when you click your
fingers near it. You may need to change the Y sensitivity to get a visible signal.
6
Tap the tuning fork and hold it near the microphone.
7
Draw the trace that you get accurately on a piece of squared paper.
8
Repeat the measurement for two other tuning forks.
9
Use the traces for the tuning forks and the timebase to calculate the period and the frequency
of the sound wave created by the tuning fork.
10 Try this experiment with a guitar and use the CRO to tune the guitar accurately. (10 marks)
Sheet 2 of 2
208
© Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free.