Lab 9 - The Oscilloscope and Function Generator

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Algonquin College *

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9104

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Electrical Engineering

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Apr 3, 2024

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ELN9104 Lab 9 – The Oscilloscope and Function Generator Purpose: The purpose of this lab is to become familiar with the basic functions of the oscilloscope and the function generator. Materials and Equipment:  Digital oscilloscope  Oscilloscope probes  BNC to allegator cables Procedure: 1. Turn on your oscilloscope and follow the instructions to reset the scope to factory settings. Instructions are located in Brightspace in a handbook for your oscilloscope. 2. Set up your oscilloscope probes: a. For each probe, remove the protector tip and replace it with the retractable tip b. Install the orange marking rings on just one of your probes as shown in figure 1c (this will be your Channel 1 probe for ever). Figure 1a Figure 1b Figure 1c Probe Compensation 3. Complete the probe compensation for each oscilloscope probe: a. Connect the BNC connector end of one of your probes to channel 1 and clip the other end to the 2V clip as shown in figure 2a. Note: all scopes have a compensation pin and the voltage may differ from manufacturer to manufacturer. b. Slide the red button on the probe to the 10X setting c. Press the Channel 1 button and set the probe voltage multiplier to 10X. Figure 2a Figure 2b Figure 2c

ELN9104 Lab 9 d. Using the volts per division scale , set channel 1 to 500mV per division. e. Adjust the position to put the square wave in the middle of the screen. f. Adjust the time per division scale so that you can see two periods of square waves. g. Your probe should give a sharp square wave, as shown in Figure 2B. If your square wave looks more like Figure 2C show your professor, who can help you to adjust the signal. h. Follow steps a-f for your other probe. When complete, reset both channels to 1X. Figure 3: Gwinstek Oscilloscope This clip is connected to earth ground! Wherever you connect it in your circuit will become earth ground for your circuit. Important note!

ELN9104 Lab 9 Measuring Voltage 4. Setting up a signal on the function generator: a. Connect the BNC to alligator cable to the function generator. b. Using the oscilloscope probe connected to CH1 of your scope, slide the red switch to 1X and connect the probe to the BNC to alligator cable. The red alligator clip should connect to the retractable clip and the black alligator cable should connect to the earth ground clip. c. On your scope, double check that the voltage multiplier is set to 1X and set the coupling to AC. d. Your function generator is your “AC power supply”. The number on the LED screen is the frequency of the function, adjust the frequency to 1kHz. e. Choose the sine wave from the function type. f. At this point, you don’t know the amplitude of the signal, you will need to measure this using the scope. Adjust the position of the signal so that it is in the middle of the screen. Then adjust the volt per division so that you can see the full sinewave on the screen, and adjust the time per division to 200µs. (You should see almost two full periods of the sinewave) Note: If your signal appears to be moving across the screen, you will need to adjust the trigger value, consult the Oscilloscope Handbook located in Brightspace for your scope. 5. Setting up the amplitude of your signal: a. Read the volts per division on your scope, this can typically be found in the bottom of the screen. Add this value to Table 1. b. Count the number of squares you have from peak to peak for your signal and add this to Table 1. c. Multiply the number of squares by the volts/division to determine the magnitude of your signal. Frequency DC Offset Amplitude Function type Figure 4: function generator Attenuation or Voltage reduction

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ELN9104 Lab 9 Table 1 Volts/division Number of squares Vpp of signal 1v 6.8 6.84v d. Adjust the volts/div to 500mV. e. Adjust the amplitude on the function generator until the signal spans 4 squares peak to peak. Your voltage should be approximately 2V pp . 6. Use the horizontal cursers to measure the peak to peak voltage. Line the cursers up so they just touch the max and min points of the signal. The peak to peak voltage will be the difference between the two lines and will typically be seen as a Δ value on the screen of the oscilloscope. 7. Use the auto measure function on the oscilloscope to measure V pp . Does your scope convert the measurement to V rms ? If so, record that value too, if not calculate the V rms value. Complete Table 2 for the different target voltages. Note: you may need to use the attenuation function on the function generator to set smaller voltages. Table 2: Target voltage V pp Volts/div Number of squares from peak to peak V pp measured using squares V pp measured using cursors V pp measured using auto measure function V rms measured or calculated 2 V pp 500mV p 4 2v 2v 2v 710mV 0.8V pp 500mV 1.6 0.8 0.8 0.8 267 6 V pp 1 6 6 5.96 6 2.06v 5 V rms 1 5 5 5.02 5.02 1.73 Measuring period and frequency 8. Set your voltage magnitude to 1 V rms . Your function should still have a frequency of 1kHz. Record the frequency reading on the generator and your current time/div settings in Table 3. 9. Count the number of squares for 1 period of the cycle and calculate the period and frequency. Recall: f = 1 T 10. Using the vertical cursers, measure the period and calculate the frequency. 11. Using the auto measure functions, measure the period and frequency. 12. Add measured and calculated values from steps 9-11 in Table 3. 13. Complete Table 3 for additional frequency values If a voltage is shown with the unit V , with no subscript, it is implied to be the RMS voltage. Voltages that are measured peak to peak or from the 0V reference line to the peak, will be shown as V pp or V p respectively.

ELN9104 Lab 9 Target f Time/div # of squares for 1T T measured using squares f calculated T measured using cursers f calculated T measured using auto measure f measured using auto measure 1 kHz 200us 5 1ms 1KHz 982us 1.0183 KHz 500us 1.003 KHz 20 kHz 10us 5 50us 20 KHz 50us 20 KHz 49us 19.98 KHz 60 Hz 5us 3.3 16.5ms 60.60 KHz 16.7ms 59.88kHz 16.6ms 60 KHz Measuring a DC offset 14. Return your signal back to 1 V rms and 1 kHz. Set the volts/div to 2V. 15. Position your signal to the bottom of your screen. Change the coupling to DC. 16. Using the DC Offset setting on your function generator set a DC offset for your signal. Notice how the signal moves higher on the screen. Set the signal towards the top of the screen and measure the DC offset. Note 1: You have just added a DC value to the signal. Note 2: If your signal appears to be moving across the screen, you will need to adjust the trigger to the new position of the signal. Consult the Oscilloscope Handbook located in Brightspace for your scope for more details. a. Take note of where your reference is and count the number of squares your signal has jumped. b. Multiply the number of squares by the volts/div to find your DC offset. c. You can also use the cursers to measure the DC offset as shown in Figure 5. d. Complete Table 6 with your findings. e. Switch the coupling on the scope to AC, what did you notice happened to your signal? f. Play with the DC offset on the function generator, what happens to the signal as the DC offset is adjusted while on AC coupling? Table 6: Volts/div Number of squares signal jumped DC Offset measured with squares DC Offset measured with cursers 2 5.5 11v 11v

ELN9104 Lab 9 Understanding the difference between the scope and the DMM 17. Set your signal to 60 Hz and 5 V rms . Measure the signal using the oscilloscope and record the value in Table 7. Convert the V pp to V rms and record that value too. 18. Disconnect the BNC to alligator cable from the oscilloscope probe and measure the signal using the DMM. Connect the alligator clips to the banana cables you use with the DMM. Note: the DMM will read the RMS voltage. 19. Record the RMS voltage from the DMM in Table 7. 20. Set the function signal to 60 kHz and repeat steps 17 through 19 for each DMM at your station. Record the brand, the manufactured name and model number of the DMM in Table 7 with your results. Did you notice a difference in voltage measurements? What did you notice? Table 7: frequency V pp measured using scope V rms measured using scope or calculated V rms measured using DMM % Difference between scope and DMM value 60 Hz 15.2v 5v 5.02v 0.4% Figure 5: DC offset 4 squares at 1 V/div 4V DC offset New reference Original reference

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ELN9104 Lab 9 60 kHz DMM Brand 14.4v 5.02v 1.55v 69.12% 60 kHz DMM Brand same same 21. Calculate the % difference using the following formula: % differnece = | V scope − V DMM | V scope × 100% 22. For each DMM used, search the internet for the specification sheet for the meter and check the AC voltage specification vs frequency performance. What happens to the percentage accuracy as frequency increases? DMM model Expected error at 60kHz GDM-8034 Maybe these are not made for high frequency. Discussion Question: What can you conclude about the different multimeters at your station? At what frequency ranges can you use a DMM to take voltage measurements? Conclusion: DMM are not precise at high frequency.

ELN9104 Lab 9