ECE 206 Lab: Oscilloscope and Signal Generator Use Cont.
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Laboratory Goals
q Familiarize students with oscilloscope phase shift measurements
q Locate the cutoff frequency (fc) for the RC, low-pass filter circuit
q Visualize zener diode characteristics using the oscilloscope
Pre-lab / lab reading
q For Lissajous curve explanation see: http://en.wikipedia.org/wiki/Lissajous_curve
q Presentation of Lissajous pattern https://www.youtube.com/watch?v=t6nGiBzGLD8
q Agilent 33220A 20 MHz Function/Arbitary Waveform Generator User Guide
http://www.keysight.com/en/pd-127539-pn-33220A/function-arbitrary-waveform-generator-20-mhz?pm=PL&nid=-536902324.536883183&cc=US&lc=eng
From this page select the Manuals(8) Link on the left under By Type of Content.
It should be the third item in the list.
q 3000X- Series Oscilloscopes User’s Guide, English (or language you want) published by Agilent Technologies,. (Copies of this reference book are available in the lab, or at the website)
http://www.keysight.com/en/pdx-x201849-pn-DSOX3052A/oscilloscope-500-mhz-2-channels?pm=rsc&nid=-32540.1150202&cc=US&lc=eng
Second Link under Manuals on left column under Key Product Information.
for the user guide of the DSOX3052A
q For the DSOX3032T user manual, User’s Guide for InfinitVision 3000T X-Series Oscilloscopes, find the second link under Manuals about 1/2 way down the left side of the page.
http://www.keysight.com/en/pdx-x202174-pn-DSOX3032T/oscilloscope-350-mhz-2-analog-channels?pm=rsc&nid=-32541.1150351&cc=US&lc=eng
Equipment needed
q Lab notebook, pen
q Agilent 54621A Digital Oscilloscope
q Agilent 33120A Function Generator/Arbitrary Waveform Generator
q 2 oscilloscope probes (from cabinets on west wall)
q 1 BNC/EZ Hook test lead
Parts needed
q Circuit breadboard
q Capacitor, mylar film, 0.1uF, 25V
q Resistor, 110 Ohm, ¼ Watt
q Zener diode, 1N4728, 3.3VDC (See TA or Instructor)
Lab safety concerns
q Make sure before you apply power to a circuit, all connections are correct, and no shorted wires exist.
q Do not short the function generator signal and ground connections together
q Do not touch the circuit wiring while power is applied to it
1. Pre-Lab Activities
q Create a table in your lab notebook similar to the one shown below:
Input Frequency / 10kHz / 12kHz / fc / 20kHzCalculated phase shift (degrees)
Measured phase shift (x-y mode)
Measured phase shift (x/t mode)
q Calculate the cut off frequency fc. fc will be a frequency point for measurements.
o The definition of the Cutoff Frequency is when the power in the signal drops to half of its maximum (-3dB).
o At this ½ power point the reactance of the capacitor equals the resistor’s value. 1/(2 * Pi * fc * C) = R so solve for fc.
q Calculate the expect phase shifts for the different frequencies. See Figure 2 below
o Using the phasor relationship principles from the Multisim Lab calculate the phase angle between the voltage on the voltage source and the voltage on the capacitor for each frequency (10 kHz, 12 kHz, fc, and 20 kHz.
Figure 1: RC Phasor Diagram
q Measure, calculate and record the phase shift at the frequencies listed in the table as directed below.
2. RC Circuit Construction and X-Y Phase Shift Measurement
q Measure the value of your resistor and capacitor, and recalculate the phase shift in the above table
q Construct the RC circuit shown below (Note that the CH 1 and CH 2 oscilloscope probe test points are shown)
q Adjust the signal generator to output a 1Vpp sine wave at 10kHz
q Connect the BNC end of the BNC/EZ Hook test lead to the function generator (marked as V1 on the schematic) OUTPUT
q Clip the red and black EZ Hook ends to the circuit input and ground connections respectively
q Clip the CH 1 oscilloscope probe and ground clip to the circuit input and ground connections respectively (This is the test point for the input waveform)
q Clip the CH 2 oscilloscope probe and ground clip to the circuit output and ground connections respectively (This is the test point for the output waveform, which is phase-shifted from the input waveform)
q Limit the bandwidth to reduce the noise. Press the [1] button then press the [BW Limit] button (3rd soft-key below the display).
q Repeat for Channel 2: [2] > [BW Limit].
q Now press the Y-Position knobs (under the [1] button and [2] button) to center the two waveforms.
q Adjust Vertical knobs so they are both set to the same values (Upper Left display readout)
q Press the [Mode/Coupling] button > [Noise Reject] soft-key (3rd under display)
q Press the Horizontal section’s [Horiz] button > [Time Mode] soft-key (1st under display) > Select X-Y. This produces an ellipse on the screen as shown in Figure 4-3 below.
q The vertical knobs can be adjusted to make the image as large as will fit on the Display. Ensure the two setting for channel 1 & 2 are the same.
q Make the measurements as shown in Figure 4-3.
q Calculate the degrees of phase shift using the formula sin (A/B)
q Record the result in your table
q Repeat the measurement for generator frequencies of 12kHz, fc, and 20kHz
q Use diagram below to calculate the phase shift from the measured values:
3. X/T Phase Shift Measurement Method 1
q Return the function generator output frequency to 10kHz
q Limit the bandwidth to reduce the noise. Press the [1] button then press the [BW Limit] button (3rd soft-key below the display).
q Repeat for Channel 2: [2] > [BW Limit].
q Adjust Display so both sine waves are visible with two or three cycles shown.
q Now press the Y-Position knobs (under the [1] button and [2] button) to center the two waveforms
q Press [Meas] button, then the [Type] soft-key (2nd under display).
q Scroll down the list using the [Push to Select] Knob until “Phase” is Highlighted and push the knob.
q Press the [Add Measurement] soft-key (3rd under display).
q Read the phase shift in the ‘Meas’ Window on the display.
q Repeat the measurement for generator frequencies of 12kHz, fc, and 20kHz (note that you need only change the input frequency, and record the phase shift value shown)
4. X/T Phase Shift Measurement Method 2
Figure 2: Time Based Phase Shift Measurement
q Return the function generator output frequency to 10kHz
q With everything set as at the start of the previous method (see above)
o Press the [Time Mode] soft-key and select the “Normal” setting
o If a two sine wave image doesn’t appear press [Auto Scale] button.
q Verify that the selected trigger Source is CH 1
q Adjust the image so you can make the measurements as shown in Figure 2: Time Based Phase Shift Measurement.
q Calculated the phase shift with the formula in Figure 2.
q Record the indicated phase shift value for this frequency in your table.
q Repeat the measurement for generator frequencies of 12kHz, fc, and 20kHz (note that you need only change the input frequency, and record the phase shift value shown)
5. Using the Oscilloscope to Visualize Zener Diode Characteristics
This oscilloscope setup allows you to see how a zener diode behaves as the input voltage varies sinusoidally.
In the X-Y mode, the I-V characteristics of the zener diode are shown on the oscilloscope. The x-axis represents the applied input voltage, and the y-axis represents the current through the resistor. Ask you T.A. to further describe the zener diode, and the curve you see on the oscilloscope.
q Construct the zener diode circuit shown below (note that the black or white banded end of the diode must connect to resistor R1)
q Adjust the signal generator to output an 11Vpp sine wave with a frequency of 100Hz
q Clip the red and black EZ Hooks to the anode end of the diode and circuit ground connections respectively
q Clip the CH 1 oscilloscope probe and ground clip to the anode end of the diode and circuit ground respectively
q Clip the CH 2 oscilloscope probe and ground clip to the cathode (i.e., the black-banded) end of the diode and circuit ground respectively
q Enable the X-Y mode of the oscilloscope per instructions for your scope.
q Use the CH1 and CH2 vertical position knobs to move the waveform to the middle of the screen (notice the CH 1 and CH 2 values show 0 volts when each channel is exactly centered on the screen)
q Adjust CH 1 vertical axis so that the waveform is as large as possible
q Create a Flash Drive copy of the oscilloscope screen using the instructions for the scope you are using and save the image as a bitmap or png image.
q Experiment with the circuit by reducing the input voltage. What happens to the waveform as you do this?
q Vary the frequency from 100Hz to 15kHz and look at the effect on the I-V characteristics. Note your observation in your report and provide your best explanation of the observed behavior
q Have the T/A check your results
q Unclip all connections to the circuit, then turn off the equipment
q Tear down the circuit and return all parts and leads to their proper place.
Before leaving the lab, take a few minutes to make sure all equipment and test leads are returned to your cabinet, and that you have cleaned up your work space.
4. Analysis
Write a brief summary report for labs (6) and (7). Be sure to also include the following topics:
For 6:
Based on your observations, does the AC voltage divider circuit behave the same as a DC voltage divider circuit?
What other features of the oscilloscope and function generator did you investigate? Explain what they are, and how they might be used for your circuits.
For 7:
Compare the measured and calculated phase shift values. Do the values generally agree? Explain possible reasons for any differences in the data.
Insert the waveform of the zener diode that you copied to a Flash drive or diskette. Label the points on the waveform where the diode begins to conduct current in the forward and reverse directions.
For both parts:
Explain any difficulties you had with these labs. (Please include any suggestions to improve them).