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ECEN 2612
RLC Phasors (10.0 points)
Lab #4
Name:
Partner:
Procedure:
1. Set up the circuit shown using L = 90 mH, C = 0.06 F, and
R = 1 k. Use a DC supply for the voltage source vg.
Using a DMM as a DC voltmeter, adjust vg to 5 V. Also,
measure and record the element values L, R, and C, using
the LCR and DM Meters with elements disconnected.
2. Using the DMM as a DC voltmeter, measure the three component voltages vL, vC, and vR, using
the polarities indicated on the circuit diagram. Set the DMM for at least 3-place precision. (Is it
already set by default?) Then do the following and answer the questions:
(a) Show how well the DMM readings (including vg) satisfy KVL.
(b) What is the effect of reversing the DMM leads when measuring vC? Describe how polarity
matters when measuring DC voltages with the DMM.
(1.0 point)
3. Replace the DC supply with a function generator. Be sure to use the Agilent 33120A. Adjust
the generator to produce a 3 kHz sine wave. Using the DMM as an AC voltmeter, adjust the
amplitude control of the generator until the DMM displays 5 V; since the DMM displays rms
values for AC signals, the amplitude of vg will be 5 Vrms. What is its peak amplitude? What is
its peak to peak amplitude?
(1.0 point)
4. Still using the DMM as an AC voltmeter, measure vL, vC, and vR without changing vg.
(a) Do the DMM readings (including vg) satisfy KVL? If you can explain your answer, give the
explanation. If not, so state; you will get another chance.
(b) What is the effect of reversing the DMM leads when measuring vC? Describe how polarity
matters when measuring AC voltages with the DMM.
(1.0 point)
5. Connect an oscilloscope to the circuit. Connect vg to CH 1 and vC to CH 2. Use 2 V/DIV
vertically with both baselines (zero levels) at the center gridline. Adjust the horizontal scale factor
to display 1 to 2 full periods of the waveforms. Set the trigger source to CH 1 (vg), the trigger
slope to (+), and the trigger level to 0 V. (Are these already set by default?) The CH 1 display (vg)
should now look like a pure sine wave. The CH 2 (vC) display should show a sinusoidal wave with
an amplitude different from CH 1 (vg) and a phase-shift wrt CH 1. Sketch or print the scope
display, and clearly label which waveform is which.
(1.0 point)
NOTE: Use the position and sensitivity controls properly to expand/reduce the trace displays in
order to get good precision in the following measurements. Describe the difference between
“accuracy” and “precision.”
P.Munro 27-Jun-2017 08:41 PM (save date)
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Measure the peak-to-peak amplitudes of vg(t) and vC(t). Then, using the 2-channel technique
where (Δ/T)*360˚ = θ (not the Lissajous method!) for measuring phase shift, measure the phase of


vC(t) with respect to vg(t). Assuming Vg = 0, what is the phasor Vg for vg(t) and what is the

phasor VC for vC(t)?
6. Physically interchange the positions of the capacitor and resistor in the original circuit and repeat
the step 5 measurements and calculations for the resistor, vR, with respect to vg. *
(1.0 point)
7. Physically interchange the positions of the capacitor and inductor in the original circuit and repeat
the step 5 measurements and calculations for the inductor, vL, with respect to vg. *
(1.0 point)
8. Convert the four measured phasors to rectangular forms and show that KVL works for phasors in
an AC circuit. Then sketch the four phasors in the complex plane (called a "phasor diagram") and
show how KVL works graphically.
(1.0 points)
9. The scope gives a "full" measurement of an AC voltage, while the DMM gives only a "partial"
measurement. Explain which part the DMM measures and how it is related to the oscilloscope
measurements. Tabulate your results to compare them.
(1.0 points)
* Note:
In the measurements for this lab, you need to remember grounding and phase concerns with respect to the
equipment being used. For example, the function generator you are using probably has a floating ground, while the
oscilloscope probably does not have a floating ground. That is the reason for the element interchanges being made in
steps 6 and 7. Your instructor can explain this to you if you do not remember it. That is, the signal and case grounds may
be the same or different.
Also note: You are instructed to measure “peak-to-peak” values with the oscilloscope because this gives better accuracy
when measuring scope waveforms. (Why would this be?) You must decide on converting values from pp to either rms or
peak so that your values are consistent when comparisons are made. The units of measured values should include a
designation to indicate these values, e.g., dc, pp, or rms. (REMEMBER for sinusoids: Vrms = Vp / √(2) and Vpp = 2 Vp )
REPORT: As always, keep a complete record of all data, results, observations, and answers to questions, written neatly
and legibly on the unlined side of standard engineering paper. Attach the lab sheet as a cover.
(2.0 points)
This report is due at the beginning of the next lab session to give you time to analyze and think about your work!
P.Munro 27-Jun-2017 08:41 PM (save date)
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