ECEN 2612RLC Phasors (10.0 points)Lab #4

Name:

Partner:

Procedure:

  1. Set up the circuit shown with L=90mH, 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.
  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)

  1. 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 is 5Vrms. What is its peak amplitude? What is its peak to peak amplitude? (1.0 point)
  2. Still using the DMM as an AC voltmeter, measure vL,vC, and vRwithout 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)

  1. Connect an oscilloscope to the circuit; connect vg to CH 1 and vC to CH2. Use 2 V/DIV vertically with both baselines (zero levels) at the center gridline. Adjust the horizontal scale factor to display 1to2 full periods of the waveforms. Set the trigger source to CH 1 (vg), the trigger slope to (+), and the trigger level to 0 V. (Is it already set by default?) The CH1 display (vg) should now look like a pure sine wave. The CH 2 (vC) display should show a sinusoidal wave of different amplitude 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 traces in order to get good precision in the following measurements. Describe the difference between “accuracy” and “precision.”

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 =0, what is the phasor for vg(t) and what is the phasor for vC(t)?

  1. 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)
  2. 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)
  3. Convert the four measured phasors to rectangular form 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)
  4. 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 information. Tabulate your results to compare them. (1.0 points)

* Note: In the measurements for this lab, you need to remember grounding and phase problems 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 interchanges being made in steps 6 and7. Your instructor can explain this to you if you do not remember it.

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: Vrms = Vp / √(2) and Vpp = 2 Vp )

REPORT: 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!

P.Munro 28-Jan-2015 05:22 PMPage 1 of 2