ECE 201L Circuit Analysis Laboratory
Lab 4

This lab provides experience with capacitors, and the bench function generator and oscilloscope.

No suggested report format is provided.

Do the following exercises. Report your results in a Word document. Submit a printed copy (and the Word file to Isidore).

  1. Capture three samples of output from the function generator: sine wave, square wave, and triangle wave. Show the measured rms voltage and frequency on the oscilloscope image. See example below:

    Use a multimeter set to AC volts to measure the rms voltage. Compare the results to the oscilloscope reading.

  2. Choose a resistor of 1-50kΩ and three capacitors of 10 nF - 1 µF covering perhaps a factor of ten range of values. Measure the resistance on the impedance meter and the bench multimeter. Tabulate the values and the nominal value.

    nominalimpedance meterbench meter



    Which measured value seems more precise?

    Measure each capacitance on the impedance meter and from the rise time measurement described below. Tabulate the values and the nominal value.

    #nominalimpedance
    meter
    calc from
    rise time
    C1


    C2


    C3


  3. Construct the following RC circuit, using one of the capacitors above.

    Set the signal generator for a square wave. Adjust the oscilloscope to obtain a display similar to that shown below. The top trace is the signal generator output (node 1), and the bottom trace is the voltage across the capacitor (node 2).

    Display the rise and fall times on the measurement line. Capture at least one image to include in your report.

    Calculate the time constant from the rise/fall times, trise = 2.2 τ. Also calculate the time constant τ = RC. Explain or discuss any differences between these calculations.

  4. Repeat the measurement above for one capacitor but using at least three different resistors, from 500Ω – 20KΩ. Plot the rise time vs. resistance and find the x-intercept of the trend line. This should be the output resistance of the signal generator and should be added to the resistance value when calculating capacitance from rise time. How does this affect the calculated capacitance in the previous exercise?

  5. Make rise time measurements for your three capacitors and complete the table of measured capacitance values above.

  6. Measure the capacitance of the following arrangements, using rise time and the impedance meter.

    ABCD

    Calculate the expected value using the capacitance values for individual capacitors that you determined previously. Tabulate measured and calculated values.

    groupimpedance
    meter
    calc from
    rise time
    calculated
    from theory
    A


    B


    C


    D


  7. Build the circuit shown below, using the same resistor and capacitor as in exercise 4 above. In this exercise, set the signal generator for a sine wave.

    Measure the AC response (as described below) using the same frequency as for the square wave measurements previously. Then vary the frequency until the phase shift is 45° and record the AC response again. The gain is the ratio of output amplitude voltage to input amplitude voltage (Vout / Vin).

    capacitorFrequencyVin VoutRatio (gain)Phase
    C1










    C2










    C3










    To determine the AC response, you will need to record the following measurements from the oscilloscope.

    These measurements can all be made using the electronic tools in the oscilloscope. The image below shows a sample measurement. The input waveform is on the top and the output waveform is on the bottom.


Maintained by John Loomis, last updated 18 October 2012