EE 100 – Electrical Engineering Concepts I
Lab 4
Revision 10/01
Name: ___________________________
Partner: ___________________________
Date: ___________
TA: ___________________________
RC Circuits
Filters
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EE 100 Lab 4: Exploring RLC Circuits and Filter Design, Lab Reports of Electrical and Electronics Engineering
A lab manual for electrical engineering concepts i (ee100) students, focusing on capacitor and inductor filter circuits. It includes lab objectives, related reading, equipment list, and instructions for setting up and conducting experiments to measure time constants, filter frequency responses, and designing various types of filters. Students are expected to record data, calculate capacitance values, and create bode plots.
Typology: Lab Reports
Pre 2010
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EE 100 – Electrical Engineering Concepts I
Lab 4
Revision 10/
Name: ___________________________
Partner: ___________________________
Date: ___________
TA: ___________________________
RC Circuits
Filters
EE100 Lab 4 Grading Sheet
Lab Grade: _________ (90 maximum)
Presentation Grade: _________ (10 maximum)
(organization, clarity, neatness)
Total: _________ (100 maximum)
Grader’s Comments:
Hand in all lab and work sheets, either stapled securely or in a
folder.
Page 2 Lab 4 EE
Set the FG to generate 60 Hz, 4 Vp-p square waves. You can use the FG readout for your frequency setting, but you will need your o-scope to set the amplitude.
Open the o-scope software and use “Quick Load Setting 5” under the File Menu.
Use a 1k Memory Buffer and confirm that your probe attenuator switches are set to X10.
Set-up the o-scope for your voltage measurement; consider the following while setting up:
- You have a screen with ten vertical divisions to measure a 4 Vp-p signal, what V/div will give the largest amplitude display to work with and still stay on the screen?
- You’re working with a low-frequency signal; you don’t want to have such a high sample rate that you only see part of the cycle in the 1k memory.
Set your scope to trigger on Ch. A2 (which is VCA from Fig. 4-1) and try to get the one-cycle display in Fig. 4-2. Note that the intersecting cursors are the two trigger cursors.
Fig. 4-
It is important that you spend some time learning how various settings affect your display, since you will be doing this in every lab to follow. If you’ve made a real effort and still can’t get this display, refer to the settings in Fig. 4-3.
1.5.2 Measuring the Time Constant τ
NOTE: Section 6.1 of Hambley covers this circuit, and gives some additional mathematical background. In this section, we see that:
⎟
⎟ ⎠
⎞ ⎜
⎜ ⎝
⎛ = −
−τ^ t vc vb 1 e , where
τ= RC
In this exercise, we will determine the value of C by computing the time constant, τ, of the circuit from the VCA signal on our o-scope.
EE 100 Lab 4 Page 3
Fig. 4-
The time constant of the system is also the amount of time required for the system to reach
- 2 %
e
of its stable state after a change. In this circuit, it can be measured on either
the rising edge or falling edge of VCA. You will be using the horizontal scale to measure the time needed for the capacitor output to equal 63% of 4 volts.
You may want to view Ch. A2 only for this part of the exercise, although it’s not a requirement.
If you didn’t already, adjust the FG to make the maximum capacitor voltage exactly 4 Vp-p.
Measure the time for the capacitor voltage to rise by ( 0. 632 )( 4 )= 2. 53 V from its minimum
level. Note that, for greater accuracy, you can change the line thickness of your signal plots and cursors under the “Timing” pull down menu.
τmeasured = ______________
From this value, calculate the capacitance:
C (^) calculate = ______________ C (^) nominal = 1 uF % Error = ______________
1.5.3 Lowpass Filter Frequency Response
Change the circuit of Figure 4-1 to use a 1 K resistor and a 0.1 uF (#9109F) capacitor. We will input a 1 V 0-peak sinusoid into the filter and measure frequency and phase response of the circuit. NOTE: Make sure you change the components to these new values!
The break frequency for this filter should be RC
f (^) b
= Given your new values for R and C,
calculate what f (^) b should be for this filter.
f (^) b = _____________ Hz
Now test the filter to see if it behaves as expected. Input a 1 Volt 0-peak sinusoid over a frequency range from 0. 01 fb to 100 fb. Use the filter plotting sheets provided in lab to record
your data.
Measuring amplitude variation is pretty easy on the oscilloscope; measuring phase difference as a bit more involved. The easiest way to measure a phase shift is to place the vertical o-scope
EE 100 Lab 4 Page 5
This should be a resonant bandpass filter with center frequency LC
f 2 π
0 =^. The sharpness,
or quality, of the filter is measured by R
f L Q (^) s^0
=. Compute these values for the circuit of
Figure 4-5.
f (^) 0 = ____________ Hz
Q s = ____________
Now test the filter to see if it behaves as expected. Input a 1 Volt 0-peak sinusoid over a frequency range from 0. 01 fb to 100 fb. Use the filter plotting sheets provided in lab to record
your data.
What is the bandwidth of your filter? That is, what is the distance from the lower –3 dB point to the highest –3 dB point? (This is where the filter response is 0.707 volts 0-peak.)
If I wanted a sharper bandpass filter at the same center frequency, what component(s) would I adjust and in which direction?
Make bode plots of the filter magnitude and phase response to hand in with your lab.