Difference between revisions of "Lab 4 RS"

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#measure the phase shift between <math>V_{in}</math> and <math>V_{out}</math> as a function of frequency <math>\nu</math>.  Hint: you could use<math> V_{in}</math> as an external trigger and measure the time until <math>V_{out}</math> reaches a max on the scope <math>(\sin(\omega t + \phi) = \sin\left ( \omega\left [t + \frac{\phi}{\omega}\right]\right )= \sin\left ( \omega\left [t + \delta t \right] \right ))</math>.
 
#measure the phase shift between <math>V_{in}</math> and <math>V_{out}</math> as a function of frequency <math>\nu</math>.  Hint: you could use<math> V_{in}</math> as an external trigger and measure the time until <math>V_{out}</math> reaches a max on the scope <math>(\sin(\omega t + \phi) = \sin\left ( \omega\left [t + \frac{\phi}{\omega}\right]\right )= \sin\left ( \omega\left [t + \delta t \right] \right ))</math>.
  
  ''See question 4 about my phase shift measurements''
+
  ''See question 3 about my phase shift measurements''
  
 
=Questions=
 
=Questions=

Revision as of 07:03, 27 January 2011

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RC High-pass filter

1-50 kHz filter (20 pnts)

1. Design a high-pass RC filter with a break point between 1-50 kHz. The break point is the frequency at which the filter's attenuation of the AC signal goes to 0(not passed). For a High pass filter, AC signals with a frequency below the 1-50 kHz range will be attenuated .

TF EIM Lab4.png


To design low-pass RC filter I had:
[math]R=10.5\ \Omega[/math]  
[math]C=1.250\ \mu F[/math]

So

[math]\omega_b = \frac{1}{RC} = 76.19\cdot 10^3\ \frac{rad}{s}[/math]
[math]f_b = \frac{\omega_b}{2\pi} = 12.13\ \mbox{kHz}[/math]


2. Now construct the circuit using a non-polar capacitor.

3. Use a sinusoidal variable frequency oscillator to provide an input voltage to your filter.

4. Measure the input and output voltages for at least 8 different frequencies which span the frequency range from 1 Hz to 1 MHz.


Table1. Voltage gain vs. frequency measurements
ν [kHz] Vin [V] Vout [V] VoutVin
0.1
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
15.0
20.0
30.0
40.0
50.0
100.0
200.0


5. Graph the log(VoutVin) -vs- log(ν)

L4 volt gain.png

phase shift (10 pnts)

  1. measure the phase shift between Vin and Vout as a function of frequency ν. Hint: you could useVin as an external trigger and measure the time until Vout reaches a max on the scope (sin(ωt+ϕ)=sin(ω[t+ϕω])=sin(ω[t+δt])).
See question 3 about my phase shift measurements

Questions

1. Compare the theoretical and experimentally measured break frequencies. (5 pnts)

Theoretical break frequency: 12.13 kHz

The fit line equation from the plot above is  y=1.14+0.9101x. From intersection point of line with x-axis we find:

log(fexper)=1.140.9101=1.252
fexp=101.252=17.86 kHz


The error is:

[math]Error = \left| \frac{f_{exp} - f_{theor}}{f_{theor}} \right| = \left| \frac{17.86 - 12.13}{12.13} \right|= 32.08\ %[/math]

Error is pretty big. Probably is something wrong with RC measurements.

2. Calculate and expression for VoutVin as a function of ν, R, and C.(5 pnts)

We have:

1) Vin=I(R+XC)=I(R+1iωC)
2) Vout=IR


Dividing second equation into first one we get the voltage gain:

 VoutVin=IRI(R+1iωC)=iωRC1+iωRC


And we are need the real part:

|VoutVin|=(VoutVin)(VoutVin)=(iωRC1+iωRC)(iωRC1iωRC)=ωRC(1+(ωRC)2=ωRC(1+(2πνRC)2

3. Compare the theoretical and experimental value for the phase shift θ. (5 pnts)

The experimental phase shift is [math]\ \Theta_{exper} = (\omega\ \delta T)_{exper}[/math]
The theoretical phase shift is [math]\ \Theta_{theory}=\arctan\ \left (\frac{1}{\omega R C}\right )[/math]

4. Sketch the phasor diagram for Vin,Vout, VR, and VC. Put the current I along the real voltage axis. (30 pnts)

L4 phase diagram.png

5. What is the phase shift θ for a DC input and a very-high frequency input?(5 pnts)

Because a DC circuit doesn't have any oscillation there are no any phase shift.

6. Calculate and expression for the phase shift θ as a function of ν, R, C and graph θ -vs ν. (20 pnts)

From the phasor diagram above (question 4) the angle between vectors Vin and Vout given by

[math]\Phi = \arctan \ (V_C/V_R) = =\arctan \left( \frac{I \left(\frac{1}{\omega C}\right)}{IR} \right) = \arctan \left ( \frac{1}{\omega RC} \right )[/math]



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