Help Measured vs Calculated - Frequency Response

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Discussion Overview

The discussion revolves around discrepancies between measured and calculated frequency response in an electrical circuit involving a resistor, inductor, and capacitor. Participants explore the transfer function and gain at varying frequencies, with a focus on understanding the differences in results from measurements and simulations.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant reports a significant difference between measured output voltage and calculated values, noting that the maximum output voltage occurs at different frequencies (9254Hz calculated vs. ~1400Hz measured).
  • The participant provides details of their circuit parameters and transfer function, seeking assistance in reconciling these differences.
  • Another participant points out the distinction between angular frequency (ω) and frequency (f), suggesting this may clarify some confusion in the calculations.
  • A different participant calculates a gain of about 2 at the resonant frequency, which contrasts with the participant's measured gain of just under 17.
  • There is an inquiry about potential reasons for the differences in gain between measured and simulated results in pSpice.

Areas of Agreement / Disagreement

Participants express differing views on the accuracy of measurements versus calculations, with no consensus on the source of discrepancies. The discussion remains unresolved regarding the reasons for the differences in gain and frequency response.

Contextual Notes

Participants have not fully explored the implications of the relationship between ω and f, nor have they resolved the differences in gain calculations. The discussion also lacks clarity on the assumptions made in the measurements and simulations.

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I have a huge difference between what I'm measuring and what I'm calculating, since I can no longer check the circuit (and everyone in the class seems to be having the same problem as me) I'm going to assume it's the calculations.

I'm trying to calculate the response of the voltage over a capacitor, see the below diagram:
sClpH.png

R = 500Ω;
L = 100mH;
C = 0.1μF.

The voltage source is an AC 1V source whose frequency is changed from 10Hz to 10kHz in steps.

For the transfer function:
V2= 1/(jωC) * I
V1= (R+jωL+(1/(jωC)) * I

Which gives the transfer function:
H(jω) = 1/ (1-ω2LC+jωRC)

Apparently this function get the highest output voltage (ie. the functions maximum) at 9254Hz.
My measured results show that the the highest output is at ~1400Hz.

When I simulate this circuit in pSpice and do an AC Sweep, I get the maximum appearing at the same point (~1400Hz), which leads me to believe that my measured results are correct.
However the results obtained from pSpice only have a gain of about 2, whereas the gain for the measured results was just under 17.

I need to compare the results I obtained with some system, be it pSpice or equations and both of them aren't working for me. Below is the setup of the pSpice system.

Please help! If you can figure out where I'm going wrong, I'll try my hardest to award you an internet!

tNMAR.png

R2 = 0.5k
L2 = 100mH
C2 = 0.1uF
V11:
VOFF=VAMPL=TD=TR=PHASE = 0
AC = 1V
FREQ=10

Simulation settings: Linear
Total Pts: 1000
Start Freq = 10
End Freq = 10k
 
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Don't confuse ω with f. What's the relationship between ω and f?
 
So it is the angular frequency, that clears up what was wrong with my assumption about my equation being wrong, do you know anything about pSpice and why my gain might be different?
 
I don't know why your measured gain would be different from the calculated or simulated ones. I calculate a gain of about 2 (in the neighborhood of 6 and a bit dB) when the circuit is at its resonant frequency.
 
Weird, I suppose I'll just have to include that in my report, thanks for your help.
Here's your internet!
 

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