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Second Contest — Parallax Forums

Second Contest

NewzedNewzed Posts: 2,503
edited 2005-03-15 03:18 in General Discussion
OK - let's have another contest.· This one should be easier.· Again, a two-part question.

It will be posted tomorrow, Sunday, as close to 12:00 EST as I can make it.· Look for it.· I'd sure like to give this EEPROM away.




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Sid Weaver
NEW! 4 MB EEPROM

http://hometown.aol.com/newzed/page4.html
·

Comments

  • NewzedNewzed Posts: 2,503
    edited 2005-03-13 17:02
    OK - here is the new question.

    I have a series RLC circuit connected across a source operating at 10VAC and 1.5KC.

    Allow two minutes for the circuit to stabilize.

    R = 1500
    L = 500mh
    C = 5uf

    Q1:· What is the total AC current flowing through the resistor?

    Give me the answer to four decimal places.· I do not need to see all of your calculations but I need the resistive value of each of the three components in the impedance triangle.

    I want to convert the circuit to a DC circuit so I replace the 5uf with a 5uf aluminum electroytic with the negative side grounded, and apply 5VDC across the RLC circuit.

    Allow two minutes for the circuit to stabilize.

    Q2:· What is the total DC current through the resistor.· Explain your answer.

    DO NOT post your aswers to the forum and give them away.· Send them to me at Newzed@aol.com.

    If you wish to participate but do not need the EEPROM, please indicate this in your e-mail.· The first correct answer RECEIVED will be the winner.

    Have fun!





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    Sid Weaver
    NEW! 4 MB EEPROM

    http://hometown.aol.com/newzed/page4.html
    ·
  • NewzedNewzed Posts: 2,503
    edited 2005-03-13 17:04
    Sorry - 1.5kHz.

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    Sid Weaver
    NEW! 4 MB EEPROM

    http://hometown.aol.com/newzed/page4.html
    ·
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-03-14 06:18
    Hints deleted, since he requested emailing him the answer, I have no way of knowing what sort of response he's getting. With his permission I will repost them tomorrow, if he indicates ther has been a lackluster response.
  • NewzedNewzed Posts: 2,503
    edited 2005-03-14 13:40
    Paul, I have not received a single reply - very disappointing.· I didn't think it was that difficult a question.

    Sid
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-03-14 17:37
    I wasn't taught the technique to solve for these until in college, Since you haven't received any responses, Ill repost my hints to solving this (Im not solving this myself because I want someone who wants the EEPROM to have a chance and getting it).

    Ok guys, while it is theoreticaly possible to solve AC analysis in the time domain (what is a value at a certain time), this is never done. Instead people use either phasors or Laplace transformations (my opinion is Laplace is much easier to work with). These transform the equation into a different domain (much like fourier transform moves from the time domain to the frequency domain). For laplace this is called the S domain. Now if you don't understand what I am talking about do a google search of the term, but this will provide results that show how the laplace is derived using calculus, don't worry, you dont need to know calculus to solve this problem. Instead search the term "Laplace Transform Impedance" and it will get you more helpful results (hit #2 in yahoo is pretty helpful), you express each element (R, L, C) in terms of it's Laplace impedence, and solving for your unknown is a matter of algebra (instead of calculus as required in the time domain). The second part of the problem is even easier, it only requires knowledge of the DC characteristics, there is one exception and that is if the L and C form a self excitation causing the circuit to oscillate, but since the resistor is there it is not likely it is a self sustaining oscillation, and·given he has asked you to wait for it to stabilize. -Good luck.

    If you need any help with what something means (such as omega), let me know and I'll explain it to you, but I will not help you set up the actual equation or aid in solving it, this is up to you.

    Post Edited (Paul Baker) : 3/14/2005 7:06:57 PM GMT
  • NewzedNewzed Posts: 2,503
    edited 2005-03-14 17:51
    Nice dissertation, Paul.

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    Sid Weaver
    NEW! 4 MB EEPROM

    http://hometown.aol.com/newzed/page4.html
    ·
  • NewzedNewzed Posts: 2,503
    edited 2005-03-14 21:04
    We have a winner !!

    clemensb@otc.edu

    He even got the part about microamp leakage in an aluminum electrolytic.

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    Sid Weaver
    NEW! 4 MB EEPROM

    http://hometown.aol.com/newzed/page4.html
    ·
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-03-14 21:25
    congrats hope you enjoy your EEPROM, Sid maybe you want to mangle his email addy to prevent spam bots from capturing it.

    hmmm otc.edu, is that you DeadBug? Quick check of your last post, yup thats you, congrats, considering you have your email addy in your sig, I guess there is no reason for Sid to mangle it.

    Post Edited (Paul Baker) : 3/14/2005 9:30:28 PM GMT
  • The Dead BugThe Dead Bug Posts: 73
    edited 2005-03-14 23:49
    Thanks...
    Yeah, my SPAM quotient has been going up but my e-mail "rules" seem to be keeping a handle on it.
    P.S. Nobody send me anything with "Urgent!!!" or "ppharmacy" or "Vioxx" etc. in the subject lines...I won't see it. [noparse];)[/noparse]

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    Name: Bruce Clemens

    Work:· Clemensb@otc.edu
    Good Stuff on my Blog: http://theDeadBug.journalspace.com
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-03-15 00:01
    Do you have a full writeup answer prepared, or did you just provide the answers? I think alot of junior members would benefit from seeing to solution posted, Laplace is an invaluable tool when analyzing AC circuits.
  • NewzedNewzed Posts: 2,503
    edited 2005-03-15 00:28
    Here is the formula for solving the impedance problem:

    Z = square root of (R2 + (XL-XC)2)

    where XL = 2 pi * frequency in cycles * L in henrys
    and
    XC = 1/(2 pi * frequency in cycles * cap in farads)

    In the DC circuit, the only current would be the leakage current of the aluminum electrolytic, normall around 2.5ua.



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    Sid Weaver
    NEW! 4 MB EEPROM

    http://hometown.aol.com/newzed/page4.html
    ·
  • The Dead BugThe Dead Bug Posts: 73
    edited 2005-03-15 03:18
    Here were my interim results using the formulae Sid quoted above.

    a. XL = 4712.3889 ohms
    XC = 21.2207 ohms

    Z = 4925.1456 ohms

    Ir = 2.0304 mA


    XL and Xc are 180 deg. out of phase so you can subtract one from the other to yield total reactance. This becomes one leg of a right triangle with the 1500 ohm resistance the other leg. The total impedance is the hypotenuse. Ohm's law gives Ir = 10 V / Z


    b. After 2 minutes the current through R would be almost zero because once
    charged no current flows through the capacitor. Since it is an aluminum
    electrolytic there will be some leakage, on the order of microamps.

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    Name: Bruce Clemens

    Work:· Clemensb@otc.edu
    Good Stuff on my Blog: http://theDeadBug.journalspace.com
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