Talk:RLC circuit

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This article may contain overly technical formulas for most readers to understand, and needs the formulas translated into English and/or visual diagrams. Please expand it to make it accessible to non-experts, without removing the technical details.

Contents 1 Fundamental versus derived parameters 2 Image 3 Parallel RLC schematic 4 To Do 4.1 Progress to date 5 Needs some work 6 new images 7 bandpass filter image 8 Simplify Zero Input Response? 9 Centering equations 10 translation request at top 11 Damping factor 12 Recent edits 13 Reply from Rdrosson 13.1 Resonance Frequency 13.2 Symbols and Notation 13.3 Passive versus Active Voice 14 Reply from Light Current 14.1 Resonance Frequency 15 Example of non-parallel non-series RLC circuit 16 embellisment of damping factor

[edit] Fundamental versus derived parameters

There seems to be some confusion about which parameters are fundamental, and which ones are derived. The article is a bit inconsistent. Right now, the article identifies the natural frequency and the Q factor as fundamental, while it says the bandwidth BW and damping factor alpha are derived. But the equations for the Q factor and the bandwidth define these parameters in terms of the damping factor alpha. So if the Q factor is fundamental, why is it defined in terms of another parameter that is supposedly derived?

Meanwhile, the damping factor is defined in terms of R and L, which are the values of the circuit elements, and not in terms of any of the other parameters. So why is alpha called a derived parameter when in fact it does not depend on any of the other parameters?

Bottom line: the fundamental parameters should be the natural frequency and the damping factor. The derived parameters should be the Q factor and the bandwidth.

Rdrosson 15:37, 13 October 2005 (UTC)

I have made this change. Notice that the two fundamental parameters are now defined in terms of the circuit elements only (R, L, and C) and not in terms of any other parameter. Notice also that you can derive any other parameter in terms of these two fundamental ones – including the Q factor, the bandwidth, the damped frequency (which is not shown), the pole locations, the zero locations, and even the second order differential equation that governs the circuit's behavior.

Notice also that the Q factor must come last, since it is defined in terms of the bandwidth BW.

Rdrosson 16:01, 13 October 2005 (UTC)

I have also added a (brief) definition of the damped resonance.Rdrosson 16:33, 13 October 2005 (UTC)

[edit] Image

This image is prettier in a way, but the other one is easier to make sense of. I think I will replace both with my own anyway. - Omegatron 02:39, Jul 16, 2004 (UTC)

[edit] Parallel RLC schematic

I suggest we use the textbook example where all components are in parallel and driven by a current source. We can show that this is the exact dual of the series case driven by a voltage source. Any thoughts? Madhu

Driven by a current source, you say? - Omegatron 20:57, Mar 26, 2005 (UTC)

I agree with Madhu. First of all, it makes no sense to connect a voltage source in parallel with a resistor. The resistor has absolutely no impact whatsoever on the circuit, you could actually remove the resistor without have any effect on the circuit's behavior. Second, a current source in parallel with a resistor (a Norton Equivalent) is the exact dual of a voltage source in series with a resistor (a Thevenin Equivalent). And third, Madhu is correct that the parallel RLC is the exact dual of the series RLC, but only if you replace the voltage source in the series circuit with a current source in the parallel circuit. Do the math, the two circuits result in the same exact differential equation, and the same results (if you swap all of your variables with their duals). – Rdrosson

I agree with Madhu and Rdrosson. I teached 30 years electric circuits in Belgium. People don't like current sources. In mechanics are force and speed sources. Nevertheless I admire the work of Omegatron.

Image:Rlc2.jpg

Tsi43318 15:22, 11 February 2007 (UTC)

[edit] To Do

1. Transient analysis using Laplace transform
2. Step function
3. Sine drive at resonance (this is interesting!) Madhu

[edit] Progress to date

1. I have started a discussion of the Laplace Transform as a method for solving the ZSR. – Rdrosson
2. ...
3. ...

[edit] Needs some work

There are some small things that needs to be fixed up:

• If the resonant frequency is in hertz then need to say what units are used for L an C (says lower down but should say before used).
• Alpha is used to categorize Overdamped/underdamped/critically damped but alpha is never defined (and I can't remember what the term for alpha is, the root something of the differential equation in math and the dampng something or other in electroincs, I think, it's been a while).

Note: I have done substantial work over the last day or so to define alpha. In the standard approach to RLC circuits, alpha (in radians per second) is called the damping factor or damping parameter. It is one of two important parameters, the other of which is the natural frequency (also in radians per second) or ω_o. – Rdrosson

The hard things is that it looks too hard (though this is a matter of opinion and I don't know what to do about it). This looks to be written at the level of a 3rd year college engineering student (who has had circuits, calculus and differential equations). I'd like to try to simplify it enough to be interesting to a freshman. Like I said, I don't know if this is possible. (I need to see if I still have my text book)

[edit] new images

Use as you please:

Anything else I should label? - Omegatron 20:55, Mar 26, 2005 (UTC)

The diagrams are fine, except I think you should change the parallel RLC by replacing the voltage source V with a current source I. The symbol for a current source is a circle (just like the voltage source) with an arrow pointing along the diameter of the circle instead of the little "+" and "–" signs. It looks like a schematic for a compass. In this case, the arrow would align with the vertical and point in the upward direction. Rdrosson

[edit] bandpass filter image

I would like this better if it were log-o-rhythmic. Or if such was added side by side. I want to try my hand at making pretty gnuplot diagrams a lá Image:dba_plot.png, but someone else is free to beat me to it. - Omegatron 23:32, Mar 28, 2005 (UTC)

[edit] Simplify Zero Input Response?

As RJFJR noted, this article is written at a fairly high level- I imagine most students are going to encounter RLCs before they do any differential equations- so I'm working on reworking this part of the article to use the cheating workaround that I've seen in classes, where you just sort of say "I(t) = Ae^kt, because it should, now let's solve for k- now we've got α" That way all we're assuming is high school algebra, simple trig, and De Moivre's Thereom.

I'm also considering adding a part that would describe a steady-state solution with a driving voltage. My biggest worry is that this article will end up being very incongruous, but I think it's preferable so long as the first part is as transparent as possible. --Hal 20:49, 1 August 2005 (UTC)

[edit] Centering equations

why are all the equations centered? Wikipedia:How_to_write_a_Wikipedia_article_on_Mathematics#Typesetting_of_mathematical_formulas

Note: I have eliminated most of the centering of equations. Equations are now left justified with an indentation of two tabs. – Rdrosson

The schematic with definitions beside it looks kind of nice, but the gray background conflicts with the schematic background. I have the original xcf files I think, and could make it transparent, but... - Omegatron 16:05, August 5, 2005 (UTC)

Also variables should really only be bold if they are vectors... - Omegatron 14:59, August 7, 2005 (UTC)

[edit] translation request at top

what is that, a joke? Pfalstad 19:29, 25 September 2005 (UTC)

oh, I see.. Wikipedia_talk:MediaWiki_namespace_text#Math_equations_to_plain_english I don't think there's much point in that, in this article anyway. (At first I thought it was a sarcastic complaint about the complexity of the formulas.) Pfalstad 23:12, 28 September 2005 (UTC)

The formula are not simple to read. It'd be nice to have a plain english translation of the equations. JDR (seem to have some support to translate formulas ... as seen here)

[edit] Damping factor

I had not realised before that damping factor has dimensions of angular frequency (rad/s)!. So I have learned something new after all these years thanks to WP. Hooray!--Light current 23:56, 13 October 2005 (UTC). I wonder if this has any deeper signigficance.- must ponder it!--Light current 00:26, 14 October 2005 (UTC)

Uh oh. There are two electrical definitions of damping factor. We need a disambig, it would seem. — Omegatron 00:13, 14 October 2005 (UTC)

Yes the one you're referring to is the audio one of Zl/Zs. for the electro mechanical damping of a speaker cone but are they different things or the same thing in another guise. I dont know!--Light current 00:23, 14 October 2005 (UTC)

To Omegatron:

where do you see two definitions of "damping factor"? I have seen an entry for damping, which provides a pretty good description of the general concept, using the well-known mass-and-spring harmonic oscillator as an example. Where are you seeing two electrical definitions? Do the two definitions conflict with one another, or are they redundant, or what? --Rdrosson 02:50, 15 October 2005 (UTC)

Nevermind....I see the problem now. The article called Damping factor is talking about a concept completely different from the use of damping factor in the RLC Circuit article. Unfortunately, it appears that the same term is used in each of these contexts to mean very different things. The term is actually a bit of a misnomer in the context of amplifiers and bridging circuits, where it might have been better to call it the "attenuation factor," which is closer to the meaning in that context. Nevertheless, I think you are right in saying that we need to add a disambiguation page. -- Rdrosson 03:02, 15 October 2005 (UTC)

On further inspection, the article entitled damping is not so great. It needs some heavy editing to clean up the notation and the flow of ideas. With a bit of work, it could be converted into a very good parallel to the RLC Circuit article, so that each article would help support the other from a different point of view. RLC is a perfect analogue for Damper-Mass-Spring.... -- Rdrosson 03:21, 15 October 2005 (UTC)

[edit] Recent edits

Moved from my talk so everyone can make comment. -- Light Current

[edit] Reply from Rdrosson

Thank you for the compliment on the editing I have done on RLC Circuit. I have worked very hard on this topic (and a few others) during the last three months, and I hope that my contributions have improved these entries.

With all due respect, I have to say that overall, I am not at all thrilled with the changes that you have made to RLC Circuit since this morning. In fact, I think the article is far more confusing than it was prior to your revisions. Let me make a few comments:

[edit] Resonance Frequency

• Terminology: there is really no such thing as a "resonance frequency." There are two correct terms, which are "resonant frequency" or "resonance." The issue is related to correct grammar: "resonance" is a noun, whereas "resonant" is an adjective. The word "frequency" is of course a noun, so you must precede "frequency" with an adjective, not with another noun.

[edit] Symbols and Notation

• Symbols: On the one hand, the choice of symbols or notation really shouldn't matter, since they are really rather arbitrary. On the other hand, making good choices about notation can help clarify a difficult topic immensely, whereas making poor choices can take the simplest idea and make it incomprehensible. That being said, the difference between good and bad notation in any particular case is obviously quite subjective and open to debate. Nevertheless, I have a lot of experience as both a student and a teacher, and I think I have pretty good judgement on this issue. Furthermore, there are large sets of notation that have become standard, at least within a functional discipline or sub-discipline such as mathematics, physics, or engineering. Unfortunately, there are often differing standards from one discipline to another, which creates some confusion. And in some cases, I believe that some of the standard notation is rather confusing and difficult to master.

In any event, I am really disappointed with the notation changes that you made to many of the equations earlier today. For example, I am really opposed to using the Greek letter zeta (ζ) as a symbol for anything, primarily because it is very seldom used and very few people have any idea what it is when they see it (including me). Furthermore, I have seen many many textbooks in electrical engineering and many many university professors who all use the Greek letter alpha (α) to represent the damping factor not only in RLC circuits, but also in all second-order linear systems.

I have never seen anyone use beta (β) to represent bandwidth (in rad/s), but I thought it was an excellent choice, and certainly better than delta-omega, since it is the next letter in the Greek alphabet after alpha, and since the letter beta is a good mnemonic for the word "bandwidth." And I didn't think anyone would be too concerned with using BW to represent bandwidth in units of hertz.

[edit] Passive versus Active Voice

• I can understand that you might want to change things from the active voice to the passive voice, since that is very common in scientific and technical writing. That, of course, does not actually improve the writing. In fact, I think it actually makes the writing substantially weaker.

Think about the difference in meaning between the words "active" and "passive." Would you rather work with people who are generally passive, sitting back and waiting for something to happen, or those who are active, who pick up the ball and run with it, who actually make things happen? It is not a perfect analogy to writing, but it's not a bad analogy either. I want writing that steps up and grabs hold of the reader, not writing that sits back and waits for the reader to figure it out.

The active voice is actually a far superior style of writing, even though it is not standard among scientists and engineers. I have never understood why anyone would choose to use the passive voice in any kind of writing, except in very rare circumstances.

I don't mean to be hyper-critical, but it is kind of frustrating to put so much effort and hard work into something only to see someone else dismantle it. Sorry.

I will probably have some more comments tomorrow, but right now I need to get some sleep.

See 'ya, Rdrosson 03:22, 14 October 2005 (UTC)

[edit] Reply from Light Current

Unfortunately, this is what often happens on WP. You put your heart and soul into an article only to have someone come along and, in your opinion, trash it!. This has happened to me on many occaisions and I used to get very angry about it. Over the past few weeks however, I have found that in some cases, the comments and changes made by others have actually been correct and I have been wrong and had to eat humble pie! But it is only after long and sometimes tense discussions that I have realised it. Remember, that no one can claim sole authorship of an article, and we all should try to help to make it the best that it possibly can be.

Now having said that, if I were you, I would take some comfort from the fact that I congratulated you on your good work. Thats more than I've ever had from anyone. I did think it was good. Very good in fact. But not perfect! Articles will never be perfect and can always be improved/corrected. Ive generally only had blanket reversions and quite a lot of (mild) abuse.

I do sympathise with you, but you really have to toughen up on WP, and try not to be too sensistive. Its not easy, but if you listen to other peoples points of view closely enough, you may even find yourself agreeng with them. Remember, in general, comments are not aimed at you personally but in improving the quality of the article. If you can bear that in mind, I think you may find things easier. The article is the important thing, not anyones ego! Generally, on the science and engineering pages, we do not get into edit wars etc. We have robust arguments on the talk pages, but we never (not usually anyway) get too personal. That way, we work together for the general good of WP>

I hope this makes you feel a bit better and would encourage you to continue to contribute. As I said you seem to have a logical mind: we could do with some of that. See you around I hope!--Light current 04:32, 14 October 2005 (UTC)

[edit] Resonance Frequency

How can a frequency be resonant? The terminology is wrong in the books and has been for years. You can have a resonant circuit or some other resonant system, but the adjective resonant cannot be used with the word frequency Im afraid! A frequency is a frequency - thats it! Could be a frequency of resonance if you prefer.

Is this more of your original research? If the books are all "wrong", then this article should contain the "wrong" terminology that's in all the books, because that's the consensus, and our job as an encylopedia is to report the consensus view, not your view. Google reports 757,000 hits for resonant frequency, 947 hits for "frequency of resonance". If you want to change the accepted terminology, go write a paper and submit it to an ee journal or something. Pfalstad 05:37, 14 October 2005 (UTC)

Now, now. No need to get uptight! I think there is at least one person who agrees with me on this one! Open your mind. You are an intelligent fellow Im sure, so you neednt believe all you read without question. By your reckoning since ten giga-giga flies eat crap- it must taste good!--Light current 05:45, 14 October 2005 (UTC)

"open your mind"? You're the one saying that all the textbooks are wrong and only you are right. It's not a question of belief, it's a question of terminology. Hey, I just noticed that the word "stopband" is wrong because a filter doesn't actually "stop" frequencies, just attenuates them. Should we remove that word from wikipedia too? Pfalstad 16:15, 14 October 2005 (UTC)

res·o·nant (rĕz'ə-nənt) pronunciation

adj.

2. Producing or exhibiting resonance — Omegatron 06:55, 14 October 2005 (UTC)

No original research. Also, Wikipedia is not a publisher of original thought or a chat room. It's fine to have some discussions about article content but lots of speculation about the way things really are and all that should go to a discussion board. We report on the way things are; not the way we think things should be (for the most part). — Omegatron 07:05, 14 October 2005 (UTC)

And what way are they?--Light current 17:04, 14 October 2005 (UTC)

Right-or-wrong, the vast majority of the literature uses one of two terms: "resonant frequency" or just plain old "resonance." I have never seen the term "resonance frequency" in any textbook or journal article on the subject. Furthermore, I simply do not think that "resonance frequency" sounds right, and frankly, it looks like a typographical error. --Rdrosson 13:01, 14 October 2005 (UTC)

Well how about 'frequency of resonance'. It sounds OK and has 947 google hits. Its more accurate than resonant because it can be applied to 'frequency' whereas 'resonant' can't. Anyway I leave it to the majority view! I smell my other fish burning! ;-)--Light current 17:04, 14 October 2005 (UTC)

No. It's non-standard, and "resonant frequency", meaning "a frequency producing or exhibiting resonance" is perfectly accurate. — Omegatron 23:05, 14 October 2005 (UTC)

OK. I said I leave it to the majority view--Light current 23:09, 14 October 2005 (UTC)

[edit] Example of non-parallel non-series RLC circuit

I think an example of a circuit with other configurations than parallel and series devices would be helpful - I know it would help me right now. I can't get these friggin DE's solved. I guess i'll just use laplace transforms.. - but if anyone could produce another example, it would be helpful to see how a more complicated RLC circuit could work out. Fresheneesz 08:40, 21 April 2006 (UTC)

[edit] embellisment of damping factor

Is there a general definition of damping factor (the type defined here)? I've been looking for a way I can derive the damping factor, but I can't seem to find anything. Can anyone help? Fresheneesz 00:34, 5 June 2006 (UTC)