Talk:Electrical impedance

From Wikipedia, the free encyclopedia
Jump to: navigation, search
          This article is of interest to the following WikiProjects:
WikiProject Electrical engineering (Rated C-class, Mid-importance)
WikiProject icon This article is within the scope of WikiProject Electrical engineering, a collaborative effort to improve the coverage of Electrical engineering on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
C-Class article C  This article has been rated as C-Class on the project's quality scale.
 Mid  This article has been rated as Mid-importance on the project's importance scale.
 
WikiProject Physics (Rated C-class, High-importance)
WikiProject icon This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
C-Class article C  This article has been rated as C-Class on the project's quality scale.
 High  This article has been rated as High-importance on the project's importance scale.
 
WikiProject Electronics (Rated B-class, High-importance)
WikiProject icon This article is part of WikiProject Electronics, an attempt to provide a standard approach to writing articles about electronics on Wikipedia. If you would like to participate, you can choose to edit the article attached to this page, or visit the project page, where you can join the project and see a list of open tasks. Leave messages at the project talk page
B-Class article B  This article has been rated as B-Class on the project's quality scale.
 High  This article has been rated as High-importance on the project's importance scale.
 

Merger proposal[edit]

It is proposed to merge Impedance of different devices (derivations) into this article. The article says little or nothing that is not already said here and said better and in places is just plain wrong. Besides which it is practically orphaned. SpinningSpark 18:42, 14 June 2008 (UTC)

I have created a version of this article including the derivations at User:DJIndica/Sandbox2. I'd appreciate any comments.--DJIndica (talk) 12:29, 18 July 2008 (UTC)

Question[edit]

Vp stands for peak voltage, right? I'm referring to the part about capacitors in the Device Examples section of the article. If not please explicitly state what Vp is, since I don't think it is something that can be easily inferred from the article. 96.60.80.133 (talk) 03:09, 13 November 2008 (UTC)

I would also like to add that I found this article very helpful. From reading some of the discussion here I understand that some of you guys are extremely intelligent and I thank you for all your contributions. 96.60.80.133 (talk) 03:38, 13 November 2008 (UTC)

Vp is the voltage amplitude, which is indeed the peak voltage given that there is no DC offset.--DJIndica (talk) 19:01, 13 November 2008 (UTC)

Collapsable tables[edit]

The collapsable tables that were hiding the device specific derivations didn't expand when the printable version was selected, so a printout made from the page would be missing fairly useful information. I removed the tables and made the table headings into subsubsections. --Autopilot (talk) 17:02, 19 January 2009 (UTC)

SVG characters look poor[edit]

Several of the SVG images on this page are rendering fonts much larger than they should be. That is, I don't think they're properly scaling with the image. For example,

Impedance symbol comparison.svg

looks fine when you click on it, but in its scaled version here and on Electrical impedance, the Z_S and Z_L in the bottom two images are HUGE. Do other people see this? —TedPavlic (talk) 16:24, 28 January 2009 (UTC)

On the bottom image, yes. On the middle image, only for Zs, not ZL. That's in Firefox 3.05. Got the same result in IE6. I'll try downloading the SVG and see what I can see in the editor. SpinningSpark 10:36, 29 January 2009 (UTC)
I have fixed the problem, not really sure what it was but I fixed it by cut-and-paste of the good parts of the image. It is showing correctly on the thumbnail in Commons, but I don't seem to be able to get Wikipedia to purge the old version by any of the usual methods. It is definitely fixed though, if I upload the image directly to the Wikipedia sandbox, I get this;
<sandbox removed as it no longer contains the relevant image>
SpinningSpark 11:17, 29 January 2009 (UTC)
Thanks. After your changes, "hard refreshing" (i.e., forcing the browser to refresh the cache) fixes the problems. I suspect "Shift+Refreshing" on your end will fix cause your new version to show. —TedPavlic (talk) 13:59, 29 January 2009 (UTC)

Poor readability of text with Greek and generated images[edit]

The text looks ugly in Internet Explorer 8 where LaTex-generated expressions and even Greek symbols are rendered into IMG elements with vertical alignment that is incorrect and fonts that are of poor quality.

Is there a reason why we should not simply use Unicode characters as per web standards and use sup and sub elements for simple inline definitions of symbols and short simple inline expressions?

I'm aware that extremely old web-browsers have problems with some Unicode characters. (IE5/win for example). But if wikipedia's engine needs to take special measures to help such old browsers then so be it, surely it's time to stop de-optimizing everything because of the limitations of the most broken software. I'd be grateful if someone would give some pointers to what I imagine may be long-established reasoning behind the design decisions in this area.CecilWard (talk) 17:32, 7 June 2009 (UTC)

The relevant guideline is Wikipedia:Manual of Style (mathematics). There is no rule against using HTML markup for formulae instead of LaTeX, however, some things can only sensibly be typeset in LaTeX, and in my view it looks an inconsistent mess to have a mixture of the two in the same article. I think the point you raise is not really a matter for (just) this article. Wikipedia wide issues are discussed at the village pump. SpinningSpark 00:19, 8 June 2009 (UTC)
I have changed the inline LaTeX to "scriptstyle" which will render in a smaller font more compatible with the text and getting a better vertical alignment - but still not perfect. It looks acceptable to me in both Firefox 3 and IE6, don't know about IE8. SpinningSpark 01:05, 8 June 2009 (UTC)

Modifications to lead[edit]

The reason I made this change was because I was unhappy with the phrase "never as a function of time"; whilst it's true that impedance expresses the ratio of a phasor at a given frequency, it's simply not the case that it can *never* vary with time.

You misunderstand the definition of impedance and the use of complex exponentials in the solutions of LTI systems. It's true that the voltage–current relationship can vary over time in such a way that can be approximated like a system with a time-varying impedance, but the concept of impedance cannot ever be extended to the time-varying case. —TedPavlic (talk/contrib/@) 12:42, 6 August 2009 (UTC)
Oh, I understand perfectly well the implications of the Fourier transform (that the integral is over all time); from a mathematical point of view, Z(f) is the voltage/current ratio of a phasor of infinite length. However, in practice, we never deal with things that last forever. So in practice, we may well see an "impedance" that vary over time, and that to all practical intents and purposes acts exactly like a "formal" impedance derived from the Fourier transform over all time of a true LTI system. The level of detail required to explain this dichotomy is overwhelming for the lead. Oli Filth(talk|contribs) 14:01, 6 August 2009 (UTC)
Again, I think you misunderstand. Impedance is a concept defined for infinite time horizon signals, and the finite time horizon signals are limits of convergent series of infinite time horizon signals. These additional components become very important when designing, say, pulsed RADAR systems. Likewise, if you pulsed a laser fast enough and passed it through a prism, the light would start to spread into different colors (even though the laser was "originally" a "single" color). Filters act on the terms of these series, and thus you get different finite-time signals. So it's entirely appropriate to discuss the infinite-time horizon properties. —TedPavlic (talk/contrib/@) 14:44, 6 August 2009 (UTC)

When I mentioned varactors/varicaps in my edit summary, I was not referring to small-signal non-linearity, instead I was alluding to the fact that system parameters may vary over time (varactors happen to be an example where the small-signal parameters are actively controlled).

Again, I think you misunderstand. The small-signal parameters are linear, but the small-signal model is just an approximation of reality. The reality is the "large signal" model. Over large signal swings, a varicap does not have a linear impedance regardless of its bias. Over small signal changes, the bias effect dominates; however, the voltage–current ratio still is not that linear. In fact, the difference between a varicap and a diode is that a varicap has been specially designed to have an excessively large linear approximation region. —TedPavlic (talk/contrib/@) 12:42, 6 August 2009 (UTC)
Again, I'm aware of that, and again I was merely trying to highlight that in many practical situations, the time-varying linear small-signal model is a perfectly valid approximation. Oli Filth(talk|contribs) 14:01, 6 August 2009 (UTC)
I'm not saying that small-signal linearization is invalid. I'm saying that within the small-signal model, the impedance does not change over time. When you ramp the bias, it's inappropriate to think of the small-signal model having a time-varying impedance. Instead, a ramping bias shifts you from one small-signal model to another. Additionally, you're not factoring in any of the transient effects that die out when moving from one bias point to the other. Saying that you can have a "time varying impedance" implies that you can do LTI-like things to systems that are time varying. —TedPavlic (talk/contrib/@) 14:44, 6 August 2009 (UTC)

I believe the latest changes has now somewhat overcomplicated the issue, and consequently the last three sentences should be removed (or at the very least, moved from the lead, as it shouldn't contain material that isn't discussed elsewhere in the article). Oli Filth(talk|contribs) 19:46, 5 August 2009 (UTC)

Done. —TedPavlic (talk/contrib/@) 12:42, 6 August 2009 (UTC)
Thanks! I've reworded the new section slightly to avoid "infinite-time-horizon" and the specific varicap example, please let me know if you object. Oli Filth(talk|contribs) 14:01, 6 August 2009 (UTC)
I'd like to put the varicap in as an e.g. Otherwise, if the present wording is better for you, it's better for some other people out there too, and so it's fine. —TedPavlic (talk/contrib/@) 14:44, 6 August 2009 (UTC)

Generalise[edit]

I moved the lead to a new paragraph and tried to write a short lead on the general topic of impedance seeing as the old one only covered ac theory. Unfortunately I dont have the time to do it properly, and I understand that it will recquire extensive further modification and hope someone else can offer the time recquired. Thanks. —Preceding unsigned comment added by 129.67.119.67 (talk) 18:13, 28 February 2010 (UTC)

I was only trying to help. But obv [1] this man thinks that (most likely because I am an IP) my contributions are unworthy. —Preceding unsigned comment added by 129.67.116.170 (talk) 17:06, 2 March 2010 (UTC)
I have to agree with the reversion, especially as this was a complete change to the lede, although the edit summary is a little bitey. The title of the article is "Electrical impedance", not "impedance of the medium" which is a completely different thing. In future, you might want to consider trailing such major revisions on the article talk page first. We already have impedance of free space which is the concept you are talking about, but there does not seem to be an article extending this idea to other mediums. You might want to think about starting a new article! SpinningSpark 16:40, 4 April 2010 (UTC)
Actually, just discovered we do have an article already, wave impedance. SpinningSpark 20:36, 4 April 2010 (UTC)

Simplify??[edit]

I would like to suggest that this article is unnecessarily difficult to read and understand, excessively mathematical, inappropriately theoretical and useless in understanding higher voltage applications. Impedance can be understood as the collective effect of resistance, inductive reactance and capacitative reactance. Changes in voltage and load can be viewed with an appropriately configured oscilloscope. When the two sine waves are 45 degrees out of phase, power is reduced because (using Ohm's Law every time either line crosses zero the power drops to zero Watts. Power lines become clogged with VARS (volt-amps reactive), rather than Watts, reducing system capacity. Since inductive reactance is the more common problem, utility companies typically install banks of large capacitors to balance out inductive reactance with a calculated mount of capacitative reactance. There should be a photo of a capacitor bank. These can be seen atop power poles all over the place. School children can learn to recognize them. Once this has all been established at the visible, practical real-world macro level, the article could refocus on the itty-bitty circuits and theory. This, by the way, represents a common problem with technical Wikipedia articles -- they get too theoretical, academic and technical to be of use to the average encyclopedia user. 97.90.105.186 (talk) 05:37, 2 June 2010 (UTC)

My guess is that this article is theoretical because it's describing the underlying theory of impedance, which is fundamentally an abstract mathematical construct. The example you give (power-factor correction) is one specific, qualitative application. This is described in the Power factor article, which in my opinion is the correct location.
Perhaps we should find a way to work appropriate links into this article, but we shouldn't be going into great detail. Oli Filth(talk|contribs) 18:16, 2 June 2010 (UTC)
I have to agree. I think it is terrible that electric effective resistance (http://en.wikipedia.org/wiki/Electric_effective_resistance) is redirected here. I came here looking for the standard definition for a network of resistors with a source and sink (DC current), and it is a mistake that the only article is in unnecessary generality. It is basically unreadable. (I say this because effective electrical resistance is a concept that has purely mathematical applications, for which electricity is just a metaphor, and AC current is meaningless. Also, I think that most hobbyists playing with electrical circuits use DC current only.) — Preceding unsigned comment added by 71.139.164.223 (talk) 21:46, 21 December 2011 (UTC)

Generalised s-plane impedance[edit]

The recently added content on s-domain impedance is problematic, IMO.

First, as far as I know, the notion that, for example, an inductor presents an impedance to, for example, a square wave source is incoherent. Rather, an inductor presents an impedance to each component of the square wave. The added section suggests that the impedance of an inductor for an arbitrary periodic signal is the sum of impedances to the individual components. Summing these impedances makes no sense at all. What would one do with this number? What current would one multiply this impedance by to get what voltage?

Second, it's unclear what the statement "Non-periodic signals will have a real part to s." means in this context. According the chart above it, the s-domain impedance of an inductor is sL. In this context, the 's' is the complex coefficient of t in the complex exponential excitation, A exp{st}. For example, v(t) = sL i(t) where i(t) = I exp{st}. That's the context of s-plane impedance.

However, the statement in question appears to be in the context of the parameter s in the Laplace transform of a signal and that's a different 's' altogether. Consider the Laplace transform of the unit step, a non-periodic function. According the statement above, there is real part to s. What is the real part of s for the unit step? And what does that real part have to do with s-plane impedance? Alfred Centauri (talk) 02:06, 12 July 2010 (UTC)

Definition of Impedance[edit]

Currently, the article states Impedance is defined as the frequency domain ratio of the voltage to the current. I've added a citation request. I've been taught that impedance is the ratio of the voltage and current phasors. Although phasors are related to the frequency domain, the definitions are not identical. Here's a cite from "Standard Handbook for Electrical Engineers", 13 edition:

An impedance of a linear constant-parameter system is the ratio of the phasor equivalent of a steady-state sine-wave voltage or voltage-like quantity (driving force) to the phasor equivalent of a steady-state sine-wave current or current-like quantity (response).

Alfred Centauri (talk) 13:11, 14 July 2010 (UTC)


The phase shift (leading or lagging terms)[edit]

Um, the opening paragraph has 1 of its primary points wrong. The phase shift or angle of impedance describes how much the Voltage leads the current, not the other way around. In a capacitor, the phenomenon has to do with voltage, so the current leads the voltage, which is why it X_c lies on the -j axis. In the correct picture, voltage leads current by -90 degrees, or voltage lags current by 90 degrees. This is exactly the opposite of what this article has written. 166.19.102.20 (talk) 14:48, 25 August 2010 (UTC)

Untitled post[edit]

I suggest instead of "the impedance of inductors increases with frequency" in paragraph "device exemple" to wright "the impedance of capacitors increases with frequency"

wright — Preceding unsigned comment added by 93.46.208.51 (talk) 13:54, 2 September 2011 (UTC)

Wrong! SpinningSpark 15:33, 2 September 2011 (UTC)
Note to the original poster, when the frequency is low, the impedance of the capacitor is high, so most current will flow through the resistor. As the frequency increases, more current is diverted through the capacitor, less to the rest of the circuit. Thus, the response is low pass. If you exchanged the capacitor and resistor, you'd have a high pass circuit. Please see, http://artsites.ucsc.edu/EMS/Music/tech_background/Z/impedance.html Sunshine Warrior04 (talk) 08:28, 26 October 2011 (UTC)

Wrong definition?[edit]

I think the definition of impedance given in the lead section "Electrical impedance, or simply impedance, describes a measure of opposition to alternating current (AC)" is wrong. Impedance = reactance + resistance (as is correctly stated later in the article) so an impedance which includes resistance would oppose DC as well as AC. Biscuittin (talk) 18:53, 20 October 2011 (UTC)

I would humbly call attention to several definitions quoted from good sources here: http://www.answers.com/topic/electrical-impedance
Perhaps someone can use one of these definitions and quote the source. If no one else chooses to do so than I can. Sunshine Warrior04 (talk) 08:02, 26 October 2011 (UTC)
I have partly reverted this; to say only that "it is the complex ratio of the voltage to the current" is only meaningful to someone who (a) understands what a complex ratio means, and (b) is already familiar with the concept of impedance. The lede paragraph needs to spell out what is different about impedance - that is its possession of phase - and that it only differs from resistance in an AC circuit. I have also added a paragraph stating the causes of impedance as the second para of the lede which I think may be a key thing a casual reader may be looking for.
I have also removed the citation. It really will not do to have answers.com as a reference, especially as it gives the Wikipedia article as one of the answers making it circular. SpinningSpark 18:38, 26 October 2011 (UTC)
I understand completely. Its interesting how Wikipedia is now being quoted as a source when it should not. When I was in school I was specifically told not to use Wikis as information sources. Guess some people tend to get lazy. Sunshine Warrior04 (talk) 22:02, 26 October 2011 (UTC)