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Bill Turner wrote: On 08 Dec 2003 20:09:43 GMT, (Avery Fineman) wrote: INDUCTANCE doesn't change over frequency __________________________________________________ _______ I maintain it does. Otherwise the formula X=2piFL is invalid. NO! In the above equation, X varies when F varies. The equation does NOT mean that L varies as F varies. Is that what you're saying? I understand what you're saying about the inductance of a coil being fixed and the reactance is the net result of that fixed inductance plus the effect of the parasitic capacitance between windings, vs frequency, of course. If one chooses to *model* a coil that way, I have no objection. You will no doubt arrive at the correct reactance for a given frequency. The disagreement here seems to depend on how one defines what inductance is. I maintain that inductance of a coil is nothing more than the reactance divided by 2piF, as derived from the formula above. Do you disagree with that? That formula has been taught for decades. Are you saying it is wrong? The formula is fine. Your understanding of it is wrong. X is inductive reactance. F is frequency. L is inductance. F is a variable, L is fixed and X (the reactance of L at the frequency) varies as the frequency varies. -- Bill, W6WRT |
On Mon, 08 Dec 2003 19:46:43 -0800, Bill Turner
wrote: On 08 Dec 2003 20:09:43 GMT, (Avery Fineman) wrote: INDUCTANCE doesn't change over frequency _________________________________________________ ________ I maintain it does. Otherwise the formula X=2piFL is invalid. Is that what you're saying? I understand what you're saying about the inductance of a coil being fixed and the reactance is the net result of that fixed inductance plus the effect of the parasitic capacitance between windings, vs frequency, of course. If one chooses to *model* a coil that way, I have no objection. You will no doubt arrive at the correct reactance for a given frequency. That is what everybody is trying to say. It is like discussing is a candle _emitting_light_ into the room or is the candle _absorbing_darkness_. This becomes quite apparent when the wick of the candle is black when the candle has been put out, clearly it has absorbed a lot of darkness :-). In an incandescent lamp, the electric current will constantly renew the filament, thus preventing a lot of darkness being concentrated on the filament. One could develop quite scientific methods to measure the amount of darkness absorbed and predict the behaviour of other lamps. This can also be debated successfully for a quite a while, until some serious disagreeing measurements are brought into the discussion. The disagreement here seems to depend on how one defines what inductance is. It has often been defined by the ability to store energy. I maintain that inductance of a coil is nothing more than the reactance divided by 2piF, as derived from the formula above. L = Xl / (2 pi f) applies only to _pure_inductive Xl It does _not_ apply to L = X / (2 pi f) in which X is some combination of Xl and Xc ! Do you disagree with that? That formula has been taught for decades. Are you saying it is wrong? The formulas taught for decades a Xl = 2 pi f L _and _ Xc = -1/(2 pi f C) How do you arrive to the incorrect L = X / (2 pi f) from the equations above ? Please note, it is the magnitude of X what you are measuring with some simple test gear, not Xl. Thus, the original claim is an artefact of the measurement method. Paul OH3LWR |
On Mon, 08 Dec 2003 19:46:43 -0800, Bill Turner
wrote: On 08 Dec 2003 20:09:43 GMT, (Avery Fineman) wrote: INDUCTANCE doesn't change over frequency _________________________________________________ ________ I maintain it does. Otherwise the formula X=2piFL is invalid. Is that what you're saying? I understand what you're saying about the inductance of a coil being fixed and the reactance is the net result of that fixed inductance plus the effect of the parasitic capacitance between windings, vs frequency, of course. If one chooses to *model* a coil that way, I have no objection. You will no doubt arrive at the correct reactance for a given frequency. That is what everybody is trying to say. It is like discussing is a candle _emitting_light_ into the room or is the candle _absorbing_darkness_. This becomes quite apparent when the wick of the candle is black when the candle has been put out, clearly it has absorbed a lot of darkness :-). In an incandescent lamp, the electric current will constantly renew the filament, thus preventing a lot of darkness being concentrated on the filament. One could develop quite scientific methods to measure the amount of darkness absorbed and predict the behaviour of other lamps. This can also be debated successfully for a quite a while, until some serious disagreeing measurements are brought into the discussion. The disagreement here seems to depend on how one defines what inductance is. It has often been defined by the ability to store energy. I maintain that inductance of a coil is nothing more than the reactance divided by 2piF, as derived from the formula above. L = Xl / (2 pi f) applies only to _pure_inductive Xl It does _not_ apply to L = X / (2 pi f) in which X is some combination of Xl and Xc ! Do you disagree with that? That formula has been taught for decades. Are you saying it is wrong? The formulas taught for decades a Xl = 2 pi f L _and _ Xc = -1/(2 pi f C) How do you arrive to the incorrect L = X / (2 pi f) from the equations above ? Please note, it is the magnitude of X what you are measuring with some simple test gear, not Xl. Thus, the original claim is an artefact of the measurement method. Paul OH3LWR |
On Tue, 09 Dec 2003 04:59:29 GMT, wrote:
Bill Turner wrote: On 08 Dec 2003 20:09:43 GMT, (Avery Fineman) wrote: INDUCTANCE doesn't change over frequency __________________________________________________ _______ I maintain it does. Otherwise the formula X=2piFL is invalid. NO! In the above equation, X varies when F varies. The equation does NOT mean that L varies as F varies. That's right. You end up with X/2piF and X and F are inter-related; they are not independent variables. -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill |
1) you guys are just arguing symantics. You both know what really happens.
".... "Inductance" vs. the total reactance measuring as inductive...." call it what you like. 1a) You are also both using (some might say mis-using) the term "linear" to mean "varies linearly with..." rather than the more common meaning that superposition applies. RLC sircuits are linear. Any given parameter may not vary linearly as the frequency is varied. Also, this use of 'linear' depends upon the type of scale being used--log or linear. 2) John, You better re-think your last statement about the series equivalent of a practical coil. It implies that there is some way to measure a low Z at the resonance of the coil under discussion. You say: "The series equivalent [impedance ? Steve] goes down as the frequency increases, and goes to zero at resonance. " While a series resonant LC exhibits this behavior, the series equivalent of a practical coil does not do this. The series equivalent must do the same thing as the parallel equivalent -- namely go to a high impedance at resonance. That's why it is called *equivalent*--the total, or terminal impedance is equal for the two representations (at a single frequency). Pretty sure I got that right.... Steve k]9]d]c]i A practical coil usually goes to parallel resonance - at which the series equivalent does not go to zero "John Woodgate" wrote in message ... I read in sci.electronics.design that Bill Turner wrote (in ) about 'Winding coils', on Sun, 7 Dec 2003: Both statements are true and easily provable. A simple air core coil which measures one microhenry at a low frequency may have an inductance of several millihenries (or even henries) when near its self resonant frequency. This is what happens to the *parallel equivalent* inductance. The series equivalent goes down as the frequency increases, and goes to zero at resonance. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! |
1) you guys are just arguing symantics. You both know what really happens.
".... "Inductance" vs. the total reactance measuring as inductive...." call it what you like. 1a) You are also both using (some might say mis-using) the term "linear" to mean "varies linearly with..." rather than the more common meaning that superposition applies. RLC sircuits are linear. Any given parameter may not vary linearly as the frequency is varied. Also, this use of 'linear' depends upon the type of scale being used--log or linear. 2) John, You better re-think your last statement about the series equivalent of a practical coil. It implies that there is some way to measure a low Z at the resonance of the coil under discussion. You say: "The series equivalent [impedance ? Steve] goes down as the frequency increases, and goes to zero at resonance. " While a series resonant LC exhibits this behavior, the series equivalent of a practical coil does not do this. The series equivalent must do the same thing as the parallel equivalent -- namely go to a high impedance at resonance. That's why it is called *equivalent*--the total, or terminal impedance is equal for the two representations (at a single frequency). Pretty sure I got that right.... Steve k]9]d]c]i A practical coil usually goes to parallel resonance - at which the series equivalent does not go to zero "John Woodgate" wrote in message ... I read in sci.electronics.design that Bill Turner wrote (in ) about 'Winding coils', on Sun, 7 Dec 2003: Both statements are true and easily provable. A simple air core coil which measures one microhenry at a low frequency may have an inductance of several millihenries (or even henries) when near its self resonant frequency. This is what happens to the *parallel equivalent* inductance. The series equivalent goes down as the frequency increases, and goes to zero at resonance. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! |
Gents,
Another practical consideration. Another area where caution is advised--paralleling bypass caps. In solid state Power Amplifier design, such a configuratin can cause problems because there is a point where one is above self resonance and acts like an inductance in parallel with the other cap which is still capacitive-- thus, resonance and no bypass. Been there, done that. We put a small Z in between. Frequently a small bead or resistor if possible. Seems there is an equivalent problem with series inductors. -- Steve N, K,9 d, c. i "Bill Turner" wrote in message ... On Sun, 7 Dec 2003 19:17:08 +0000, John Woodgate wrote: This is a 1920s problem. Just as you parallel capacitors of different type, electrolytic, metallized foil and ceramic, to get a wideband component, so you put inductors of different construction in series to get a wide band component. You can wind them all on a bit of wax- impregnated dowel if you like. (;-) __________________________________________________ _______ That will work, no doubt. My point was that it takes some serious engineering and careful testing; you can't just wrap some wire on a form and expect it to work correctly across a wide range of frequencies. -- Bill, W6WRT |
Gents,
Another practical consideration. Another area where caution is advised--paralleling bypass caps. In solid state Power Amplifier design, such a configuratin can cause problems because there is a point where one is above self resonance and acts like an inductance in parallel with the other cap which is still capacitive-- thus, resonance and no bypass. Been there, done that. We put a small Z in between. Frequently a small bead or resistor if possible. Seems there is an equivalent problem with series inductors. -- Steve N, K,9 d, c. i "Bill Turner" wrote in message ... On Sun, 7 Dec 2003 19:17:08 +0000, John Woodgate wrote: This is a 1920s problem. Just as you parallel capacitors of different type, electrolytic, metallized foil and ceramic, to get a wideband component, so you put inductors of different construction in series to get a wide band component. You can wind them all on a bit of wax- impregnated dowel if you like. (;-) __________________________________________________ _______ That will work, no doubt. My point was that it takes some serious engineering and careful testing; you can't just wrap some wire on a form and expect it to work correctly across a wide range of frequencies. -- Bill, W6WRT |
You're still doing it. Paul (I think) said "measure" and Bill, no, looks
like Len (I think) said "finding", meaning "calculating". "Avery Fineman" wrote in message ... In article , Bill Turner writes: On Sun, 07 Dec 2003 13:55:35 +0200, Paul Keinanen wrote: .snip Not only can you *not* measure them separately, they can not be physically separated either, since the parasitic capacitance is always present between adjacent windings.... Nonsense. General Radio had a nice little formula way back before 1956 for finding the distributed capacity of an inductor. Len Anderson retired (from regular hours) electronic engineer person |
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