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Kitchen Man wrote:
On Sun, 12 Jun 2005 14:33:39 -0500, John Fields wrote: On 12 Jun 2005 09:01:11 -0700, wrote: It's a shame you have to weed thru all the crap from some of the posters here who have a lot of time on their hands and have no tolerance for those who are just learning their craft.... --- It's a shame that those of us who give of our time in an effort to edify the ignorant are often abused by imbeciles who can't take correction gracefully. It is equally a shame that there are those that are sometimes incapable of offering correction gracefully, eh, John? If it pains you so much to engage in your ungracious edifying, perhaps you would do well to bugger off, and leave the stress of educating imbeciles to those with more patience. Interesting! I thought John's response to the op was called for. The OP is going to get himself into trouble with the attitutde he's exhibited. In my opinion, John saw through the BS and called a spade a spade. I don't know whether the OP got it or not - but John made it clear that the BS wasn't fooling anybody. I'll have to go back and read it again in light of your post. Ed |
"Don Lancaster" wrote in message ... "AC" or "DC" are gross and meaningless oversimplifications. True but pointless. We know what we mean. Even 'current' is a borrowed term used as an analogy as is 'potential' or even 'pressure'. If we have voltage surely we should only speak of amperage. N |
On Sun, 12 Jun 2005 16:50:51 -0500, John Fields
wrote: On Sun, 12 Jun 2005 13:39:22 -0700, Kitchen Man wrote: On 10 Jun 2005 23:06:10 -0700, wrote: You actually proved my point that DC is DEFINED (i.e. by convention) as "zero frequency". Is it that weird to posit that the superior concept with respect to considering any signal as AC or DC, be the actual NET current flow? I could see your point if signals were classified as either "ZF" ("zero frequency") or "NZF" (non-zero frequency") but we are dealing with "DC" or "AC" If nothing else, your stubborn adherence to a flawed terminology and lack of openness to furthering your understanding will make you look like an idiot in a job interview, should you ever decide to pursue career advancement in the electronics industry. Please note that I am not saying you are an idiot, just that you will look like one in an interview. The interviewers will assume you know very little about the basics of the craft if you carry on like this, or at the very least will see you as a detriment to teamwork. HTH. --- His attitude, if he persists with it, will be a serious detriment no matter what field of endeavor he chooses to enter. Oh, I agree. I just think it helps to be a bit patient. Not that I'm all that good at patience, myself. But we should try. We have all been rookies, once or twice. Starting to see it my way, Al?-) -- Al Brennan "If you only knew the magnificence of the 3, 6 and 9, then you would have a key to the universe." Nicola Tesla |
Don Lancaster wrote:
Floyd L. Davidson wrote: Don Lancaster wrote: DC, of course, cannot exist at all ever. Because it would have to be unvarying through infinite time. Boy, you are *pedantic*! Can't we just define DC as current that doesn't vary "much" for at last a "long" time. Granted that is ambiguous, but what else would we the argue about, weather? No. Sum a 1 volt peak sinewave with a 0.6 volt dc term and you have a waveform whose polarity continuously changes but whose average value is continuous. Looking at the Fourier terms makes this waveform perfectly clear. Calling it "AC" or "DC" does not. "AC" or "DC" are gross and meaningless oversimplifications. That's going a bit far. "Meaningless" means no meaning, and that is not really an accurate description for the terms AC and DC. They have a pretty well understood meaning, despite some suggestions in this thread. "quotes with no meaning, are meaningless" - Kevin Aylward Kevin Aylward http://www.anasoft.co.uk SuperSpice, a very affordable Mixed-Mode Windows Simulator with Schematic Capture, Waveform Display, FFT's and Filter Design. |
Floyd L. Davidson wrote:
Bob Penoyer wrote: On Sat, 11 Jun 2005 10:36:54 -0400, "Tam/WB2TT" wrote: snip Yes. DC by definition is zero frequency. Um, no. DC is Direct Current, i.e., current that flows in one direction. For example, the output from a rectifier is DC but it certainly isn't "zero frequency." Actually, DC from a rectifier *is* "zero frequency", to the degree that it is DC. Of course until the AC is filtered out, it has both AC and DC components. The output of a rectifier contains both AC and DC. You put a filter on it to get close to pure DC. That is *precisely* correct. (It just doesn't tell enough of the story to explain the confusion of this "flows in one direction" definition of DC.) A rectified AC waveform contains DC and AC components but if the current isn't changing direction, it isn't alternating current. And, if it isn't AC, it's DC. The output of a rectifier until filtered *does* have both AC and DC, which actually is another way of saying that yes it *does* change directions. What? you say! The problem is that "direction" only has meaning when measured in comparison some specific point of reference. If you have three different reference points, one at the DC level, one at the peak positive swing and one at the peak negative swing, you have three very different views of "direction" for current flow: Since we are quibbling her on terms, lets get this bit straight shall we. "Current flow" is wrong. Its simply "current" or "charge flow". "Current" already contains the notion of "flow". Kevin Aylward http://www.anasoft.co.uk SuperSpice, a very affordable Mixed-Mode Windows Simulator with Schematic Capture, Waveform Display, FFT's and Filter Design. |
On Sun, 12 Jun 2005 22:59:18 -0500, "operator jay"
wrote: You are the one with the requirements, assertions, and definitions, not me. Actually, the ones with the requirements, assertions, and definitions are codes and organizations such as the NEC and the IEEE, and the bothersome universities that teach the stuff. On this point: Picture my flashlight, battery powered. Generally this is considered a dc circuit. When I turn it on or off, there is 'change'. So is it in fact an AC flashlight? If the battery starts to die there is a change so is it in fact an AC battery? Etcetera. (These questions are rhetorical by the way). I know better than to try to pin a strict name on these things where there is not an (adequately) universal and strict definition. You are talking about transients, and if you intend for the questions to be rhetorical, then I think you should demonstrate some expertise in the subject matter that shows why the questions' answers must be obvious. I don't think they are, so I will answer the questions: The behavior of the flashlight in your example is neither AC nor DC, it is transient. The first case is the instantaneous step function caused by the closing of a source to a circuit. The second case is a long-term curved ramp caused by the decay of a voltage source. AC and DC analyses are steady-state. AC analysis will never apply to the example. DC analysis must be performed prior to the transient analysis in order to provide a steady state model for the application of time-sensitive mathematics. There is quite a bit of information available on the web about circuit analysis. Your curiosity is to be commended; you might consider a web crawling adventure, or even an education in the field. And hey operator jay, what do you operate? Not electrical substations, I wouldn't guess. -- Al Brennan "If you only knew the magnificence of the 3, 6 and 9, then you would have a key to the universe." Nicola Tesla |
"Floyd L. Davidson" wrote in message ... "operator jay" wrote: It is not changing polarity. I would hesitate to call it alternating current. On the "dc sine wave" issue, I wouldn't even get into that debate. To me the terms involved are open to too many interpretations. As evidenced in this thread, I suppose. Where *do* you get this requirement for changing polarity? We don't call it "Alternating Polarity", we call it "Alternating Current". If the current is being altered, it's AC. You keep talking about AP, and it isn't the same. 'Alternating' is not the same as 'altering'. "Alternating current" is an electrical current where the magnitude and *direction* [emphasis added] varies cyclically. http://en.wikipedia.org/wiki/Alternating_current One may 'alter' the magnitude of a DC current without it becoming 'alternating current' daestrom |
"Floyd L. Davidson" wrote in message ... John Fields wrote: On Sun, 12 Jun 2005 14:00:23 -0800, (Floyd L. Davidson) wrote: My point still stands, that if the current is changing, it is by definition AC, and current not changing is DC. Trying to look at it as DC is all in one direction and anything else is AC, doesn't work. --- Your point is flawed. Alternating Current, by definition, causes electrons to move in one direction for a time, and then to reverse direction for a time. That isn't true. It is true by most definitions of 'Alternating Current'. http://en.wikipedia.org/wiki/Alternating_current 'Alternating' means both magnitude and direction vary over time. A current that varies in magnitude but not direction is not 'alternating'. Since the voltage varies, the current will also, but the _direction_ in which the electrons are travelling will never change. If it varies, it's AC. Only by your apparent definition. But your definition does not agree with the established industry. That means that the signal is DC. A varying DC, but DC nonetheless. If there is such a think as "varying DC", connect a load to it... through a capacitor. Now, how do you describe the effect that load has on your "varying DC". The load see's *only* AC, even according to your definition. That AC came from somewhere, and it certainly was not generated by the capacitor. By adding a capacitor in series, you have altered the circuit. The capacitor filters out the DC component of a the original varying DC voltage applied. The capacitor has a varying DC voltage across it, but it never changes polarity (you can use an electrolytic capacitor that is polarity sensitive without damage). The current through the resulting series circuit *does* alternate in magnitude and *direction*, even though the voltage applied to the circuit varies in magnitude only. So yes, the 'AC came from somewhere'. But that doesn't mean the applied voltage is AC. Such logic is flawed. There is no 'law of conservation of AC' that says it can't be 'generated by the capacitor'. That's because AC is *not* defined by any change in direction, but only by a rate of movement change. Repeating yourself doesn't make you correct. daestrom |
"daestrom" wrote:
"Floyd L. Davidson" wrote in message ... John Fields wrote: On Sun, 12 Jun 2005 14:00:23 -0800, (Floyd L. Davidson) wrote: 'Alternating' means both magnitude and direction vary over time. A current that varies in magnitude but not direction is not 'alternating'. Then you'll have a very difficult time explaining now a transistor amplifier works if it uses AC coupling that involves capacitors. Since the voltage varies, the current will also, but the _direction_ in which the electrons are travelling will never change. If it varies, it's AC. Only by your apparent definition. But your definition does not agree with the established industry. Which industry? You can't do AC circuit analysis with any other definition. If there is such a think as "varying DC", connect a load to it... through a capacitor. Now, how do you describe the effect that load has on your "varying DC". The load see's *only* AC, even according to your definition. That AC came from somewhere, and it certainly was not generated by the capacitor. By adding a capacitor in series, you have altered the circuit. The Capacitors don't generate voltage or current. The circuit alteration merely demonstrates that the voltage and current on one side meets all of your requirements, while the identical charge flow on the other side does not, which indicates a flaw in your specification. capacitor filters out the DC component of a the original varying DC voltage applied. Yes, which leaves the AC that was there all along. It's AC after, and it was AC before. If you do circuit analysis the treatment is exactly the same on both sides of the capacitor. The capacitor has a varying DC voltage across it, but it never changes polarity (you can use an electrolytic capacitor that is polarity sensitive without damage). Exactly. Yet there *is* current through the capacitor, which only passes AC. That AC current isn't generated inside that capacitor. It comes out one side, so it *had* to be coming in the other side. The current through the resulting series circuit *does* alternate in magnitude and *direction*, even though the voltage applied to the circuit varies in magnitude only. So yes, the 'AC came from somewhere'. But that doesn't mean the applied voltage is AC. Such logic is flawed. There is no 'law of conservation of AC' that says it can't be 'generated by the capacitor'. That's hilarious. DC applied to a capacitor generates AC???? I don't think so. That's because AC is *not* defined by any change in direction, but only by a rate of movement change. Repeating yourself doesn't make you correct. Won't help your point either. And it makes no difference how many places you find it ill defined either. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
"operator jay" wrote:
"Floyd L. Davidson" wrote: Picture my flashlight, battery powered. Generally this is considered a dc circuit. When I turn it on or off, there is 'change'. You were doing pretty good up to that point. So is it in fact an AC flashlight? No. But that doesn't mean there is never any AC present in the circuit. It happens that with a battery powered flashlight that is rare (but predictable too), and of no consequence whatever. It can be ignored in design and operation of the flashlight. But that doesn't mean there is never any AC in the circuit, or that there are no circuits where it is significant. If the battery starts to die there is a change so is it in fact an AC battery? Etcetera. (These questions are rhetorical by the way). I know better than to try to pin a strict name on these things where there is not an (adequately) universal and strict definition. Every time you flip the switch on or off, there is AC in that circuit. You can probably prove it too, relatively easy. Tune an AM receiver to a frequency where no station is being received, and hold the flashlight up close to the antenna. Flip it on and off a few times. I suspect, though I haven't actually tried this, that you'll hear a pop in the radio's speaker almost every time you flip the switch. That is because some of the AC produced by flipping that switch is RF. On another note, how long are the days getting to be way up there? Do you get continuous sunshine? It's been 24 hours of daylight for quite some time now. The sun hasn't actually gone down for a month (May 10th), but of course we had 24 hours of light long before that. The next time it gets below the horizon will be August 1, and it will be late August before it gets "dark". The temperature is 30F right now, with a reported 18 mph wind and fog. It was gusting up to 30 mph last night. It probably won't get much warmer than maybe 36F today. That is actually very comfortable weather, mostly because it is unlikely to rain. I hate getting wet... :-) -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
"Kevin Aylward" wrote:
Don Lancaster wrote: "AC" or "DC" are gross and meaningless oversimplifications. That's going a bit far. "Meaningless" means no meaning, and that is not really an accurate description for the terms AC and DC. They have a pretty well understood meaning, despite some suggestions in this thread. Given the significant experience of several people involved in this discussion, and the wide variety of interpretations they are giving to those terms, it would seem that just about the *only* thing one could positively take away from this particular discussion is that, as Don says, those terms are meaningless. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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"--" wrote:
"Floyd L. Davidson" wrote: John Fields wrote: On Sun, 12 Jun 2005 17:15:06 -0700, Don Lancaster wrote: Sum a 1 volt peak sinewave with a 0.6 volt dc term and you have a waveform whose polarity continuously changes but whose average value is continuous. --- No, you have a waveform with a polarity which changes _periodically_, making it an AC signal. Do the electrons traversing the circuit change direction? Yes. Do the electrons in a DC circuit ever change direction? No. Ergo, because of the periodic polarity reversals what you're looking at is AC. And, according to what you've said in other posts, if that were a 0.6 volt peak sinewave with 1.0 volt dc, it wouldn't be. But your definition of AC is faulty, because in fact they are the same thing, and *both* of them contain an AC component and a DC component, even if the general direction of electrons is always the same. No, both do not - only one of the 1 volt/.6 volt examples given has an _alternating_ direction component - both examples do have a _variation_ in their magnitude component. ( This is not a new discussion - and all of the dozen or so engineering and physics texts and training manuals I have researched on the matter adhere to the "alternating is reversing" definition of AC. It has been custom and practice for at least 40 years.) 1) the 1 volt dc with the .6 sine variation does not alternate its direction of flow. Its flow only varies in the magnitude of the charge flowing always in one direction. It has no alternating current ( i.e, it has no regularly reversing, i.e. _alternating_, charge flow direction) 2) the 1 volt sinewave with the .6 volt dc does reverse charge flow direction. It is alternating in its flow direction. It also varies in its magnitude. The direction of the description vector must alternate in order to have Alternating Current. If it does not change direction but only varies in magnitude, the descriptive vector is not alternating, it is merely varying in magnitude. 3) Impedance laws apply equally to varying DC and to AC. Item 3 is correct. That is because "varying DC" *is* AC. It is AC even if the axis is shifted far enough to avoid polarity reversals relative only to some specifically defined 0 current. The reversals are relative... to the steady state condition, not to some magical 0 current where supposedly no electrons are flowing. Otherwise, instead of two types, you are dividing circuit analysis into three types, two of which are identical in all significant respects other than an arbitrary definition that is meaningless. It makes no sense to say that "Impedance laws apply equally" and then claim that the two are not identical. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
NSM wrote:
"Choreboy" wrote in message ... To call a waveform an AC sine wave implies that there is no DC, but this thread is the first time I've read the claim that all sine waves are AC sine waves. FWIW, most waveforms can be created as the sum of sine waves. I wrote an interesting computer demo once that showed how a sine and it's harmonics could be added graphically to form a better and better approximation of a square wave, running through what looked like Butterworth etc. responses. N With high frequency and amplitude, a sine wave could be very steep at 0 and 180 degrees. It could also turn sharply at 90 and 270, like the corner of a square wave. You would need low frequency and amplitude for a sine wave to approximate the flat peaks of a square wave. That part is simple enough for me, but I don't understand harmonics. If you overdrive an amplifier with a sine wave, the output will resemble a square wave. I know the output can be broken down into the input frequency and its odd multiples. I'll have to accept it on faith. |
On Sun, 12 Jun 2005 16:35:48 -0800, (Floyd L.
Davidson) wrote: John Fields wrote: On Sun, 12 Jun 2005 14:00:23 -0800, (Floyd L. Davidson) wrote: My point still stands, that if the current is changing, it is by definition AC, and current not changing is DC. Trying to look at it as DC is all in one direction and anything else is AC, doesn't work. --- Your point is flawed. Alternating Current, by definition, causes electrons to move in one direction for a time, and then to reverse direction for a time. That isn't true. --- Yes, it is. If you have proof, instead of just a statement to the effect that it isn't, I'd love to see it. --- The sinusoidally varying unipolar voltage under consideration _always_ forces electrons to move in one direction only. A non-sequitor. --- "Non sequitur." No. A non-sequitur is an inference or a conclusion that does not follow from the premises, or a comment that is unrelated to a preceding one. My error was the omission of a reference, Mr. Lancaster's: "1 volt peak sinewave with a 0.6 volt dc term" --- Since the voltage varies, the current will also, but the _direction_ in which the electrons are travelling will never change. If it varies, it's AC. --- No, it isn't. What's necessary is the polarity reversal before it can be considered AC. --- That means that the signal is DC. A varying DC, but DC nonetheless. If there is such a think as "varying DC", connect a load to it... through a capacitor. Now, how do you describe the effect that load has on your "varying DC". The load see's *only* AC, even according to your definition. That AC came from somewhere, and it certainly was not generated by the capacitor. --- It most certainly was! Consider a DC coupled audio amplifier running from a single 12V supply, with its output set to Vcc/2 and feeding an 8 ohm load with a 4VPP sinusoidal signal. Like this: +12 | +--o--+ | AMP |---+--Vout +--o--+ | | [4R] | | GND GND Now, with phi being equal to the phase angle of the signal and zero degrees corresponding the voltage halfway between the most positive and least positive output voltage, the output voltage excursions will look like this: phi Vout -----+------ 0° 6V 90° 8V 180° 6V 270° 4V 360° 6V Now, connect that magical capacitor between the amp and the load, as shown below, and watch what happens: +12 | +--o--+ | AMP |---[cap]--+--Vout +--o--+ | | [4R] | | GND GND phi Vout -----+------ 0° 0V 90° +2V 180° 0V 270° -2V 360° 0V Why? Well,for starters, consider that under quiescent conditions the left-hand side of the cap will be charged to 6V and the right hand side will be at zero volts since there is no galvanic path to the output of the amp through the cap. Now, imagine that the voltage at the amp's outout starts to go positive. What will happen is that the amp will start sucking electrons out of the cap, generating a potential difference across the cap's plates which causes electrons to flow through the resistor, making the top of the resistor more positive than the bottom. Continuing in time, a point will be reached where the output of the amp will start forcing electrons _into_ the resistor, at which point the direction of travel of the electrons will be reversed. This periodic reversal will cause the polarity of the signal into the resistor to alternate. This alternating voltage will then give rise to an _alternating current_ in the resistor. --- That's because AC is *not* defined by any change in direction, but only by a rate of movement change. --- Poppycock. It's precisely the alternations in the direction of charge flow which cause it to be called "Alternating Current". Your way would have it be called AC by assigning some arbitrary rate of change, irrespective of direction as the delineation point, which makes no sense at all. That is, what would you specify as the rate of change which would delineate between between AC and DC? 0.5A/s? 0.001A/s? 0.1V/s? -- John Fields Professional Circuit Designer |
Strictly speaking, I believe the reactance (part of impedance)
equations apply to any variation in current magnitude. Their appropriate application does not in any way require reversing the charge. 1) I think one needs to define the term "alternating current" by its phenomena rather than define it by what applies to "AC". In other words, define AC as alternating current -rather than defining AC as "anything requiring an impedance calculation because of its magnitude variation". ( OK, all scientific definitions require definitions in terms of other defined concepts; thus voltage and charge are defined in terms of force. And yes, any phenomena in its purest defined form uses the fewest of the core units, and only the core units, of the measuring system. And yes, since, unlike in the British ft-sec-lb system, force is not a core unit of the metric kg-sec-m system, one cannot be as "pure" in the metric system with many definitions as one can be in the British system, "decile" convenience notwithstanding) 2) There are two phenomena and two descriptive words if one uses the mathematical description of the changes associated with current: changes in current _direction_ and changes in current _magnitude_. There are three (or more) phenomena if one uses only the two descriptive terms _AC_ and _DC_, well evidenced in this thread: changes in direction and magnitude, changes in magnitude only, or no changes in either magnitude or direction. Three phenomena defined using only two words for those three cannot be specific and exclusive enough for a rigorous definition. The middle condition, the overlap as it were, ends up wanting. 3) In the definition approach to a phenomena, one deals with the descriptive term and the phenomena itself and ignores the present attached effects. Once the definition is had, then the phenomena's interaction with other phenomena can be determined. Yes, having such rigor in a definition can be more complicated in its application. In the application approach to defining a phenomena, one defines by addressing what equations, etc., apply to the condition. In this approach, you end up in circular arguments, chasing your tail. Something always will not fit. Like changes in magnitude without changes in direction. "Floyd L. Davidson" wrote in message ... "--" wrote: "Floyd L. Davidson" wrote: John Fields wrote: On Sun, 12 Jun 2005 17:15:06 -0700, Don Lancaster wrote: Sum a 1 volt peak sinewave with a 0.6 volt dc term and you have a waveform whose polarity continuously changes but whose average value is continuous. --- No, you have a waveform with a polarity which changes _periodically_, making it an AC signal. Do the electrons traversing the circuit change direction? Yes. Do the electrons in a DC circuit ever change direction? No. Ergo, because of the periodic polarity reversals what you're looking at is AC. And, according to what you've said in other posts, if that were a 0.6 volt peak sinewave with 1.0 volt dc, it wouldn't be. But your definition of AC is faulty, because in fact they are the same thing, and *both* of them contain an AC component and a DC component, even if the general direction of electrons is always the same. No, both do not - only one of the 1 volt/.6 volt examples given has an _alternating_ direction component - both examples do have a _variation_ in their magnitude component. ( This is not a new discussion - and all of the dozen or so engineering and physics texts and training manuals I have researched on the matter adhere to the "alternating is reversing" definition of AC. It has been custom and practice for at least 40 years.) 1) the 1 volt dc with the .6 sine variation does not alternate its direction of flow. Its flow only varies in the magnitude of the charge flowing always in one direction. It has no alternating current ( i.e, it has no regularly reversing, i.e. _alternating_, charge flow direction) 2) the 1 volt sinewave with the .6 volt dc does reverse charge flow direction. It is alternating in its flow direction. It also varies in its magnitude. The direction of the description vector must alternate in order to have Alternating Current. If it does not change direction but only varies in magnitude, the descriptive vector is not alternating, it is merely varying in magnitude. 3) Impedance laws apply equally to varying DC and to AC. Item 3 is correct. That is because "varying DC" *is* AC. It is AC even if the axis is shifted far enough to avoid polarity reversals relative only to some specifically defined 0 current. The reversals are relative... to the steady state condition, not to some magical 0 current where supposedly no electrons are flowing. Otherwise, instead of two types, you are dividing circuit analysis into three types, two of which are identical in all significant respects other than an arbitrary definition that is meaningless. It makes no sense to say that "Impedance laws apply equally" and then claim that the two are not identical. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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The freezing point and boiling point of water are both have
a clearly defined intrinsic meaning to a chemist. "DC sine wave" is a non-sequiter. It's a made-up self-contradictory term that won't have an unambiguous meaning to anybody who knows electronics, no matter how clear it is to you. wrote: Go back to the original few posts to see how it got started....despite being explicit about the specs of the wave, someone childishly objected to my casual usage of "DC sine wave".....would it have been objectionable had I used "a fully DC-offset sine wave"?......again, I've never claimed that I was using "official" or conventionally-correct teminology or nomenclature....I just really object that anyone would object to what I was saying, when its meaning was explicitly stated (using actual numbers) and the phrase "fully DC sine wave", although conventionly queer, is not at all cryptic or hard to figure out......if I were a chemist and someone said "200 degrees above the freezing point of water", I wouldn't mock them, just respectfully point out that it's more common to say "20 degrees above the boiling point of water".....I would consider the person ignorant of the conventional terminology, but I would consider the person dead-on if he were talking about 232 degrees F. |
John Fields wrote:
On Sun, 12 Jun 2005 16:35:48 -0800, (Floyd L. Davidson) wrote: That means that the signal is DC. A varying DC, but DC nonetheless. If there is such a think as "varying DC", connect a load to it... through a capacitor. Now, how do you describe the effect that load has on your "varying DC". The load see's *only* AC, even according to your definition. That AC came from somewhere, and it certainly was not generated by the capacitor. --- It most certainly was! Do a reality check on what you are saying! Capacitors do *not* generate AC, and when the rest of your theory depends on the idea that they do, you've made a mistake. Consider a DC coupled audio amplifier running from a single 12V supply, with its output set to Vcc/2 and feeding an 8 ohm load with a 4VPP sinusoidal signal. Like this: +12 | +--o--+ | AMP |---+--Vout +--o--+ | | [4R] | | GND GND You haven't drawn the schematic of an amplifier. There is no input. Call it what you like, but it isn't an amplifier. Add the input, and then we know where the AC originated... Now, with phi being equal to the phase angle of the signal and zero degrees corresponding the voltage halfway between the most positive and least positive output voltage, the output voltage excursions will look like this: phi Vout -----+------ 0° 6V 90° 8V 180° 6V 270° 4V 360° 6V Clearly AC. (And if you don't treat it as AC, your circuit analysis will be flawed.) Now, connect that magical capacitor between the amp and the load, as shown below, and watch what happens: +12 | +--o--+ | AMP |---[cap]--+--Vout +--o--+ | | [4R] | | GND GND phi Vout -----+------ 0° 0V 90° +2V 180° 0V 270° -2V 360° 0V Why? Because you feed an AC signal to the capacitor, and hence you see an AC signal on the other side. What's your point? Capacitors pass AC and block DC. All you've done is *prove* that there was AC coming out of the AMP (as well as DC). Well,for starters, consider that under quiescent conditions the left-hand side of the cap will be charged to 6V and the right hand side will be at zero volts since there is no galvanic path to the output of the amp through the cap. Now, imagine that the voltage at the amp's outout starts to go positive. What will happen is that the amp will start sucking electrons out of the cap, generating a potential difference across the cap's plates which causes electrons to flow through the resistor, making the top of the resistor more positive than the bottom. And clearly you have an alternating voltage on both sides of the capacitor, and an AC current passing through it. Not generated by it, but passing through it. Continuing in time, a point will be reached where the output of the amp will start forcing electrons _into_ the resistor, at which point the direction of travel of the electrons will be reversed. This periodic reversal will cause the polarity of the signal into the resistor to alternate. This alternating voltage will then give rise to an _alternating current_ in the resistor. --- That's because AC is *not* defined by any change in direction, but only by a rate of movement change. --- Poppycock. It's precisely the alternations in the direction of charge flow which cause it to be called "Alternating Current". It is defined by a differential (which necessarily will have a sign reversal), not "polarity" reversals. Your way would have it be called AC by assigning some arbitrary rate of change, irrespective of direction as the delineation point, which makes no sense at all. That is, what would you specify as the rate of change which would delineate between between AC and DC? 0.5A/s? 0.001A/s? 0.1V/s? *Any* rate of change (differential) that you can detect, means you have detected AC. There simply is no way to do circuit analysis with any other definition. Or do we really want three states: A) DC B) Varying DC[1] C) AC[2] [1] Varying DC is exactly like AC and all functions are identical. [2] AC is exactly like Varying DC and all functions are identical. That is 3 states in your mind, and only 2 in fact. Not very reasonable from a logical point of view, but that is exactly what we do have because of the historical baggage that we carry along. Remember when every electrical engineer would tell you that current flows from the positive terminal of a battery to the negative terminal... and every electronics engineer would tell you that when the B battery is connected to a vacuum tube circuit the current flows from the cathode to the anode. Of course the positive battery terminal is connected to the anode, so they can't both be correct. Of course, then solid state electronics came along, and it became clear that current wasn't even necessarily the movement of electrons, but could also be the movement of a lack of electrons! How does *that* fit your "polarity" requirements? You are telling me the positive terminal supplies the current, and the return path is to the negative terminal. I'm telling you that electrons flow from the cathode to the anode, and I don't care how many reference books you cite saying that current comes from the positive terminal on that battery. Same sort of historical baggage. (And can the spelling flames. If you haven't got any better manners than you do logic, you have no place complaining that I forgot to run the spell check on that article. Your claim that the referenced statement was not the non-sequitur that I pointed out it was didn't hold water according to the very definition *you* supplied!) -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
John Fields wrote:
On Sun, 12 Jun 2005 18:28:16 -0800, (Floyd L. Davidson) wrote: "operator jay" wrote: It is not changing polarity. I would hesitate to call it alternating current. On the "dc sine wave" issue, I wouldn't even get into that debate. To me the terms involved are open to too many interpretations. As evidenced in this thread, I suppose. Where *do* you get this requirement for changing polarity? We don't call it "Alternating Polarity", we call it "Alternating Current". If the current is being altered, it's AC. --- No, if the direction of charge flow alternates between two states, then it's Alternating Current. That fits my definition, but not yours! Are you changing your definition or is that just a momentary bit of logical thought? The states do *not* have to be plus and minus polarity. Just different current levels... --- You keep talking about AP, and it isn't the same. --- Yes, it is. In order for the current in a load to alternate, the polarity of the generator's output voltage must alternate as well. Sure. But it doesn't need to change polarity. All it needs to do is change level. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
"--" wrote:
Strictly speaking, I believe the reactance (part of impedance) equations apply to any variation in current magnitude. Their appropriate application does not in any way require reversing the charge. Exactly. 1) I think one needs to define the term "alternating current" by its phenomena rather than define it by what applies to "AC". In other words, define AC as alternating current -rather than defining AC as "anything requiring an impedance calculation because of its magnitude variation". What value does that have? The problem is circuit analysis, which requires the division between DC and AC, and the only division that makes sense is between non-changing current and changing current. 3) In the definition approach to a phenomena, one deals with the descriptive term and the phenomena itself and ignores the present attached The problem is defining something with no practical value. If AC is a changing current, that includes changing polarity, and covers the actual significant difference from DC. If AC is defined only as changing polarity, we also have to have an entire separate set of identical functions and definitions, one for "varying DC" and one for "AC". Since the analysis is the same, there is no point in separation of the two. And "varying DC" is a contradiction in terms to begin with. Do we actually need *four* states: 1 -- DC 2 -- Varying DC 3 -- AC 4 -- Steady AC Boy, that should may first year text books *really* interesting! Either that or we are back to Don Lancaster's correct statement that they are meaningless terms anyway. They certainly are if that is the way they are defined! -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
Choreboy wrote:
With high frequency and amplitude, a sine wave could be very steep at 0 and 180 degrees. It could also turn sharply at 90 and 270, like the corner of a square wave. You would need low frequency and amplitude for a sine wave to approximate the flat peaks of a square wave. That part is simple enough for me, but I don't understand harmonics. If you overdrive an amplifier with a sine wave, the output will resemble a square wave. I know the output can be broken down into the input frequency and its odd multiples. I'll have to accept it on faith. You might want to look into the basis of Fourier analysis. It all falls out of a very simple mathematical property of the sine wave. If you take any periodic waveform, and multiply its value at every point in time with the value of any frequency of sine wave at the same points in time, over all time and add up (integrate) all the products and divide by the total time (an infinite amount of time), only sine waves that fit an integral number of cycles within the period of the waveform will produce nonzero results (infinite integral divided by infinite time). In fact, it can be shown that you get the same quotient for harmonics if you use any integral number of periods of the waveform, including one period. Testing an infinite number of waves is only necessary to show that non harmonics always produce a zero contribution. For instance, if you test a sine wave that fits 1.000001 cycles into a cycle of the waveform, you don't reach the first zero result till you include a million periods of the waveform (and you get more zeros at every integer multiple of a million cycles, with a smaller and smaller cycle of results between those millions as the number of cycles increases because you are dividing by larger and larger times). Harmonics (sine waves that fit an integral number of cycles within the waveform) will produce a finite result representing that frequencies contribution to the waveform. (Actually you have to test both the sine and cosine against the waveform to cover all possible phase shifted versions of the sine. Any phase shifted sine can be broken sown into sine and cosine components. Another nice property of sine waves.) Since only harmonics contribute to the total wave shape, you can skip all the other frequencies, and just evaluate the part each harmonic contributes to making the total waveform. That is Fourier analysis. The rest is about making the math more efficient. |
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On Mon, 13 Jun 2005 07:37:08 -0800, (Floyd L.
Davidson) wrote: John Fields wrote: On Sun, 12 Jun 2005 16:35:48 -0800, (Floyd L. Davidson) wrote: That means that the signal is DC. A varying DC, but DC nonetheless. If there is such a think as "varying DC", connect a load to it... through a capacitor. Now, how do you describe the effect that load has on your "varying DC". The load see's *only* AC, even according to your definition. That AC came from somewhere, and it certainly was not generated by the capacitor. --- It most certainly was! Do a reality check on what you are saying! Capacitors do *not* generate AC, and when the rest of your theory depends on the idea that they do, you've made a mistake. --- Well, Floyd, Take a look at the schematics below and you may notice that while the first one (the one without the cap in series with the load) puts out a sinusoidally varying unipolar signal, (DC) the second one (the one _with_ the cap in series with the load) puts out a sinusoidally varying bipolar signal. (AC) Now, since the only difference between them is the cap and one puts out a varying DC signal while the other one puts out a true signal, then the cap _must_ be generating the AC signal. If you have a problem with 'generating' then perhaps 'converting' would be more to your liking. I doubt it though, you seem to be in this only for the argument and I'm sure you'll come up with reason why you're unhappy with 'convert'. --- Consider a DC coupled audio amplifier running from a single 12V supply, with its output set to Vcc/2 and feeding an 8 ohm load with a 4VPP sinusoidal signal. Like this: +12 | +--o--+ | AMP |---+--Vout +--o--+ | | [4R] | | GND GND You haven't drawn the schematic of an amplifier. There is no input. Call it what you like, but it isn't an amplifier. Add the input, and then we know where the AC originated... --- LOL, you're grasping at straws! I already said the amp was DC coupled, so showing an input isn't necessary. But for you... +12 | +--o--+ INPUT---| AMP |---+--Vout +--o--+ | | [4R] | | GND GND Assume a gain of 1. Happy now? --- Now, with phi being equal to the phase angle of the signal and zero degrees corresponding the voltage halfway between the most positive and least positive output voltage, the output voltage excursions will look like this: phi Vout -----+------ 0° 6V 90° 8V 180° 6V 270° 4V 360° 6V Clearly AC. (And if you don't treat it as AC, your circuit analysis will be flawed.) --- You seem to want to put the cart before the horse in that you're spouting 'circuit analysis' before you've gotten a grasp of the basics. But if you want to play that way, OK. It's clearly a fluctuating DC signal, and if you don't take that _fact_ into consideration _your_ circuit analysis will be erroneous. --- Now, connect that magical capacitor between the amp and the load, as shown below, and watch what happens: +12 | +--o--+ | AMP |---[cap]--+--Vout +--o--+ | | [4R] | | GND GND phi Vout -----+------ 0° 0V 90° +2V 180° 0V 270° -2V 360° 0V Why? Because you feed an AC signal to the capacitor, and hence you see an AC signal on the other side. --- No, look a little more closely and you'll see (well, maybe...) that the current on the input side never changed direction (remained DC), while the current into the load alternated between going into the load and coming out of the load. IOW, it went into the cap as fluctuating DC and came out AC. --- What's your point? Capacitors pass AC and block DC. All you've done is *prove* that there was AC coming out of the AMP (as well as DC). --- No, there was _no_ AC coming out of the amp, (no changes in the direction of charge flow, only changes in the magnitude) just fluctuating DC which the cap converted into AC. --- Well,for starters, consider that under quiescent conditions the left-hand side of the cap will be charged to 6V and the right hand side will be at zero volts since there is no galvanic path to the output of the amp through the cap. Now, imagine that the voltage at the amp's outout starts to go positive. What will happen is that the amp will start sucking electrons out of the cap, generating a potential difference across the cap's plates which causes electrons to flow through the resistor, making the top of the resistor more positive than the bottom. And clearly you have an alternating voltage on both sides of the capacitor, and an AC current passing through it. Not generated by it, but passing through it. --- No, there is a fluctuating DC on the input side of the cap which the cap converts to AC to present to the load. --- Continuing in time, a point will be reached where the output of the amp will start forcing electrons _into_ the resistor, at which point the direction of travel of the electrons will be reversed. This periodic reversal will cause the polarity of the signal into the resistor to alternate. This alternating voltage will then give rise to an _alternating current_ in the resistor. --- That's because AC is *not* defined by any change in direction, but only by a rate of movement change. --- Poppycock. It's precisely the alternations in the direction of charge flow which cause it to be called "Alternating Current". It is defined by a differential (which necessarily will have a sign reversal), not "polarity" reversals. --- Specious gobbledygook. A reversal of sign is, by definition, a reversal of polarity. --- Your way would have it be called AC by assigning some arbitrary rate of change, irrespective of direction as the delineation point, which makes no sense at all. That is, what would you specify as the rate of change which would delineate between between AC and DC? 0.5A/s? 0.001A/s? 0.1V/s? *Any* rate of change (differential) that you can detect, means you have detected AC. --- Only if it's accompanied by a change in the direction of charge flow. --- .. .. Snipped a lot of irrelevant trash apparently designed to change the .. subject. .. (And can the spelling flames. If you haven't got any better manners than you do logic, you have no place complaining that I forgot to run the spell check on that article. Your claim that the referenced statement was not the non-sequitur that I pointed out it was didn't hold water according to the very definition *you* supplied!) --- The point is that you didn't point out a non sequitur. (notice that there's no apostrophe in there) The definition, which I got from Webster's College Dictionary and posted for your edification, should have made that clear. And, speaking of manners, I suggest that yours need a little trip past Emily Post. -- John Fields Professional Circuit Designer |
On Mon, 13 Jun 2005 07:47:51 -0800, (Floyd L.
Davidson) wrote: John Fields wrote: On Sun, 12 Jun 2005 18:28:16 -0800, (Floyd L. Davidson) wrote: "operator jay" wrote: It is not changing polarity. I would hesitate to call it alternating current. On the "dc sine wave" issue, I wouldn't even get into that debate. To me the terms involved are open to too many interpretations. As evidenced in this thread, I suppose. Where *do* you get this requirement for changing polarity? We don't call it "Alternating Polarity", we call it "Alternating Current". If the current is being altered, it's AC. --- No, if the direction of charge flow alternates between two states, then it's Alternating Current. That fits my definition, but not yours! Are you changing your definition or is that just a momentary bit of logical thought? --- Try not to be a stupid ****. Flames will get you nothing back but more flames. Is that what you want? --- The states do *not* have to be plus and minus polarity. Just different current levels... --- Go back and read it again. Concentrate especially hard on the part about the _direction_ of charge flow alternating between two states and maybe you'll get it. --- You keep talking about AP, and it isn't the same. --- Yes, it is. In order for the current in a load to alternate, the polarity of the generator's output voltage must alternate as well. Sure. But it doesn't need to change polarity. All it needs to do is change level. --- I'm starting to think you're having a real problem with reading comprehension. I write that for the current in a load to alternate, the polarity of the generator's output voltage must alternate as well, and then you agree but state that it doesn't need to change polarity. Don't you understand that an alternation in polarity means that the polarity changed??? -- John Fields Professional Circuit Designer |
"John Fields" wrote in message
... .... Yes, it is. In order for the current in a load to alternate, the polarity of the generator's output voltage must alternate as well. Consider a voltage source with output Eo = 2 + sin(w t) driving a capacitor as its load. The voltage does not alternate but the current will. -- --Larry Brasfield email: Above views may belong only to me. |
"Floyd L. Davidson" wrote in message ... "--" wrote: Strictly speaking, I believe the reactance (part of impedance) equations apply to any variation in current magnitude. Their appropriate application does not in any way require reversing the charge. Exactly. 1) I think one needs to define the term "alternating current" by its phenomena rather than define it by what applies to "AC". In other words, define AC as alternating current -rather than defining AC as "anything requiring an impedance calculation because of its magnitude variation". What value does that have? The problem is circuit analysis, No, rather the problem is that many of the fundamental physical sciences and most of electrical engineering use the concept, and it is not used merely by a small corner of circuit analysis. The definition has to work for all the sciences where it may be used. E.g., many switches use the "AC as reversing" concept for quenching contact arcs during switching (as the current passes thru zero as direction reverses) and the defintion of AC as varying DC falls flat for that purpose. Install an AC designed switch on a varying DC circuit, and you may well have a safety switch contacts welded shut. Here, AC DEFINITELY means reversing direction. which requires the division between DC and AC, I believe the equations are not DC-AC specific - the "AC" term drops to zero if the change in magnitude drops to zero. Your rationale of using the equations does not hold up. and the only division that makes sense is between non-changing current and changing current. changing in direction or magnitude? You suggest we use AC is defined as: "regularly or irregularly varying uni- or bi- directional current if it varies at a frequency that could have an effect for that application; unless it is digital, where then the one-time rise time and the fall time of each state change is calculated as AC, too, even though it 'alternates' once for each pulse" vs. AC is defined as: charge flow that changes direction. which leaves the calculations for reactance out of the definition. 3) In the definition approach to a phenomena, one deals with the descriptive term and the phenomena itself and ignores the present attached The problem is defining something with no practical value. We define air, and black holes, and impracticality. The circular logic that has your AC/DC missing half the paramters of the phenomena also has no use for defining air since we only feel wind, for not defining black holes which have no practical value since we have never seen one, and no use for the definition of impracticality because by definition it has no practical value. If AC is a changing current, that includes changing polarity, and covers the actual significant difference from DC. If AC is defined only as changing polarity, we also have to have an entire separate set of identical functions and definitions, one for "varying DC" and one for "AC". not if we consider the two paramters that make up the phenomena - direction and magnitude. And if memory serves me correctly, the "AC" equations are rigorous, and apply equally well to your one-voltage DC when the frequerncy drops to zero- the reactance term of the changing magnitude goes to zero. Since the analysis is the same, there is no point in separation of the two. And "varying DC" is a contradiction in terms to begin with. Do we actually need *four* states: 1 -- DC 2 -- Varying DC 3 -- AC 4 -- Steady AC no, just two - reversing flow direction, and varying magnitude. Because the reactance equations only apply to varying magnitude, and they do not apply to reversing direction. Boy, that should may first year text books *really* interesting! Either that or we are back to Don Lancaster's correct statement that they are meaningless terms anyway. They certainly are if that is the way they are defined! If one has never heard of the ocean, one finds the ocean meaningless. And for the memebrs of that society, they also would find ocean-going boats useless. because they have to define the ocean thru their own experience. As I understood, scienctific method is designed to remove personal views from science. Thus the definition,must stand alone, and since we can't see all that is ahead, science has to fall in behind a definition of that phenomena in pure terms. imho....... ---------------- Alternating-direction Current, aka Alternating Current Direction-specific Current, aka Direct Current. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
On Mon, 13 Jun 2005 11:20:43 -0700, "Larry Brasfield"
wrote: "John Fields" wrote in message ... ... Yes, it is. In order for the current in a load to alternate, the polarity of the generator's output voltage must alternate as well. Consider a voltage source with output Eo = 2 + sin(w t) driving a capacitor as its load. The voltage does not alternate but the current will. --- True, but in the context of the post from which the excerpt came capacitive loads had not yet been introduced into the discussion. -- John Fields Professional Circuit Designer |
John Fields wrote:
On Mon, 13 Jun 2005 07:37:08 -0800, (Floyd L. Davidson) wrote: --- Well, Floyd, Take a look at the schematics below and you may notice that while the first one (the one without the cap in series with the load) puts out a sinusoidally varying unipolar signal, (DC) the second one (the one _with_ the cap in series with the load) puts out a sinusoidally varying bipolar signal. (AC) Now, since the only difference between them is the cap and one puts out a varying DC signal while the other one puts out a true signal, then the cap _must_ be generating the AC signal. Reality check! Capacitors are passive devices. They do *NOT* generate signals. All that has happened is the capacitor does not pass DC. You haven't generated AC on one side, you've merely removed the DC. I don't see how that could be any more obvious. You did take a high school physics class, didn't you? *Use* what you learned! Poppycock. It's precisely the alternations in the direction of charge flow which cause it to be called "Alternating Current". It is defined by a differential (which necessarily will have a sign reversal), not "polarity" reversals. --- Specious gobbledygook. A reversal of sign is, by definition, a reversal of polarity. Okay, so you not only need to restudy high school physics, but differential equations too. The point is that you didn't point out a non sequitur. (notice that there's no apostrophe in there) The definition, which I got from Webster's College Dictionary and posted for your edification, should have made that clear. If you had read the definition you posted, you might have noticed that it perfectly described the remark that I was commenting on. It had nothing to do with the discussion. And, speaking of manners, I suggest that yours need a little trip past Emily Post. You are the one stooping to spelling flames. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
John Fields wrote:
On Mon, 13 Jun 2005 07:47:51 -0800, (Floyd L. Davidson) wrote: No, if the direction of charge flow alternates between two states, then it's Alternating Current. That fits my definition, but not yours! Are you changing your definition or is that just a momentary bit of logical thought? --- Try not to be a stupid ****. Flames will get you nothing back but more flames. Is that what you want? Oh, my. And you said what about Emily Post. Nothing I said was a flame. And I'd suggest you go practice (a *lot*) before you try me on for a flame war. Especially if you think *that* is a flame. I'm starting to think you're having a real problem with reading comprehension. Apparently I read a lot better than you write. I write that for the current in a load to alternate, You write a lot of things that are not valid. Don't you understand that an alternation in polarity means that the polarity changed??? Do you understand that is not significant? The reactance of circuit components, the fundamental significance of AC circuit analysis, does not depend upon polarity alternation in any way. What else is there to talk about? How many chocolate drops should be in each chocolate chip cookie? I await your essay on *something* of significance. But please, that is the *end* of discussion on your confusion about AC. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
John Popelish wrote:
Choreboy wrote: With high frequency and amplitude, a sine wave could be very steep at 0 and 180 degrees. It could also turn sharply at 90 and 270, like the corner of a square wave. You would need low frequency and amplitude for a sine wave to approximate the flat peaks of a square wave. That part is simple enough for me, but I don't understand harmonics. If you overdrive an amplifier with a sine wave, the output will resemble a square wave. I know the output can be broken down into the input frequency and its odd multiples. I'll have to accept it on faith. You might want to look into the basis of Fourier analysis. It all falls out of a very simple mathematical property of the sine wave. If you take any periodic waveform, and multiply its value at every point in time with the value of any frequency of sine wave at the same points in time, over all time and add up (integrate) all the products and divide by the total time (an infinite amount of time), only sine waves that fit an integral number of cycles within the period of the waveform will produce nonzero results (infinite integral divided by infinite time). In fact, it can be shown that you get the same quotient for harmonics if you use any integral number of periods of the waveform, including one period. Testing an infinite number of waves is only necessary to show that non harmonics always produce a zero contribution. For instance, if you test a sine wave that fits 1.000001 cycles into a cycle of the waveform, you don't reach the first zero result till you include a million periods of the waveform (and you get more zeros at every integer multiple of a million cycles, with a smaller and smaller cycle of results between those millions as the number of cycles increases because you are dividing by larger and larger times). Harmonics (sine waves that fit an integral number of cycles within the waveform) will produce a finite result representing that frequencies contribution to the waveform. (Actually you have to test both the sine and cosine against the waveform to cover all possible phase shifted versions of the sine. Any phase shifted sine can be broken sown into sine and cosine components. Another nice property of sine waves.) Since only harmonics contribute to the total wave shape, you can skip all the other frequencies, and just evaluate the part each harmonic contributes to making the total waveform. That is Fourier analysis. The rest is about making the math more efficient. That's easy for you to say! I think you've shown me something. When I hear "sine wave" I imagine one cycle. I guess that's wrong, and a wave is a train of cycles. Musical harmony is in a sustained interaction between trains of cycles. The interaction won't be simple enough to hear unless the quotient between the frequencies is a small integer. When they talk about harmonics in an electrical wave, I guess they're talking about the potential for energy transfer. In that case, only odd multiples of the fundamental will stay in phase to tap the energy from the distortion. Where a wave is flattened it may resemble part of a sine curve with a longer period than the fundamental, but that doesn't count because you can't tap energy from the flat part. If there's any truth in what I've said, I'll forget in a flash. In 1975 I was working in a repair facility. We'd use Bird Wattmeters to see forward and reflected power in antenna feeds. We knew the jargon and how to use the meters, but one day it struck me that none of us understood why they worked. I had a flash of insight and everybody stopped work to listen to me explain. Their faces lit up with comprehension. I felt pretty smart. The next day I couldn't remember whatever it was I'd figured out. |
The Phantom wrote:
On Mon, 13 Jun 2005 07:58:46 -0800, (Floyd L. Davidson) wrote: *Snip* Either that or we are back to Don Lancaster's correct statement that they are meaningless terms anyway. They certainly are if that is the way they are defined! Don first said: --------------------------------------- '"DC" is simply the first (or "offset" term in the Fourier expression of any repetitive waveform. "AC" are all of the remaining components.' ---------------------------------------- Then he said: ---------------------------------------- '"AC" or "DC" are gross and meaningless oversimplifications.' ---------------------------------------- Which are we to believe? There is no contradiction, so what is wrong with understanding both statements? -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
"--" wrote:
"Floyd L. Davidson" wrote: "--" wrote: Strictly speaking, I believe the reactance (part of impedance) equations apply to any variation in current magnitude. Their appropriate application does not in any way require reversing the charge. Exactly. 1) I think one needs to define the term "alternating current" by its phenomena rather than define it by what applies to "AC". In other words, define AC as alternating current -rather than defining AC as "anything requiring an impedance calculation because of its magnitude variation". What value does that have? The problem is circuit analysis, No, rather the problem is that many of the fundamental physical sciences and most of electrical engineering use the concept, and it is not used merely by a small corner of circuit analysis. The definition has to work for all the sciences where it may be used. E.g., many switches use the "AC as reversing" concept for quenching contact arcs during switching (as the current passes thru zero as direction reverses) and the defintion of AC as varying DC falls flat for that purpose. Install an AC designed switch on a varying DC circuit, and you may well have a safety switch contacts welded shut. Here, AC DEFINITELY means reversing direction. Bad example. That does *not* require a direction reversal. All it requires is understanding that it is relative to the static state. It does happen that the static state in that specific case is when a polarity reversal takes place, but in the general case it is not required. In other examples both sides of the switch might well be at some DC potential, that happens to be equal on both sides at the time the switch is made, even though there is no direction reversal. which requires the division between DC and AC, I believe the equations are not DC-AC specific - the "AC" term drops to zero if the change in magnitude drops to zero. Your rationale of using the equations does not hold up. Everything concerned with reactance is AC specific. Nothing concerned with reactance requires a polarity reversal. Reactance is the essence of the difference between DC and AC, not some notion of reversing polarity. AC is defined as: charge flow that changes direction. which leaves the calculations for reactance out of the definition. Which means it is worthless. Reactance *is* the significance. 3) In the definition approach to a phenomena, one deals with the descriptive term and the phenomena itself and ignores the present attached The problem is defining something with no practical value. We define air, and black holes, and impracticality. All of which *does* have practical value. And if memory serves me correctly, the "AC" equations are rigorous, and apply equally well to your one-voltage DC when the frequerncy drops to zero- the reactance term of the changing magnitude goes to zero. That is an hilarious idea! If the magnitude is zero all the way around... we aren't talking about AC or DC... maybe about blown breakers or taking a coffee break, but not about current. And "varying DC" is a contradiction in terms to begin with. Do we actually need *four* states: 1 -- DC 2 -- Varying DC 3 -- AC 4 -- Steady AC no, just two - reversing flow direction, and varying magnitude. Oh? DC doesn't exist? What about "steady AC"? (That's two exactly equal signals 180 degrees out of phase, combined in that capacitor which can generate AC mentioned by John Fields, perhaps???) Because the reactance equations only apply to varying magnitude, and they do not apply to reversing direction. Then why would we be concerned at all about this reversing direction, and give it a specific name and have a whole separate field of study for it? Sounds like we need to be concerned with varying magnitude, *not* with reversing direction. (Which is what I've been saying...) As I understood, scienctific method is designed to remove personal views from science. Thus the definition,must stand alone, and since we can't see all that is ahead, science has to fall in behind a definition of that phenomena in pure terms. imho....... A nice goal. ---------------- Alternating-direction Current, aka Alternating Current Except that alternating direction has no significance. Changing magnitude does. Why bother with alternating-direction at all, it is just an insignificant, though interesting, part of the more general case of changing magnitude. All of the same equations apply. Direction-specific Current, aka Direct Current. And if you claim that only alternating direction current is AC, then you have to have two sets of equations for DC, one for non-varying magnitude and one for varying magnitude. That doesn't make a lick of sense. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
Choreboy wrote:
John Popelish wrote: (snip) That is Fourier analysis. The rest is about making the math more efficient. That's easy for you to say! I think you've shown me something. When I hear "sine wave" I imagine one cycle. I guess that's wrong, and a wave is a train of cycles. True mathematical sine waves extend from infinite negative time to infinite positive time. Practical sine waves last long enough for things to respond to their frequency. How long that is, depends o what is reacting to it. A frequency counter operating in period mode needs only a single cycle to make its measurement. An ear needs several cycles to several dozen cycles, depending on exactly what part of the audible spectrum being detected (this property of ears is part o the MP3 music encoding scheme). A quartz lattice filter may need thousands of cycles to of a pure frequency before it develops a nearly steady state output. Musical harmony is in a sustained interaction between trains of cycles. The interaction won't be simple enough to hear unless the quotient between the frequencies is a small integer. Something like that. Each frequency component in the signal has to last long enough for the time response of that frequency of the ear's sorting system to respond to it. If two frequencies fall within a single reception band, they are not heard as two tones, but as a beat addition and cancellation) as a single tone at about the average of the two frequencies and an AM modulation at the difference of the two frequencies. Obviously, if the beat is very long period, you have to hear the two beating tomes for a cycle or two of the beat period to detect that effect. Harmonically related tones just produce a repeating pattern at some integer multiples of each of the component frequencies. This can produce a very pleasing effect. You hear sound from one musical source as a fundamental and several harmonically related frequencies. If a second musical source (a harmonizing voice, for example) has its fundamental at one of the harmonics of the other signal, your brain recognizes this simple multiple relationship as a pleasing musical harmony. For some ratios. This page shows some of the approximate ratios between notes that sound interesting together: http://www.jimloy.com/physics/scale.htm When they talk about harmonics in an electrical wave, I guess they're talking about the potential for energy transfer. Not really. since linear circuit components react to many frequencies by the addition if the effect of each frequency, it is a very powerful analytical procedure to break a signal down into its harmonics and evaluate the response of a circuit to each of those harmonics, and add all the effects together to get the total response. In that case, only odd multiples of the fundamental will stay in phase to tap the energy from the distortion. Symmetrical distortion of a sine wave (shape of positive half cycle is a mirror image of that on the negative half cycle) can be shown to be made up of only the fundamental and odd harmonics (3 times. 5 times, etc.). If the distortion peaks up one half cycle and flattens the other or shifts the zero crossing so that one half cycle lasts longer than the other, there are even harmonics in the wave shape. There may also be odd ones, too. Got to do that Fourier analysis to quantify that. Where a wave is flattened it may resemble part of a sine curve with a longer period than the fundamental, but that doesn't count because you can't tap energy from the flat part. You can with a resistor. From a Fourier perspective, that flat part just represents a time when the curve of some frequencies is nearly canceled by the curve from other frequencies. You need an infinite number of harmonics to make a truly flat square wave with perfectly square corners. If there's any truth in what I've said, I'll forget in a flash. In 1975 I was working in a repair facility. We'd use Bird Wattmeters to see forward and reflected power in antenna feeds. We knew the jargon and how to use the meters, but one day it struck me that none of us understood why they worked. I had a flash of insight and everybody stopped work to listen to me explain. Their faces lit up with comprehension. I felt pretty smart. The next day I couldn't remember whatever it was I'd figured out. I hate it when that happens. |
On Mon, 13 Jun 2005 11:59:48 -0800, (Floyd L.
Davidson) wrote: John Fields wrote: On Mon, 13 Jun 2005 07:37:08 -0800, (Floyd L. Davidson) wrote: --- Well, Floyd, Take a look at the schematics below and you may notice that while the first one (the one without the cap in series with the load) puts out a sinusoidally varying unipolar signal, (DC) the second one (the one _with_ the cap in series with the load) puts out a sinusoidally varying bipolar signal. (AC) Now, since the only difference between them is the cap and one puts out a varying DC signal while the other one puts out a true signal, then the cap _must_ be generating the AC signal. Reality check! Capacitors are passive devices. They do *NOT* generate signals. --- Hah! Just as I thought you would, you disingenuous little ****, you snipped my: "If you have a problem with 'generating' then perhaps 'converting' would be more to your liking. I doubt it though, you seem to be in this only for the argument and I'm sure you'll come up with reason why you're unhappy with 'convert'." for the purpose of being able to reiterate the obvious. Seems that's one of your devices, reiteration. Jumble the right with the wrong, but just keep saying them over and over and perhaps you'll confuse someone with a lower mentality than yours into believing that you know what you're talking about. Not bloody likely, boyo, since someone like that would be hard to find outside of Mickey D's and you're about as transparent as they come. BTW, capacitors, (even though passive) are quite capable of actually generating signals. Consider ceramic capacitors with lead zirconate-titanate dielectrics. Often capable of _generating_ acoustic signals. Also consider passive electrets. Nice little microphones they are. And, even parametrically varying caps can be used as pumps to _generate_ RF signals. But, I digress... We're really talking about your colors starting to show and what a dishonest little sneak you're turning into. --- All that has happened is the capacitor does not pass DC. You haven't generated AC on one side, you've merely removed the DC. I don't see how that could be any more obvious. You did take a high school physics class, didn't you? *Use* what you learned! --- Rather than merely parroting: "removing the DC", ad nauseam, it might be helpful if you actually studied the mechanism which causes that phenomenon to occur. Hint: the capacitor allows the load to "float" without regard to the voltage on the other side of the cap since there's a galvanic barrier between the load and its driver. --- Poppycock. It's precisely the alternations in the direction of charge flow which cause it to be called "Alternating Current". It is defined by a differential (which necessarily will have a sign reversal), not "polarity" reversals. --- Specious gobbledygook. A reversal of sign is, by definition, a reversal of polarity. Okay, so you not only need to restudy high school physics, but differential equations too. --- No, for this exercise all I have to do is point out the untenability of your position and watch you squirm trying to work your way out from under my thumb. --- The point is that you didn't point out a non sequitur. (notice that there's no apostrophe in there) The definition, which I got from Webster's College Dictionary and posted for your edification, should have made that clear. If you had read the definition you posted, you might have noticed that it perfectly described the remark that I was commenting on. It had nothing to do with the discussion. --- If you think that what I posted was a non sequitur, then I invite you to expound on why you think that. --- And, speaking of manners, I suggest that yours need a little trip past Emily Post. You are the one stooping to spelling flames. --- A correction isn't a flame unless you take it that way. -- John Fields Professional Circuit Designer |
On Mon, 13 Jun 2005 12:10:18 -0800, (Floyd L.
Davidson) wrote: John Fields wrote: On Mon, 13 Jun 2005 07:47:51 -0800, (Floyd L. Davidson) wrote: No, if the direction of charge flow alternates between two states, then it's Alternating Current. That fits my definition, but not yours! Are you changing your definition or is that just a momentary bit of logical thought? --- Try not to be a stupid ****. Flames will get you nothing back but more flames. Is that what you want? Oh, my. And you said what about Emily Post. --- I said nothing about Emily Post. What I alluded to was that you have bad manners and could use a little training in etiquette. --- Nothing I said was a flame. And I'd suggest you go practice (a *lot*) before you try me on for a flame war. Especially if you think *that* is a flame. --- Oh, my! She says one thing, then does another and pulls herself up to her full 4 foot height and threatens to strike a match! Don't forget what your mommy taught you about playing with fire. --- I'm starting to think you're having a real problem with reading comprehension. Apparently I read a lot better than you write. --- More unsubstantiated twaddle. --- I write that for the current in a load to alternate, You write a lot of things that are not valid. --- Just because you can't understand them doesn't mean they're not valid. --- Don't you understand that an alternation in polarity means that the polarity changed??? Do you understand that is not significant? --- It most certainly _is_, since it's what determines the difference between fluctuating direct current and true alternating current. --- The reactance of circuit components, the fundamental significance of AC circuit analysis, does not depend upon polarity alternation in any way. What else is there to talk about? How many chocolate drops should be in each chocolate chip cookie? I await your essay on *something* of significance. --- Well, since you consider matters of significance to be what you can understand and what pleases your ego, it's not likely that your wait will bear fruit. --- But please, that is the *end* of discussion on your confusion about AC. --- I see. You've come to the end of your rope and your exit strategy is to make it seem like everyone is wrong but you. -- John Fields Professional Circuit Designer |
John Fields wrote:
Hah! Just as I thought you would, you disingenuous little ****, you snipped my: .... what you're talking about. Not bloody likely, boyo, since someone like that would be hard to find outside of Mickey D's and you're about as transparent as they come. .... But, I digress... We're really talking about your colors starting to show and what a dishonest little sneak you're turning into. .... No, for this exercise all I have to do is point out the untenability of your position and watch you squirm trying to work your way out from under my thumb. .... A correction isn't a flame unless you take it that way. Your flaming is as poor as your electrical theory. You need to get a handle on your temper as well as learn some manners and some theory. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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John Fields wrote:
I said nothing about Emily Post. ... .... Oh, my! She says one thing, ... .... More unsubstantiated twaddle. .... Just because you can't ... .... --- It most certainly _is_, since it's what determines the difference between fluctuating direct current and true alternating current. --- .... Well, since you consider matters of significance ... .... I see. You've come to the end of your rope ... One statement (quoted in full above) that (even though wrong) at least has something to do with the topic, Six out of seven comments are piddly attempts a childish and gratuitous insults. No discussion John. I don't waste time teaching basics to grown men who have temper tantrums in public. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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