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| Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#81
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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." The output of a rectifier contains both AC and DC. You put a filter on it to get close to pure 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. |
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#83
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Rich The Newsgroup Wacko wrote:
"Since the sky is green, I guess I'll plant some bluegrass, and paint my house clear." You truly are an idiot. Bluegrass is growing all over kentucky, and some gets planted every year. Notr only that, but you can listen to it on the radio or TV. -- Former professional electron wrangler. Michael A. Terrell Central Florida |
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#84
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TimPerry wrote:
"Pooh Bear" wrote in message ... wrote: .see also this previous thread where someone else uses the same terminology ("DC sine wave").... Just because someone else used the term doesn't make it right ! There's plenty of rubbish spouted on the net. Graham Once in a while someone coins a new term like Heinleins' waldo... but I don't think its going to happen here. What has been described is similar to the waveform one would see on the grid of a class A tube circuit. (but negative voltage of course) There are a number of waveforms that go in only one direction relative to ground such as sawtooth waves, square waves, and triangle waves. To refer to these as say a "DC triangle wave" would be equally confusing without further qualification. The closest descriptor that I can think of offhand that might meet with general acceptance would be "bias signal". Another waveform that's very similar ( albeit more of a sawtooth waveform rather than sine wave ) is power line ripple on a DC supply rail. Graham |
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#85
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"Bob Penoyer" wrote in message ... 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. It's DC with a ripple riding on top of it. With no filtering the ripple runs down to zero. N |
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#86
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NSM wrote:
wrote in message ups.com... 2 questions about a fully DC Sine Wave One answer. Sine waves aren't DC. N I like Jack's terminology. The wave itself isn't DC, but I think "fully DC" is an acceptable way of describing its location. AC generators and transformers are usually designed to produce sine waves with no DC, but sine waves were known long before those inventions. A wave is a succession of curves. A sine wave is a wave whose displacement follows the form of a sine. A pure acoustic tone is a sine wave regardless of ambient pressure. A ripple on a pond is a sine wave regardless of the water level. As not all voltage variations are curves, our generic term was "waveforms". If the plate voltage of an amplifier tube varied from 998 to 1000 volts in the form of a sawtooth, we'd call that two-volt variation a sawtooth waveform. If it was sinusoidal we'd call it a sine wave. 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. |
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#87
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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: Reference Direction Point of flow ========= ===================================== Peak Pos All Negative DC level Equal cycles of Positive and Negative Peak Neg All Positive Obviously the only point of reference you are thinking about is the Peak Negative swing, and just as clearly that is *not* appropriate. The correct reference point is necessarily the DC level, and measured from that point of reference the current is going to go alternately in each direction. Bingo, there is your AC. This is very similar to confusing the negative side of a rectifer circuit with ground. Rectifiers are most often grounded on the negative side, but that is absolutely arbitrary. They can be grounded on the postive side, and with some effort can have ground at other levels either between those two, or even beyond either of them. But rather than look at DC as current going all going in one direction, and AC as anything else, it is *far* easier to view it as AC is any current that is changing, and DC is anything else (i.e., the current is steady). Technically those definitions are exactly the same, but one leads to a lot of confusion. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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#88
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"Floyd L. Davidson" wrote in message ... 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: Reference Direction Point of flow ========= ===================================== Peak Pos All Negative DC level Equal cycles of Positive and Negative Peak Neg All Positive I think "zero" is a good reference for current flow, and that the actual (absolute) direction can be measured. Voltages have the reference issues. j |
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#89
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Andy writes:
This type of problem is analyzed using the superposition theorem.. One source is +10 VDC The second source is a 10 V pk-pk sine wave. Just add the two results for the answer, into a common load. For the DC, allow time for the transient to settle.... If you can use PSPICE, or the equivalent, you can do this easily , with additional experiments which may improve your understanding...... Andy PS 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.... |
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#91
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"operator jay" wrote:
"Floyd L. Davidson" wrote in message ... 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: Reference Direction Point of flow ========= ===================================== Peak Pos All Negative DC level Equal cycles of Positive and Negative Peak Neg All Positive I think "zero" is a good reference for current flow, and that the actual Sure... now, can you define "zero"? (absolute) direction can be measured. Voltages have the reference issues. E =IR Since our resistance is fixed, it's the exact same issue, though perhaps easier to understand, with voltage. (I gave some consideration as to whether to post that with voltage or current references, and since "AC" and "DC" use the term "current", decided to go with current to avoid the easier path to the same statement you are making.) -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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#92
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wrote:
2 questions about a fully DC Sine Wave....let's suppose you have a DC Sine wave which varies from +5V to +15V peak-to-peak going into a load with R, L, and C components..... Question #1: Is the load's impedance a function of R, L, and C (and wave frequency) or is it simply just R (i.e. Z=R)? In other words does non-resistive impedance (L + C) really only matter with an AC signal OR anytime voltage varies periodically (even if it is all DC)? Yes, the load impedance is a function R, L, C and frequency. L and C do matter anytime the voltage varies even on non-periodic wave and even if the voltage is always positive. On a pure DC voltage (constant, non-varying), L will represent a short-circuit while C will represent an open-circuit. If the R+L+C are all in series, the +5V to +15V sine wave will, during the transient phase, first charge the capacitor to +10V, then (during the steady-state phase) the current will start to behave as a normal sine wave (reversing directions) even if the driving voltage never goes negative. Question #2: Would a "regular" negative peak detector ciruit, like shown he http://www.elektroda.net/cir/index/D...CTOR.htmgative work for the DC Wave described? Will it output +5V or do negative peak detectors only work for AC signals? The circuit is pretty much unconventional (but sure smart!). No, it will not output +5V. The circuit is meant to detect only negative voltages and can only output zero or negative voltage. But I suggest that your try building it and see what happens. You might just get lucky. Thank you. You're welcome. I hope you now understand that your +5V to +15V voltage is better called "varying DC". I've never seen an EE book that will say "DC Sine Wave" for the voltage you described, and rightly so because a sine wave implies reversing directions. |
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#93
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"Floyd L. Davidson" wrote in message ... "operator jay" wrote: "Floyd L. Davidson" wrote in message ... 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: Reference Direction Point of flow ========= ===================================== Peak Pos All Negative DC level Equal cycles of Positive and Negative Peak Neg All Positive I think "zero" is a good reference for current flow, and that the actual Sure... now, can you define "zero"? Put an ammeter there and it says zero. That's zero. Electrons bouncing around in the conductor have an average net displacement, over time, of 0. (absolute) direction can be measured. Voltages have the reference issues. E =IR Since our resistance is fixed, it's the exact same issue, though perhaps easier to understand, with voltage. (I gave some consideration as to whether to post that with voltage or current references, and since "AC" and "DC" use the term "current", decided to go with current to avoid the easier path to the same statement you are making.) Current is a different issue from voltage because voltage is a relative quantity. It is a type of measurement of a change in field between two locations. Current is a rate of flow of charge at a single location (well, typically, through a single Gaussian surface), and is measurable at that location, and does not have the ambiguity that voltage has. It does not need a reference. If I say that my toaster is running at 120V and 8A, you may ask "120V relative to what" and I'll answer "neutral". You would not ask "8A relative to what". j |
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#94
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"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 |
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#95
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wrote in message oups.com... PS 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.... Who do you want operating on your gall bladder? Someone who knows what he is doing or someone who is making it up as he goes along? N |
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#96
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#97
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On Sun, 12 Jun 2005 12:21:01 -0500, "operator jay"
wrote: Put an ammeter there and it says zero. That's zero. Electrons bouncing around in the conductor have an average net displacement, over time, of 0. "Put and ammeter there" and if it says +300mA to +800mA back and forth, then it's Alternating Current, innit? |
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#98
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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. -- 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 |
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#99
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#101
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"kinyo" wrote in message oups.com... wrote: snip work for the DC Wave described? Will it output +5V or do negative peak detectors only work for AC signals? The circuit is pretty much unconventional (but sure smart!). No, it will not output +5V. The circuit is meant to detect only negative voltages and can only output zero or negative voltage. But I suggest that your try building it and see what happens. You might just get lucky. Thank you. You're welcome. I hope you now understand that your +5V to +15V voltage is better called "varying DC". I've never seen an EE book that will say "DC Sine Wave" for the voltage you described, and rightly so because a sine wave implies reversing directions. Or, one might refer to this as 10VDC with an AC waveform superimposed. The AC waveform varies sinusoidally with 10 V peak-peak. One can then solve two circuits, the DC one with just R and 10VDC, and the AC one with R-L-C. Combining the currents from the two solutions should be equivalent to the original circuit. I agree, that 'DC sine wave' is a misnomer. It makes it sounds like the speaker doesn't know AC from DC. In order to not sound foolish, it would be better to use one of the alternatives suggested. daestrom |
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#102
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On Sun, 12 Jun 2005 13:30:26 -0700, 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. --- Well, Al, correction (no matter how gently offered) is often met with varying degrees of resistance, particularly by those who have become convinced that their way should be temporarily accepted as the 'right' way, for their convenience, regardless of whether their way conforms to universally accepted standards. Case in point, the OP, whose attitude seems to be (and I paraphrase) "You know what I mean, so why should I have to say it your way?" As for me, I'm perfectly capable of conducting myself politely in the presence of polite company. I'm also perfectly capable of atrocious behavior and have no qualms about stooping to that level if, in my opinion, the situation warrants it. Finally, I don't see how you came to the conclusion that it pains me to engage in the edification of imbeciles. Actually, it's quite gratifying to be able to take on the challenge of breaking through the barrier of ignorance and realize that you've shown someone how to use a tool they didn't even know they owned. -- John Fields Professional Circuit Designer |
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#103
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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. Starting to see it my way, Al?-) -- John Fields Professional Circuit Designer |
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#104
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"operator jay" wrote:
"Floyd L. Davidson" wrote in message ... "operator jay" wrote: "Floyd L. Davidson" wrote in message ... 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: Reference Direction Point of flow ========= ===================================== Peak Pos All Negative DC level Equal cycles of Positive and Negative Peak Neg All Positive I think "zero" is a good reference for current flow, and that the actual Sure... now, can you define "zero"? Put an ammeter there and it says zero. That's zero. Electrons bouncing around in the conductor have an average net displacement, over time, of 0. Is this an AC ammeter, or a DC ammeter? (And isn't that just a voltmeter anyway, in most actual cases????) Hmmm... (absolute) direction can be measured. Voltages have the reference issues. E =IR You can't escape the fact that voltage and current are joined at the hip, they are for all practical purposes different expressions of the same thing. Whatever affects one *has* to have affected the other. Since our resistance is fixed, it's the exact same issue, though perhaps easier to understand, with voltage. (I gave some consideration as to whether to post that with voltage or current references, and since "AC" and "DC" use the term "current", decided to go with current to avoid the easier path to the same statement you are making.) Current is a different issue from voltage because voltage is a relative quantity. No more or less than current. They are joined at a hip called Ohm's Law. It is a type of measurement of a change in field between two locations. Current is a rate of flow of charge at a single location (well, typically, through a single Gaussian surface), and is measurable at that location, and does not have the ambiguity that voltage has. It does not need a reference. If I say that my toaster is running at 120V and 8A, you may ask "120V relative to what" and I'll answer "neutral". You would not ask "8A relative to what". 8 Amps from where? To where? Through were? Relative to where? Since we can discuss current using only voltage as the variable (resistance being a constant in this example), *anything* you can say about voltage is directly related to current. One of the overall things that you *have* to keep in mind is that periodic reality checks are necessary. One of them is the fact, repeated by many in this thread, that "DC sine wave" is a contradiction of terms. If your definition makes it possible, your definition *can't* be right. 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. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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#105
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Bob Penoyer wrote:
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. Total and utter horse****. "DC" is simply the first (or "offset" term in the Fourier expression of any repetitive waveform. "AC" are all of the remaining components. Changing the relative amplitude of the terms does NOT in any manner change which is the first term and which are the remaining terms. DC, of course, cannot exist at all ever. Because it would have to be unvarying through infinite time. Tutorials on my website. -- Many thanks, Don Lancaster Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552 voice: (928)428-4073 email: Please visit my GURU's LAIR web site at http://www.tinaja.com |
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#106
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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? -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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#107
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"Kitchen Man" wrote in message news  On Sun, 12 Jun 2005 12:21:01 -0500, "operator jay" wrote: Put an ammeter there and it says zero. That's zero. Electrons bouncing around in the conductor have an average net displacement, over time, of 0. "Put and ammeter there" and if it says +300mA to +800mA back and forth, then it's Alternating Current, innit? 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. j |
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#108
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Kitchen Man wrote:
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. Is patience required though? I'm always reminded of a young lady I met once, many years ago employed by Northern Telecom Inc to provide training on a mainframe computer program to USAF personnel. This lady showed up and started teaching the GI's, one at time. She first latched onto a 16 year Staff Sargent (that suggests he might not have been too bright). He'd been working with telecommunications for all 16 of those years and didn't know that a Class C Autovon line was the kind he could call home on for free (every Airman figured that out in 6 days). So, we thought the lady probably ought to be warned. And not being a GI myself, it was sort of agreed that I'd tell her. We had not counted on this lady being, ahem... perceptive. Not to mention independent, ornery, and several other adjectives. I hinted to her that the Sarge was the worst case example, and maybe she shouldn't waste too much time on him. She growled at me, and said something about my head and a dark place, and said she had "A degree in teaching ****ing idiots." Apparently patience is not part of the requirement? Somewhat ruffled at a gal 10 years younger than me getting the best of me in that way, I decided to get back! There was this almost friendly young Security Policeman who came by now and then to check our credentials to be in a secure area. Of course every SP lives for the day he can "jack up" somebody. So I suggested we had a really good candidate to play games with! He figured that was just a great idea, and followed me as I led him to where he could perform this duty for his country. But, alas, he came around the corner and this asshole young lady looked at this asshole young Security Policeman, and he looked at her... and I saw the look in their eyes and knew all was lost. It was like in a movie! They locked on, you could hear the bells ring! You could see them shiver! It was a *classic* love at first sight! Danged guy spent the next *two* *hours* talking to her, and they dated the entire time she was there. Patience... did teach me something! -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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#109
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#110
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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. -- Many thanks, Don Lancaster Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552 voice: (928)428-4073 email: Please visit my GURU's LAIR web site at http://www.tinaja.com |
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#111
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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. Hey, you moved *my* goal post! I said nothing about average values. If it wiggles, it's AC. The difference is that you are being so precise that you're saying if it wiggled since the dawn of time, it's AC. I'm just saying that if it was so long ago that I can't remember (which seems to be a pretty short time anymore), that's long enough. :-) 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. EXACTLY! And while you and I can make jokes about just how pedantic we should be with definition of terms, the fact is that anyone who actually thinks "AC" and "DC" are the determinative definitions based on word meanings, is going to be wrong. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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#112
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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. The sinusoidally varying unipolar voltage under consideration _always_ forces electrons to move in one direction only. A non-sequitor. 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. 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. That's because AC is *not* defined by any change in direction, but only by a rate of movement change. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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#113
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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. --- Looking at the Fourier terms makes this waveform perfectly clear. Calling it "AC" or "DC" does not. --- Why go there? Your description was adequate to indicate that polarity reversals occur, therefore making the signal voltage alternate between two different polarities, therefore making the current alternate between polarities as well. That's why it's called "Alternating Current". --- "AC" or "DC" are gross and meaningless oversimplifications. --- Uh-huh... -- John Fields Professional Circuit Designer |
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#114
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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. --- Looking at the Fourier terms makes this waveform perfectly clear. Calling it "AC" or "DC" does not. --- Why go there? Your description was adequate to indicate that polarity reversals occur, therefore making the signal voltage alternate between two different polarities, therefore making the current alternate between polarities as well. That's why it's called "Alternating Current". --- "AC" or "DC" are gross and meaningless oversimplifications. --- Uh-huh... It's not unusual to speak of the AC and DC _components_ of a waveform that does not readily satisfy the simplification. One also speaks of _DC offset_ of an otherwise AC signal. -- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
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#115
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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. --- Looking at the Fourier terms makes this waveform perfectly clear. Calling it "AC" or "DC" does not. --- Why go there? Your description was adequate to indicate that polarity reversals occur, therefore making the signal voltage alternate between two different polarities, therefore making the current alternate between polarities as well. That's why it's called "Alternating Current". Except, polarity reversals are not significant to the definition of AC. --- "AC" or "DC" are gross and meaningless oversimplifications. --- Uh-huh... He's right. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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#116
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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. 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. Didn't you just say in your immediately previous post: ---------------------------------------------------------------- ""DC" is simply the first (or "offset" term in the Fourier expression of any repetitive waveform. "AC" are all of the remaining components." ---------------------------------------------------------------- Did you intend to offer these descriptions knowing that they were "gross and meaningless oversimplifications"? Why bother in that case? |
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#117
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"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. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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#118
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On Sun, 12 Jun 2005 15:22:00 -0700, Don Lancaster
wrote: Bob Penoyer wrote: 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. Total and utter horse****. Look, if the current's not alternating its direction, it's not alternating current. To be clear, just because its amplitude is changing does not mean it is alternating. In particular, a rectified AC waveform it isn't changing direction. There are certainly AC components in the waveform. But the sum of all the components, including the DC component, never changes direction, so the total signal is a DC signal. Here, "DC" does NOT mean "constant"; it means unidirectional. |
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#119
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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. So you are saying that DC varying from 5 to 15 as the op referenced is AC? If you put a DC source across a capacitor and vary the source up and down, sometimes electrons are flowing into the capacitor, and sometimes they are flowing out of it. Same with an inductor. For the record, I don't want to take one side or another in the debate about AC vs DC in this thread. The waters are muddy enough already. I view the op's scenario as DC with an AC signal imposed on it. This whole discussion of whether it is AC or DC is a trap and diversion from the original. It does not matter whether it is AC or DC that the components see. For example, a capacitor operates the same on DC as it does on AC. If there is a path for it to charge, and a source sufficient to charge it, it charges. If there is a path for it to discharge, and no source applied sufficient to keep it charged, it discharges. Same thing for an inductor below saturation. The op asked about a sinusoidal varying DC, but gave no info about frequency. He then asks about impedance of the (unknown) RLC circuit. The answer has to be arrived at by a consideration of how each component reacts. To say (not that you said it) the cap won't pass DC is crap. Connect a 15 V, 500 ohm relay coil to ground, and the other side to a 470 uF cap. Connect the other side of the cap to +12. The relay energizes briefly, proving that the cap did pass DC. Try the same thing with a supply that starts at 5 volts and increases to 15 volts at a rate of 1 cycle per hour, and it does not energize. But the relay coil DOES charge. For the op to understand the load impedance, he has to understand what each component does in his circuit. I see no other way to answer his question, in the absence of specifics. Ed Ergo, because of the periodic polarity reversals what you're looking at is AC. --- Looking at the Fourier terms makes this waveform perfectly clear. Calling it "AC" or "DC" does not. --- Why go there? Your description was adequate to indicate that polarity reversals occur, therefore making the signal voltage alternate between two different polarities, therefore making the current alternate between polarities as well. That's why it's called "Alternating Current". --- "AC" or "DC" are gross and meaningless oversimplifications. --- Uh-huh... |
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#120
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"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. You are the one with the requirements, assertions, and definitions, not me. Where are you coming up with them? If it's from the same place where - zero current is not definable - magnitude of current needs an outside reference - voltage and current are for all practical purposes different expressions of the same thing - alter is the same thing as alternate then I don't even want to know. You need to come to realize there is no clear cut correct answer on this 'AC' vs 'DC' issue at this time. If there was one, there would be much more consensus between people on what the correct answer is. This big long thread would not have occurred. Now let's turn it around and look at it the other way. This big long thread did occur. We can plainly see that there is disagreement between groups on what exactly the precise meanings of AC and DC entail. Therefore there effectively is no single exact definition for "AC" or for "DC" that will allow us to resolve which is correct and which is not correct. 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. On another note, how long are the days getting to be way up there? Do you get continuous sunshine? j |
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