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Everything Else » Electrical Engineering question: phaser mathematics?

July 20, 2011
by missle3944
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Hi guys,

I just toured North Dakota state university today and I asked what kind of math do you use in electrical engineering? The professor mentioned phaser mathematics which (correct me if I'm wrong) is a spin off of calculus? i just wiki'ed it and it sounds like it is used in AC stuff. But my real question is: when do you use it in circuits? Is it for waves or something similar. Keep in mind I'm only a softmore in High school, So pleaseee don't blow my mind out with diffrent mathamatics lingo. :) Also thank you nerdkitters and the guys Mike and Humberto for putting together this great kit! It really got me interested in electrical engineering. It looks very cool and a bit of a challenge :)

-missle3944

July 21, 2011
by 6ofhalfdozen
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heya Missle3944,

I am not an eletrical engineer or anything, but I have done a little reading on this in the past. My take on it is that is sort of calculus based in that there are integrals and such, but instead focusing on typical angular notation (sine, cosine, etc) this uses a phase relationship based formulas to get there. Think of the difference between regular angular formulas versus polar formulas(dunno if you have seen them yet), it will get you the correct answer but its done a different way.. I believe it is this style of difference. As far as I can tell, this is really only used in serious AC circuits where you need to know specific details at specific times. The few real world examples I saw were talking about multi-phase AC at very high voltages, like at a hydroelectric plant trying to balance outputs from generators. I would imagine you could use this on high frequency lower voltage signals too, but I think that might be overkill. Hopefully that helps more than it confuses...

July 21, 2011
by missle3944
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Hi 6ofhalfdozen,

Thanks for clearing that up. I guess that makes sense trying to determine the position of the shaft and the voltage drops and rises. My dad is an EE and he said that he hardly ever used it in his job which was microwave and rf calibration. He said that they use it to teach AC stuff I guess in school. Your reply cleared it up more thanks

-missle3944

July 21, 2011
by bretm
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It's phasor, with an "O". While calculus would be required to fully understand what's going on with a phasor quantity, they're also useful if you don't know calculus.

It's definitely an AC thing, and it's handy to do a lot of things in AC circuits, more than just high voltage.

With DC you just have to worry about the level--with AC you also sometimes have to worry about the phase--that is, how far forward or backward the waves are shifted compared to another AC signal at the same frequency.

If you add two DC signals together, the sum is just the two voltages added together. If you add two AC signals with the same phase, it's also just an addition. But if they're sine waves 180 degrees out of phase (the sine wave of one is shifted exactly a half-cycle from the other) then the two signals completely cancel each other out. As one sine wave is rising, the other is falling. If they're not 0 or 180 degrees out of phase, they will partially cancel each other out. Phasors make it easier to do some of these calculations.

A phasor quantity has a magnitude and an angle. You can plot one as a point on graph paper where the magnitude is the distance the point is from the origin, and the angle is the angle measured counter-clockwise from the positive X axis, measured in radians.

If you want to add two AC signals together and you know their phasor representation, you just start with the first phasor, pretend that's the origin, and find where the second phasor would be relative to that one (magnitude=distance, angle=counterclockwise in radians). That will give you another point on the graph paper that represents the phasor of the two signals added together. If the two signals are "in phase" which means they have the same phase angle, you'll just end up adding the two magnitudes together. If they're 180 degrees out of phase (opposite angle) you'll end up moving back toward the real origin (smaller magnitude). If they're different by some other phase angle, you'll move to some other arbitrary point and you can calculate the new magnitude and phase angle by measuring how far the new point is from the origin and what angle it makes with the positive X axis.

Here's a great explanation of using phasors to understand how the Fourier Transform does is magic and determines the spectrum of a complicated signal.

July 21, 2011
by 6ofhalfdozen
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bretm,

Once again, a great explanation! Also the link to that fourier transform discussion is awesome. Something I have been struggling to understand a long time. Thanks!

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