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#128283 - 01/03/03 11:31 AM Supply Wave shape sinusoidal or square  
FAHardy  Offline
Junior Member
Joined: Jan 2003
Posts: 2
Why is sinusoidal supply generated and not another wave shape eg. A square wave

Tools for Electricians:

#128284 - 01/03/03 11:41 AM Re: Supply Wave shape sinusoidal or square  
wolfdog  Offline
Joined: Oct 2001
Posts: 135
A sine wave is naturally produced as the magnetic field saturates and collapses while the generator rotates.

You get a modified square wave with a 12v-120v inverter because it produces multiple short duration square wave signals and adds them together to approximate a sine wave.

#128285 - 01/03/03 02:18 PM Re: Supply Wave shape sinusoidal or square  
ElectricAL  Offline
Joined: Oct 2001
Posts: 597
Minneapolis, MN USA
Like Wolfdog says. . .the sinusoid is a map of effects in a conductor cutting magnetic lines of force as the conductor is spun on the perimeter of a drum. An elegantly simple machine.

It is the analog to the square wave's digital.

In the physical world, a square wave that is actually "square" can not exist. The ideal square wave changes states instantaneously. The real square wave ramps from one state to another. . .the better the generator, the quicker the change, but it never happens fast enough to be instantaneous. So the real world square wave is really a highly distorted form of a sine wave, and (this is the interesting part, IMHO) can be created by summing pure sine waves of different amplitude and frequency. That is, a square wave can be thought of as the result of adding a bunch of sine waves together. The square wave may be created by purely mechanical means, and still, there will be high frequency components in it.


Al Hildenbrand

#128286 - 01/03/03 03:32 PM Re: Supply Wave shape sinusoidal or square  
electric-ed  Offline
Joined: Jul 2002
Posts: 175
Maybe this sketch will help.

[Linked Image]


#128287 - 01/03/03 05:25 PM Re: Supply Wave shape sinusoidal or square  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Ed's diagram shows the generation of the sinewave quite effectively. What you have to keep in mind is that as the magnetic field rotates, the rate at which lines of magnetic flux cross the coils is not constant. It is this varying rate of change which results in the sinusoidal wave shape.

As Al mentioned, the sinewave is the purest form of signal. If you inject a pure sinewave into any combination of reactive components (i.e. any circuit which contains capacitance and/or inductance) then you will still get a sinewave at the output. The waveform may be attentuated and phase shifted, but it will still be a sinewave.

Injecting any other sort of waveform into reactive circuit components results in distortion. Trying to send a squarewave down long lines (which have inherent inductance and capacitance) results in a very distorted waveform at the distant end. That's because the higher-frequency components of the waveform are affected differently to the lower ones, thus upsetting the balance which produces the original squarewave.

#128288 - 01/05/03 09:11 AM Re: Supply Wave shape sinusoidal or square  
Scott35  Offline

Broom Pusher and
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
Great information posted by everyone here! Also, great drawing by Ed!

Just to sum things up, a Rotating Generating device (such as Alternators) will produce "Somewhat Sinusodal" AC output (not going into details regarding any internal things within the generating device which might either distort or alter the wave format).

Now what the AC looks like after connecting various loads to the generating device, is going to result in anything but a nice looking Sine Wave!!!

Harmonic Distortion will turn that neat and uniform wave into something with jagged spikes, sharp peaks and a bunch of multi frequency pulsations within the overall envelope!

The output of some DC/AC Inverters will be morelike something between a plain-old square wave and a "Saw-Tooth" wave - depending on how the power amp Transistors are driven.

Scott s.e.t.

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

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