RE: [CAD_CAM_EDM_DRO] Re: What is Rms?

Jon:

That is one the best explanations of RMS, with a great example, that I
have ever seen.

I am constantly amazed how many people think that the only reason we do
the "squaring" is to "rectify" the waveform.

Thanks,


Andy Wander
Verrex Corporation

-----Original Message-----
From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Jon Elson
Sent: Saturday, November 26, 2005 5:28 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Re: What is Rms?

turbulatordude wrote:

>I was under the impression that RMS only applied to sine wave type
>power (or half wave) but not to square wave. After all, isn't duty
>cycle used to calculate current ?
>
>
>

No, RMS can apply to any waveform. Ordinary voltmeters are corrected
for sine waves, only, and will give incorrect AC readings on anything
other than a sine wave. Duty cycle can be used simply to calculate the
average voltage or current. But, if a square wave voltage is applied to
a resistive device, the power delivered will not match the duty cycle *
voltage. That is because power is volts X amps. When the voltage goes
up, the current ALSO goes up, by the same factor. Therefore, a change
in voltage causes a change in power equal to the SQUARE of the change in
voltage. This is the whole key to the thing.

So, if you were to apply 120 V DC to a 120 Ohm resistor, it would draw
one amp, and dissipate 120 Watts. If you applied 240 V 50% of the time,
it would draw 2 A, and dissipate 480 W during the on time, and of course
zero during the off time. The average power dissipation would be 240 W
(480 / 2). So, although the average VOLTAGE is the same 240/2 = 120,
the average POWER is twice as large, in this example.

Jon




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