Re: [CAD_CAM_EDM_DRO] What is Rms?

On Thu, 2005-11-24 at 07:49 +0000, robertokx wrote:

> Hello,
>
> I was hoping someone could explain what RMS means in simple terms.

[snip]
Well - these terms may or may not be simple, but here goes :)

RMS means "Root-Mean-Square". You do these things in the reverse order
(square, mean, root) to get an RMS number. The reason this is used is
that power is proportional to the square of voltage or current. If you
were to take some voltage readings and just average them, it wouldn't
give you a good approximation of the power provided by that voltage
waveform. RMS measurements do.

Here's an example:
let's assume that you have a 10V pulse, at 10% duty cycle.
If you just take the average, you get 1V:
10V * 0.1 + 0V * 0.9 = 1V.

Now, let's do RMS.
First , square the readings, so we have 100(V^2) for 10% of the time,
and 0(V^2) for 90% of the time.
Next, get the mean (average):
100 (V^2) * 0.1 + 0 (V^2) * 0.9 = 10 (V^2) average.
Now, take the square root:
sqrt(10 V^2) ~= 3.16 V RMS

The amount of power provided by a 10V, 10% duty cycle waveform is the
same as that provided by a 3.16V DC source.

As for your motor - someone with better experience than I will have to
answer your question.

- Steve