Re: Wattmeter

• To: tesla-at-pupman-dot-com
• Subject: Re: Wattmeter
• From: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br> (by way of Terry Fritz <twf-at-verinet-dot-com>)
• Date: Sun, 24 Jan 1999 21:32:57 -0700
• Approved: twf-at-verinet-dot-com

I wrote:

> An electronic
> Wattmeter must take scaled samples of the voltage and the current in the
> load, multiply them, average the result, and take the square root.

Oops... There is no square root. The average power is just the average
of the V*I product.

The square root appears in the computation of RMS values:
Xrms = sqrt(average of X(t)^2)
For sinusoidal values of the same frequency, the average power is:
P=Vrms*Irms*cos(angle between V and I)
But this is valid only for sinusoidal signals.

Antonio Carlos M. de Queiroz

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